introduction example in research paper example

How to Write a Research Paper Introduction (with Examples)

Table of Contents

The research paper introduction section, along with the Title and Abstract, can be considered the face of any research paper. The following article is intended to guide you in organizing and writing the research paper introduction for a quality academic article or dissertation.

The research paper introduction aims to present the topic to the reader. A study will only be accepted for publishing if you can ascertain that the available literature cannot answer your research question. So it is important to ensure that you have read important studies on that particular topic, especially those within the last five to ten years, and that they are properly referenced in this section. 1

What should be included in the research paper introduction is decided by what you want to tell readers about the reason behind the research and how you plan to fill the knowledge gap. The best research paper introduction provides a systemic review of existing work and demonstrates additional work that needs to be done. It needs to be brief, captivating, and well-referenced; a well-drafted research paper introduction will help the researcher win half the battle.

The introduction for a research paper is where you set up your topic and approach for the reader. It has several key goals:

• Present your research topic
• Capture reader interest
• Summarize existing research
• Position your own approach
• Define your specific research problem and problem statement
• Highlight the novelty and contributions of the study
• Give an overview of the paper’s structure

The research paper introduction can vary in size and structure depending on whether your paper presents the results of original empirical research or is a review paper. Some research paper introduction examples are only half a page while others are a few pages long. In many cases, the introduction will be shorter than all of the other sections of your paper; its length depends on the size of your paper as a whole.

What is the introduction for a research paper?

The introduction in a research paper is placed at the beginning to guide the reader from a broad subject area to the specific topic that your research addresses. They present the following information to the reader

• Scope: The topic covered in the research paper
• Context: Background of your topic
• Importance: Why your research matters in that particular area of research and the industry problem that can be targeted

Why is the introduction important in a research paper?

The research paper introduction conveys a lot of information and can be considered an essential roadmap for the rest of your paper. A good introduction for a research paper is important for the following reasons:

• It stimulates your reader’s interest: A good introduction section can make your readers want to read your paper by capturing their interest. It informs the reader what they are going to learn and helps determine if the topic is of interest to them.
• It helps the reader understand the research background: Without a clear introduction, your readers may feel confused and even struggle when reading your paper. A good research paper introduction will prepare them for the in-depth research to come. It provides you the opportunity to engage with the readers and demonstrate your knowledge and authority on the specific topic.
• It explains why your research paper is worth reading: Your introduction can convey a lot of information to your readers. It introduces the topic, why the topic is important, and how you plan to proceed with your research.
• It helps guide the reader through the rest of the paper: The research paper introduction gives the reader a sense of the nature of the information that will support your arguments and the general organization of the paragraphs that will follow.

What are the parts of introduction in the research?

A good research paper introduction section should comprise three main elements: 2

• What is known: This sets the stage for your research. It informs the readers of what is known on the subject.
• What is lacking: This is aimed at justifying the reason for carrying out your research. This could involve investigating a new concept or method or building upon previous research.
• What you aim to do: This part briefly states the objectives of your research and its major contributions. Your detailed hypothesis will also form a part of this section.

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How to write a research paper introduction?

The first step in writing the research paper introduction is to inform the reader what your topic is and why it’s interesting or important. This is generally accomplished with a strong opening statement. The second step involves establishing the kinds of research that have been done and ending with limitations or gaps in the research that you intend to address.

Finally, the research paper introduction clarifies how your own research fits in and what problem it addresses. If your research involved testing hypotheses, these should be stated along with your research question. The hypothesis should be presented in the past tense since it will have been tested by the time you are writing the research paper introduction.

The following key points, with examples, can guide you when writing the research paper introduction section:

1. Introduce the research topic:

• Highlight the importance of the research field or topic
• Describe the background of the topic
• Present an overview of current research on the topic

Example: The inclusion of experiential and competency-based learning has benefitted electronics engineering education. Industry partnerships provide an excellent alternative for students wanting to engage in solving real-world challenges. Industry-academia participation has grown in recent years due to the need for skilled engineers with practical training and specialized expertise. However, from the educational perspective, many activities are needed to incorporate sustainable development goals into the university curricula and consolidate learning innovation in universities.

2. Determine a research niche:

• Reveal a gap in existing research or oppose an existing assumption
• Formulate the research question

Example: There have been plausible efforts to integrate educational activities in higher education electronics engineering programs. However, very few studies have considered using educational research methods for performance evaluation of competency-based higher engineering education, with a focus on technical and or transversal skills. To remedy the current need for evaluating competencies in STEM fields and providing sustainable development goals in engineering education, in this study, a comparison was drawn between study groups without and with industry partners.

3. Place your research within the research niche:

• State the purpose of your study
• Highlight the key characteristics of your study
• Describe important results
• Highlight the novelty of the study.
• Offer a brief overview of the structure of the paper.

Example: The study evaluates the main competency needed in the applied electronics course, which is a fundamental core subject for many electronics engineering undergraduate programs. We compared two groups, without and with an industrial partner, that offered real-world projects to solve during the semester. This comparison can help determine significant differences in both groups in terms of developing subject competency and achieving sustainable development goals.

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Step 3: Fill in the specifics, such as your field of study, brief description or details you want to include, which will help the AI generate the outline for your Introduction.

Step 4: Use this outline and sentence suggestions to develop your content, adding citations where needed and modifying it to align with your specific research focus.

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You can use the same process to develop each section of your article, and finally your research paper in half the time and without any of the stress.

Frequently Asked Questions

What is the purpose of the introduction in research papers.

The purpose of the research paper introduction is to introduce the reader to the problem definition, justify the need for the study, and describe the main theme of the study. The aim is to gain the reader’s attention by providing them with necessary background information and establishing the main purpose and direction of the research.

How long should the research paper introduction be?

The length of the research paper introduction can vary across journals and disciplines. While there are no strict word limits for writing the research paper introduction, an ideal length would be one page, with a maximum of 400 words over 1-4 paragraphs. Generally, it is one of the shorter sections of the paper as the reader is assumed to have at least a reasonable knowledge about the topic. 2

For example, for a study evaluating the role of building design in ensuring fire safety, there is no need to discuss definitions and nature of fire in the introduction; you could start by commenting upon the existing practices for fire safety and how your study will add to the existing knowledge and practice.

What should be included in the research paper introduction?

When deciding what to include in the research paper introduction, the rest of the paper should also be considered. The aim is to introduce the reader smoothly to the topic and facilitate an easy read without much dependency on external sources. 3

Below is a list of elements you can include to prepare a research paper introduction outline and follow it when you are writing the research paper introduction.

• Topic introduction: This can include key definitions and a brief history of the topic.
• Research context and background: Offer the readers some general information and then narrow it down to specific aspects.
• Details of the research you conducted: A brief literature review can be included to support your arguments or line of thought.
• Rationale for the study: This establishes the relevance of your study and establishes its importance.
• Importance of your research: The main contributions are highlighted to help establish the novelty of your study
• Research hypothesis: Introduce your research question and propose an expected outcome. Organization of the paper: Include a short paragraph of 3-4 sentences that highlights your plan for the entire paper

Should I include citations in the introduction for a research paper?

Cite only works that are most relevant to your topic; as a general rule, you can include one to three. Note that readers want to see evidence of original thinking. So it is better to avoid using too many references as it does not leave much room for your personal standpoint to shine through.

Citations in your research paper introduction support the key points, and the number of citations depend on the subject matter and the point discussed. If the research paper introduction is too long or overflowing with citations, it is better to cite a few review articles rather than the individual articles summarized in the review.

A good point to remember when citing research papers in the introduction section is to include at least one-third of the references in the introduction.

Should I provide a literature review in the research paper introduction?

The literature review plays a significant role in the research paper introduction section. A good literature review accomplishes the following:

• Introduces the topic
• Establishes the study’s significance
• Provides an overview of the relevant literature
• Provides context for the study using literature
• Identifies knowledge gaps

However, remember to avoid making the following mistakes when writing a research paper introduction:

• Do not use studies from the literature review to aggressively support your research
• Avoid direct quoting
• Do not allow literature review to be the focus of this section. Instead, the literature review should only aid in setting a foundation for the manuscript. 

Key points to remember

Remember the following key points for writing a good research paper introduction: 4

• Avoid stuffing too much general information: Avoid including what an average reader would know and include only that information related to the problem being addressed in the research paper introduction. For example, when describing a comparative study of non-traditional methods for mechanical design optimization, information related to the traditional methods and differences between traditional and non-traditional methods would not be relevant. In this case, the introduction for the research paper should begin with the state-of-the-art non-traditional methods and methods to evaluate the efficiency of newly developed algorithms.
• Avoid packing too many references: Cite only the required works in your research paper introduction. The other works can be included in the discussion section to strengthen your findings.
• Avoid extensive criticism of previous studies: Avoid being overly critical of earlier studies while setting the rationale for your study. A better place for this would be the Discussion section, where you can highlight the advantages of your method.
• Avoid describing conclusions of the study: When writing a research paper introduction remember not to include the findings of your study. The aim is to let the readers know what question is being answered. The actual answer should only be given in the Results and Discussion section.

To summarize, the research paper introduction section should be brief yet informative. It should convince the reader the need to conduct the study and motivate him to read further. If you’re feeling stuck or unsure, choose trusted AI academic writing assistants like Paperpal to effortlessly craft your research paper introduction and other sections of your research article.

• Jawaid, S. A., & Jawaid, M. (2019). How to write introduction and discussion. Saudi Journal of Anaesthesia, 13(Suppl 1), S18.
• Dewan, P., & Gupta, P. (2016). Writing the title, abstract and introduction: Looks matter!. Indian pediatrics, 53, 235-241.
• Cetin, S., & Hackam, D. J. (2005). An approach to the writing of a scientific Manuscript1. Journal of Surgical Research, 128(2), 165-167.
• Bavdekar, S. B. (2015). Writing introduction: Laying the foundations of a research paper. Journal of the Association of Physicians of India, 63(7), 44-6.

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How to write a research paper introduction (with examples).

I hope you enjoy reading this blog post.

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Welcome to our comprehensive guide on crafting the perfect introduction for your research paper. In this blog, we’ll explore the crucial elements of a strong introduction, highlight common pitfalls to avoid, and provide practical tips to effectively set the stage for your study’s objectives and significance. 

Table of Contents

Lack of a clear thesis statement, lack of clear objectives and scope, failure to establish the research significance, insufficient background information, inadequate literature review, ignoring the research gap, overly technical language, poor organization and flow, neglecting the audience, the importance of a good introduction.

A strong introduction sets the tone for the entire paper, guiding the reader through the research journey. It provides context, establishes relevance, and ensures the reader understands the importance of the study.

Starting a research project is exciting, but getting the introduction right is key. It’s like opening the door to your study and inviting readers in. However, there are some common missteps that can trip you up along the way.

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Common mistakes to avoid.

A thesis statement is the central argument or claim that guides the entire research paper. It is a concise summary of the main point or claim of the paper and is typically found at the end of the introduction. A clear thesis statement helps to focus the research, provide direction, and inform the reader of the paper’s purpose. Expert reviewers may even skip the rest of the introduction (as they are well versed in the topic) and focus only on your thesis statement, so it’s vital to make sure it is perfect!

When a research introduction lacks a clear thesis statement, several issues can arise:

• Ambiguity : Without a clear thesis, the reader may be confused about the paper’s purpose and the main argument. Do not talk in vague terms. Whenever possible, use terminology established in recent literature. Narrow down the key aspects of the association that you are investigating (the study sample, the outcome and predictor measures) as much as possible.
• Lack of Focus : The paper can become unfocused and meander through unrelated topics, making it difficult for the reader to follow the argument. Do not try to have more than 1-2 main aims in a paper. Even if you have done supplementary analysis, it is better to say so in the discussion. As a rule of thumb, try to answer one major question only!
• Weak Argumentation : A well-defined thesis provides a strong foundation for building arguments. Without it, the arguments may appear weak and unsupported.

Let's be more practical:

1- In this paper, I will discuss climate change.

• Problem: This statement is too broad and vague. It does not provide a clear direction or specific argument.

2- This paper argues that climate change, measured by global average temperature change, is primarily driven by human activities, such as deforestation and the burning of fossil fuels, and proposes policy measures to mitigate its impact.(1)

• Strengths: – Specificity : It clearly states that the paper will focus on human activities as the main drivers of climate change. – Argument : It presents a specific claim that the paper will argue. – Direction : It hints at the structure of the paper by mentioning policy measures.

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Powerful Tips:

• Be Specific : Clearly define the main argument or claim. Avoid vague or broad statements.
• Be Concise : Keep the thesis statement concise, ideally one to two sentences.
• Provide Direction : Indicate the structure of the paper by hinting at the main points that will be discussed.
• Revise as Needed : Be prepared to revise the thesis statement as your research progresses and your understanding deepens.

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A clear statement of objectives and scope is crucial in a research paper introduction because it outlines what the study aims to achieve and defines the boundaries within which the research will be conducted.

Example of Lacking Clear Objectives and Scope: This paper examines the impacts of climate change on agriculture.

• Problem : This statement is too broad and vague. It does not specify what aspects of climate change or agriculture will be studied, nor does it define the geographical or temporal scope.

Example with Clear Objectives and Scope: This study aims to investigate the effects of rising temperatures and changing precipitation patterns on crop yields in the Midwest United States from 2000 to 2010. The objectives are to (1) assess the impact of temperature changes on corn and soybean yields, (2) analyze how variations in precipitation affect crop growth, and (3) identify adaptive strategies employed by farmers in the region.(2)

Powerful tips:

• Be Specific : Clearly state what the study aims to achieve and avoid vague or broad statements.
• Identify Key Areas : Outline the main areas or aspects that the research will focus on.
• Set Boundaries : Define the geographical, temporal, and conceptual boundaries of the research.
• List Objectives : Clearly articulate specific research objectives or questions that the study will address.
• Stay Realistic : Ensure that the objectives and scope are achievable within the constraints of the research project.
• Make it flow : Make sure you are not repeating the same concepts as the thesis statement, as these two sections are often presented back-to-back in the final paragraph of the introduction! Remember: the thesis statement is your hypothesis or question, and your objectives are ‘how’ you are going to test your thesis.

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This mistake can result in the research appearing trivial or irrelevant, diminishing its potential impact. When the significance of the research is not well-established, readers may struggle to understand the value of the study and why they should care about it.

Example of Failure to Establish Research Significance: This study investigates the effects of social media usage on sleep patterns among teenagers.

• Problem : The significance of studying social media’s impact on sleep patterns is not explained. The reader may wonder why this research is important or what implications it has.

Example with Established Research Significance: This study investigates the effects of social media usage on sleep patterns among teenagers. Understanding this relationship is crucial because insufficient sleep is linked to numerous health issues, including decreased academic performance, heightened stress levels, and increased risk of mental health problems. With the pervasive use of social media among adolescents, identifying how it impacts sleep can inform strategies for promoting healthier habits and improving overall well-being in this vulnerable age group.(3)

• Link to Broader Issues : Connect the research topic to broader issues or trends that highlight its relevance and importance.
• Explain Practical Implications : Discuss the potential practical applications or benefits of the research findings.
• Address Gaps in Knowledge : Identify gaps in the existing literature that the research aims to fill.
• Highlight Potential Impact : Emphasize the potential impact of the research on the field, society, or specific populations.
• Use Concrete Examples : Provide concrete examples or scenarios to illustrate the significance of the research.

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Insufficient background information in the introduction of a research paper refers to failing to provide enough context for the reader to understand the research problem and its significance. Background information sets the stage for the research by offering necessary details about the topic, relevant theories, previous studies, and key terms.

This may lead to:

• Reader Confusion : Without adequate context, readers may struggle to understand the research question, its importance, and how it fits into the broader field of study.
• Weak Justification : Insufficient background can undermine the rationale for the research, making it difficult to justify why the study is necessary or valuable.
• Misinterpretation : Lack of context can lead to misinterpretation of the research objectives, methods, and findings.

Example of Insufficient Background Information: In recent years, many researchers have studied the effects of social media on teenagers. This paper explores the relationship between social media use and anxiety among teenagers.

• Problem : This introduction lacks specific details about the previous research, the theoretical framework, and key terms. It does not provide enough context for the reader to understand why the study is important.

Example of Adequate Background Information: Social media platforms have become an integral part of teenagers’ daily lives, with studies showing that 95% of teens have access to a smartphone and 45% are online almost constantly. Previous research has linked excessive social media use to various mental health issues, including anxiety and depression. However, the mechanisms underlying this relationship remain unclear. This paper explores the impact of social media use on anxiety levels among teenagers, focusing on the roles of social comparison and cyberbullying.(4)

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• Review Relevant Literature : Summarize key studies and theories related to your topic.
• Provide Context : Explain the broader context of your research problem.
• Define Key Terms : Ensure that any specialized terms or concepts are clearly defined.
• Identify the Research Gap : Highlight what is not yet known or understood about your topic.
• Be Concise : Provide enough information to set the stage without overwhelming the reader with details.

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This mistake can occur when the literature review is too brief, lacks depth, omits key studies, or fails to critically analyze previous work. An inadequate literature review can undermine the foundation of the research by failing to provide the necessary context and justification for the study.

Inadequate Literature Review: There has been some research on the relationship between exercise and mental health. This paper will investigate this relationship further.

• Problem : This review is too general and does not provide sufficient detail about the existing research or how it informs the current study.

Example with Adequate Literature Review: Research has consistently shown that regular physical activity has positive effects on mental health. For example, a study by Gujral et al. (2019) demonstrated that aerobic exercise can significantly reduce symptoms of depression and anxiety. Similarly, Smith and Lee (2020) found that strength training also contributes to improved mood and reduced stress levels. However, much of the existing research has focused on adult populations, with relatively few studies examining these effects in adolescents. Additionally, the specific types of exercise that are most beneficial for different mental health outcomes have not been thoroughly investigated. This study aims to explore the effects of various types of exercise on the mental health of high school students, thereby addressing these gaps in the literature.(5-6)

• Be Comprehensive : Review a broad range of studies related to the research topic to provide a thorough context.
• Be Specific : Cite specific studies, including their methodologies, findings, and relevance to the current research.
• Be Critical : Analyze and evaluate the existing research, identifying strengths, weaknesses, and gaps.
• Be Structured : Organize the literature review logically, grouping studies by themes or findings to create a coherent narrative.
• Be Relevant : Focus on the most relevant studies that directly relate to the research question and objectives.

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Ignoring the research gap in a research paper introduction means failing to identify and articulate what specific aspect of the topic has not been explored or adequately addressed in existing literature. The research gap is a critical component because it justifies the necessity and originality of the study. Without highlighting this gap, the research may appear redundant or lacking in significance.

How huge is this mistake?

• Lack of Justification : The study may not appear necessary or relevant, diminishing its perceived value.
• Redundancy : The research may seem to duplicate existing studies, offering no new insights or contributions to the field. Even if you are using methodology similar to previous studies, it is important to note why you are doing so e.g., few studies have used that specific methodology, and you would like to validate it in your sample population!
• Reader Disinterest : Readers may lose interest if they do not see the unique contribution or purpose of the research.

Example of Ignoring the Research Gap: Many studies have examined the effects of exercise on mental health. This paper looks at the relationship between physical activity and depression.

• Problem : This introduction does not specify what aspect of the relationship between physical activity and depression has not been studied, failing to highlight the unique contribution of the research.

Example of Identifying the Research Gap: Numerous studies have demonstrated the general benefits of physical activity on mental health, particularly its role in alleviating symptoms of depression. However, there is limited research on how different types of exercise (e.g., aerobic vs. anaerobic) specifically impact depression levels among various age groups. This study investigates the differential effects of aerobic and anaerobic exercise on depression in young adults, aiming to fill this gap in the literature.(6)

• Conduct a Thorough Literature Review : Understand the current state of research in your field to identify what has been studied and where gaps exist.
• Be Specific : Clearly articulate what specific aspect has not been covered in existing studies.
• Link to Your Study : Explain how your research will address this gap and contribute to the field.
• Use Evidence : Support your identification of the gap with references to previous studies.
• Emphasize Significance : Highlight why filling this gap is important for advancing knowledge or practical applications.

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Overly technical language refers to the excessive use of jargon, complex terms, and highly specialized language that may be difficult for readers, especially those not familiar with the field, to understand. While technical language is sometimes necessary in academic writing, overusing it in the introduction can create several problems:

• Reader Alienation : Readers may find the text intimidating or inaccessible, leading to disengagement.
• Lack of Clarity : The main points and significance of the research can become obscured by complex terminology.
• Reduced Impact : The research may fail to communicate its importance effectively if readers struggle to understand the introduction.

Example of Overly Technical Language: The present study examines the metacognitive strategies employed by individuals in the domain of second language acquisition, specifically focusing on the interaction between declarative and procedural memory systems in the process of syntactic parsing.

• Problem : This sentence is loaded with jargon (“metacognitive strategies,” “second language acquisition,” “declarative and procedural memory systems,” “syntactic parsing”), which can be overwhelming and confusing for readers not familiar with these terms.

Example with Simplified Language: This study looks at the thinking strategies people use when learning a second language. It focuses on how different types of memory, such as the knowledge of facts and the skills for doing things, help in understanding sentence structures.(7)

• Know Your Audience : Tailor the language to the intended audience, ensuring it is accessible to both specialists and non-specialists.
• Define Term s: When technical terms are necessary, provide clear definitions or explanations.
• Use Analogies : Simplify complex concepts using analogies or examples that are easy to understand.
• Avoid Jargon : Limit the use of jargon and specialized terms, especially in the introduction.
• Seek Feedback : Ask peers or non-experts to read the introduction and provide feedback on clarity and accessibility.

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Poor organization and flow in a research paper introduction refer to a lack of logical structure and coherence that makes the introduction difficult to follow. This can occur when ideas are presented in a haphazard manner, transitions between sections are weak or non-existent, and the overall narrative is disjointed. A well-organized introduction should smoothly guide the reader from the general context to the specific objectives of the study.

Example of Poor Organization and Flow: “Climate change affects agriculture in various ways. Many studies have looked at the impact on crop yields. This paper will discuss the economic implications of these changes. Climate models predict increased variability in weather patterns, which will affect water availability. Researchers have found that higher temperatures reduce the growing season for many crops.”

• Problem : The ideas are presented in a scattered manner without clear connections. The mention of economic implications seems out of place, and there are abrupt shifts between topics.

Example with Good Organization and Flow: Climate change poses significant challenges to agriculture by altering weather patterns, impacting crop yields, and affecting water availability. Numerous studies have shown that increased temperatures can shorten the growing season for many crops, leading to reduced yields. Additionally, climate models predict increased variability in weather patterns, which complicates water management for farmers. These changes not only affect food production but also have substantial economic implications for agricultural communities. This paper will examine the economic impacts of climate-induced changes in agriculture, focusing on crop yield variability and water resource management.(1)

• Create an Outline : Before writing, outline the main points you want to cover in the introduction.
• Think in terms of an inverted triangle : Begin broadly to introduce basic concepts related to your topic. As you progress through the introduction, you can introduce more and more specific topics until you have enough information to justify your thesis statement
• Use Transitional Phrases : Employ transitional phrases and sentences to connect ideas and sections smoothly.
• Follow a Logical Sequence : Present information in a logical order, moving from general context to specific objectives.
• Maintain Focus : Stay focused on the main topic and avoid introducing unrelated ideas.
• Revise for Coherence : Review and revise the introduction to ensure that it flows well and that each part contributes to the overall narrative.

