Advances in hydrogel research: a 25-year bibliometric overview

Abstract

This study presents a comprehensive bibliometric analysis of hydrogel research from 2000 to 2025, examining 101,291 publications from the OpenAlex database to highlight the field’s evolution, trends, and impact, providing a better landscape of the field. The analysis demonstrates significant growth in the research output, from ~350 publications in 2000 to nearly 11,000 in 2024, with 37% being open access. Publication patterns demonstrate Physical Sciences leading with about 50,000 publications, followed by Life Sciences (~30,000) and Health Sciences (~21,000). The citation analysis emphasizes that 20% of all citations result from the top 1% of papers, demonstrating the concentration of the research impact. The study identifies key research hubs, with China as a leader in the publication (27,931 publications), while the United States maintains the highest citation impact (>1 million citations). Network analysis reveals increasingly complicated international collaborations, particularly between the United States and China. Topic modeling using Latent Dirichlet Allocation identifies 17 distinct research themes, emphasizing the field’s diversification from fundamental material features to advanced applications in the tissue engineering, drug delivery, and regenerative medicine. This analysis provides valuable insights into the dynamic landscape of hydrogel research, highlighting opportunities for future innovation and collaboration.

Graphical Abstract

Introduction

Since the discovery and the development of hydrogels in 1894, there has been significant attention towards the hydrogels and improving their biomedical application. Currently, hydrogels have been significantly applied in both fields of medicine and engineering [1, 2]. Hydrogels are considered 3D-crosslinked polymeric networks with superior capacity in absorbing and retaining high volumes of water through their hydrophilic structure [3–5]. The versatile and multifaceted function of hydrogels results from their diverse structural components, including both natural polymers (polypeptides, polysaccharides, DNA) and synthetic polymers (polyacrylamide, poly(vinyl alcohol)), which can be engineered to exhibit desirable properties such as mechanical strength, elasticity, self-healing ability, and conductivity. Noteworthy, hydrogels have been developed from both synthetic [6] and natural polymers [7]. Such features of hydrogels and their versatility has led to their application in other fields beyond medicine including soft robotics [8, 9], environmental engineering [10, 11], biosensors [12, 13], and wearable devices [14, 15], driven by continuous advances in material science and nanotechnology [16]. Moreover, the recent studies have focused on the development of 3D-printing hydrogels [17, 18], as an attempt to improve their features and application in medicine and engineering. Regarding to the fact that hydrogels have demonstrated versatile biomedical and engineering applications, it is of importance to emphasize on the research trends and directions in the field. This would be beneficial in directing current research in the application or the design of novel hydrogels. Currently, the studies about hydrogels have been on the development of novel hydrogels using a combination of materials or introduction of hydrogels for the new fields of medicine and engineering.

In respect to the significant number of research on the hydrogels in the recent decades, a systematic bibliometric analysis could further improve the emerging trends in this field. The rapid expansion of hydrogel applications across multiple sectors, coupled with the increasing complexity of research networks and collaborative efforts, necessitates a comprehensive evaluation of the scientific landscape. Bibliometric analysis can reveal patterns in research productivity, highlight influential contributions, and identify gaps in current knowledge, providing valuable insights for researchers, funding agencies, and policymakers in directing future research efforts [19]. Therefore, the present study could further demonstrate the emerging trends and future directions for the researchers in the field to improve their collaboration and novelty.

Recent bibliometric analyzes have provided valuable insights into specific domains of hydrogel research. In an effort to highlight the application of hydrogels in cancer immunotherapy [20], a systematic analysis of research from 2013 to 2023 has been performed. After 2021, there was an increase in the number of studies, and it was stable for 2 years. The highest number of articles in this field was published by China. Notably, “Biomaterials” journal published the highest number of papers in this field, and different numbers of keywords were used, including immunogenic cell death and immunotherapy, among others. Another study focused on the engineering aspect of hydrogels in water treatment [21]. In years between 2000 and 2024, the number of publications in this field has been enhanced, and the leading country in publication has been China. Three journals, including International Journal of Biological Macromolecules, Chemical Engineering Journal, and Carbohydrate Polymers, published the highest number of studies in this field, and different kinds of synthetic methods have been utilized, such as freezing method and cross-linking method. Another study has focused on the analysis of nanocomposite hydrogels [22]. From January 1, 2010, to February 3, 2022, the study of nanocomposite hydrogels (NHs) showed consistent development, with research papers constituting over 77% of the total publications. China, the United States, and India emerged as the foremost nations in NH research contributions. The principal institutions engaged in this domain were Tabriz University of Medical Sciences, the Chinese Academy of Sciences, and Tshwane University of Technology. Regarding journal production, “Advanced Functional Materials” published the greatest number of papers, whilst “International Journal of Biological Macromolecules (Int J Biol Macro)” had the largest amount of citations. Varaprasad K was recognized as the most prolific author, whereas Haraguchi K was ranked first among co-cited writers. The most commonly referenced work was “Nanocomposite Hydrogels for Biomedical Applications” by Gaharwar AK. Moreover, “drug delivery” emerged as the predominant term in the research. In contrast, our study presents the first comprehensive bibliometric analysis of the entire hydrogel research landscape across all domains from 2000 to 2025. This broader approach enables us to not only identify cross-domain patterns and emerging interdisciplinary opportunities but also to map the complex network of global collaborations and research impacts across the full spectrum of hydrogel applications. Furthermore, our analysis employs advanced topic modeling techniques and examines the evolution of research themes across multiple disciplines, providing a more nuanced understanding of the field’s trajectory and identifying gaps that may not be apparent in domain-specific analyzes.