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Neglecting the audience refers to failing to consider the background, knowledge level, and interests of the intended readers when writing the introduction of a research paper. This mistake can manifest in several ways, such as using overly technical language for a general audience, providing insufficient background information for readers unfamiliar with the topic, or failing to engage the readers’ interest.

Example of Neglecting the Audience: For experts in genomic sequencing, this study explores the epigenetic modifications resulting from CRISPR-Cas9 interventions, focusing on the methylation patterns and histone modifications observed in gene-edited cells.

• Problem : This introduction assumes a high level of expertise in genomic sequencing and epigenetics, which may alienate readers without this background.

Example with Audience Consideration: CRISPR-Cas9 is a groundbreaking tool in genetic research that allows scientists to edit DNA with precision. However, altering genes can lead to unexpected changes in how genes are expressed, known as epigenetic modifications. This study investigates these changes by looking at specific markers on DNA, such as methylation patterns, and how they affect gene activity in cells that have been edited using CRISPR-Cas9. Our goal is to understand the broader implications of gene editing on cellular functions, which is crucial for advancing medical research and treatments.(8)

• Identify the Audience : Determine who the intended readers are (e.g., experts, students, general public) and tailor the language and content accordingly. Read papers from the journals you are considering for submission. Professional editors curate the language used in these papers and are a great starting point to identify the level of expertise of your audience!
• Simplify Language : Use clear and straightforward language, avoiding jargon and technical terms unless they are necessary and well-explained.
• Provide Background Information : Include sufficient background information to help readers understand the context and significance of the research.
• Engage the Reader : Start with an engaging introduction that highlights the relevance and importance of the research topic.
• Anticipate Questions : Consider what questions or concerns the audience might have and address them in the introduction

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By following these guidelines and avoiding common pitfalls, you can create an introduction that not only grabs the attention of your readers but also sets the stage for a compelling and impactful research paper.

Final Tips:

• Revise and refine your introduction multiple times to ensure clarity and coherence.
• Seek feedback from peers, mentors, or advisors to identify areas for improvement.
• Keep your audience in mind and tailor your language and content to their needs and interests.
• Stay focused on your research objectives and ensure that every part of your introduction contributes to achieving them.
• Be confident in the significance of your research and its potential impact on your field or community.

Let your introduction be more than just words on a page. It’s a doorway to understanding. To help you along, we’ve created a practical course on writing and publishing research projects. It’s 100% risk-free, with a money-back guarantee if you’re not satisfied. Try it out now by clicking here .

Wishing you success on your research journey!

Marina Ramzy Mourid, Hamza Ibad, MBBS

Dr. Ibad graduated from the Aga Khan University Medical College and completed a post-doctoral research fellowship at Johns Hopkins in the Department of Radiology (Musculoskeletal Division). Dr. Ibad’s research and clinical interests include deep-learning applications for automated image interpretation, osteoarthritis, and sarcopenia-related health outcomes.

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About thematchguy, become a researcher in the united states, interested in learning more about literature search with examples from published literature, the comprehensive research course, the systematic review course, the medical statistics course, how to find research positions in the us.

1. Abbass K, Qasim MZ, Song H, Murshed M, Mahmood H, Younis I. A review of the global climate change impacts, adaptation, and sustainable mitigation measures. Environ Sci Pollut Res. 2022;29(28):42539-42559. doi:10.1007/s11356-022-19718-6

2. Cai X, Wang D, Laurent R. Impact of climate change on crop yield: a case study of rainfed corn in central illinois. Journal of Applied Meteorology and Climatology. 2009;48(9):1868-1881. doi:10.1175/2009JAMC1880.1

3. Van Den Eijnden RJJM, Geurts SM, Ter Bogt TFM, Van Der Rijst VG, Koning IM. Social media use and adolescents’ sleep: a longitudinal study on the protective role of parental rules regarding internet use before sleep. IJERPH. 2021;18(3):1346. doi:10.3390/ijerph18031346

4. Schmitt, M. (2021). Effects of social media and technology on adolescents: What the evidence is showing and what we can do about it. Journal of Family and Consumer Sciences Education, 38(1), 51-59.

5. Gujral S, Aizenstein H, Reynolds CF, Butters MA, Erickson KI. Exercise effects on depression: Possible neural mechanisms. General Hospital Psychiatry. 2017;49:2-10. doi:10.1016/j.genhosppsych.2017.04.012

6. Smith PJ, Merwin RM. The role of exercise in management of mental health disorders: an integrative review. Annu Rev Med. 2021;72(1):45-62. doi:10.1146/annurev-med-060619-022943

7. Sun Q, Zhang LJ. Understanding learners’ metacognitive experiences in learning to write in English as a foreign language: A structural equation modeling approach. Front Psychol. 2022;13:986301. doi:10.3389/fpsyg.2022.986301

8. Kolanu ND. Crispr–cas9 gene editing: curing genetic diseases by inherited epigenetic modifications. Glob Med Genet. 2024;11(01):113-122. doi:10.1055/s-0044-1785234

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Writing an Introduction for a Scientific Paper

Dr. michelle harris, dr. janet batzli, biocore.

This section provides guidelines on how to construct a solid introduction to a scientific paper including background information, study question , biological rationale, hypothesis , and general approach . If the Introduction is done well, there should be no question in the reader’s mind why and on what basis you have posed a specific hypothesis.

Broad Question : based on an initial observation (e.g., “I see a lot of guppies close to the shore. Do guppies like living in shallow water?”). This observation of the natural world may inspire you to investigate background literature or your observation could be based on previous research by others or your own pilot study. Broad questions are not always included in your written text, but are essential for establishing the direction of your research.

Background Information : key issues, concepts, terminology, and definitions needed to understand the biological rationale for the experiment. It often includes a summary of findings from previous, relevant studies. Remember to cite references, be concise, and only include relevant information given your audience and your experimental design. Concisely summarized background information leads to the identification of specific scientific knowledge gaps that still exist. (e.g., “No studies to date have examined whether guppies do indeed spend more time in shallow water.”)

Testable Question : these questions are much more focused than the initial broad question, are specific to the knowledge gap identified, and can be addressed with data. (e.g., “Do guppies spend different amounts of time in water <1 meter deep as compared to their time in water that is >1 meter deep?”)

Biological Rationale : describes the purpose of your experiment distilling what is known and what is not known that defines the knowledge gap that you are addressing. The “BR” provides the logic for your hypothesis and experimental approach, describing the biological mechanism and assumptions that explain why your hypothesis should be true.

The biological rationale is based on your interpretation of the scientific literature, your personal observations, and the underlying assumptions you are making about how you think the system works. If you have written your biological rationale, your reader should see your hypothesis in your introduction section and say to themselves, “Of course, this hypothesis seems very logical based on the rationale presented.”

• A thorough rationale defines your assumptions about the system that have not been revealed in scientific literature or from previous systematic observation. These assumptions drive the direction of your specific hypothesis or general predictions.
• Defining the rationale is probably the most critical task for a writer, as it tells your reader why your research is biologically meaningful. It may help to think about the rationale as an answer to the questions— how is this investigation related to what we know, what assumptions am I making about what we don’t yet know, AND how will this experiment add to our knowledge? *There may or may not be broader implications for your study; be careful not to overstate these (see note on social justifications below).
• Expect to spend time and mental effort on this. You may have to do considerable digging into the scientific literature to define how your experiment fits into what is already known and why it is relevant to pursue.
• Be open to the possibility that as you work with and think about your data, you may develop a deeper, more accurate understanding of the experimental system. You may find the original rationale needs to be revised to reflect your new, more sophisticated understanding.
• As you progress through Biocore and upper level biology courses, your rationale should become more focused and matched with the level of study e ., cellular, biochemical, or physiological mechanisms that underlie the rationale. Achieving this type of understanding takes effort, but it will lead to better communication of your science.

***Special note on avoiding social justifications: You should not overemphasize the relevance of your experiment and the possible connections to large-scale processes. Be realistic and logical —do not overgeneralize or state grand implications that are not sensible given the structure of your experimental system. Not all science is easily applied to improving the human condition. Performing an investigation just for the sake of adding to our scientific knowledge (“pure or basic science”) is just as important as applied science. In fact, basic science often provides the foundation for applied studies.

Hypothesis / Predictions : specific prediction(s) that you will test during your experiment. For manipulative experiments, the hypothesis should include the independent variable (what you manipulate), the dependent variable(s) (what you measure), the organism or system , the direction of your results, and comparison to be made.

If you are doing a systematic observation , your hypothesis presents a variable or set of variables that you predict are important for helping you characterize the system as a whole, or predict differences between components/areas of the system that help you explain how the system functions or changes over time.

Experimental Approach : Briefly gives the reader a general sense of the experiment, the type of data it will yield, and the kind of conclusions you expect to obtain from the data. Do not confuse the experimental approach with the experimental protocol . The experimental protocol consists of the detailed step-by-step procedures and techniques used during the experiment that are to be reported in the Methods and Materials section.

Some Final Tips on Writing an Introduction

• As you progress through the Biocore sequence, for instance, from organismal level of Biocore 301/302 to the cellular level in Biocore 303/304, we expect the contents of your “Introduction” paragraphs to reflect the level of your coursework and previous writing experience. For example, in Biocore 304 (Cell Biology Lab) biological rationale should draw upon assumptions we are making about cellular and biochemical processes.
• Be Concise yet Specific: Remember to be concise and only include relevant information given your audience and your experimental design. As you write, keep asking, “Is this necessary information or is this irrelevant detail?” For example, if you are writing a paper claiming that a certain compound is a competitive inhibitor to the enzyme alkaline phosphatase and acts by binding to the active site, you need to explain (briefly) Michaelis-Menton kinetics and the meaning and significance of Km and Vmax. This explanation is not necessary if you are reporting the dependence of enzyme activity on pH because you do not need to measure Km and Vmax to get an estimate of enzyme activity.
• Another example: if you are writing a paper reporting an increase in Daphnia magna heart rate upon exposure to caffeine you need not describe the reproductive cycle of magna unless it is germane to your results and discussion. Be specific and concrete, especially when making introductory or summary statements.

Where Do You Discuss Pilot Studies? Many times it is important to do pilot studies to help you get familiar with your experimental system or to improve your experimental design. If your pilot study influences your biological rationale or hypothesis, you need to describe it in your Introduction. If your pilot study simply informs the logistics or techniques, but does not influence your rationale, then the description of your pilot study belongs in the Materials and Methods section.  

How will introductions be evaluated? The following is part of the rubric we will be using to evaluate your papers.

Ertugrul Portakal

Apr 12, 2024

Writing a Research Paper Introduction (with 3 Examples)

Nail your research paper's introduction! Learn to captivate and inform readers from the start—our guide shows how!

TABLE OF CONTENTS

A catchy and informative introduction is essential in academic writing, especially if you want your readers to have background information about your paper. However, writing an interesting and informative introduction can sometimes be a time-consuming and tiring process. If you don't know where to start when crafting an introduction, no need to worry - we've got you covered!

In this article, we will explain step by step what an introduction is in academic writing and how to write it!

Ready? Let's start!

• An introduction is a paragraph that provides information about your entire paper and aims to attract and inform the reader.
• Before writing an introduction or even starting your paper, you need to research academic sources.
• The first one or two sentences of an introduction paragraph should be a hook to attract the reader's attention.
• Afterwards, you need to prepare the reader for your argument by giving background information about your topic.
• Finally, you should state your argument about your topic with a thesis statement.
• If you are writing a longer paper, you can inform your readers about the map of your paper.
• If you are looking for an AI assistant to support you throughout your writing process, TextCortex is designed for you with its advanced features.

What is an Introduction in a research paper?

In any academic writing, including essays and research papers, an introduction is the first paragraph that the reader will encounter. This paragraph should both attract the reader's attention and give them the necessary information about the paper. In any academic paper, the introduction paragraph constitutes 10% of the paper's total word count. For example, if you are preparing a 3,000-word paper, your introduction paragraph should consist of approximately 300 words. You should also write sentences within these 300 words that will attract the reader's attention and provide them with information about the paper.

Importance of an Introduction Paragraph

The biggest function of an introduction paragraph is to prepare the reader for the author's thesis statement. A traditional introduction paragraph begins with a few sentences or questions that will catch the reader's attention. After attracting the reader's attention, necessary background information on the subject is given. Finally, the author explains to the readers what the whole paper is about by stating the thesis. A thesis statement is the final sentence that summarizes the main points of your paper and conveys your claim.

First Things First: Preliminary Research

When working on any academic writing type, it is essential to start by researching your topic thoroughly before beginning to type. What sets academic writing apart from other writing types is the requirement for it to be written using accurate information from reliable sources.

Researching academic sources can be a time-consuming and unnecessary process. One has to read through hundreds of pages, review dozens of articles and verify the accuracy of each source. However, if you're looking to reduce your workload and maximize efficiency by automating repetitive tasks such as literature review, ZenoChat is the perfect solution for you. With its web search feature, ZenoChat can use the entire internet as a data source. Additionally, by activating the "scholar" option of the ZenoChat web search feature, you can ensure that it only uses academic sources when generating output.

How to Create an Introduction for Academic Writing?

Creating an introduction paragraph that is interesting, informative, and conveys your thesis is an easier process than it seems. As long as you have sufficient information about your topic and an outline , you can write engaging introductions by following a few simple steps. Let's take a closer look at how to write an introduction for academic writing.

1-) Start with a Catchy Hook

Your first sentence is one of the factors that most influence a reader's decision to read your paper. This sentence determines the tone of your paper and attracts the reader's attention. For this reason, we recommend that you start your introduction paragraph with a strong and catchy hook sentence.

• Avoid long and complex sentences
• Use clear and concise sentences
• Write a sentence that will spark the reader's curiosity
• You can ask questions that will encourage the reader to read the remaining paragraph
• Avoid fact or overly broad sentences
• Avoid using dictionary definitions as your hook

2-) Give Background Information

After writing a strong hook sentence, you need to provide basic information about your topic so that the reader can understand what they will learn about when they read your paper. In this section, you can benefit from opinions that support or oppose your argument. Additionally, this section should refer to the body paragraphs of your writing.

• You can write a background information sentence for each body paragraph.
• The information here should be concise and compact
• Avoid talking about your evidence and results unless necessary.

3-) State Your Thesis 

After attracting the reader's attention and providing background information, it is time to present your approach and argument towards the topic with a thesis statement. A thesis statement usually comprises one or two sentences and communicates the paper's argument to the reader. A well-written thesis statement should express your stance on the topic.

• Avoid merely stating a fact
• Claim your argument

4-) Tell Reader About Your Paper

Although you need to move on to body paragraphs after the thesis statement in short papers, it will be useful to add a few sentences that will guide the reader in your longer papers. This way, your readers can better understand which arguments they will encounter on which pages and the course of your paper. That leads the reader to clearly understand and follow your content.

Let’s Wrap it Up

Writing an interesting and informative introduction is usually a long process that requires a lot of rewriting. You may need to rewrite a sentence dozens of times so that your words and sentences clearly describe your paper and argument. Fortunately, you can generate state-of-the-art introductions using AI tools and use them with a little editing.

When it comes to text generation, paraphrasing, and grammar & spelling checking, TextCortex is the way to go with its advanced LLMs and customization options. With TextCortex, you can generate all writing types, including introduction, from scratch, rewrite your existing texts, change their tone of voice, or fix their grammar. TextCortex is available as a web application and browser extension. The TextCortex browser extension is integrated with 30,000+ websites and apps. So, you can complete your AI-driven writing tasks anywhere and anytime.

Let's examine a few sample introductions generated by TextCortex.

Example Introduction #1

“Should social media platforms be banned from collecting their users' data?”

Example Introduction #2

“Do electric vehicles decrease overall emissions?”

Example Introduction #3

“Is graffiti an act of vandalism or the creation of art?”

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Our AI copilot learned how to write from more than 3 billion sentences and has the ability to create unique content. However, fact-checking is something which still requires a human approval.

TextCortex supports more than 25 languages including English, Dutch, German, Ukranian, Romanian, Spanish, Portuguese, French, Italian.

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Research Paper Introduction Examples

Looking for research paper introduction examples? Quotes, anecdotes, questions, examples, and broad statements—all of them can be used successfully to write an introduction for a research paper. It’s instructive to see them in action, in the hands of skilled academic writers.

Let’s begin with David M. Kennedy’s superb history, Freedom from Fear: The American People in Depression and War, 1929–1945 . Kennedy begins each chapter with a quote, followed by his text. The quote above chapter 1 shows President Hoover speaking in 1928 about America’s golden future. The text below it begins with the stock market collapse of 1929. It is a riveting account of just how wrong Hoover was. The text about the Depression is stronger because it contrasts so starkly with the optimistic quotation.

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“We in America today are nearer the final triumph over poverty than ever before in the history of any land.”—Herbert Hoover, August 11, 1928 Like an earthquake, the stock market crash of October 1929 cracked startlingly across the United States, the herald of a crisis that was to shake the American way of life to its foundations. The events of the ensuing decade opened a fissure across the landscape of American history no less gaping than that opened by the volley on Lexington Common in April 1775 or by the bombardment of Sumter on another April four score and six years later. (adsbygoogle = window.adsbygoogle || []).push({}); The ratcheting ticker machines in the autumn of 1929 did not merely record avalanching stock prices. In time they came also to symbolize the end of an era. (David M. Kennedy, Freedom from Fear: The American People in Depression and War, 1929–1945 . New York: Oxford University Press, 1999, p. 10)

Kennedy has exciting, wrenching material to work with. John Mueller faces the exact opposite problem. In Retreat from Doomsday: The Obsolescence of Major War , he is trying to explain why Great Powers have suddenly stopped fighting each other. For centuries they made war on each other with devastating regularity, killing millions in the process. But now, Mueller thinks, they have not just paused; they have stopped permanently. He is literally trying to explain why “nothing is happening now.” That may be an exciting topic intellectually, it may have great practical significance, but “nothing happened” is not a very promising subject for an exciting opening paragraph. Mueller manages to make it exciting and, at the same time, shows why it matters so much. Here’s his opening, aptly entitled “History’s Greatest Nonevent”:

On May 15, 1984, the major countries of the developed world had managed to remain at peace with each other for the longest continuous stretch of time since the days of the Roman Empire. If a significant battle in a war had been fought on that day, the press would have bristled with it. As usual, however, a landmark crossing in the history of peace caused no stir: the most prominent story in the New York Times that day concerned the saga of a manicurist, a machinist, and a cleaning woman who had just won a big Lotto contest. This book seeks to develop an explanation for what is probably the greatest nonevent in human history. (John Mueller, Retreat from Doomsday: The Obsolescence of Major War . New York: Basic Books, 1989, p. 3)

In the space of a few sentences, Mueller sets up his puzzle and reveals its profound human significance. At the same time, he shows just how easy it is to miss this milestone in the buzz of daily events. Notice how concretely he does that. He doesn’t just say that the New York Times ignored this record setting peace. He offers telling details about what they covered instead: “a manicurist, a machinist, and a cleaning woman who had just won a big Lotto contest.” Likewise, David Kennedy immediately entangles us in concrete events: the stunning stock market crash of 1929. These are powerful openings that capture readers’ interests, establish puzzles, and launch narratives.

Sociologist James Coleman begins in a completely different way, by posing the basic questions he will study. His ambitious book, Foundations of Social Theory , develops a comprehensive theory of social life, so it is entirely appropriate for him to begin with some major questions. But he could just as easily have begun with a compelling story or anecdote. He includes many of them elsewhere in his book. His choice for the opening, though, is to state his major themes plainly and frame them as a paradox. Sociologists, he says, are interested in aggregate behavior—how people act in groups, organizations, or large numbers—yet they mostly examine individuals:

A central problem in social science is that of accounting for the function of some kind of social system. Yet in most social research, observations are not made on the system as a whole, but on some part of it. In fact, the natural unit of observation is the individual person…  This has led to a widening gap between theory and research… (James S. Coleman, Foundations of Social Theory . Cambridge, MA: Harvard University Press, 1990, pp. 1–2)

After expanding on this point, Coleman explains that he will not try to remedy the problem by looking solely at groups or aggregate-level data. That’s a false solution, he says, because aggregates don’t act; individuals do. So the real problem is to show the links between individual actions and aggregate outcomes, between the micro and the macro.

The major problem for explanations of system behavior based on actions and orientations at a level below that of the system [in this case, on individual-level actions] is that of moving from the lower level to the system level. This has been called the micro-to-macro problem, and it is pervasive throughout the social sciences. (Coleman, Foundations of Social Theory , p. 6)

Explaining how to deal with this “micro-to-macro problem” is the central issue of Coleman’s book, and he announces it at the beginning.

Coleman’s theory-driven opening stands at the opposite end of the spectrum from engaging stories or anecdotes, which are designed to lure the reader into the narrative and ease the path to a more analytic treatment later in the text. Take, for example, the opening sentences of Robert L. Herbert’s sweeping study Impressionism: Art, Leisure, and Parisian Society : “When Henry Tuckerman came to Paris in 1867, one of the thousands of Americans attracted there by the huge international exposition, he was bowled over by the extraordinary changes since his previous visit twenty years before.” (Robert L. Herbert, Impressionism: Art, Leisure, and Parisian Society . New Haven, CT: Yale University Press, 1988, p. 1.) Herbert fills in the evocative details to set the stage for his analysis of the emerging Impressionist art movement and its connection to Parisian society and leisure in this period.

David Bromwich writes about Wordsworth, a poet so familiar to students of English literature that it is hard to see him afresh, before his great achievements, when he was just a young outsider starting to write. To draw us into Wordsworth’s early work, Bromwich wants us to set aside our entrenched images of the famous mature poet and see him as he was in the 1790s, as a beginning writer on the margins of society. He accomplishes this ambitious task in the opening sentences of Disowned by Memory: Wordsworth’s Poetry of the 1790s :

Wordsworth turned to poetry after the revolution to remind himself that he was still a human being. It was a curious solution, to a difficulty many would not have felt. The whole interest of his predicament is that he did feel it. Yet Wordsworth is now so established an eminence—his name so firmly fixed with readers as a moralist of self-trust emanating from complete self-security—that it may seem perverse to imagine him as a criminal seeking expiation. Still, that is a picture we get from The Borderers and, at a longer distance, from “Tintern Abbey.” (David Bromwich, Disowned by Memory: Wordsworth’s Poetry of the 1790s . Chicago: University of Chicago Press, 1998, p. 1)

That’s a wonderful opening! Look at how much Bromwich accomplishes in just a few words. He not only prepares the way for analyzing Wordsworth’s early poetry; he juxtaposes the anguished young man who wrote it to the self-confident, distinguished figure he became—the eminent man we can’t help remembering as we read his early poetry.

Let us highlight a couple of other points in this passage because they illustrate some intelligent writing choices. First, look at the odd comma in this sentence: “It was a curious solution, to a difficulty many would not have felt.” Any standard grammar book would say that comma is wrong and should be omitted. Why did Bromwich insert it? Because he’s a fine writer, thinking of his sentence rhythm and the point he wants to make. The comma does exactly what it should. It makes us pause, breaking the sentence into two parts, each with an interesting point. One is that Wordsworth felt a difficulty others would not have; the other is that he solved it in a distinctive way. It would be easy for readers to glide over this double message, so Bromwich has inserted a speed bump to slow us down. Most of the time, you should follow grammatical rules, like those about commas, but you should bend them when it serves a good purpose. That’s what the writer does here.

The second small point is the phrase “after the revolution” in the first sentence: “Wordsworth turned to poetry after the revolution to remind himself that he was still a human being.” Why doesn’t Bromwich say “after the French Revolution”? Because he has judged his book’s audience. He is writing for specialists who already know which revolution is reverberating through English life in the 1790s. It is the French Revolution, not the earlier loss of the American colonies. If Bromwich were writing for a much broader audience—say, the New York Times Book Review—he would probably insert the extra word to avoid confusion.

The message “Know your audience” applies to all writers. Don’t talk down to them by assuming they can’t get dressed in the morning. Don’t strut around showing off your book learnin’ by tossing in arcane facts and esoteric language for its own sake. Neither will win over readers.

Bromwich, Herbert, and Coleman open their works in different ways, but their choices work well for their different texts. Your task is to decide what kind of opening will work best for yours. Don’t let that happen by default, by grabbing the first idea you happen upon. Consider a couple of different ways of opening your thesis and then choose the one you prefer. Give yourself some options, think them over, then make an informed choice.

Using the Introduction to Map out Your Writing

Whether you begin with a story, puzzle, or broad statement, the next part of the research paper introduction should pose your main questions and establish your argument. This is your thesis statement—your viewpoint along with the supporting reasons and evidence. It should be articulated plainly so readers understand full well what your paper is about and what it will argue.

After that, give your readers a road map of what’s to come. That’s normally done at the end of the introductory section (or, in a book, at the end of the introductory chapter). Here’s John J. Mearsheimer presenting such a road map in The Tragedy of Great Power Politics . He not only tells us the order of upcoming chapters, he explains why he’s chosen that order and which chapters are most important:

The Plan of the Book The rest of the chapters in this book are concerned mainly with answering the six big questions about power which I identified earlier. Chapter 2, which is probably the most important chapter in the book, lays out my theory of why states compete for power and why they pursue hegemony. In Chapters 3 and 4, I define power and explain how to measure it. I do this in order to lay the groundwork for testing my theory… (John J. Mearsheimer, The Tragedy of Great Power Politics . New York: W. W. Norton, 2001, p. 27)

As this excerpt makes clear, Mearsheimer has already laid out his “six big questions” in the research paper introduction. Now he’s showing us the path ahead, the path to answering those questions.

At the end of the research paper introduction, give your readers a road map of what’s to come. Tell them what the upcoming sections will be and why they are arranged in this particular order.

Learn how to write an introduction for a research paper .

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• How to write an essay introduction | 4 steps & examples

How to Write an Essay Introduction | 4 Steps & Examples

Published on February 4, 2019 by Shona McCombes . Revised on July 23, 2023.

A good introduction paragraph is an essential part of any academic essay . It sets up your argument and tells the reader what to expect.

The main goals of an introduction are to:

• Catch your reader’s attention.
• Give background on your topic.
• Present your thesis statement —the central point of your essay.

This introduction example is taken from our interactive essay example on the history of Braille.

The invention of Braille was a major turning point in the history of disability. The writing system of raised dots used by visually impaired people was developed by Louis Braille in nineteenth-century France. In a society that did not value disabled people in general, blindness was particularly stigmatized, and lack of access to reading and writing was a significant barrier to social participation. The idea of tactile reading was not entirely new, but existing methods based on sighted systems were difficult to learn and use. As the first writing system designed for blind people’s needs, Braille was a groundbreaking new accessibility tool. It not only provided practical benefits, but also helped change the cultural status of blindness. This essay begins by discussing the situation of blind people in nineteenth-century Europe. It then describes the invention of Braille and the gradual process of its acceptance within blind education. Subsequently, it explores the wide-ranging effects of this invention on blind people’s social and cultural lives.

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Table of contents

Step 1: hook your reader, step 2: give background information, step 3: present your thesis statement, step 4: map your essay’s structure, step 5: check and revise, more examples of essay introductions, other interesting articles, frequently asked questions about the essay introduction.

Your first sentence sets the tone for the whole essay, so spend some time on writing an effective hook.

Avoid long, dense sentences—start with something clear, concise and catchy that will spark your reader’s curiosity.

The hook should lead the reader into your essay, giving a sense of the topic you’re writing about and why it’s interesting. Avoid overly broad claims or plain statements of fact.

Examples: Writing a good hook

Take a look at these examples of weak hooks and learn how to improve them.

• Braille was an extremely important invention.
• The invention of Braille was a major turning point in the history of disability.

The first sentence is a dry fact; the second sentence is more interesting, making a bold claim about exactly  why the topic is important.

• The internet is defined as “a global computer network providing a variety of information and communication facilities.”
• The spread of the internet has had a world-changing effect, not least on the world of education.

Avoid using a dictionary definition as your hook, especially if it’s an obvious term that everyone knows. The improved example here is still broad, but it gives us a much clearer sense of what the essay will be about.

• Mary Shelley’s  Frankenstein is a famous book from the nineteenth century.
• Mary Shelley’s Frankenstein is often read as a crude cautionary tale about the dangers of scientific advancement.

Instead of just stating a fact that the reader already knows, the improved hook here tells us about the mainstream interpretation of the book, implying that this essay will offer a different interpretation.

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Next, give your reader the context they need to understand your topic and argument. Depending on the subject of your essay, this might include:

• Historical, geographical, or social context
• An outline of the debate you’re addressing
• A summary of relevant theories or research about the topic
• Definitions of key terms

The information here should be broad but clearly focused and relevant to your argument. Don’t give too much detail—you can mention points that you will return to later, but save your evidence and interpretation for the main body of the essay.

How much space you need for background depends on your topic and the scope of your essay. In our Braille example, we take a few sentences to introduce the topic and sketch the social context that the essay will address:

Now it’s time to narrow your focus and show exactly what you want to say about the topic. This is your thesis statement —a sentence or two that sums up your overall argument.

This is the most important part of your introduction. A  good thesis isn’t just a statement of fact, but a claim that requires evidence and explanation.

The goal is to clearly convey your own position in a debate or your central point about a topic.

Particularly in longer essays, it’s helpful to end the introduction by signposting what will be covered in each part. Keep it concise and give your reader a clear sense of the direction your argument will take.

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As you research and write, your argument might change focus or direction as you learn more.

For this reason, it’s often a good idea to wait until later in the writing process before you write the introduction paragraph—it can even be the very last thing you write.

When you’ve finished writing the essay body and conclusion , you should return to the introduction and check that it matches the content of the essay.

It’s especially important to make sure your thesis statement accurately represents what you do in the essay. If your argument has gone in a different direction than planned, tweak your thesis statement to match what you actually say.

To polish your writing, you can use something like a paraphrasing tool .

You can use the checklist below to make sure your introduction does everything it’s supposed to.

Checklist: Essay introduction

My first sentence is engaging and relevant.

I have introduced the topic with necessary background information.

I have defined any important terms.

My thesis statement clearly presents my main point or argument.

Everything in the introduction is relevant to the main body of the essay.

You have a strong introduction - now make sure the rest of your essay is just as good.

• Argumentative
• Literary analysis

This introduction to an argumentative essay sets up the debate about the internet and education, and then clearly states the position the essay will argue for.

The spread of the internet has had a world-changing effect, not least on the world of education. The use of the internet in academic contexts is on the rise, and its role in learning is hotly debated. For many teachers who did not grow up with this technology, its effects seem alarming and potentially harmful. This concern, while understandable, is misguided. The negatives of internet use are outweighed by its critical benefits for students and educators—as a uniquely comprehensive and accessible information source; a means of exposure to and engagement with different perspectives; and a highly flexible learning environment.

This introduction to a short expository essay leads into the topic (the invention of the printing press) and states the main point the essay will explain (the effect of this invention on European society).

In many ways, the invention of the printing press marked the end of the Middle Ages. The medieval period in Europe is often remembered as a time of intellectual and political stagnation. Prior to the Renaissance, the average person had very limited access to books and was unlikely to be literate. The invention of the printing press in the 15th century allowed for much less restricted circulation of information in Europe, paving the way for the Reformation.

This introduction to a literary analysis essay , about Mary Shelley’s Frankenstein , starts by describing a simplistic popular view of the story, and then states how the author will give a more complex analysis of the text’s literary devices.

Mary Shelley’s Frankenstein is often read as a crude cautionary tale. Arguably the first science fiction novel, its plot can be read as a warning about the dangers of scientific advancement unrestrained by ethical considerations. In this reading, and in popular culture representations of the character as a “mad scientist”, Victor Frankenstein represents the callous, arrogant ambition of modern science. However, far from providing a stable image of the character, Shelley uses shifting narrative perspectives to gradually transform our impression of Frankenstein, portraying him in an increasingly negative light as the novel goes on. While he initially appears to be a naive but sympathetic idealist, after the creature’s narrative Frankenstein begins to resemble—even in his own telling—the thoughtlessly cruel figure the creature represents him as.

If you want to know more about AI tools , college essays , or fallacies make sure to check out some of our other articles with explanations and examples or go directly to our tools!

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Your essay introduction should include three main things, in this order:

• An opening hook to catch the reader’s attention.
• Relevant background information that the reader needs to know.
• A thesis statement that presents your main point or argument.

The length of each part depends on the length and complexity of your essay .

The “hook” is the first sentence of your essay introduction . It should lead the reader into your essay, giving a sense of why it’s interesting.

To write a good hook, avoid overly broad statements or long, dense sentences. Try to start with something clear, concise and catchy that will spark your reader’s curiosity.

A thesis statement is a sentence that sums up the central point of your paper or essay . Everything else you write should relate to this key idea.

The thesis statement is essential in any academic essay or research paper for two main reasons:

• It gives your writing direction and focus.
• It gives the reader a concise summary of your main point.

Without a clear thesis statement, an essay can end up rambling and unfocused, leaving your reader unsure of exactly what you want to say.

The structure of an essay is divided into an introduction that presents your topic and thesis statement , a body containing your in-depth analysis and arguments, and a conclusion wrapping up your ideas.

The structure of the body is flexible, but you should always spend some time thinking about how you can organize your essay to best serve your ideas.

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How to write an effective introduction for your research paper

Last updated

20 January 2024

Reviewed by

However, the introduction is a vital element of your research paper . It helps the reader decide whether your paper is worth their time. As such, it's worth taking your time to get it right.

In this article, we'll tell you everything you need to know about writing an effective introduction for your research paper.

• The importance of an introduction in research papers

The primary purpose of an introduction is to provide an overview of your paper. This lets readers gauge whether they want to continue reading or not. The introduction should provide a meaningful roadmap of your research to help them make this decision. It should let readers know whether the information they're interested in is likely to be found in the pages that follow.

Aside from providing readers with information about the content of your paper, the introduction also sets the tone. It shows readers the style of language they can expect, which can further help them to decide how far to read.

When you take into account both of these roles that an introduction plays, it becomes clear that crafting an engaging introduction is the best way to get your paper read more widely. First impressions count, and the introduction provides that impression to readers.

• The optimum length for a research paper introduction

While there's no magic formula to determine exactly how long a research paper introduction should be, there are a few guidelines. Some variables that impact the ideal introduction length include:

Field of study

Complexity of the topic

Specific requirements of the course or publication

A commonly recommended length of a research paper introduction is around 10% of the total paper’s length. So, a ten-page paper has a one-page introduction. If the topic is complex, it may require more background to craft a compelling intro. Humanities papers tend to have longer introductions than those of the hard sciences.

The best way to craft an introduction of the right length is to focus on clarity and conciseness. Tell the reader only what is necessary to set up your research. An introduction edited down with this goal in mind should end up at an acceptable length.

• Evaluating successful research paper introductions

A good way to gauge how to create a great introduction is by looking at examples from across your field. The most influential and well-regarded papers should provide some insights into what makes a good introduction.

Dissecting examples: what works and why

We can make some general assumptions by looking at common elements of a good introduction, regardless of the field of research.

A common structure is to start with a broad context, and then narrow that down to specific research questions or hypotheses. This creates a funnel that establishes the scope and relevance.

The most effective introductions are careful about the assumptions they make regarding reader knowledge. By clearly defining key terms and concepts instead of assuming the reader is familiar with them, these introductions set a more solid foundation for understanding.

To pull in the reader and make that all-important good first impression, excellent research paper introductions will often incorporate a compelling narrative or some striking fact that grabs the reader's attention.

Finally, good introductions provide clear citations from past research to back up the claims they're making. In the case of argumentative papers or essays (those that take a stance on a topic or issue), a strong thesis statement compels the reader to continue reading.

Common pitfalls to avoid in research paper introductions

You can also learn what not to do by looking at other research papers. Many authors have made mistakes you can learn from.

We've talked about the need to be clear and concise. Many introductions fail at this; they're verbose, vague, or otherwise fail to convey the research problem or hypothesis efficiently. This often comes in the form of an overemphasis on background information, which obscures the main research focus.

Ensure your introduction provides the proper emphasis and excitement around your research and its significance. Otherwise, fewer people will want to read more about it.

• Crafting a compelling introduction for a research paper

Let’s take a look at the steps required to craft an introduction that pulls readers in and compels them to learn more about your research.

Step 1: Capturing interest and setting the scene

To capture the reader's interest immediately, begin your introduction with a compelling question, a surprising fact, a provocative quote, or some other mechanism that will hook readers and pull them further into the paper.

As they continue reading, the introduction should contextualize your research within the current field, showing readers its relevance and importance. Clarify any essential terms that will help them better understand what you're saying. This keeps the fundamentals of your research accessible to all readers from all backgrounds.

Step 2: Building a solid foundation with background information

Including background information in your introduction serves two major purposes:

It helps to clarify the topic for the reader

It establishes the depth of your research

The approach you take when conveying this information depends on the type of paper.

For argumentative papers, you'll want to develop engaging background narratives. These should provide context for the argument you'll be presenting.

For empirical papers, highlighting past research is the key. Often, there will be some questions that weren't answered in those past papers. If your paper is focused on those areas, those papers make ideal candidates for you to discuss and critique in your introduction.

Step 3: Pinpointing the research challenge

To capture the attention of the reader, you need to explain what research challenges you'll be discussing.

For argumentative papers, this involves articulating why the argument you'll be making is important. What is its relevance to current discussions or problems? What is the potential impact of people accepting or rejecting your argument?

For empirical papers, explain how your research is addressing a gap in existing knowledge. What new insights or contributions will your research bring to your field?

Step 4: Clarifying your research aims and objectives

We mentioned earlier that the introduction to a research paper can serve as a roadmap for what's within. We've also frequently discussed the need for clarity. This step addresses both of these.

When writing an argumentative paper, craft a thesis statement with impact. Clearly articulate what your position is and the main points you intend to present. This will map out for the reader exactly what they'll get from reading the rest.

For empirical papers, focus on formulating precise research questions and hypotheses. Directly link them to the gaps or issues you've identified in existing research to show the reader the precise direction your research paper will take.

Step 5: Sketching the blueprint of your study

Continue building a roadmap for your readers by designing a structured outline for the paper. Guide the reader through your research journey, explaining what the different sections will contain and their relationship to one another.

This outline should flow seamlessly as you move from section to section. Creating this outline early can also help guide the creation of the paper itself, resulting in a final product that's better organized. In doing so, you'll craft a paper where each section flows intuitively from the next.

Step 6: Integrating your research question

To avoid letting your research question get lost in background information or clarifications, craft your introduction in such a way that the research question resonates throughout. The research question should clearly address a gap in existing knowledge or offer a new perspective on an existing problem.

Tell users your research question explicitly but also remember to frequently come back to it. When providing context or clarification, point out how it relates to the research question. This keeps your focus where it needs to be and prevents the topic of the paper from becoming under-emphasized.

Step 7: Establishing the scope and limitations

So far, we've talked mostly about what's in the paper and how to convey that information to readers. The opposite is also important. Information that's outside the scope of your paper should be made clear to the reader in the introduction so their expectations for what is to follow are set appropriately.

Similarly, be honest and upfront about the limitations of the study. Any constraints in methodology, data, or how far your findings can be generalized should be fully communicated in the introduction.

Step 8: Concluding the introduction with a promise

The final few lines of the introduction are your last chance to convince people to continue reading the rest of the paper. Here is where you should make it very clear what benefit they'll get from doing so. What topics will be covered? What questions will be answered? Make it clear what they will get for continuing.

By providing a quick recap of the key points contained in the introduction in its final lines and properly setting the stage for what follows in the rest of the paper, you refocus the reader's attention on the topic of your research and guide them to read more.

• Research paper introduction best practices

Following the steps above will give you a compelling introduction that hits on all the key points an introduction should have. Some more tips and tricks can make an introduction even more polished.

As you follow the steps above, keep the following tips in mind.

Set the right tone and style

Like every piece of writing, a research paper should be written for the audience. That is to say, it should match the tone and style that your academic discipline and target audience expect. This is typically a formal and academic tone, though the degree of formality varies by field.

Kno w the audience

The perfect introduction balances clarity with conciseness. The amount of clarification required for a given topic depends greatly on the target audience. Knowing who will be reading your paper will guide you in determining how much background information is required.

Adopt the CARS (create a research space) model

The CARS model is a helpful tool for structuring introductions. This structure has three parts. The beginning of the introduction establishes the general research area. Next, relevant literature is reviewed and critiqued. The final section outlines the purpose of your study as it relates to the previous parts.

Master the art of funneling

The CARS method is one example of a well-funneled introduction. These start broadly and then slowly narrow down to your specific research problem. It provides a nice narrative flow that provides the right information at the right time. If you stray from the CARS model, try to retain this same type of funneling.

Incorporate narrative element

People read research papers largely to be informed. But to inform the reader, you have to hold their attention. A narrative style, particularly in the introduction, is a great way to do that. This can be a compelling story, an intriguing question, or a description of a real-world problem.

Write the introduction last

By writing the introduction after the rest of the paper, you'll have a better idea of what your research entails and how the paper is structured. This prevents the common problem of writing something in the introduction and then forgetting to include it in the paper. It also means anything particularly exciting in the paper isn’t neglected in the intro.

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How to Write an Introduction for a Research Paper

Table of Contents

Writing an introduction for a research paper is a critical element of your paper, but it can seem challenging to encapsulate enormous amount of information into a concise form. The introduction of your research paper sets the tone for your research and provides the context for your study. In this article, we will guide you through the process of writing an effective introduction that grabs the reader's attention and captures the essence of your research paper.

Understanding the Purpose of a Research Paper Introduction

The introduction acts as a road map for your research paper, guiding the reader through the main ideas and arguments. The purpose of the introduction is to present your research topic to the readers and provide a rationale for why your study is relevant. It helps the reader locate your research and its relevance in the broader field of related scientific explorations. Additionally, the introduction should inform the reader about the objectives and scope of your study, giving them an overview of what to expect in the paper. By including a comprehensive introduction, you establish your credibility as an author and convince the reader that your research is worth their time and attention.

Key Elements to Include in Your Introduction

When writing your research paper introduction, there are several key elements you should include to ensure it is comprehensive and informative.

• A hook or attention-grabbing statement to capture the reader's interest.  It can be a thought-provoking question, a surprising statistic, or a compelling anecdote that relates to your research topic.
• A brief overview of the research topic and its significance. By highlighting the gap in existing knowledge or the problem your research aims to address, you create a compelling case for the relevance of your study.
• A clear research question or problem statement. This serves as the foundation of your research and guides the reader in understanding the unique focus of your study. It should be concise, specific, and clearly articulated.
• An outline of the paper's structure and main arguments, to help the readers navigate through the paper with ease.

Preparing to Write Your Introduction

Before diving into writing your introduction, it is essential to prepare adequately. This involves 3 important steps:

• Conducting Preliminary Research: Immerse yourself in the existing literature to develop a clear research question and position your study within the academic discourse.
• Identifying Your Thesis Statement: Define a specific, focused, and debatable thesis statement, serving as a roadmap for your paper.
• Considering Broader Context: Reflect on the significance of your research within your field, understanding its potential impact and contribution.

By engaging in these preparatory steps, you can ensure that your introduction is well-informed, focused, and sets the stage for a compelling research paper.

Structuring Your Introduction

Now that you have prepared yourself to tackle the introduction, it's time to structure it effectively. A well-structured introduction will engage the reader from the beginning and provide a logical flow to your research paper.

Starting with a Hook

Begin your introduction with an attention-grabbing hook that captivates the reader's interest. This hook serves as a way to make your introduction more engaging and compelling. For example, if you are writing a research paper on the impact of climate change on biodiversity, you could start your introduction with a statistic about the number of species that have gone extinct due to climate change. This will immediately grab the reader's attention and make them realize the urgency and importance of the topic.

Introducing Your Topic

Provide a brief overview, which should give the reader a general understanding of the subject matter and its significance. Explain the importance of the topic and its relevance to the field. This will help the reader understand why your research is significant and why they should continue reading. Continuing with the example of climate change and biodiversity, you could explain how climate change is one of the greatest threats to global biodiversity, how it affects ecosystems, and the potential consequences for both wildlife and human populations. By providing this context, you are setting the stage for the rest of your research paper and helping the reader understand the importance of your study.

Presenting Your Thesis Statement

The thesis statement should directly address your research question and provide a preview of the main arguments or findings discussed in your paper. Make sure your thesis statement is clear, concise, and well-supported by the evidence you will present in your research paper. By presenting a strong and focused thesis statement, you are providing the reader with the information they could anticipate in your research paper. This will help them understand the purpose and scope of your study and will make them more inclined to continue reading.

Writing Techniques for an Effective Introduction

When crafting an introduction, it is crucial to pay attention to the finer details that can elevate your writing to the next level. By utilizing specific writing techniques, you can captivate your readers and draw them into your research journey.

Using Clear and Concise Language

One of the most important writing techniques to employ in your introduction is the use of clear and concise language. By choosing your words carefully, you can effectively convey your ideas to the reader. It is essential to avoid using jargon or complex terminology that may confuse or alienate your audience. Instead, focus on communicating your research in a straightforward manner to ensure that your introduction is accessible to both experts in your field and those who may be new to the topic. This approach allows you to engage a broader audience and make your research more inclusive.

Establishing the Relevance of Your Research

One way to establish the relevance of your research is by highlighting how it fills a gap in the existing literature. Explain how your study addresses a significant research question that has not been adequately explored. By doing this, you demonstrate that your research is not only unique but also contributes to the broader knowledge in your field. Furthermore, it is important to emphasize the potential impact of your research. Whether it is advancing scientific understanding, informing policy decisions, or improving practical applications, make it clear to the reader how your study can make a difference.

By employing these two writing techniques in your introduction, you can effectively engage your readers. Take your time to craft an introduction that is both informative and captivating, leaving your readers eager to delve deeper into your research.

Revising and Polishing Your Introduction

Once you have written your introduction, it is crucial to revise and polish it to ensure that it effectively sets the stage for your research paper.

Self-Editing Techniques

Review your introduction for clarity, coherence, and logical flow. Ensure each paragraph introduces a new idea or argument with smooth transitions.

Check for grammatical errors, spelling mistakes, and awkward sentence structures.

Ensure that your introduction aligns with the overall tone and style of your research paper.

Seeking Feedback for Improvement

Consider seeking feedback from peers, colleagues, or your instructor. They can provide valuable insights and suggestions for improving your introduction. Be open to constructive criticism and use it to refine your introduction and make it more compelling for the reader.