Green biomaterials are essential in creating sustainable hydrogels [23], providing environmentally benign substitutes for synthetic polymers sourced from fossil fuels. These biomaterials, frequently derived from renewable resources including cellulose [24], chitosan [25], alginate [26], and proteins [27], exhibit biodegradability, biocompatibility, and non-toxicity, rendering them suitable for drug administration, tissue engineering, and wound healing applications. There have been efforts to utilize natural polymers to develop hydrogels with adjustable mechanical characteristics, reactivity to environmental stimuli, and improved biocompatibility. The utilization of green biomaterials corresponds with worldwide initiatives to diminish environmental effects and advocate for circular economy concepts, since they reduce waste and dependence on non-renewable resources. This methodology not only propels hydrogel technology forward but also fosters the creation of sustainable solutions for biomedical and environmental issues.

Hydrogels have emerged as flexible and useful materials in wound healing [28], tissue regeneration [29], and cancer therapy [30] due to their unique qualities, including high water content, biocompatibility, and adjustable mechanical and chemical characteristics. Hydrogels facilitate wound healing by maintaining a moist environment that encourages cell migration, diminishes inflammation, and expedites tissue repair [31–33]. Their porous architecture enables the regulated release of antimicrobial agents, growth factors, and other therapeutic compounds to avert infection and improve healing outcomes. In tissue regeneration, hydrogels function as scaffolds that replicate the extracellular matrix, facilitating cell adhesion, proliferation, and differentiation, so rendering them optimal for the repair of injured tissues, including cartilage, bone, and skin [29, 34–36]. Moreover, hydrogels may be designed to react to certain stimuli, such as pH, temperature, or enzyme activity, facilitating tailored medication delivery in cancer treatment. They can encapsulate chemotherapeutic drugs [37] or immunomodulators [38] and release them in a regulated way at the tumor site, therefore reducing systemic toxicity and enhancing therapy effectiveness. Moreover, hydrogels are under investigation for their application in post-surgical cancer management, since they can occupy tissue voids and provide specific treatments to avert recurrence.

However, despite these valuable domain-specific analyzes, there remains a critical gap in understanding the holistic landscape of hydrogel research across all applications and domains. This gap is particularly significant as it limits our ability to identify synergies between different fields, understand broader technological convergence, and recognize emerging opportunities that exist at the intersections of various hydrogel applications. Addressing this gap is crucial for several reasons: first, it enables researchers to identify untapped opportunities for cross-disciplinary innovation; second, it helps funding agencies and institutions to make more informed decisions about resource allocation; and third, it provides a comprehensive understanding of global research dynamics that can guide international collaboration strategies. This study addresses this fundamental gap by conducting a comprehensive bibliometric analysis that spans all domains of hydrogel research, employing advanced topic modeling and network analysis techniques to uncover patterns and trends that would remain hidden in narrower, field-specific analyzes.

In other words, the present study also aims to perform a comprehensive bibliometric analysis of hydrogel research from 2000 to 2025, assessing the growth, trends, and impact of scientific contributions in this rapidly evolving field. Since the hydrogels are important structures in wound healing, tissue engineering, and other aspects of biomedical engineering, highlighting their trend is of importance. The analysis begins by identifying and gathering all publications related to hydrogels, followed by a general bibliometric distribution focusing on aspects such as identifying the most influential authors, leading institutions, key journals, and collaborative networks driving hydrogel innovation. Additionally, the analysis reveals emerging trends, hot topics, research gaps, and highlights technological advancements and interdisciplinary applications across various fields. By mapping the intellectual landscape and evaluating citation patterns, research productivity, and collaborative connections, this work provides valuable insights to inform future research directions, funding strategies, and policy decisions (Fig. 1).

Fig. 1.