Writing an introduction for a research paper requires careful thought and planning. By understanding the purpose of the introduction, preparing adequately, structuring effectively, and employing writing techniques, you can create an engaging and informative introduction for your research. Remember to revise and polish your introduction to ensure that it accurately represents the main ideas and arguments in your research paper. With a well-crafted introduction, you will capture the reader's attention and keep them inclined to your paper.

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How to Write a Research Introduction

Last Updated: December 6, 2023 Fact Checked

This article was co-authored by Megan Morgan, PhD . Megan Morgan is a Graduate Program Academic Advisor in the School of Public & International Affairs at the University of Georgia. She earned her PhD in English from the University of Georgia in 2015. There are 7 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 2,657,674 times.

The introduction to a research paper can be the most challenging part of the paper to write. The length of the introduction will vary depending on the type of research paper you are writing. An introduction should announce your topic, provide context and a rationale for your work, before stating your research questions and hypothesis. Well-written introductions set the tone for the paper, catch the reader's interest, and communicate the hypothesis or thesis statement.

Introducing the Topic of the Paper

• In scientific papers this is sometimes known as an "inverted triangle", where you start with the broadest material at the start, before zooming in on the specifics. [2] X Research source
• The sentence "Throughout the 20th century, our views of life on other planets have drastically changed" introduces a topic, but does so in broad terms.
• It provides the reader with an indication of the content of the essay and encourages them to read on.

• For example, if you were writing a paper about the behaviour of mice when exposed to a particular substance, you would include the word "mice", and the scientific name of the relevant compound in the first sentences.
• If you were writing a history paper about the impact of the First World War on gender relations in Britain, you should mention those key words in your first few lines.

• This is especially important if you are attempting to develop a new conceptualization that uses language and terminology your readers may be unfamiliar with.

• If you use an anecdote ensure that is short and highly relevant for your research. It has to function in the same way as an alternative opening, namely to announce the topic of your research paper to your reader.
• For example, if you were writing a sociology paper about re-offending rates among young offenders, you could include a brief story of one person whose story reflects and introduces your topic.
• This kind of approach is generally not appropriate for the introduction to a natural or physical sciences research paper where the writing conventions are different.

Establishing the Context for Your Paper

• It is important to be concise in the introduction, so provide an overview on recent developments in the primary research rather than a lengthy discussion.
• You can follow the "inverted triangle" principle to focus in from the broader themes to those to which you are making a direct contribution with your paper.
• A strong literature review presents important background information to your own research and indicates the importance of the field.

• By making clear reference to existing work you can demonstrate explicitly the specific contribution you are making to move the field forward.
• You can identify a gap in the existing scholarship and explain how you are addressing it and moving understanding forward.

• For example, if you are writing a scientific paper you could stress the merits of the experimental approach or models you have used.
• Stress what is novel in your research and the significance of your new approach, but don't give too much detail in the introduction.
• A stated rationale could be something like: "the study evaluates the previously unknown anti-inflammatory effects of a topical compound in order to evaluate its potential clinical uses".

Specifying Your Research Questions and Hypothesis

• The research question or questions generally come towards the end of the introduction, and should be concise and closely focused.
• The research question might recall some of the key words established in the first few sentences and the title of your paper.
• An example of a research question could be "what were the consequences of the North American Free Trade Agreement on the Mexican export economy?"
• This could be honed further to be specific by referring to a particular element of the Free Trade Agreement and the impact on a particular industry in Mexico, such as clothing manufacture.
• A good research question should shape a problem into a testable hypothesis.

• If possible try to avoid using the word "hypothesis" and rather make this implicit in your writing. This can make your writing appear less formulaic.
• In a scientific paper, giving a clear one-sentence overview of your results and their relation to your hypothesis makes the information clear and accessible. [10] X Trustworthy Source PubMed Central Journal archive from the U.S. National Institutes of Health Go to source
• An example of a hypothesis could be "mice deprived of food for the duration of the study were expected to become more lethargic than those fed normally".

• This is not always necessary and you should pay attention to the writing conventions in your discipline.
• In a natural sciences paper, for example, there is a fairly rigid structure which you will be following.
• A humanities or social science paper will most likely present more opportunities to deviate in how you structure your paper.

Research Introduction Help

Community Q&A

• Use your research papers' outline to help you decide what information to include when writing an introduction. Thanks Helpful 0 Not Helpful 1
• Consider drafting your introduction after you have already completed the rest of your research paper. Writing introductions last can help ensure that you don't leave out any major points. Thanks Helpful 0 Not Helpful 0

• Avoid emotional or sensational introductions; these can create distrust in the reader. Thanks Helpful 51 Not Helpful 12
• Generally avoid using personal pronouns in your introduction, such as "I," "me," "we," "us," "my," "mine," or "our." Thanks Helpful 32 Not Helpful 7
• Don't overwhelm the reader with an over-abundance of information. Keep the introduction as concise as possible by saving specific details for the body of your paper. Thanks Helpful 25 Not Helpful 14

You Might Also Like

• ↑ https://library.sacredheart.edu/c.php?g=29803&p=185916
• ↑ https://www.aresearchguide.com/inverted-pyramid-structure-in-writing.html
• ↑ https://libguides.usc.edu/writingguide/introduction
• ↑ https://writing.wisc.edu/Handbook/PlanResearchPaper.html
• ↑ https://dept.writing.wisc.edu/wac/writing-an-introduction-for-a-scientific-paper/
• ↑ https://writing.wisc.edu/handbook/assignments/planresearchpaper/
• ↑ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3178846/

About This Article

To introduce your research paper, use the first 1-2 sentences to describe your general topic, such as “women in World War I.” Include and define keywords, such as “gender relations,” to show your reader where you’re going. Mention previous research into the topic with a phrase like, “Others have studied…”, then transition into what your contribution will be and why it’s necessary. Finally, state the questions that your paper will address and propose your “answer” to them as your thesis statement. For more information from our English Ph.D. co-author about how to craft a strong hypothesis and thesis, keep reading! Did this summary help you? Yes No

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Starting Your Research Paper: Writing an Introductory Paragraph

• Choosing Your Topic
• Define Keywords
• Planning Your Paper
• Writing an Introductory Paragraph

The Dreaded Introductory Paragraph

Writing the introductory paragraph can be a frustrating and slow process -- but it doesn't have to be.  If you planned your paper out, then most of the introductory paragraph is already written.  Now you just need a beginning and an end.

Here's an introductory paragraph for a paper I wrote.  I started the paper with a factoid, then presented each main point of my paper and then ended with my thesis statement.

  Breakdown:

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How to Write the BEST Introduction for a Research Paper

by  Antony W

June 6, 2024

This is a complete guide on how to write an introduction for a research paper.

To be clear, writing the introduction section of a research paper isn’t rocket science, but it can be a little intimidating if you don’t know where or how to start.

To avoid confusion, and to make sure your research paper assignment is a lot less overwhelming, we’ve written this post to give you some handy tips you can use to write a more comprehensive and coherent introduction for your research paper.

Why is the Introduction for a Research Paper Important? 

Introductions form the thesis of the paper and usually provide a summary of the research issue you plan to investigate and report.

A good introduction for a research paper should do two things very well: make it clear what the topic under investigation is and explain the significance of the research and the results.

There’s no magic bullet to writing the introduction.

Some students opt to leave the introduction to be the final part of the assignment and work on the other parts of the essay first.

Others write the section first. Whichever approach you use, the aim should be to introduce your research in a way that sparks an interest for further reading.

How to Write an Introduction for a Research Paper 

The right approach to writing a good introduction for a research paper is to write it as  the last assignment.

First work on the other parts of the paper and then come back later to work on the introduction.

We do recommend doing this for the simple reason that with the other parts covered, you get a clear picture of the main points and ideas to include in the introduction.

Remember, the aim of the introduction is to get your readers to look into your research paper with the depth that it deserves.

By telling them exactly what to expect in the paper, you easily grab their attention and pique their interest to read further.  

With that said, below are some handy tips that you can use to write a good introduction for your research paper.

1. Understand Your Research Theme 

The human attention span is so short that you have only a few seconds to grab their attention. If the introduction of your research paper is boring or too general, you lose them completely, which means your paper may not attract the attention that it should.

A creative way to hook readers to introduction   of a research paper is to use the inverted triangle strategy.

Here’s how this works

The first sentence of the introduction should be about the general topic you wish to explore in your research. You then follow this some details about the specific research question . 

By starting from a broad topic and then narrowing down to a broad topic, it’s easy to draw a reader’s attention and interest to explore the topic in question even further.

2. Explain Important Terms 

You will use some key terms in different sections of your research paper.

So it’s important to make sure you explain them in the introduction to avoid confusion.

By explaining the key terms in the research paper, you make it easy for readers to understand your investigation.

3. Be Original

Writing a research paper is like holding a contest. You have to craft every section a way that grabs the attention of the reader.

You’re fighting to stand out, and it’s not an easy battle given the number of students you’re competing with. To stand out from the others, you have to be original.

Humans have no limits when it comes to creativity, and you’re not an exception. Provided your creativity doesn’t bend the rules of formal writing, at least in the case of a research paper, you’re good to go.

Being original doesn’t mean re-writing pre-written introductions on the topics so they pass plagiarism .  It means trying your best to come up with solid, reasonable, and interesting ideas that no other student in your class has.

Here are two interesting examples :

• If you’re exploring a topic in humanities, consider starting the introduction to your research paper with a story or a relevant quotation
• If you’re a science or medical student, include some scientific facts or less known medical anecdotes in the introduction to keep reader hooked.

The two example above are effective strategies that we’ve used in our research paper writing service and they tend to earn students high scores almost all the time.

4. State the Thesis Statement 

While it marks the conclusive part of the introduction, a thesis statement is an important part of the assignment because it transitions a reader from the introduction to the actual research.

The statement should be a sentence long – and you can have a maximum of only two sentences if you wish to give it a bit of a stretch.

Make sure the statement supports everything you said before b putting all your ideas in a logical, concise way.

Generally, your thesis statement should:

• Give a reader clear information on the topic
• Be as engaging and precise as possible
• Highlight the significance of the main issue

5. Mind the Length of the Introduction 

There’s no specific word limit for the introduction for a research paper. That leaves you with the option to find a length that’s ideal for you.

It shouldn’t be too long or too short, just the ideal length necessary to grab the attention of your readers and to communicate your message.

You may have to re-read the introduction and make it shorter or longer depending on the depth of your research.  Doing so is important for two reasons:

• It helps to ensure you don’t leave out important information
• You’re able to delete unnecessary words and phrases while retaining the intended message for your audience.

6. Don’t Hesitate to Ask for Help 

It’s easy to feel so overwhelmed with college and university work that writing your research paper in good time becomes difficult.

However, many assignments should not be the reason why you fail to get your research paper completed.

Take advantage of our research paper writing help and get professional academic insight to complete the assignment on time.

About the author 

Antony W is a professional writer and coach at Help for Assessment. He spends countless hours every day researching and writing great content filled with expert advice on how to write engaging essays, research papers, and assignments.

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Home » Research Paper – Structure, Examples and Writing Guide

Research Paper – Structure, Examples and Writing Guide

Table of Contents

Research Paper

Definition:

Research Paper is a written document that presents the author’s original research, analysis, and interpretation of a specific topic or issue.

It is typically based on Empirical Evidence, and may involve qualitative or quantitative research methods, or a combination of both. The purpose of a research paper is to contribute new knowledge or insights to a particular field of study, and to demonstrate the author’s understanding of the existing literature and theories related to the topic.

Structure of Research Paper

The structure of a research paper typically follows a standard format, consisting of several sections that convey specific information about the research study. The following is a detailed explanation of the structure of a research paper:

The title page contains the title of the paper, the name(s) of the author(s), and the affiliation(s) of the author(s). It also includes the date of submission and possibly, the name of the journal or conference where the paper is to be published.

The abstract is a brief summary of the research paper, typically ranging from 100 to 250 words. It should include the research question, the methods used, the key findings, and the implications of the results. The abstract should be written in a concise and clear manner to allow readers to quickly grasp the essence of the research.

Introduction

The introduction section of a research paper provides background information about the research problem, the research question, and the research objectives. It also outlines the significance of the research, the research gap that it aims to fill, and the approach taken to address the research question. Finally, the introduction section ends with a clear statement of the research hypothesis or research question.

Literature Review

The literature review section of a research paper provides an overview of the existing literature on the topic of study. It includes a critical analysis and synthesis of the literature, highlighting the key concepts, themes, and debates. The literature review should also demonstrate the research gap and how the current study seeks to address it.

The methods section of a research paper describes the research design, the sample selection, the data collection and analysis procedures, and the statistical methods used to analyze the data. This section should provide sufficient detail for other researchers to replicate the study.

The results section presents the findings of the research, using tables, graphs, and figures to illustrate the data. The findings should be presented in a clear and concise manner, with reference to the research question and hypothesis.

The discussion section of a research paper interprets the findings and discusses their implications for the research question, the literature review, and the field of study. It should also address the limitations of the study and suggest future research directions.

The conclusion section summarizes the main findings of the study, restates the research question and hypothesis, and provides a final reflection on the significance of the research.

The references section provides a list of all the sources cited in the paper, following a specific citation style such as APA, MLA or Chicago.

How to Write Research Paper

You can write Research Paper by the following guide:

• Choose a Topic: The first step is to select a topic that interests you and is relevant to your field of study. Brainstorm ideas and narrow down to a research question that is specific and researchable.
• Conduct a Literature Review: The literature review helps you identify the gap in the existing research and provides a basis for your research question. It also helps you to develop a theoretical framework and research hypothesis.
• Develop a Thesis Statement : The thesis statement is the main argument of your research paper. It should be clear, concise and specific to your research question.
• Plan your Research: Develop a research plan that outlines the methods, data sources, and data analysis procedures. This will help you to collect and analyze data effectively.
• Collect and Analyze Data: Collect data using various methods such as surveys, interviews, observations, or experiments. Analyze data using statistical tools or other qualitative methods.
• Organize your Paper : Organize your paper into sections such as Introduction, Literature Review, Methods, Results, Discussion, and Conclusion. Ensure that each section is coherent and follows a logical flow.
• Write your Paper : Start by writing the introduction, followed by the literature review, methods, results, discussion, and conclusion. Ensure that your writing is clear, concise, and follows the required formatting and citation styles.
• Edit and Proofread your Paper: Review your paper for grammar and spelling errors, and ensure that it is well-structured and easy to read. Ask someone else to review your paper to get feedback and suggestions for improvement.
• Cite your Sources: Ensure that you properly cite all sources used in your research paper. This is essential for giving credit to the original authors and avoiding plagiarism.

Research Paper Example

Note : The below example research paper is for illustrative purposes only and is not an actual research paper. Actual research papers may have different structures, contents, and formats depending on the field of study, research question, data collection and analysis methods, and other factors. Students should always consult with their professors or supervisors for specific guidelines and expectations for their research papers.

Research Paper Example sample for Students:

Title: The Impact of Social Media on Mental Health among Young Adults

Abstract: This study aims to investigate the impact of social media use on the mental health of young adults. A literature review was conducted to examine the existing research on the topic. A survey was then administered to 200 university students to collect data on their social media use, mental health status, and perceived impact of social media on their mental health. The results showed that social media use is positively associated with depression, anxiety, and stress. The study also found that social comparison, cyberbullying, and FOMO (Fear of Missing Out) are significant predictors of mental health problems among young adults.

Introduction: Social media has become an integral part of modern life, particularly among young adults. While social media has many benefits, including increased communication and social connectivity, it has also been associated with negative outcomes, such as addiction, cyberbullying, and mental health problems. This study aims to investigate the impact of social media use on the mental health of young adults.

Literature Review: The literature review highlights the existing research on the impact of social media use on mental health. The review shows that social media use is associated with depression, anxiety, stress, and other mental health problems. The review also identifies the factors that contribute to the negative impact of social media, including social comparison, cyberbullying, and FOMO.

Methods : A survey was administered to 200 university students to collect data on their social media use, mental health status, and perceived impact of social media on their mental health. The survey included questions on social media use, mental health status (measured using the DASS-21), and perceived impact of social media on their mental health. Data were analyzed using descriptive statistics and regression analysis.

Results : The results showed that social media use is positively associated with depression, anxiety, and stress. The study also found that social comparison, cyberbullying, and FOMO are significant predictors of mental health problems among young adults.

Discussion : The study’s findings suggest that social media use has a negative impact on the mental health of young adults. The study highlights the need for interventions that address the factors contributing to the negative impact of social media, such as social comparison, cyberbullying, and FOMO.

Conclusion : In conclusion, social media use has a significant impact on the mental health of young adults. The study’s findings underscore the need for interventions that promote healthy social media use and address the negative outcomes associated with social media use. Future research can explore the effectiveness of interventions aimed at reducing the negative impact of social media on mental health. Additionally, longitudinal studies can investigate the long-term effects of social media use on mental health.

Limitations : The study has some limitations, including the use of self-report measures and a cross-sectional design. The use of self-report measures may result in biased responses, and a cross-sectional design limits the ability to establish causality.

Implications: The study’s findings have implications for mental health professionals, educators, and policymakers. Mental health professionals can use the findings to develop interventions that address the negative impact of social media use on mental health. Educators can incorporate social media literacy into their curriculum to promote healthy social media use among young adults. Policymakers can use the findings to develop policies that protect young adults from the negative outcomes associated with social media use.

References :

• Twenge, J. M., & Campbell, W. K. (2019). Associations between screen time and lower psychological well-being among children and adolescents: Evidence from a population-based study. Preventive medicine reports, 15, 100918.
• Primack, B. A., Shensa, A., Escobar-Viera, C. G., Barrett, E. L., Sidani, J. E., Colditz, J. B., … & James, A. E. (2017). Use of multiple social media platforms and symptoms of depression and anxiety: A nationally-representative study among US young adults. Computers in Human Behavior, 69, 1-9.
• Van der Meer, T. G., & Verhoeven, J. W. (2017). Social media and its impact on academic performance of students. Journal of Information Technology Education: Research, 16, 383-398.

Appendix : The survey used in this study is provided below.

Social Media and Mental Health Survey

• How often do you use social media per day?
• Less than 30 minutes
• 30 minutes to 1 hour
• 1 to 2 hours
• 2 to 4 hours
• More than 4 hours
• Which social media platforms do you use?
• Others (Please specify)
• How often do you experience the following on social media?
• Social comparison (comparing yourself to others)
• Cyberbullying
• Fear of Missing Out (FOMO)
• Have you ever experienced any of the following mental health problems in the past month?
• Do you think social media use has a positive or negative impact on your mental health?
• Very positive
• Somewhat positive
• Somewhat negative
• Very negative
• In your opinion, which factors contribute to the negative impact of social media on mental health?
• Social comparison
• In your opinion, what interventions could be effective in reducing the negative impact of social media on mental health?
• Education on healthy social media use
• Counseling for mental health problems caused by social media
• Social media detox programs
• Regulation of social media use

Thank you for your participation!

Applications of Research Paper

Research papers have several applications in various fields, including:

• Advancing knowledge: Research papers contribute to the advancement of knowledge by generating new insights, theories, and findings that can inform future research and practice. They help to answer important questions, clarify existing knowledge, and identify areas that require further investigation.
• Informing policy: Research papers can inform policy decisions by providing evidence-based recommendations for policymakers. They can help to identify gaps in current policies, evaluate the effectiveness of interventions, and inform the development of new policies and regulations.
• Improving practice: Research papers can improve practice by providing evidence-based guidance for professionals in various fields, including medicine, education, business, and psychology. They can inform the development of best practices, guidelines, and standards of care that can improve outcomes for individuals and organizations.
• Educating students : Research papers are often used as teaching tools in universities and colleges to educate students about research methods, data analysis, and academic writing. They help students to develop critical thinking skills, research skills, and communication skills that are essential for success in many careers.
• Fostering collaboration: Research papers can foster collaboration among researchers, practitioners, and policymakers by providing a platform for sharing knowledge and ideas. They can facilitate interdisciplinary collaborations and partnerships that can lead to innovative solutions to complex problems.

When to Write Research Paper

Research papers are typically written when a person has completed a research project or when they have conducted a study and have obtained data or findings that they want to share with the academic or professional community. Research papers are usually written in academic settings, such as universities, but they can also be written in professional settings, such as research organizations, government agencies, or private companies.

Here are some common situations where a person might need to write a research paper:

• For academic purposes: Students in universities and colleges are often required to write research papers as part of their coursework, particularly in the social sciences, natural sciences, and humanities. Writing research papers helps students to develop research skills, critical thinking skills, and academic writing skills.
• For publication: Researchers often write research papers to publish their findings in academic journals or to present their work at academic conferences. Publishing research papers is an important way to disseminate research findings to the academic community and to establish oneself as an expert in a particular field.
• To inform policy or practice : Researchers may write research papers to inform policy decisions or to improve practice in various fields. Research findings can be used to inform the development of policies, guidelines, and best practices that can improve outcomes for individuals and organizations.
• To share new insights or ideas: Researchers may write research papers to share new insights or ideas with the academic or professional community. They may present new theories, propose new research methods, or challenge existing paradigms in their field.

Purpose of Research Paper

The purpose of a research paper is to present the results of a study or investigation in a clear, concise, and structured manner. Research papers are written to communicate new knowledge, ideas, or findings to a specific audience, such as researchers, scholars, practitioners, or policymakers. The primary purposes of a research paper are:

• To contribute to the body of knowledge : Research papers aim to add new knowledge or insights to a particular field or discipline. They do this by reporting the results of empirical studies, reviewing and synthesizing existing literature, proposing new theories, or providing new perspectives on a topic.
• To inform or persuade: Research papers are written to inform or persuade the reader about a particular issue, topic, or phenomenon. They present evidence and arguments to support their claims and seek to persuade the reader of the validity of their findings or recommendations.
• To advance the field: Research papers seek to advance the field or discipline by identifying gaps in knowledge, proposing new research questions or approaches, or challenging existing assumptions or paradigms. They aim to contribute to ongoing debates and discussions within a field and to stimulate further research and inquiry.
• To demonstrate research skills: Research papers demonstrate the author’s research skills, including their ability to design and conduct a study, collect and analyze data, and interpret and communicate findings. They also demonstrate the author’s ability to critically evaluate existing literature, synthesize information from multiple sources, and write in a clear and structured manner.

Characteristics of Research Paper

Research papers have several characteristics that distinguish them from other forms of academic or professional writing. Here are some common characteristics of research papers:

• Evidence-based: Research papers are based on empirical evidence, which is collected through rigorous research methods such as experiments, surveys, observations, or interviews. They rely on objective data and facts to support their claims and conclusions.
• Structured and organized: Research papers have a clear and logical structure, with sections such as introduction, literature review, methods, results, discussion, and conclusion. They are organized in a way that helps the reader to follow the argument and understand the findings.
• Formal and objective: Research papers are written in a formal and objective tone, with an emphasis on clarity, precision, and accuracy. They avoid subjective language or personal opinions and instead rely on objective data and analysis to support their arguments.
• Citations and references: Research papers include citations and references to acknowledge the sources of information and ideas used in the paper. They use a specific citation style, such as APA, MLA, or Chicago, to ensure consistency and accuracy.
• Peer-reviewed: Research papers are often peer-reviewed, which means they are evaluated by other experts in the field before they are published. Peer-review ensures that the research is of high quality, meets ethical standards, and contributes to the advancement of knowledge in the field.
• Objective and unbiased: Research papers strive to be objective and unbiased in their presentation of the findings. They avoid personal biases or preconceptions and instead rely on the data and analysis to draw conclusions.

Advantages of Research Paper

Research papers have many advantages, both for the individual researcher and for the broader academic and professional community. Here are some advantages of research papers:

• Contribution to knowledge: Research papers contribute to the body of knowledge in a particular field or discipline. They add new information, insights, and perspectives to existing literature and help advance the understanding of a particular phenomenon or issue.
• Opportunity for intellectual growth: Research papers provide an opportunity for intellectual growth for the researcher. They require critical thinking, problem-solving, and creativity, which can help develop the researcher’s skills and knowledge.
• Career advancement: Research papers can help advance the researcher’s career by demonstrating their expertise and contributions to the field. They can also lead to new research opportunities, collaborations, and funding.
• Academic recognition: Research papers can lead to academic recognition in the form of awards, grants, or invitations to speak at conferences or events. They can also contribute to the researcher’s reputation and standing in the field.
• Impact on policy and practice: Research papers can have a significant impact on policy and practice. They can inform policy decisions, guide practice, and lead to changes in laws, regulations, or procedures.
• Advancement of society: Research papers can contribute to the advancement of society by addressing important issues, identifying solutions to problems, and promoting social justice and equality.

Limitations of Research Paper

Research papers also have some limitations that should be considered when interpreting their findings or implications. Here are some common limitations of research papers:

• Limited generalizability: Research findings may not be generalizable to other populations, settings, or contexts. Studies often use specific samples or conditions that may not reflect the broader population or real-world situations.
• Potential for bias : Research papers may be biased due to factors such as sample selection, measurement errors, or researcher biases. It is important to evaluate the quality of the research design and methods used to ensure that the findings are valid and reliable.
• Ethical concerns: Research papers may raise ethical concerns, such as the use of vulnerable populations or invasive procedures. Researchers must adhere to ethical guidelines and obtain informed consent from participants to ensure that the research is conducted in a responsible and respectful manner.
• Limitations of methodology: Research papers may be limited by the methodology used to collect and analyze data. For example, certain research methods may not capture the complexity or nuance of a particular phenomenon, or may not be appropriate for certain research questions.
• Publication bias: Research papers may be subject to publication bias, where positive or significant findings are more likely to be published than negative or non-significant findings. This can skew the overall findings of a particular area of research.
• Time and resource constraints: Research papers may be limited by time and resource constraints, which can affect the quality and scope of the research. Researchers may not have access to certain data or resources, or may be unable to conduct long-term studies due to practical limitations.

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Management Paper Blog Academic Writing Guides And Tips

• Three Research Paper Introduction Examples: Learn How to Initiate and Hook
• ManagementPaper
• Apr 13, 2021

A research paper introduction holds perhaps the most importance for a study to be successful. After a good research paper abstract , it is the introduction that builds the interest in a reader to continue reading the research paper. If the introduction turns out to be dull and drab, then the study would be a failed one.

A good research paper needs a lot of background study, which you often fail to do. To make your work easier, Management Paper is there for you to help you write yours efficiently.

Key Features of a Research Paper Introduction

• It forms the basic part of both the research paper as well as the research proposal .
• Apart from giving a general notion about the research paper topic , it includes important elements such as background, aim, objectives, questions and many more.
• It must contain the questions ‘WHY’: why is the research conducted, why it is important, why this chosen topic and so on is.
• It helps in pointing out the knowledge gaps and fills them up throughout the paper.
• Use precise and clear points.

The Most Commonly Included Elements in The Research Papers

There are different kinds of research papers like essays, reports, dissertations and journals. The introduction which is generally used in case of all other types of research paper except dissertations are similar in nature. Such an introduction is similar to a summary of the topic, defining the problem, stating the aims and objectives that are going to be established through the research.

But in case of dissertation, in a good research paper format the introduction is presented in great detail by dividing the section into the following parts:

• Research background
• Research problem
• Research rationale
• Research aim
• Research objectives
• Research hypothesis
• Research questions

Apart from this, many papers include time plan, scope and limitations of the research too. The experts from the team of Management Paper can help you with your paper writing and also make you understand the various aspects of a research paper.

Some Significant Examples of Research Paper Introduction

Research paper introduction example #1, topic: impact of leadership effectiveness on employees for the company amazon (dissertation).

The history and the various past events related to the topic are being mentioned in this section. Thsi supplies context to the paper and contains both relevant and important studies. Authenticating your information is a must by in-text citations.

The research problem states a specific area of concern, a bothering question, a difficulty which is to be eliminated or a condition that demands improvement. The missing knowledge about the topic is being found out through this and then only you can do further research about the problem.

The rationale answers the question of why the research is being conducted and thus states its importance.

The things that are expected to be achieved at the end of the research are generally mentioned here.

The objectives are the various goals or targets that are to be established and achieved throughout the study.

The research question points out the facts that are to be established through the paper and provides the research with a clear focus and purpose.

This is a specific predictive statement about the possible future outcome of the study which is mostly based upon the relationship between different variables or on a single variable.

Research Paper Introduction Example # 2

Topic: implementing online customer support service through chat portal at aldi.

Research Paper Introduction Example # 3

Topic: compare and contrast the policies for the aged people in various countries.

In both the second and the third example, the introduction is written in a single paragraph. In the first line itself you must introduce the topic. Try to avoid embellishments. Write any remarkable event about the topic then. Explain the problem and the purpose of the research. Try to build a reasonable thesis statement. Then with few lines, insert a smooth transition to make a shift from the introduction to the body.

 You can check out more examples from the page of Management paper, and can also avail paper writing service from them with ease. We do not compromise with quality and believe in time management.

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Research Paper Introduction Example: Academic Writing Insight

How to write an introductory paragraph for research paper.

The writing of the research paper is a multi-aspect process. Because this type of academic assignment consists of several parts. If you fail to complete one of the levels, you will fail the whole paper.

Introduction is not a Literal Beginning

As you know, the hardest part is just to begin the paper. And what should do student at the beginning? Not writing an outline. And not working on the introduction. He should make massive research on his topic . You cannot start writing an introduction without having a personal view on the issue that you are going to study. You have to prepare for introduction writing though analyzing facts available online and making notes. If it’s hard to do it yourself, the  online essay help service by Edusson.com will solve this problem instantly!

Why do We Need an Introduction?

The key aim of the introduction is to introduce to the reader the purpose of your research. Just imagine any academic writing starting from the main body section. You cannot pour on the reader your evidence, ideas, and arguments without an explanation of what are you writing about. In the introduction, you must clearly indicate the hypothesis you want to prove or deny. You must explain the necessity of your research, its urgency, and significance for your study, and, finally, hook readers to continue reading it!

What Information Can I Get From my Search for the Introduction?

It depends on the discipline you are writing the research paper on. If your field of study is Humanities, it is likely that you can find a relevant quote, aphorism, or anecdote to introduce your topic to the reader. In case you study tech, social, and medical sciences quotes are irrelevant. More precise and specific facts will fit such an introduction. There is a general rule for all specialties too. You must find a fact that will intrigue a reader. You must hook him.

Attract the Reader in Any Case

Imagine that your research paper is a product that you want to sell and be paid for it. Figuratively, it is true because your aim is to be rewarded with high mark. The first thing salesmen do to sell their product is a promotion of it. They put effort into and use various methods to hook clients. So, what should research paper writers  do to attract a reader? Even if you write a research paper, and the style of writing is formal, it is still necessary and possible to draw his attention. For example, your research paper topic is “How has the music industry been affected by the internet and digital downloading?”. After a hasty internet search, you can find out that there are many legendary musicians like Radiohead that gave up being dependent on music labels and started to issue their LPs by themselves, online. Also, there is a site Pledge Music which is a popular crowdfunding platform for modern musicians. Such popular synth-pop band as IAMX raises money there to record and promote their albums. These two facts prove that digital downloading somehow affects the music industry, and it is urgent to research this topic to learn the character of this effect. Connect with a professional writer in 5 simple steps. Start now Please provide as many details about your writing struggle as possible. Next What's the area of study of your paper? English Business and Entrepreneurship Nursing History African-American Studies Accounting Anthropology Architecture Art, Theatre and Film Biology Business and Entrepreneurship Chemistry Communication Strategies Computer Science Criminology Economics Education English Engineering Environmental Issues Ethics Finance Geography Healthcare History International and Public Relations Law and Legal Issues Linguistics Literature Management Marketing Mathematics Music Nursing Nutrition Other Philosophy Physics Political Science Psychology Religion and Theology Sociology Sport Technology Tourism Next How many pages do you need? Next When is it due? 01 AM 02 AM 03 AM 04 AM 05 AM 06 AM 07 AM 08 AM 09 AM 10 AM 11 AM 12 AM 01 PM 02 PM 03 PM 04 PM 05 PM 06 PM 07 PM 08 PM 09 PM 10 PM 11 PM 12 PM Next What's your e-mail? Next Done!

Writing a Thesis Statement

Research paper writing is one of the most challenging tasks for students. To write your research papers in a relevant way, it is important to add new information and to connect the text with the research topic. For example, a research paper introduction example can help you learn how to create an introduction that grabs the attention of the reader. The introduction should not only explain the topic but should also provide enough detail to set up the body of the paper. This can be done by providing background information, presenting a hypothesis, or discussing existing research on the topic. Adding new information will make the introduction more interesting and will lead the reader to the body of the paper.

What do you feel when you watch a good teaser for the movie? You feel hooked, intrigued, and eager to watch the story till the end. The same result you must achieve with the thesis statement in a research paper. You must indicate the highlights of your essay, and leave an open question, a mystery, which the reader will want to learn for sure. To provide a worthy example of a research paper thesis statement let’s return to the discussed above topic “How has the music industry been affected by the internet and digital downloading?”. A thesis statement is a point that you will have to defend. It mandatorily must not be general. For example, if you declare this statement during the conversation, it will surely provoke a conflict and make all people differ in their attitude and take a side. Wrong way: “Downloading music from the internet is bad and we must fight it.” It leaves too many questions to answer. And this statement is way too objective, it does not reflect the controversy of your topic. The truth is that there are no absolutely good or totally bad phenomena. And your thesis statement must show the reality.

Right way: “The culture of digital music consumption must be changed because the creations of musicians become worthless due to activity of web pirates and people stop valuing music according to its merit .”

In this example of thesis, I’ve narrowed my argument to the consequences of digital music downloads on the culture of music consumption. I’ve also focused on the fact that the main harm to the music industry present web pirates.  It induces readers to assume that I will argue against them in the main body. To check if you have created a debatable thesis statement for the research paper, you must figure out whether it is debatable. It means that you must make the reader argue either for or against this statement. Wrong way : “The music industry has changed because of the era of the internet.” It is a statement, but not a thesis statement. It is a general truth. There is no point to argue with that fact. You can narrate about that, but not argue and make research to provide proper evidence to prove your point.

Right way: “Free music download sites must become commercial because recording a music is a full-time job of musicians and every work must be rewarded.” Now it is debatable. Opponents can argue that product that music product is not principal way to earn money for musicians, and internet is a the most effective way to promote their creation and lure audience to visit their concerts, what is a real way to earn money.

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Research paper Introduction Writing Tips

Research paper introduction is an essential part of your writing and it must be created according to certain rules. It is true that when you write any kind of text you can push yourself too hard and cross the borders of norms. Because academic styles of writing are referred to as creative writing as well. You look for information, then analyze it, come up with thoughts, and ideas, and reflect it in a coherent text. The next tips will show you how to fulfill the purpose of the research paper introduction and get rid of the creative mess.

• Size matters. Before a tutor starts reading the article, he reviews it visually. If the size of the introduction is too large, it will make a bad impression on your paper. Just remember, all you have to present in the introduction is: the definition of the topic idea and its urgency, an explanation of the aim of the research, facts to hook the reader, and a thesis statement.
• Be logical. Your introduction will be really strong if it contains key ideas only in a few sentences. To reach such a result it is important to satisfy the logical connection of the thoughts. Your goal is to make the reader understand in the end of the introduction what exactly you attempted to achieve in a research paper and why this problem is worth profound research.
• Make it the last part. Many successful students first work on the whole outline, write the body of the paper and only then form the introduction. That’s because a person becomes more sure in what direction his research goes only after at least a shallow search and analysis of sources.
• Review previous studies on your topic. Every person can study the same topic in a different way. Before you start your own research, you must become aware of the discoveries other scholars made on this issue. Any result will be a reliable background for future work. Note that it is better to indicate recent developments in the primary research rather than a lengthy report.

Research Paper Introduction Example

Finally, when we have analyzed all highlights of introduction writing we can gather all parts of it in one, ultimate part of a paper. Let’s refresh the exemplary topic of it:  “How has the music industry been affected by the internet and digital downloading?”. Now, have a look at the research paper introduction example: “The musical marketing turns to be digital according to demands of current online epoche. Such underground, but worldwide famous bands like Radiohead and IAMX gain profit from the internet and use it as a primary source to show the audience their creation. On the other hand, many artists find the digital era harmful and destructive to their creativity because there are many sites that offer their products for free, giving no profit to the creator. Currently, there are more and more studies that reveal the business side of the music industry is far from the positive side. This research paper will define whether the culture of digital music consumption must be changed because the creations of musicians become worthless due to the activity of web pirates and because people have stopped valuing music according to its merit.”

As you see, all main components are preserved in the example above. The first sentences hook readers, the mid part of the introduction prove the reason for the research, and the thesis statement puts a debatable argument that needs further analysis and the right solution.

Integrity is a Key

After you created the final paper, be decisive to make necessary changes and corrections, especially before the submission. It usually happens that at the end of the research, a writer can face with inconsistencies in all sections of his writing. If the whole paper does not sound like a cohesive text, make improvements. If your main part does not answer the question raised in the introduction nothing obstructs you from adjusting its sense to the ideas from the main body. A paper with cohesive text deserves a high mark, so rule your writing!

Now You’re a Winner

I suppose that before you came across this article you underestimated the value of a worthy introductive paragraph. In fact, I have not introduced you to another meaningful feature of it. You know that all academic essays must end with a conclusive paragraph. There is an assumption that this is the hardest part of research paper completion. In fact, if you have succeeded in making of impressive introduction, you will significantly facilitate the process of conclusion writing. You don’t think it is easy for you? Ask professionals “ write an essay for me ” because writing your essay does not have to be a difficult job.

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Research Paper Introduction

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The introduction of a research paper is a critical component that sets the tone for the entire study. It serves as the gateway for readers to delve into the research topic, understand its significance, and grasp the context of the study. A well-crafted introduction captures the attention of readers, provides a clear overview of the research, and sets the stage for the subsequent sections. In this article, we will explore what makes an effective research paper introduction, provide a step-by-step guide on how to write one, address frequently asked questions, and conclude with a touch of creativity.

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What is an Effective Research Paper Introduction

An effective research paper introduction is a concise and engaging opening section that entices readers to continue reading. It presents the research topic, outlines the objectives and purpose of the study, and highlights the relevance and significance of the research. A well-written introduction provides a clear and logical flow of information, guiding readers through the research problem, and establishing the groundwork for the subsequent sections of the paper.

How to Write an Effective Research Paper Introduction

Crafting an effective research paper introduction is crucial for capturing readers’ attention and setting the stage for your study. This guide will provide you with a step-by-step approach to master the art of writing an engaging and informative introduction. By following these guidelines, you can create a compelling opening that establishes the context, outlines objectives, and conveys the significance of your research.

Step 1: Understand the Research Paper Format:

Before diving into the introduction, familiarize yourself with the required research paper format . Depending on the discipline, you may need to follow specific guidelines such as APA format , MLA paper format , or others. Understanding the text structure and citation requirements is crucial for creating a cohesive and well-structured introduction.

Step 2: Define the Research Design:

In the introduction, briefly describe the research design employed in the study. Explain whether it is a qualitative, quantitative, or mixed methods approach. This information will help readers understand the type of data collection and analysis methods used to address the research problem.

Step 3: Craft a Research Outline:

Develop a research outline that acts as a roadmap for your study. This outline will help you organize your thoughts and ensure a logical flow of information in the introduction. Include the main sections and subsections that will be discussed in the paper, giving readers a preview of the paper’s structure.

What is the difference between APA and MLA format?

APA and MLA are two commonly used formatting styles for research papers. APA (American Psychological Association) format is typically used in the social sciences, while MLA (Modern Language Association) format is more common in the humanities. Both styles have specific guidelines for formatting citations, references, margins, fonts, and other elements. Check out our article on “ 14+ APA vs MLA Format Examples in PDF ” for more detailed comparisons.

Can you provide examples of research summary papers?

Certainly! We have a collection of research summary examples that can serve as a guide for summarizing research papers effectively. These examples demonstrate the essential components of a research summary and showcase different writing styles and approaches.

Where can I find research outline examples?

If you’re looking for research outline examples , we have a comprehensive article that provides a variety of sample outlines across different disciplines. These examples will help you structure your research paper effectively, ensuring a logical flow of ideas and information.

Writing an effective research paper introduction requires careful planning, clarity of thought, and attention to detail. By following the step-by-step guide provided here, you can create an engaging introduction that captivates readers and sets the stage for your research. Remember to adhere to the prescribed research paper format, such as APA or MLA, and utilize appropriate citations to support your claims. With a compelling introduction , your research paper will not only pique readers’ interest but also lay a solid foundation for the rest of your study.

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Overview of research on additive manufacturing of hydrogel-assisted lab-on-chip platforms for cell engineering applications in photodynamic therapy research

• Open access
• Published: 18 September 2024
• Volume 191 , article number  608 , ( 2024 )

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• Adrianna Cieślak   ORCID: orcid.org/0000-0003-1769-8006 1 ,
• Agnieszka Krakos 2 ,
• Julita Kulbacka 3 , 4 &
• Jerzy Detyna 1  

Lab-on-chips supported by hydrogel matrices are excellent solutions for cell culture; thus, this literature review presents examples of scientific research in this area. Several works are presenting the properties of biocompatible hydrogels that mimic the cellular environment published recently. Hydrogels can also be treated as cell transporters or as a structural component of microfluidic devices. The rapidly growing scientific sector of hydrogel additive manufacturing is also described herein, with attention paid to the appropriate mechanical and biological properties of the inks used to extrude the material, specifically for biomedical purposes. The paper focuses on protocols employed for additive manufacturing, e.g., 3D printing parameters, calibration, ink preparation, crosslinking processes, etc. The authors also mention potential problems concerning manufacturing processes and offer example solutions. As the novel trend for hydrogels enriched with several biocompatible additives has recently risen, the article presents examples of the use of high-quality carbon nanotubes in hydrogel research enhancing biocompatibility, mechanical stability, and cell viability. Moving forward, the article points out the high applicability of the hydrogel-assisted microfluidic platforms used for cancer research, especially for photodynamic therapy (PDT). This innovative treatment strategy can be investigated directly on the chip, which was first proposed by Jędrych E. et al. in 2011. Summarizing, this literature review highlights recent developments in the additive manufacturing of microfluidic devices supported by hydrogels, toward reliable cell culture experiments with a view to PDT research. This paper gathers the current knowledge in these intriguing and fast-growing research paths.

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Introduction

There is an apparent increase in the incidence of cancer worldwide. According to 2020, more than 19 million cases of cancer have been diagnosed globally [ 1 ]. Due to the rapidly increasing incidence of cancer, the scientific world is focused on developing increasingly innovative cancer research methods. Combining knowledge and skills in biomedicine and engineering is the key to achieving this development. Innovative methods make it possible to raise the standards of health care through more accurate and controlled research. This dissertation focuses on microfluidic devices provided in the form of lab-on-chip (LOC) solutions used for cell engineering investigation. Fabrication methods, especially additive manufacturing, as well as materials, with a view to hydrogels, will be described thoroughly to review the applicability of LOCs in cell culturing research. Current state-of-the-art concerning photodynamic therapy (PDT), as a promising and noninvasive anticancer therapy to be evaluated directly on hydrogel-assisted LOCs, will be presented in detail. The following topics will be described in the relevant sections of the paper: hydrogel additive manufacturing techniques, 3D printing of hydrogel for cell engineering, lab-on-chip assisted by hydrogels in cell engineering, carbon nanotube (CNT)-doped hydrogels, and photodynamic therapies on-chip. These various topics merge to form a new approach to the development and evaluation of anticancer therapies.

Lab-on-chips are innovative microlaboratories like integrated analytical microsystems, used, among other things, in cell or tissue engineering in vitro. The main advantage of such biosystems is the ability to simultaneously culture and analyze cells in real-time, bypassing the cell-killing step. In addition, by minimizing such systems to the microscale, production and culture costs can be reduced, and thus, biological and chemical wastes are also reduced, minimizing environmental pollution. Lab-on-chips are also portable and easy to handle and transport. Lab-on-chip fabrication materials are usually glasses and polymers (the most common is poly(dimethylsiloxane) PDMS [ 2 , 3 ]). Apart from the standard microengineering techniques like photolithography, wet etching and bonding, additive manufacturing techniques such as extrusion-based printing, jetting-based printing, and vat photopolymerization-based printing are becoming more and more popular. The structure of LOCs is distinguished by characteristic tubules, chambers, and channels in the microsize, allowing microfluidics to control the cellular environment [ 4 ]. These types of microchannels are intended to imitate biological capillaries [ 5 ].

Hydrogels are spatially cross-linked materials composed of hydrophilic synthetic or natural polymers. They can absorb sizable amounts of liquid while maintaining a three-dimensional structure, thus, hydrogel materials can swell in water or body fluids. The liquid in hydrogels is the medium that allows the diffusion of substances, while the degree of cross-linking of the hydrogel polymer is responsible for the efficiency of their transport. The polymer chains that form the hydrogel network can be chemical (irreversible) or physical (reversible) in nature. The mechanical properties of hydrogels depend primarily on the concentration of ingredients or the degree of crosslinking, i.e., the time, concentration, and type of crosslinking agent. Crosslinking of a polymer solution is a process that leads to a hydrogel gaining stability in geometry and structure, and increasing its mechanical strength. Studies conducted on hydrogels include analysis of hydrogel pore size, cross-linking and mechanical strength, viscosity, degree of swelling, and other rheological properties [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. It is common practice to enrich hydrogels with various additives. An example known in the literature, but not so common, is the use of biocompatible carbon nanotubes (CNTs), which are one of the allotropic varieties of carbon. Single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNT) are distinguished. Both kinds of additives are used in the biomedical field. CNTs are so special because they can imitate natural collagen material because of their similar form and dimensions [ 14 ].

As mentioned earlier in this paper, one of the current challenges in the scientific world is the development of new cancer therapies. For this reason, many researchers have recently focused on a relatively new, non-invasive treatment strategy—photodynamic therapy. Photodynamic therapy is a local treatment of oncological cancers (head, lung, skin) and non-oncological diseases (lichen sclerosis). Photodynamic therapies can be the main treatment pathway or can be combined with other known solutions, such as radiotherapy or chemotherapy. The PDT mechanism involves using light-sensitive compounds known as photosensitizers (PS), which are selectively accumulated in tumor cells and destructive only for them. The effectiveness of photodynamic therapies is determined by the presence of intracellular oxygen and light absorbed by such PS (Fig.  1 ). Phototoxic reactions are initiated by activating the mentioned photosensitizer (accumulated in cancer cells) with light of a given wavelength and power. Next, the generation of reactive oxygen forms (ROFs) occurs, which have toxic effects on cell growth by, among other things, the occurrence of so-called oxidative stress [ 15 , 16 ].

Photodynamic therapy (PDT)—mechanism of action [ 73 ]

Based on all of this, the purpose of this literature review is to highlight the recent achievements in the fields of additive manufacturing of microfluidic devices supported by hydrogels (bare and CNT-doped) for cell engineering, towards research on PDT, as a modern anti-cancer therapy, investigated directly on-chip. According to the best authors’ knowledge, this is the first review paper in the interesting fields, focusing on the mentioned subjects as a whole. It is possible to read about the issues separately, for example [ 13 , 17 , 18 , 19 , 20 ].

Hydrogel additive manufacturing techniques

The use of additive manufacturing to fabricate hydrogels, as well as entire LOC constructs, is becoming increasingly common. Additive manufacturing involves the direct fabrication of objects in a single process by depositing various materials. As a result, raw material compositions can be used more efficiently, resulting in less waste and less material utilization. This feature provides several benefits, particularly for small-scale production or custom approaches, including shorter production times and lower costs. In biomedicine, the use of AM technology is of great importance. One example is the microscale manufacturing of microfluidic devices and 3D printing with hydrogels for cell or tissue engineering applications. This advanced technology facilitates the development of novel solutions that are often too complicated or cannot be manufactured using traditional methods. The ability to use AM allows for the continuous development of these technologies, but also the evolution of biomedicine. There are several AM techniques used in biomedicine, and their choice largely depends on the specific application, the material used, and the requirements imposed on the final component. The components and by-products produced must be biocompatible (no destructive effects on living cells). Also important is the durability of the 3D print under specific conditions, such as the cell environment, external and internal forces, stress formation, or corrosion. Manufactured parts must be produced with high precision and accuracy to fit the computer-designed 3D model [ 21 ]. Regarding this literature review, technologies for AM-fabricated microscale lab-on-chip devices with hydrogel structures will be presented exclusively.

According to ASTM standards, three main techniques for additive manufacturing of hydrogels can be mentioned, such as extrusion-based 3D printing, jetting-based 3D printing, and vat photopolymerization-based 3D printing.

Ink extrusion is carried out mainly by pneumatic pressure, mechanical compression, or a solenoid. The 3D-printed object is formed layer-by-layer, and the extruded fiber is characterized by a diameter in the range of 150–300 μm. The literature overview shows that this is the most common 3D printing process. This technology is characterized by low process costs, a wide range of available materials, and the availability of dedicated 3D printers. The weaknesses of extrusion technology include low resolution and printing speed, as well as clogging of the printing nozzle. In addition, a cell-killing phenomenon can occur due to the shear stresses created during the extrusion of the bioink (ink with cells). In summary, it provides a lower cell survival rate compared to other 3D bioprinting methods [ 13 , 17 , 22 ].

Jetting-based 3D printing, in turn, is a less popular AM technology in which ink is formed into droplets. Ink droplets are carried out mostly by acoustic and thermal methods. This technology has better resolution and cell survival compared to extrusion processes. However, there are fewer commercial inks and inkjet 3D printers suitable for this technology available. Droplet ink leads to less efficient additive manufacturing. Moreover, the hydrogel inks should have a relatively low viscosity to avoid clogging the printing head. Thus, the effects of 3D bioprinting utilizing this method and the subsequent biological activity of cells are still not well-known [ 23 , 24 ]. Lastly, jetting-based 3D printing was performed in the research of Negro A. et al. in 2018 [ 25 ] and Walczak R. et al. in 2018 [ 26 ].

It is also necessary to consider ink requirements and the impact of bioprinting parameters, as well as bioink properties on cell viability from the jetting-based bioprinting point of view. Ng et al. (Ng 2021) conducted research using a drop-on-demand material jetting technique and a thermal 3D printer. The results were presented by evaluation of surface tension, density, and viscosity experiments, among others. The authors proved that the increase in cell concentration (primary human dermal fibroblasts, 4 mln cells/ml) resulted in a slower droplet impact speed (optimal 5.77 m/s) when spraying droplets containing sub-nanoliter volume cells. Reducing the droplet impact velocity led to higher cell viability and improved 3D print quality. Moreover, the authors highlighted that printing speed was crucial regarding cellular viability. Each of the layers was 3D bioprinted within two minutes to prevent excessive droplet evaporation, which negatively affects cell survival rate (hypertonic environment occurring, causing fibroblast apoptosis). Moreover, the higher the cell concentration, the higher the values of density and viscosity of the bioinks, and the lower the surface tension. The study confirmed that controlling droplet impact velocity and droplet volume led to high short-term (1 day) fibroblast viability and long-term (7 days) proliferation of 3D-printed cells [ 27 ]. A slightly older study of the same scientific team (Ng 2017) investigated the influence of synthetic bioink properties on 3D bioprinting and cell activity during that process. They prepared five different concentrations of polyvinylpyrrolidone (PVP)-based bioink and also characterized their density, viscosity, and surface tension. The authors found that the viscosity and density of PVP-based bioinks increased with rising substance concentration. In contrast, the surface tension of the bioink decreased as its concentration increased. Printing parameters included, among other things, a constant pressure of 25 kPa, since above this value—shear stress has been shown to hurt living cells contained in the bioink. Other findings were that the viscosity of the bioink increased with increasing cell concentration (0.5–2.5 mln cells/ml), and also reduced the surface tension due to a decrease in the total free energy of the bioink. Cell viability is strongly influenced by the Z-factor, defined as the inverse of the Ohnesorge number, meaning the ratio of the Reynolds number to the square root of the Weber number; independent of the bioink velocity. During the research, the following Z-factor range of values was obtained: 5.75 ≤ Z ≤ 64.36. According to the performed experiments, printable bioink with a low Z-value (< 9.3) is suitable for achieving high cell viability (> 90%) [ 28 ].

Laser-assisted 3D (bio)printing (also known as Laser-Induced Forward Transfer—LIFT) belongs to the group of jetting-based printing technology. It is another layer-by-layer process using a laser beam of appropriate power (tiny droplets are ejected during the 3D printing process using the laser source). The process singles out the ink and the photoabsorbent material just above it. Laser-assisted 3D printing is the most expensive and complicated method among those mentioned above. The 3D-printed parts have low mechanical stability, but due to the lack of a printing nozzle, there is no problem with printing head clogging or shear stress (a major benefit of this technology concerning bioinks). Moreover, laser 3D printing shows the highest resolution, precision, and cell viability. However, ink viscosity, layer thickness, and laser parameters are crucial in laser AM [ 23 , 24 ]. There are several biomaterials and biological objects that can be processed using this technique. The sample research using this technology was carried out by Kingsley D. et al. in 2019 [ 29 ]. Various parameters affect cell viability during LIFT processes, for example, laser parameters such as wavelength. The laser wavelength should be carefully selected. Typically, near-infrared or UV lasers are used to minimize thermal damage to cells by reducing the interaction with biological tissues. Another parameter is pulse duration—shorter pulse durations (femto/pico-seconds) may reduce the heat-affected zone, thus minimizing thermal damage to cells. However, excessively short pulses can lead to high peak intensities that may cause photomechanical damage. It should be highlighted that the viscosity of the bioink affects the formation of the jet or droplet during the LIFT process (bioprinting). Higher viscosity may require higher laser energy to induce transfer, potentially increasing the risk of cell thermal damage. Crucial is choosing the cell type during experiments. Different cell types have varying levels of tolerance to the mechanical and thermal stresses induced by LIFT. For example, some stem cells or primary cells may be more sensitive compared to immortalized cell lines. Selecting a laser parameter set that matches the tolerance level of the specific cell type being printed is essential [ 30 , 31 , 32 , 33 ].

The last technique, vat photopolymerization-based 3D printing, is a method that does not use a nozzle. In this case, the inks must exhibit sensitivity to light, which leads to their polymerization, thus giving structural stability to the 3D prints. The light source can be UV radiation. The most common form of vat photopolymerization is stereolithography, which presents low cost, a short printing time, and a relatively high resolution. Examples of photo-initiators used in stereolithography are complex substances of lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP, 0.5% w/v) and commercially available Irgacure 2959 (1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propanone) [ 34 , 35 ], Irgacure 819 (phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO, 3% w/v relative to the polymer) [ 36 ]. The materials used in this technology are light-curing resins (commercial e.g. Dental SG and Dental LT Clear or self-made). The safe parameters of UV light (LED) from the cell viability point of view are as follows – 5 mW cm −2 at 365 nm and 30 mW cm −2 at 405 nm, UV exposure time: 15 min. [ 37 ], or 20 mW cm −2 with radiation 30 s [ 36 ]. Interestingly, this method allows the processing of inks with higher viscosity. There is also no problem with clogging or shear stress. Unfortunately, the main limitation of stereolithography is the poor choice of light-sensitive and biocompatible materials at the same time [ 23 , 24 ]. Interesting stereolithography applications were presented in the research of Xue D. et al. in 2018 [ 34 ] and Piironen K. et al. in 2020 [ 37 ].

3D printing of hydrogel for cell engineering

A variety of natural and synthetic inks are used to obtain stable hydrogel structures through 3D bioprinting or 3D printing and post-processing (e.g., cross-linking method). The inks should exhibit adequate rheological properties to enable the printability of the material, and the hydrogels themselves must exhibit satisfactory mechanical and biological properties concerning the strength of the hydrogel matrix to ensure cell culturing [ 38 ]. As mentioned earlier, in 3D printing, the following AM technologies are distinguished: extrusion-based 3D printing, jetting-based 3D printing, and vat photopolymerization-based 3D printing, Fig.  2 .

Visualization of the main AM technologies dedicated to hydrogels—from the left: extrusion-based 3D printing, jetting-based 3D printing, and vat photopolymerization-based 3D printing (Own source)

The specification of the AM technologies is presented in Table  1 [ 22 ]. The base of the AM process is to select an appropriate ink, that is, a printable biomaterial, which may contain living cells in its composition (then bioink). Hydrogels are excellent bioinks because of their extracellular matrix-like properties [ 20 , 39 ].

The impact of extrusion-based bioprinting processes on cell activity requires greater attention. More precisely, 3D bioprinting can affect not only cell death but also cell growth, differentiation, or shape. The bioink applied in 3D bioprinting is a unique ink composition containing living cells. Thus, the AM process is characterized by the extrusion of biological cells immersed in biocompatible ink (natural or synthetic). In that dynamic procedure, cells are exposed to a variety of interactions, especially mechanical ones, which might be fatal. That is why 3D bioprinting is such a specific and demanding process. Whether cells survive the 3D bioprinting process corresponds to the functionality of the designed structure, including tissues, biosensors, and scaffolds, among others. Certainly, the 3D bioprinting process is a more expensive procedure than standard ink extrusion, and this is important to emphasize. In addition, the preparation and establishment of parameters in 3D bioprinting is more complex and time-consuming. One of the most serious problems faced during bioprinting is the formation of inappropriate shear stress values, which destructively affect the living cells contained in the bioink. Attention to this issue is drawn by Boularaoui S. et al. (Boularaoui 2020). In the process of extrusion of bioink by pneumatic method, pressure is applied to the extruded material. The narrower the diameter of the nozzle, the greater the pressure that must be applied to the bioink. The most vulnerable cells are those near the walls of the printing nozzle. Therefore, cells within the core of the extruded fiber are more secure, as shown in Fig.  3 . Furthermore, the shear stress created in the 3D bioprinting process is more deadly the higher the values it reaches. The lethal effect of the induced shear stress is determined by the printing parameters and the properties of the bioink (biomaterial composition, cell type and concentration, etc.). Shear stresses generated during bioprinting may reach values of up to 60 kPa at high 3D printing speeds. In the context of 3D bioprinting by extrusion, the authors paid attention to the bioink (its composition, properties, concentration, etc.) as well as the 3D printing parameters and related consequences. The phenomena occurring in the printing nozzle filled with bioink were highlighted. Namely, how the choice of materials and 3D printer parameters could affect the printing process and the biological activity of the cells contained in the bioink [ 13 ]. The described research needs optimizing bioink formulations and printing parameters, developing better bioreactor systems for post-printing tissue maturation, and exploring new materials that mimic the ECM.

The effect of shear stress on cells during extrusion-based 3D bioprinting [ 13 ]

Stumberger G. and Vihar B. (Stumberger 2018) described the additive manufacturing of hydrogels and developed perfused microfluidics within hydrogel matrices. In the study, the FRESH method was used to deposit the material inside a matrix (gelatin hydrogel) that supports the printed ink, allowing any geometry to be made. The hydrogel matrix was enriched with cross-linking calcium ions so the microchannel-forming material could polymerize when applied to the matrix. Once the channel-making process was completed, the matrix could be removed by heating and liquefying the material. The fabrication procedure involved placing the gelatinous suspension in a mold and then 3D printing the channel path. The matrix was then solidified so that the structure became stable and could be removed from the mold, and the support material could also be removed. The stages of manufacturing the hydrogel matrix are shown in Fig.  4 . Based on this study, the following observations were made: smaller gelatin grains in the matrix provided better microchannel resolution and shape fidelity. In contrast, larger grains caused a structure to be more stable. According to the Authors, the optimal grain size was in the range of 90–200 µm. To test the versatility of the fabrication technique, an alginate matrix was prepared and tested, showing positive test results. Thus, potential applications of this research cover, e.g., the development of invisible vascular tissues – vascular grafts [ 40 ]. Although the article demonstrated the feasibility of creating microfluidic structures within hydrogels, it did not thoroughly address the scalability of the technique for large-scale production. Moreover, the long-term stability and durability of the embedded microfluidic channels within the hydrogel matrices were not extensively discussed. Future research in this area should focus primarily on scalability and long-term stability to develop this technology into real-world applications.

Scheme of fabrication of a hydrogel microfluidic device [ 40 ]

Another research by Chrenek J. et al. (Chrenek 2022) presented the tissue bioprinting protocol employed for the BIO X 3D printer from the CELLINK company, as shown in Fig.  5 . The authors checked application possibilities for that 3D printer and commercial hydrogel ink based on fibrine, self-made hydrogel consisting of alginate (2%) and gelatin (2%) (high viscosity), as well as hydrogel bioink containing living mesenchymal cells were used. The scientists proposed, i.e., an agarose support bath to increase the stability of the hydrogel structures printed utilizing commercial, low-viscosity ink. The protocols were provided thoroughly, e.g., calibration, printing parameters, ink preparation, and cross-linking methodology (solution, concentration, time, etc.) were described. Moreover, scientists indicated the maximum pressure of the 3D printing process to be 200 kPa. This parameter is crucial, especially for cell viability, as too much pressure could kill the cells. According to the article, the appropriate pressures are 11 kPa for commercial ink and 20 kPa for alginate-gelatin ink. Selected 3D printing parameters indicated in this paper are shown in Table  2 .

The BIO X 3D printer from CELLINK. Extrusion 3D printing process (Own source)

The authors also mentioned some potential problems that could occur during 3D printing and proposed interesting solutions. For instance, the formation of air bubbles could be minimized by slowly stirring with the tip of the pipet or centrifugation of the gel in a laboratory centrifuge. The missing or inconsistent extrusion of material can be offset by increasing the printing pressure, replacing the print head tip if it is clogged or damaged, or filling the print syringe with a new gel. If there is a problem with a clogged nozzle tip, it is worth removing the hydrogel clot by increasing the pressure in the printer or manually removing it and moving the print tip away from the work table to prevent possible cross-linking of the ink. To eliminate the problem of maintaining the structure shape after printing, the cross-linking agent should be applied to the substrate for a few minutes and then removed. Another possibility is to extend the cross-linking time of the ink. If there is a problem with a leaking nozzle tip between prints, the pressure in the 3D printer should be reduced, or just the printing tip should be wiped [ 41 ]. Despite the innovative approach in this article, several limitations must be considered. Namely, technical challenges – print resolution focused on the pneumatic printhead of the BIO X 3D printer. Achieving the fine spatial precision needed for intricate neural networks could be difficult, potentially impacting the fidelity of printed tissues compared to natural neural structures​. One of the major challenges in tissue engineering is providing sufficient vascularization for nutrient and oxygen delivery. Among other things, the presented protocol did not take into account what could limit the size and durability of the printed neural tissues.

Another interesting work of Tarassoli S. et al. (Tarassoli 2021) presented a systematic review concerning bioinks for 3D bioprinting. Eligibility for inclusion of articles in this paper was as follows: focusing on extrusion 3D bioprinting, testing animal or human cells, in vitro, as well as in vivo tests, research articles, and English language articles only. Natural inks, synthetic inks, and inks resulting from a combination of the two were distinguished. According to the paper, the most common hydrogels used as inks were alginates, polycaprolactone (PCL, synthetic), gelatin, and methacrylate gelatin. The others included, e.g., chitosan, collagen, gellan gum, or Matrigel. The average resolution of the bioprinting process for natural bioinks was defined as 1 mm and 0.5 mm for synthetic bioinks (Table  3 ). According to the authors, the lowest resolution obtained was 0.025 mm [ 20 ].

From the review article’s point of view, the reviews might predominantly include studies that report positive outcomes. Negative results are less likely to be published. This bias can skew the understanding of bioink effectiveness and applicability. Moreover, review articles may emphasize bioinks that are already well-documented, potentially neglecting innovative or experimental bioinks that could offer unique properties and benefits. Furthermore, review articles usually compare results (e.g., biological, mechanical, and others) obtained with different equipment and even laboratory methods, which can influence possible inconsistencies.

In the paper of Antich C. et al. (Antich 2020), the development of a hydrogel bioink based on hyaluronic acid (1%) and sodium alginate (2%) with the potential to manufacture articular cartilage additively was presented. The tests performed were in vitro type. The cell scaffold was based on a synthetic polylactide (PLA), into which pores the bioink was imprinted. Calcium ions (Ca 2+ ) were used as the cross-linking agent to obtain the hydrogel. The additive manufacturing of PLA was performed using the extrusion of the bioink, as shown in Fig.  6 . Next, a mixture of hydrogel and human articular chondrocyte cells was applied to a scaffold. To verify the solution durability and investigate the degradation of hydrogels in the cellular environment in vitro, obtained hydrogel constructs were mechanically validated at first. For this purpose, compression tests and shear tests were performed. The research results indicated that the designed hydrogels showed a higher modulus of elasticity compared to the control groups (PLA + sodium alginate and pure PLA). This may be related to the viscoelastic properties of the hydrogel based on hyaluronic acid and alginate (the ability to transfer loads). When it comes to biological research, it was focused on cell viability, proliferation, and selected biological activities of the cells. Live/dead assays were performed before and after the 3D bioprinting processes. Based on the tests, it was shown that 3D bioprinting of the designed scaffolds allowed for the regeneration of joint cartilage. Therefore, the scaffolds promoted chondrogenesis, i.e. the process of cartilage formation. According to the authors, a hydrogel consisting of alginate and hyaluronic acid dissolved in deionized water was a suitable biomaterial for use in 3D bioprinting for such biomedical applications [ 42 ]. Nevertheless, the research referred to a specific type of cells and hydrogels. The authors did not report on the possibility of extending the research to other materials or cells, which affects the versatility of the described research. The discrepancy in the properties of 3D-printed tissues and natural tissues can affect the performance and durability of bioprinted constructs under physiological conditions. However, the data obtained allows for further steps and provides opportunities to perform in vivo tests and their real use.

Scheme of 3D bioprinting process [ 42 ]

In turn, Kiyotake E. et al. (Kiyotake 2019) developed a pentanoate-modified hyaluronic acid hydrogel, as a new biomaterial constituting a bioink in AM and, more specifically, in extrusion processes. The Authors prepared several different hydrogels that differed in concentration of hyaluronic acid. The bioink was a mixture of hydrogel stem cells and nerve cells (two different types separately). Cross-linking processes were performed using ultraviolet (UV) light. The biofabrication process is presented in Fig.  7 . The scientists characterized the rheological properties of prepared hydrogels, such as viscosity, yield strength, and recovery modulus of storage. These parameters are inherent in the printability of the material. According to rheological research results, the behavior of viscosity informed about the bioink thinning properties under the influence of shear during 3D bioprinting. In turn, the parameter of the yield strength was crucial to maintain the fidelity of the shape to the designed model. The authors found that cell concentration had a negligible effect on the printability of the bioink. In addition, cell viability after the 3D bioprinting process was satisfactory for the two types of cells tested. Nevertheless, the authors pointed out the need for further research focused on, among others, cell concentration or sterilization methods of the bioink. Although the scientists referred to a specific hydrogel (hyaluronic acid enriched with pentanoate), the versatility of rheological research methods gives the possibility to extend the studies to other bioinks. The study of additional biomaterials would strengthen the validity and correctness of the research. Scientists made a qualitative assessment of shape fidelity, but to obtain reliable results, a quantitative analysis should also be performed, e.g., by the use of dedicated programs analyzing, among others, the size or number of hydrogel pores. In conclusion, the authors emphasized the need to focus on standardizing bioink and 3D bioprinting parameters, not only on a trial-and-error approach [ 43 ]. The study focused on three specific rheological parameters (yield stress, viscosity, and storage modulus recovery) to assess printability. While these are critical, other factors such as thermal stability or long-term mechanical stability were not thoroughly examined. According to biological experiments, the study reported minimal impact on printability with increasing cell concentrations but did not extensively evaluate the long-term viability and functionality of encapsulated cells after 3D printing. To ensure that the bioink supports cell proliferation and differentiation, detailed biological assessments are necessary.

Scheme of biofabrication steps: a ) 3D bioprinting, b ) cross-linking, c ) mounting of silicone cover [ 43 ]

The next research was described by Shi Y. et al. (Shi 2018), who presented a bioink based on methacrylate gelatin (5%) and collagen (8%) with the addition of tyrosinase. Different concentrations of tyrosinase: 0, 100, 300, 500, and 800 u/ml were applied to achieve the 3D bioprint skin-like structures with living cells (human melanocytes, keratinocytes, and dermal fibroblasts). The 3D bioprinting was performed using the bioink extrusion. The cross-linking process was performed in two steps by tyrosinase enzyme and UV light. An innovation in these studies was the use of tyrosinase, which increased the stability of the hydrogel and gave the effect of skin color. According to the results of the biological tests, all cells were characterized by a high percentage of viability, exceeding 90%. The presence of tyrosinase reduced the growth and mobility of fibroblasts, increased the proliferation of melanocyte cells, and was neutral for keratinocytes. Moreover, in vivo tests showed that the addition of tyrosinase shortened the healing time of wounds and, more specifically, the reconstruction of the damaged epidermis and dermis [ 44 ]. Although the study reported high initial cell viability (> 90%) for human melanocytes, keratinocytes, and dermal fibroblasts, the long-term viability and functionality of these cells within the bioprinted constructs were not thoroughly investigated. Moreover, from the mechanical point of view, long-term stability and degradation rates of bioink are also important factors that were not fully addressed.

Another study conducted by Jain T. et al. (Jain 2021) was based on the evaluation of the 3D bioprinting process when incorporating the L929 mouse fibroblast cell line into a gelatine methacrylate (GelMA, 10% w/v) ink at different concentrations: 1, 5, and 10 × 10 6 cells /ml. The AM process was based on 3D bioprinting by extrusion of the bioink. The cross-linking process was performed using UV light. The motivation for the study was the instability of the physicochemical properties of bioink dedicated to 3D bioprinting. The scientists performed mechanical-rheological tests and evaluated viscosity variation, shape fidelity, and compressive strength of 3D prints. It was shown that when the concentration of cells in the bioink increased, the homogeneity of their distribution in the hydrogel was improved. Furthermore, GelMA ink (in the concentration range of 7–15% w/v) was found to be suitable for biomedical applications with cells directly incorporated into this biomaterial or separately. To sum up, the addition of cells in the bioink did not statistically significantly affect the rheological properties of the biomaterial or the 3D printing process in this study [ 45 ]. The question is what if higher concentrations of cells or other cell types were used? Normalizing the standards for the 3D printing of biomedical products for in vitro and in vivo applications is the major issue. Furthermore, the study did not extensively examine long-term cell viability and functioning within 3D-printed constructs, which is crucial for practical applications.

The research of Wu Y. et al. (Wu 2018) related to the 3D bioprinted liver scaffolds using bioink based on sodium alginate, cellulose nanocrystals, fibroblast cells, and liver cells. Hydrogel extrusion technology was employed to obtain the structure. Fibroblasts were used to 3D bioprint the edges of the scaffold, while liver cells formed its central part. The cross-linking agent herein was a solution of calcium chloride. The fabrication procedure is shown in Fig.  8 . In particular, the rheological properties of the bioinks (extrusion, shear thinning, and shape fidelity) and the biological activity of the cells were investigated thoroughly. According to the results of biological research, 3D bioprinting had no statistically significant effect on cell viability. The inclusion of cellulose in alginate-based hydrogels improved shear properties and did not affect the viscosity of the bioinks. Furthermore, cells in bioinks did not affect the hydrogel viscosity either. The tests also indicated satisfactory shape fidelity of the hydrogel 3D prints. According to the authors, the best bioink (in terms of 3D bioprinting, structural stability, and cell culture) was an alginate-based hydrogel (2% w/v) with cellulose nanocrystals (4% w/v). As presented here studies were preliminary, the researchers further propose incorporating gelatin into the hydrogel to improve cell binding to its structure [ 46 ]. It is worth noting that although the study showed minimal cell damage during the 3D bioprinting process, long-term cell viability and activity were not thoroughly examined. Thus, more extensive investigation is needed.

Scheme of hydrogel structure biofabrication [ 46 ]

Other research in this field focused on different hydrogel additives, as presented by Cleymand F. et al. (Cleymand 2021), who developed chitosan-based ink with guar gum biopolymer. The main aims were the fabrication of novel hydrogel ink and the optimization of the 3D printing extrusion process. Enriching chitosan hydrogels with guar gum increased the viscosity of the ink, and simultaneously increased the precision of 3D prints (relative to 3D models). According to the authors, the best hydrogel was based on chitosan (85%) with the addition of guar gum at a concentration of 15%. The hydrogel exhibited improved rheological and strength properties, allowing the AM of three-dimensional structures to be used for potential biomedical applications, e.g., for 3D printing of scaffolds [ 47 ]. The study needs to be expanded to assess the biocompatibility and long-term viability of cells within 3D-printed constructs.

Based on the aforementioned articles, critical features of the additive manufacturing of hydrogels were defined and analyzed.

First, the accuracy and resolution of the printing are primarily affected by the material type, thickness of the layer, sterilization procedure, 3D print size, and surface tension.

The thickness of the layer is mainly influenced by the diameter of the nozzle and the surface tension.

The fidelity of the shape is primarily influenced by cross-linking of the polymer ink (polymerization process), the composition of the material, its stiffness, yield stress value, and swelling. The real challenge is to develop a hydrogel that, while maintaining its shape (compatible with the 3D computer-designed model), will exhibit appropriate stiffness without adversely affecting the cell viability.

The biological activity of living cells in the bioink is primarily influenced by, e.g., cell type, cell concentration, residence time, temperature, the porosity of the hydrogel, the formation of shear stresses, viscosity, and viscoelasticity, yield stress value, cross-linking procedure, the biocompatibility of materials or by-products, and polymer concentration.

In turn, the mechanical properties of 3D prints are primarily influenced by cross-linking of the polymer ink, the viscosity of the ink, hydrogel yield strength, temperature, time, cells presence, and their even or uneven distribution, load action on the hydrogel component, layer defects, weak interlayer adhesion, molecular weight of the ink, or amount of liquid inside the hydrogel.

The printability is mainly affected by the viscosity of the biomaterial, surface tension, cross-linking (e.g., cross-linking density), molecular weight, polymer concentrations, shear thinning, biodegradation, biocompatibility, shear rate, or yield stress value.

The viscosity of the ink is primarily influenced by the molecular weight of the material, the concentration of the polymer solution, the complexity of the chemical structure, the temperature, as well as the presence of shear-thinning materials.

The swelling of hydrogels is mainly influenced by cross-linking of the ink, molecular weight, and amount of liquid in the hydrogel (e.g., culture medium).

The degradation and biodegradation rate predominantly depend on several factors including the presence of cells within the hydrogel structure, culturing time, temperature, hydrogel composition, polymer concentration, and the inclusion of hydrophilic and hydrophobic polymers [ 24 ].

Summarizing the issue of hydrogel 3D printing process (Fig.  9 ), an ideal hydrogel ink should be characterized by the following properties: easy extrusion and printability, the ability to manipulate physical, chemical, and biological properties , allowing a homogeneous distribution of cells in its structure , biocompatibility (enabling the survival of cells, promoting their biological activity, such as proliferation or migration), required rheological properties, such as adjusted viscosity and stability during printing, as well as after the process [ 13 , 17 , 20 ].

Mechanism of additive manufacturing of hydrogels [ 73 ]

The key advantages of using hydrogels for 3D printing in cell engineering are as follows. 3D printing of hydrogels makes it possible to achieve a microenvironment similar to in vivo conditions (ECM-like properties), including complex geometries of the structure. In the area of hydrogel AM, it is possible to 3D bioprint with cells immersed in bioink or 3D print with hydrogel ink and apply cells already into the printed structure. The choice of 3D printing or 3D bioprinting methods depends on the nature of the research being done, it remains a matter of choice for researchers. The second option is more complex and complicated because of the impact of e.g. printing parameters on cell viability. Nevertheless, hydrogels have a high water content, which improves the diffusion of nutrients and oxygen, promoting cell viability and functions. The appropriate hydrogel composition provides biocompatible properties, which means they can be designed to support cellular activity. The 3D-printed hydrogels integrated into lab-on-a-chip platforms offer several performance enhancements over traditional platforms (e.g., fabricated using glass or PDMS). Additively manufactured hydrogel platforms allow the integration of multiple cell types and the incorporation of microsensors, providing real-time monitoring and feedback within a single microchip. By providing a more accurate representation of the human cellular environment, 3D-printed hydrogel lab-on-chip systems reduce the reliance on animal models, which could allow the elimination of animal experiments in the future. Overall, 3D printing of hydrogel LOC platforms represents significant advances in cell engineering, offering a more accurate, scalable, and ethically sound approach to biomedical research [ 48 , 49 ].

Lab-on-chip assisted by hydrogels in cell engineering

Lab-on-chips assisted by hydrogels are innovative solutions for cell cultures in a microscale. Biocompatible hydrogels imitate cell environments, such as the extracellular matrix (ECM), where cells grow, differentiate, proliferate, and migrate. Hydrogels can be treated as cell transporters or as a structural part of the LOC device [ 24 , 50 , 51 , 52 ]. A representation of the cellular environment in a fluidic microdevice is shown in Fig.  10 .

Visualization of the similarity of cancer environments and lab-on-chip platform [ 74 ]

The connection between LOC platforms and hydrogels is described for instance, by Ayuso J. et al. (Ayuso 2016) who developed and characterized a microfluidic device that imitates a tumor environment. The cultivated HCT-116 colon cancer and U-251 MG glioblastoma multiforme cell lines mixed with collagen hydrogel were injected into LOC. First, the authors analyzed the fluid flow through the microchannels that imitate blood vessels. Parallel flow to the central microchamber was observed after injection of 10 µl of the mixture. Thus, there was no interaction with the hydrogel caused by the high specific resistance of collagen filling in the main chamber. In the next step, 300 µl of the medium was supplied through the microchannel and a clear intrahydrogel flow was observed. The authors decided that 1–2 ml of liquid is needed to replace or supplement the cell medium, considering the volume of the central microchamber – 2 µl. Scientists also analyzed cell viability. When the cell concentration applied to the LOC was the highest (40 million cells/ml), many dead cells were found in the central part of the microchamber. Moreover, a band of dead cells formed the so-called necrotic core. However, after reducing the concentration of cells in the hydrogel to 4 or 10 cells/ml, the necrotic core was much smaller. As observed, the dead band of HCT-116 was significantly greater than for MG U-251. Meanwhile, the authors also analyzed cell proliferation and the results showed that cells growing near the microchannels proliferated much more frequently than cells located around the necrotic core. According to this, as the cells moved farther away from the lateral microchannels, the intensity of proliferation decreased until the band of dead cells. What is more important, a similar phenomenon occurs in the tumor environment. The next step was to analyze the oxygen and glucose gradient in the microdevices. The results showed that hypoxia is generated in microdevices but simultaneously, there is a possibility to monitor and evaluate this adverse phenomenon in real-time. Moreover, hypoxia levels can be manipulated by intrahydrogel fluid flow. In the case of the glucose analysis, based on the confocal images, it was found that synthetic glucose rapidly diffused through the hydrogel in the absence of the cells. The difference in fluorescence intensity between the glucose-perfused microchannel and the opposite channel was about 30%. In the presence of U-251 MG cells, the glucose diffusion profile was similar to the LOC without cells. On the contrary, a different glucose gradient was generated with HCT-116 cells, in which a higher glucose fluorescence intensity was observed near the lateral microchannel of the perfused glucose. The gradient increased by about 50% compared to experiments with control or U-251 MG cells. The researchers also assessed quantitively reactive oxygen forms (ROS) to be quite low. The highest amount of ROS was observed near the microchannels, where oxygenation was the largest. The last research concerned drug penetration and its impact on the microenvironment (doxorubicin (DOC)—HCT-116, alkylating agent temozolomide (TMZ)—U-251 MG)). As a result of the experiments, the DOC drug initiated cell death at a high level, mostly near the microchannel. However, this destructive impact was significantly weaker as the necrotic band approached. Referring to the TMZ, a considerably lower cell-killing influence than in the control group (2D cell culture) could be noticed utilizing the LOC platform. Nevertheless, the authors claim that the described and tested LOC platform is suitable for the validation of cancer cell treatments and the development of new cancer therapies using cytotoxic drugs, and further research will be conducted [ 53 ]. Nevertheless, this particular model may not fully replicate the complexity of the tumor microenvironment, including the variety of cell types, extracellular matrix components, and signaling pathways present in vivo. The model is primarily designed for short-term experiments, thus there is a need for long-term investigations.

Only a year later (2017), a team headed by Ayuso J. presented research about glioblastoma multiforme on a microfluidic chip, which was fabricated using the photolithography technique. The LOC platform consisted of a central microchamber for the location of cells mixed with collagen hydrogel and lateral microchannels with cell medium. C-6 glioma cells and U-251-MG multiform glioma cells were cultivated. The results of the viability test showed that cell viability in LOC was similar to the results of the control group, exceeding 95%. Moreover, constant fluid flow nourishing the culture did not mechanically affect the hydrogel or embedded cells. The scientists, similarly as in the previous studies, also analyzed the glucose gradient and compared the diffusion profiles between LOC with and without cells. The analysis indicated that it was similar for both cases. On that basis, the potential application of the described solution can be focused on, e.g., drug delivery and drug screening [ 54 ]. It is worth remembering that microfluidic chips, despite their many advantages, have limitations in mimicking the full tumor microenvironment. For example, they might not completely replicate the heterogeneity of cell types, ECM components, or the complex interactions between tumor cells and surrounding tissues. Moreover, it is crucial to ensure that observations in the microchip correlate with actual glioblastoma behavior in patients, so there is a need for in vivo studies.

There is also a possibility that hydrogels can be structural parts of a microfluidic device. An interesting literature review in this area was done by Goy C. et al. in 2019 (Goy 2019) [ 18 ]. In this paper, e.g., the research of Sun H. et al. (Sun 2016), who focused on the development of a cell-on-hydrogel platform for fast, cheap, and multifunctional research, was described. The microdevice was fabricated by molding method using a polymer solution and casting to a PDMS template. Next, a cross-linking process was provided to receive hydrogel matrix bonded to biocompatible glass substrates. The hydrogel matrix consisted of natural polymers such as agar (1,5%) and sodium alginate (1,5%). What is more interesting, scientists provided E. coli bacteria culture on the LOC surface, not in the microchambers or microchannels, to eliminate shear flow. Moreover, diffusion studies using fluorescence microscopy and, among others, fluorescein (332 g/mol) as a deflating substance (its molecular weight is close to the molecular weight of well-known drugs) were conducted. The results showed that there was a constant gradient and an appropriate linearity between the two microchannels. Moreover, it was found that the proposed method led to the generation of a stable gradient for a long time. It was possible thanks to the continuous refreshing of the gradient source and drains by the flow inside the channels [ 55 ]. Agar and alginate hydrogels used in these studies are cost-effective and accessible materials, but simultaneously, these hydrogels might have limitations in terms of their mechanical properties, nutrient diffusion, and compatibility with various cell types. The study did not fully address how these factors affect the performance and accuracy of antimicrobial susceptibility testing.

On the other hand, Nie J. et al. (Nie 2018) investigated vessel-on-chip, based on hydrogels. The scientists used the casting and bonding method to prepare hydrogel structures as shown in Fig.  11 . The crucial in this method was a double cross-linking process to obtain an entirely homogeneous structure. There were three hydrogel compositions: alginate and gelatine, alginate and methacrylate gelatin (GelMA), and gelatine and GelMA. In the case of alginate-gelatin hydrogel, the removal process from the mold was based on the gelation properties of gelatin at 4 °C. On the other hand, the binding process was based on ionic cross-linking of alginate with a calcium chloride solution (4% w/v). For alginate and GelMA hydrogel, in turn, the removal process from the mold was based on ionic cross-linking of alginate with Ca 2+ , while the bonding of hydrogel layers was based on photo cross-linking (UV) of GelMA polymer. The last polymer composite, gelatin and GelMA, based on gelatin gelation at low temperature (4 °C) during the mold removal process. The layer-bonding process requires UV light to act on GelMA. The molds for casting polymer solutions were designed in several ways, differing in the geometry of the microchannels. Next, diverse structure verification tests were provided. According to the results, hydrogels based on alginate and gelatin, as well as gelatin and GelMA hydrogels, were characterized by microchannels with high transparency. On the contrary, the third composite hydrogel was structurally imprecise, damaged, and non-transparent. For bioassays, human umbilical vein endothelial cells HUVEC were used and placed on the surface of hydrogel microchannels. All fabricated hydrogels were characterized by an ordered and porous surface, which positively affects the adhesion, proliferation, and migration of cultured HUVEC cells. Based on the Authors’ test results (biocompatibility, microstructure, and processing), gelatin and GelMA composition was chosen as the best. The selected hydrogel allowed for the best representation of vascular function for the biological cells under study [ 56 ]. While the vessel-on-a-chip model aims to mimic vascular behavior, the complexity of real blood vessels, including their interactions with various cell types and biochemical signals, might not be fully captured. The simplifications made for practical reasons could limit the model's ability to accurately reflect complex vascular dynamics.

The procedure employed for the fabrication of a microfluidic platform [ 56 ]

Similar research was performed by He J. et al. (He 2016), who fabricated a gelatine-based hydrogel, but more complex microchannels were proposed. The researchers again took advantage of the gelatine gelling properties at low temperatures (4 °C) and the high degree of biocompatibility of this biopolymer. Cross-linking of the polymer solution occurred by enzyme action. In this study, human umbilical cord endothelial cells HUVEC were cultured in the microchannels. The barrier function of the endothelial microfluidic network was characterized during this research. According to the results, HUVEC cells were able to form a uniform biological layer around the microchannels creating a barrier [ 57 ]. Further research in this area could encompass vascularization tests, organ-on-chip fabrication, or drug testing. Nevertheless, it is important to focus primarily on long-term studies of cell cultures and biological activity, and optimization of flows in microchannels to get as close to physiological conditions as possible.

Another study was performed by Yuk H. et al. (Yuk 2016) who developed and fabricated a skin-like microfluidic platform based on hydrogel and elastomer films. The crucial aspect herein was to focus on the adhesion of these two biomaterial layers and the structural stability of the designed microplatform. Well-fitted biomaterials, such as elastomers, may be equivalent to the epidermis, while hydrogels might be counterparts of the dermis, as shown in Fig.  12 .

Comparison of the structure of the fabricated lab-on-chip platform versus that of the mammalian skin [ 58 , 75 ]

The general mechanism for fabricating such microdevice involved pre-polymerization of the hydrogels for geometric stabilization, functionalization of the elastomer surfaces with benzophenone to buffer the effect of oxygen inhibition, and activation of the elastomer surfaces to graft the hydrogel polymer. The last step involved overlapping the two films by cross-linking using UV radiation of the hydrogels overlaid on the elastomeric structures. According to the Authors, the method is versatile for elastomers, such as Sylgard 184, latex, and Ecoflex, and for hard hydrogels, such as polyacrylamide-alginate, polyacrylamide-chitosan, polyacrylamide-hyaluronan, or their equivalents. The manufactured hybrid platforms showed high structural stability and flexibility. According to the mechanical test results, even greater adhesion was indicated by the hydrogel-elastomer combination than by the epidermis and dermis. Additionally, the designed microchannels imitated the blood and lymphatic vessels of mammalian skin. A potential application outlined by the authors is the use of such hybrid platforms to fabricate flexible bioelectronics, i.e., wearables. Moreover, the researchers directed future research toward the additive manufacturing of elastomeric and hydrogel components of microfluidic platforms [ 58 ]. Concluding this work, it is worth to notice that the mechanical properties of hydrogel–elastomer hybrids need to be carefully balanced. Hydrogels and elastomers have different mechanical characteristics, and ensuring that the hybrid material maintains desirable properties such as flexibility, strength, and durability under various conditions is crucial. Furthermore, the study showcased potential applications, but the performance of these hybrids may vary depending on the specific use case. That is why there may be a need for additional functionality to optimize the solution.

Microfluidic platforms, based on silk hydrogel, were also recently developed by Zhao S. et al. (Zhao 2016). Silk is a biocompatible protein material with controlled degradation, which can be suitable for in vivo applications. The process of fabrication of the multilayer microfluidic silk hydrogel using gelatin molding and the layer-by-layer method is presented in Fig.  13 . To obtain microchannels, gelatin was melted at 37 °C. To provide appropriate durability of the hydrogel platform, it was encased using PDMS and acrylic. Next, structure performance was verified and according to the mechanical test results, the stiffness of the hydrogels could be adjusted in the range of 1 kPa to 1 MPa, which corresponds to the values of natural biological tissues, demonstrating the feasibility of forging the presented hydrogel biomaterial. However, different concentrations of the silk solution and the content of the crystalline β-sheet affected the stiffness of the structure (the higher the concentration, the higher the stiffness of the hydrogel). As mentioned in the text, the major advantages of the structure were, e.g., high transparency (essential for in vitro research), stability, and biocompatibility. Thus, biological research could be performed utilizing the solution. Human HUVEC cells were cultured in chip microchannels. In turn, human fibroblast cells were cultured within the hydrogel bulk. In both cases, long-term cultures with a high degree of viability and proliferation were obtained. Moreover, in contrast to microfluidic solutions based on PDMS, it was possible to confluently culture HUVEC cells in microchannels (the cells migrated and aggregated to form a whole). In the next research, the authors will focus on the optimization of fabrication methods, which could reduce the process time and labor intensity [ 59 ]. Possibly, additive manufacturing of hydrogel layers might be applied for this purpose. Nevertheless, it should be highlighted that silk hydrogels can exhibit variability in their mechanical and biochemical properties depending on their preparation methods and the source of the silk.

The procedure employed for the fabrication of the multilayer microfluidic platform [ 59 ]

On the other hand, Shin S. and Hyuna J. (Shin 2017) developed and additively manufactured a hydrogel matrix based on cellulose nanofibers as a paper microfluidic device. The fabrication process was the 3D printing of a structure utilizing a mixture of vaseline and paraffin in a nanocellulose hydrogel mass (0.4–1.0% w/v). The following step was drying the print (lining a flexible film) and successively removing the vaseline-paraffin ink by raising the temperature above 70 °C with air assistance. According to the paper, a versatile approach was shown, and it was possible to manufacture different geometries of microchannels (Fig.  14 ). The microfluidic structure showed high transparency, stability, and excellent rheological properties, which can be used for the fabrication of a wide range paper-based biosensors [ 60 ]. Analyzing the article, the mechanical strength and durability of microfluidic devices based on cellulose nanofibers are critical to their practical applications. Research should be expanded to include the effects of mechanical stress and the long-term stability of microfluidic devices.

Flexible microfluidic thin film with multilayer microchannels manufactured by 3D printing on a nanocellulose hydrogel matrix [ 60 ]

One year later, the team of Jafarkhani M. et al. (Jafakhani 2018) proposed a procedure to optimize additive manufacturing of microfluidic hydrogel structures. The goal was to achieve the best geometry and size of the microchannels for cell cultures and the transport of nutrients and by-products. The collagen-based hydrogel (1, 2, 3% w/v) was prepared using the molding technique. The microchannels were implemented by AM using microneedles (diameters: 100, 300, 500 μm) removed after the collagen hydrogel solidified, as shown in Fig.  15 . The scientists performed physical–chemical and biological studies on the prepared hydrogel LOC. In this research, commonly known human umbilical vein endothelial cells (HUVEC) were used. The studies showed, among others, that as the concentration of collagen increased, the porosity of the hydrogels decreased and thus, the efficiency of diffusion and transport of substances also decreased. Regarding cell behavior, more efficient transport of culture medium through the microchannels increased HUVEC viability. Authors claim that the platform will be used in further studies to evaluate its practical application for regenerative medicine and tissue engineering [ 61 ]. The authors should focus future research, among others, on the long-term stability and durability of the structure.

Scheme of microfluidic device and fabricated prototype. a ) PMMA device and collagen gel in the middle chamber and culture media inside the tanks, b ) scheme of the microfluidic solution, and c ) scheme of microfluidic device fabrication [ 61 ]

A significant application of additive manufacturing of LOCs is the fabrication of perfusion structures using 3D bioprinting techniques. An example is a micro perfusion device for antiangiogenic drug screening—a type of vessel on a chip, developed by Gu Z. et al. (Gu 2022). The aims of the research were the long-term perfusion and real-time monitoring of angiogenesis (the formation of new blood vessels). The authors focused on biaxial manufacturing by extrusion (Fig.  16 ) using hydrogels consisting of well-known GelMA (5% w/v) and gelatin (5% w/v) polymers. To prepare the bioink, human umbilical vein endothelial HUVEC cells (3 × 10 6 cells/ml) were applied. Key elements of this research included the use of a polycaprolactone (PCL) stent, which provided structural support to the tubular lumen, ensuring consistent perfusion over extended periods. The cover of the LOC was manufactured using polyester, PLA, and PDMS components. The authors compared the hydrogel constructs with and without a PCL stent. According to the mechanical test results, at the same stress, higher strength was demonstrated by the samples with a stent, exhibiting lower deformations (by about 10%). Consequently, samples consisting only of hydrogel were more likely to collapse. Biological experiments showed clear differences in cell growth at different drug concentrations, highlighting the great potential of the system for precision drug screening. The ability to maintain perfusion for up to 10 days, depending on the hydrogel used, underscored the robustness of the system and its suitability for long-term studies. Traditional methods of testing these drugs often fall short in replicating the complex, three-dimensional (3D) environment of human tissues. The vessel-on-a-chip system addresses these limitations by offering a more physiologically relevant platform for drug testing. This vessel-on-a-chip technology not only advanced antiangiogenic drug screening but also held promise for broader applications in tissue engineering, pharmacokinetics, and regenerative medicine. By providing a more accurate and controlled environment to study vascular dynamics, this system could significantly improve the development and testing of new therapeutic agents [ 62 ]. From the critical point of view, despite its advancements, the study acknowledges certain limitations. The complexity of replicating the full range of physiological conditions in vitro remains a challenge. Additionally, the long-term stability and scalability of the model for high-throughput screening require further exploration.

Schematic picture of outer and inner diameters of the fiber [ 62 ]

Another approach is described by Nothdurfter D. et al. (Nothdurfter 2022), who 3D bioprinted vascularized tumor environment in microfluidic chip devices for drug testing, as shown in Fig.  17 . Scientists made efforts to mimic the complex tumor environment. Traditional two-dimensional cell cultures and animal models are often unable to accurately replicate the human tumor microenvironment, preventing the development of cancer therapies for this malignant childhood disease. The authors focused their study on examining tumor growth, metastasis, and drug response. The following cell lines were used in the study: neuroblastoma cells and endothelial cells, which are essential for the formation of the vascular network within the tumor. The microchannels in the printed tumor were prepared through the use of Pluronic—F127, a commercial hydrogel that dissolves at 15 °C. The LOC platform consisted of interconnected layers of polymethylmethacrylate (PMMA). The microfluidic device allowed researchers to study the effects of different concentrations and combinations of drugs in real-time. This approach may lead to more accurate predictions of how a patient’s tumor would respond to treatment, allowing for the development of more effective, tailored therapies in the future. This points to high developments in personalized medicine. An important innovation in this study is the successful incorporation of the vascular network into a 3D bioprinted tumor model. Vascularization is crucial because it facilitates the delivery of nutrients and oxygen to tumor cells, mirroring the behavior of real tumors in the human body. This vascularized environment also allows for the study of drug delivery and efficacy under conditions that closely resemble human physiology. The study showed that the presence of a vascular network significantly affects the behavior of tumor cells, including growth patterns and drug resistance [ 63 ].

Scheme of 3D bioprinting of soft tissues into laser-engraved microfluidic chips [ 63 ]

CNT-doped hydrogels

Moving on, carbon nanotubes (CNTs) are divided into two main groups, such as SWCNT and MWCNT, as shown in Fig.  18 . As mentioned, CNT can mimic human collagen, because of its fibrous form and similar dimensions. Carbon nanotubes are biocompatible and increase biosensor sensibility, e.g., biosensor-on-chip (BOC) [ 19 , 64 ]. CNTs can be added to hydrogel structure based on collagen, gelatin, alginate, chitosan, or agarose, to enhance its performance in different biomedical solutions. The combination of hydrogels and CNTs increases the biocompatibility of the material. CNTs also improve mechanical stability, Young modulus, cell adhesion, proliferation, differentiation, and tissue formation. In addition, CNTs reduce hydrogel impedance, which allows for different electrical stimulation studies [ 64 ]. The example procedure for CNTs-based hydrogel fabrication is presented in Fig.  19 [ 14 ]. The following paragraphs of the chapter describe the articles concerning CNT application in the interesting field of hydrogel LOCs.

Visualization of two main types of carbon nanotubes, on the left SWCNT, on the right MWCNT [ 76 ]

The manufacturing process of hydrogel enriched with carbon nanotubes [ 14 ]

For example, Chen X. et al. (Chen 2023) researched 3D printing of graphene oxide (GO)/carbon nanotubes (SWCNT) combined with sodium alginate. The scientists analyzed, among others, the viscosity and mechanical properties of the hydrogels. It was shown that after adding GO and CNT, the viscosity of the structures increased, but only by 12.4%. Thus, it was still within the material viscosity range that can be printed. In turn, to check the mechanical properties of such hybrid structures, scientists performed uniaxial tensile testing of hydrogel samples, and Young’s modulus (longitudinal modulus of elasticity) was calculated. The results showed that Young’s modulus was higher (more than 6.5 times) in the GO and CNT-enriched hydrogels compared to the control hydrogels (pure sodium alginate). In summary, CNT increased mechanical stability and did not affect the 3D printing process since the appropriate viscosity of the ink was ensured [ 65 ]. It is noteworthy that the study used as many as two additives that change the functionality of the origin material. As a result, the study is more complicated and complex. Moreover, it can be difficult and not repeatable to achieve an even distribution of carbon additives in the hydrogel matrix, which affects the quality of the final product. In the future, a potential problem may arise in larger-scale production due to the high purchase costs of CNTs or graphene oxide.

Further research by Abalymov A. et al. (Abalymov 2021) focused on gellan gum hydrogel (GG, 1%) enriched with CNT of different concentrations (0, 0.5, 1.0, 1.5%). It was found that the presence of CNT affects hydrogel bulk significantly. For instance, the hydrogel pore size decreased as the CNT concentration increased. Therefore, a more regular structure was presented by hydrogels with higher amounts of CNT. The roughness of the hybrid hydrogel was also higher and comparable over a range of CNT concentrations. The following research focused on mechanical compression tests to indicate the longitudinal modulus of elasticity. The obtained values showed that this parameter was significantly lower for hydrogels with the highest CNT concentration (1.5%) compared to hydrogels with a lower CNT content (0.5, 1.0%). This phenomenon could be explained by the disruption of the structural integrity of polymeric compounds by the incorporation of CNTs into hydrogels. In these studies, some preliminary biological investigation was also conducted to evaluate the biocompatibility of the solution on the example of MC3T3-E1 osteoblast cell cultures. For instance, the best cell adhesion was indicated for hydrogels with the highest CNT concentration. Similarly, the highest cell viability was indicated for 1.5% CNT hydrogels, which is consistent with the relation that low cell adhesion results in cell death. To confirm the presence and distribution of CNT in hydrogels, the scientists performed experiments related to light absorbance and spectroscopy. The results showed that the higher the CNT concentration, the higher the absorbance coefficient (light absorption). In this article, tests concerning hydrogel swelling were also done. Swelling levels were compared between the GG hydrogel and the 1.5% CNT hydrogel. The conclusion was that high concentrations of CNT reduced the degree of hydrogel swelling. In summary, CNT addition in hydrogel matrices can enhance the mechanical properties of hydrogels and simultaneously be beneficial for different cell engineering studies [ 14 ]. The authors, in their follow-on research, should focus on the long-term mechanical and chemical stability of CNT-gellan gum composites, which will complete the transferred knowledge on gellan gum hydrogels enriched with CNT for biomedical applications.

In turn, the research of Van den Broeck L. et al. (Van den Broeck 2019) focused on carbon nanotube-reinforced polyethylene glycol composite hydrogels (PEGCNT). CNT was used in different concentrations, such as 0.015, 0.03, 0.045, 0.15, and 0.2%. Moreover, L929 fibroblast cells were cultured in these structures, as in cell growth matrices. As a result of the tests, at first, the hydrogel swelling coefficient was evaluated and was found not to be changed after CNT addition. Therefore, carbon nanotubes did not affect the hydrogel cross-linking density. The rheological investigation of the properties of the biomaterials showed that PEGCNT hydrogels (0.015%) received higher storage modulus values (1915.0 ± 101.7 Pa) than PEG hydrogels (1196.7 ± 125.0 Pa). On that basis, CNT addition notably reinforced the hydrogel structure, without providing substantial chemical changes. Moreover, compression tests were performed on the swollen hydrogel samples and higher values of modulus of elasticity were presented by hydrogels with CNT (PEGCNT). The last research related to biological investigation towards cell viability assessment in contact with the developed hydrogel structures. The tests showed that L929 fibroblasts survived in all prepared biomaterials, and cell viability was higher for PEGCNT hydrogels (83.3 ± 10.7%) than for PEG hydrogels (51.9 ± 8.3%). According to the paper, similar correlations were discovered in the case of nerve cells [ 66 ] and cardiomyocytes of rats [ 67 ]. Scientists believe that this phenomenon is related to the random distribution of CNTs in the hydrogel matrix, which resembles collagen fibers and ECM properties. In summary, research confirmed enhanced biocompatibility of CNT combined with hydrogels, which was advantageous for cell adhesion, proliferation, and differentiation [ 64 ]. Nevertheless, long-term biocompatibility and potential cytotoxic effects of CNTs need to be investigated.

Wang R. et al. (Wang 2019) worked on hydrogel composites consisting of polyelectrolytes enriched with CNT. This research showed, i.e., that the proposed structures had better mechanical properties compared to the pure hydrogel. CNT-enriched hydrogels exhibited, e.g., higher tensile strength. As the concentration of CNTs increased, the strain increased and the fracture stress decreased. Moreover, the CNT-doped hydrogels were characterized by different adsorption properties compared to the control hydrogels. Namely, CNT-doped hydrogels showed greater adsorption of methylene blue. On the contrary, in the case of rhodamine B (a carcinogenic compound), pure hydrogel exhibited better adsorption [ 68 ]. Further research in this field, especially in the context of optical hydrogel properties, is needed to unambiguously evaluate hydrogel applications for biomedical studies, in which cell staining is a standard procedure.

Fan X. et al. (Fan 2022) developed a hydrogel consisting of sodium alginate, polyvinyl alcohol, acacia-magnesium tannin, and silver. and carbon nanotubes (CNT content in the hydrogel was 0, 10, 20, and 30 mg). The procedure for preparing the hydrogel is described in detail in the source article [ 69 ]. The proposed hydrogel was characterized by extremely high extensibility (717%), biocompatibility, good adhesion, and self-healing properties with an efficiency of more than 99%. According to the microscopic observations, the homogeneous distribution of carbon nanotubes in the hydrogel structure was confirmed. The presence of CNTs improved the electrical conductivity of the hydrogel (approximately two-fold increase in the conductivity of the CNT-doped hydrogel compared to control hydrogels), as well as increased the mechanical stability. Based on the results from the mechanical tests and, more specifically, tensile tests, it was found that as the CNT concentration in the hydrogels increased, the tensile strength increased and the hydrogel strain decreased. Moreover, the structure exhibited antibacterial properties due to the content of silver nanoparticles. The Authors proposed using the designed hydrogels in the fabrication of wearable electronics to continuously monitor human activity at room and low temperatures [ 69 ]. In this context, there is a need to perform in vivo tests evaluating the long-term impact of the CNT or Ag nanoparticles on e.g. human skin.

In summary, the biggest challenges for researchers in the use of carbon nanotubes include achieving their uniform dispersion in the hydrogel matrix. CNTs tend to agglomerate due to strong van der Waals interactions, which can result in local concentrations, non-uniform material properties, and reproducibility problems. Others are a matter of cost, as CNTs have a high purchase cost.

Photodynamic therapy on-chip

Lab-on-chip microfluidic devices can be used for cell culturing and photodynamic therapy applications to further facilitate the validation of new PDT strategies. As mentioned earlier, PDT is a non-invasive alternative to chemotherapy or radiotherapy treatment [ 16 ].

In recent times, interesting research on three-dimensional lung spheroids cultured on the lab-on-chip platform for PDT validation was conducted by Żuchowska A. et al. (Zuchowska 2017). The authors fabricated LOCs with microchannels and microchambers using PDMS material and casting method. A549 cancer cells and normal fetal lung fibroblasts MRC-5 were cultured. The PDT procedure employed in this work is presented in Fig.  20 . Different concentrations of ALA were used (0.75, 1.00, 2.00, 3.00, 5.00, and 9.00 mM) as a photosensitizer precursor. The light source was a light-emitting diode (LED).

Mechanism of action of photodynamic therapy directly on the chip [ 16 ]

First, the cytotoxicity of ALA was assessed and the studies showed that it did not significantly influence the viability for both cell types (cell viability was about 90%). The next analysis was related to the accumulation of PpIX in the tested cells. The aim was to explain the viability differences between A549 and MRC-5 cells after PDT treatment. As a result, the measured fluorescence intensity was much higher for the first cell type. According to the knowledge, the fluorescence intensity (in quantitative cell viability measurements) is directly proportional to the metabolic activity and viability of the cells. Furthermore, the fluorescence intensity was 1.35 times higher for ALA treatment (3 mM) than in the control group (0 mM ALA). Therefore, it was confirmed that the photosensitizer accumulated selectively in cancer cells was toxic only in the presence of light. Reactive oxygen forms (ROF) were produced during the successful treatment with PDT but only in A549 cells [ 16 ].

The team of Jedrych E. et al. (Jedrych 2011) also evaluated PDT treatment utilizing LOC, at which A549 cells were cultured. This time, the microfluidic device was made of PDMS and sodium glass. The scientists found out that PpIX accumulation is related to the ALA photosensitizer concentration. Furthermore, the number of dead cells was comparable to the PDT research performed in Petri dishes. To summarize, cell culture in the proposed microdevice ensured adequate cell adhesion and proliferation. Simultaneously, absorbance measurements reflected the cell accumulation of PpIX. It was found that PpIX accumulation depended on cell type [ 70 ].

Another study by Marzioch J. et al. (Marzioch 2015) focused on the observation of cell metabolic processes on the LOC platform during PDT. Lab-on-chip was fabricated out of borosilicate glass. T-47D human breast tumor cells were cultivated within the chip microchambers. Once again, ALA (50, 70, 90 uM) was used as a precursor of the photosensitizer and LED as a light source (lightning time: 0, 2, 5 min.). After preliminary tests, the highest ALA concentration and the longest lightning time were chosen for further research. The authors measured cellular respiration before, during, and after PDT treatment. At the beginning (before PDT), there was a decrease in oxygen concentration due to cell respiration, cell proliferation, and an overall increase in oxygen consumption. After PDT, the oxygen concentration was constant, thus cellular respiration did not occur, which ultimately resulted in cell death. In comparison, control LOC (the same cell cultivation, but without performing photodynamic therapy) was characterized by a continuous decrease in oxygen concentration—the cells consumed oxygen and proliferated. Especially interesting in this research was the repopulation effect observed after the PDT. Treated cells could regenerate, which was confirmed by oxygen consumption. The scientists also measured temperature to check if the light treatment heated up the microdevice and cellular temperature. It was found that the light source did not significantly increase the temperature of the LOC or cultivated cells. Therefore, exposure to LED light has no negative effect on PDT results. To sum up, continuous observations of cell metabolism presented in this paper can be considered as more reliable than simple live/dead assays, which show only final cell viability [ 71 ].

Tokarska K. et al. (Tokarska 2019) also worked on nano-photosensitizers to perform photodynamic therapy directly on the chip. The nano-PS fabrication guideline is presented in detail in the source article [ 72 ]. The biocompatible nano-PS consisted of multilayer capsules loaded with tetraphenyl porphyrin with an oil core. The microfluidic LOC platform was fabricated out of PDMS and glass layers (Fig.  21 ). The red LED (625 nm) was used as a light source during PDT. To investigate the biological activity of cells cultured in the microdevice, A549 human lung adenocarcinoma epithelial cells, and MRC-5 human fetal lung fibroblasts were selected. To test cellular responses and relationships after PDT, co-cultures of fibroblasts and pathological cells were used (such dual cell culture allowed for better mimicking in vivo conditions). According to the research results, the selective effect of the photosensitizer was proven and PS accumulated mainly in tumor cells. To test the cytotoxicity of free and encapsulated tetraphenyl porphyrin (PS) in the dark or after exposure to red LED light, cell viability assays were performed. Cells unexposed to PS constituted the control group. Cancer cells in the presence of encapsulated nano-PS in the dark showed the greatest loss of cell viability at a concentration of 20 µM. Fibroblasts also showed dose-dependent toxicity in the dark, but it was much lower than that of A549 cells. According to the research after illumination processes, while using tetraphenyl porphyrin in free form, no cellular phototoxicity occurred. On the other hand, nano-PS significantly affected the phototoxic effect, reducing the viability of the neoplastic cells to about 55%. In the case of MRC-5 fibroblasts, no toxicity was detected in any range of nano-photosensitizer concentrations. Reactive oxygen species that are destructive to cells were generated when tested with A-549 cancer cells. Moreover, more efficient ROS generation occurred with nano-PS than with the free tetraphenyl porphyrin photosensitizer. The highest phototoxicity was proven at a nano-PS concentration of 30 µM in monoculture. However, slightly lower phototoxicity was found for A549 in double cell culture, which can be the result of the presence of healthy fibroblasts nearby. To summarize, the developed and fabricated nano-photosensitizers were characterized by selective accumulation in cancer cells, high biocompatibility, and stability [ 72 ].

Lab-on-chip platform fabrication steps [ 72 ]

Summarizing this section, it is worth noting that the variability of spheroid formation each time can lead to inconsistent PDT results and complicated data interpretation. Moreover, although 3D spheroids are more reflective of the tumor environment than 2D cell cultures, they still do not fully reflect the complexity of actual tumor lesions.

Conclusions

As mentioned in the “ Introduction ” section, the incidence of cancer globally is increasing year by year, and the worsening epidemiological situation of cancer has directed the scientific world to develop innovative cancer research methods. In this context, a comprehensive collection of scientific articles is presented relating to the future development of photodynamic therapy as a non-invasive approach to cancer cell research conducted directly on-chip. The concept combines theoretical and practical knowledge of mechanics, biomedical engineering, microsystems, and molecular and cellular biology.

To summarize the above content, lab-on-chip platforms supported by hydrogel matrices are excellent solutions for in vitro and ex vivo research. Biocompatible hydrogels mimic the three-dimensional cellular environment, such as the extracellular matrix, in which cells develop, differentiate, proliferate, and migrate. Therefore, a suitable hydrogel is an excellent environment for living cells because it replicates their natural conditions. Hydrogels could be considered cell transporters (more common) or structural parts of microdevices [ 20 , 24 ]. The second application refers precisely to lab-on-chip platforms. The appropriate structure of such microchips, i.e., the presence of an ECM-like hydrogel environment (3D culture) and the presence of microchannels and microchambers allow for cell culture and transport of relevant substances. An allegory can be seen for the functioning of capillaries in a living organism and microchannels in LOC, where in both cases they perform transport-like functions. In addition, the ability to culture cells three-dimensionally enables cell–cell and cell-extracellular interactions, which are limited in two-dimensional cultures [ 13 ].

Moreover, a rapidly growing sector of science is focused on the additive manufacturing of hydrogels. Both natural and synthetic inks for 3D printing should exhibit adequate rheological properties to enable biomaterial printability. Furthermore, the hydrogels themselves must exhibit satisfactory mechanical and biological properties regarding hydrogel matrix strength and cell culture. According to ASTM standards, the following main technologies are distinguished in AM: extrusion-based 3D printing, jetting-based 3D printing, and vat photopolymerization-based 3D printing. According to the literature review, the extrusion technique is the most popular. Nevertheless, it presents a lower resolution and quite low printing speed in comparison with other technologies. The main advantages of extrusion are wide access to 3D printers and biocompatible inks and lower costs of the procedure. That is why, the extrusion of the ink is more widespread than the aforementioned techniques [ 17 ].

The 3D printing of LOC parts makes it possible to speed up microchip production, simplify the manufacturing procedure, and sometimes reduce the cost of the process, for example, by extruding the self-developed inks or bioinks. It should be highlighted that AM allows for the fabrication of complex, intricate structures that are often necessary for lab-on-chip devices. It may enable the design of customized geometries, including microchannels, microchambers, and integrated functional components tailored to specific applications. Moreover, AM facilitates rapid prototyping, allowing for quick iterations during development. This capability is particularly advantageous in research and development, where design changes can be easily implemented without the need for expensive and time-consuming tooling. Additive manufacturing enables the simultaneous use of different materials, especially hydrogels, but also other polymers and conductive inks. This capability is crucial for developing multifunctional LOC platforms with integrated sensors, actuators, and other components. For small-scale fabrication, AM is more cost-effective than traditional manufacturing methods. It eliminates the need for expensive molds and reduces material waste, making it ideal for producing small batches of customized LOC devices. Despite the many advantages of using additive manufacturing for hydrogel-assisted lab-on-chip platforms, several limitations could be mentioned. Despite the versatility of AM, the range of materials that can be used, particularly in hydrogel-assisted applications, is still limited. Not all hydrogels are suitable for 3D printing, and the mechanical properties of printed hydrogels can sometimes be inferior to those produced by traditional methods. Also restrictive are the requirements for the rheological properties of the hydrogel material constituting the ink concerning 3D printing. The resolution of AM processes may not always meet the stringent requirements needed for certain LOC applications, especially those requiring ultra-fine features at the microscale. Additionally, the post-processing of 3D-printed components may require more complex and time-consuming operations. Ensuring the biocompatibility and long-term stability of 3D-printed microfluidic devices, especially those incorporating hydrogels, can be challenging. Some 3D printing materials can degrade over time, affecting the performance and safety of the devices. Furthermore, the most presented research focused primarily on small-scale constructs. Scaling up to clinically relevant sizes while maintaining structural integrity and cell distribution remains challenging.

As mentioned in the paper, hydrogels can be enriched with functional additives, such as carbon nanotubes. The CNTs mimic collagen due to their fibrous form and similar dimensions. Because of the CNTs biocompatibility, they can be combined with several natural hydrogels to perform diverse biological studies. In addition to biocompatibility, the combination of hydrogels and CNT also improves mechanical stability, cell adhesion, and development [ 64 ]. Moreover, the inclusion of CNTs in the hydrogel structure is neutral for the AM processes [ 65 ].

One of the first papers focusing on photodynamic therapy performed in a microfluidic system was published by Polish researchers (E. Jędrych et al., 2011). The researchers compared the results of PDT for macroscale (Petri dish) and microscale (lab-on-chip) cell cultures. The efficacy of this particular anti-cancer therapy was comparable in both cases and as a result, the authors proved the validity of using microfluidic platforms in subsequent tests and optimizations of PDT processes. This ensured, i.e., a reduction of manufacturing costs and the development of anti-cancer therapies [ 70 ]. Since then, many innovative and future-oriented solutions (examples: [ 16 , 71 ]) for performing PDT directly on the microchip have been developed and presented to the scientific world.

The content of this review article makes up the whole, gathering knowledge in the development of anti-cancer therapies (concerning technical and biological aspects) and raising the level of skills in biomedical research.

Data availability

No datasets were generated or analysed during the current study.

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Department of Mechanics, Materials and Biomedical Engineering, Faculty of Mechanical Engineering, Wrocław University of Science and Technology, Wrocław, Poland

Adrianna Cieślak & Jerzy Detyna

Department of Microsystems, Faculty of Electronics, Photonics and Microsystems, Wrocław University of Science and Technology, Wrocław, Poland

Agnieszka Krakos

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Julita Kulbacka

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Cieślak, A., Krakos, A., Kulbacka, J. et al. Overview of research on additive manufacturing of hydrogel-assisted lab-on-chip platforms for cell engineering applications in photodynamic therapy research. Microchim Acta 191 , 608 (2024). https://doi.org/10.1007/s00604-024-06683-9

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DOI : https://doi.org/10.1007/s00604-024-06683-9

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