Comprehensive bibliometric analysis of hydrogel research from 2000 to 2025. The left hemisphere (blue) illustrates the multidisciplinary applications of hydrogel across various disciplines such as medicine, engineering, health, chemistry, and manufacturing sectors. The right hemisphere (orange) represents the bibliometric analytical approaches used in this study, including global networks, co-authorship patterns, publication metrics, and keyword clustering

Data collection and methodology

Figure 2 illustrates the step-by-step process of this bibliometric analysis, from data retrieval using the OpenAlex database to the application of various analytical tools, including Gephi, NetworkX, and Power BI, for network and trend analysis, followed by topic modeling with Latent Dirichlet Allocation (LDA) to identify research themes.

Fig. 2.

Schematic illustrations of steps involved in the bibliometric analysis workflow in this study

Data collection

This study undertook a comprehensive bibliometric analysis of hydrogel research spanning from 2000 to 2025. To ensure data consistency, all literature retrieval and data downloads were completed on January 10, 2025, using the OpenAlex database. OpenAlex, a freely accessible platform, provides a rich repository of scholarly metadata, including publication details, author information, institutional affiliations, citation data, and research domains. The search query was limited to publications with “hydrogel” in their titles or abstracts, yielding a dataset of 139,300 publications. To focus the analysis, the study was restricted to articles, reviews, preprints, books, book chapters, and dissertations in the English language, resulting in a final dataset of 101,291 publications.

Data analysis

To conduct the bibliometric Quantitative data analysis, a variety of data visualization and network analysis tools were used. Gephi was employed to generate visual representations of the data, facilitating the examination of author collaboration networks, institutional partnerships, and citation trends. Additionally, the Python library NetworkX was leveraged for further network analysis, helping to identify prominent authors, institutions, and research clusters. Power BI was used for interactive visualization, allowing for in-depth exploration of trends, citation patterns, and contributions from different countries over time.

Topic modeling and hotspot trends

LDA, a statistical topic modeling technique, can create a vocabulary of terms and then classify the included publications into different topics. We used the Gensim package in the Python language to conduct LDA analysis of the included keywords, enabling the identification of key research themes and their evolution over time.

Results and discussion

Quantitative analysis

Publication number trends in hydrogel research (2000–2025)

Figure 3a illustrates a significant increase in the volume of scientific publications from 2000 to 2025, with the total number of publications rising from around 350 in 2000 to nearly 11,000 by 2024. Notably, 37% of these publications are open access, as shown in the insert of Fig. 3a. This growing proportion of open access publications over time (Fig. S1) signals an encouraging shift towards broader accessibility, making scientific knowledge more readily available to the global research community. In terms of publication types, journal articles constitute the vast majority, representing ~85% of all publications (Fig. 3b). While reviews and preprints also contribute, the latter have seen a marked increase in recent years. This trend suggests that while traditional journal articles remain the dominant means of disseminating research findings, preprints are gaining traction due to their ability to facilitate faster dissemination, enabling quicker peer feedback and fostering enhanced collaboration among researchers.

Fig. 3.

Trends and distribution of hydrogel-related publications from 2000 to 2025. a Annual growth in the number of publications, showing a steady increase from ~350 in 2000 to nearly 11,000 in 2024, with 37% of publications being open access (insert). b Distribution of publication types, highlighting journal articles as the dominant format (~85%). c Domain research area distribution, with the highest publication counts in Physical Sciences (~50,000), Life Sciences (~30,000), and Health Sciences (~21,000). d number of publications across different field of research: substantial outputs in Engineering and Biochemistry, Genetics, and Molecular Biology, each exceeding 20,000 publications

The distribution of hydrogel-related publications across research fields highlights the dominance of Physical Sciences, with ~50,000 publications, followed by Life Sciences with around 30,000, and Health Sciences with roughly 21,000 (Fig. 3c). This trend reflects the substantial research efforts and funding in these fields, driven by technological advancements, societal needs, and the growing importance of innovation. The notable number of publications in Health Sciences is likely due to the significant potential of hydrogels in biomedical applications, especially for developing new treatments and therapies. Additionally, the data demonstrates the broad interdisciplinary nature of hydrogel research, with key fields such as Engineering, Biochemistry, Genetics, and Molecular Biology each (Fig. 3d). This highlights the extensive range of applications and collaborative efforts spanning various domains. The distribution emphasizes the diverse contributions across disciplines, showcasing the interconnectedness of hydrogel research.

Together, these visualizations provide a comprehensive picture of the substantial growth in hydrogel-related scientific activity. The increasing volume of publications across different fields and publication types can be attributed to a variety of factors, including advancements in technology, greater research funding, and a global emphasis on scientific innovation, all of which continue to drive the expansion of hydrogel research.

Citation analysis in hydrogel research (2000–2025)

Figure 4a illustrates the annual citation counts from 2000 to 2025, categorized by publication type: article, book, book chapter, dissertation, preprint, and review. Almost a clear and steady upward trend in citation numbers is evident from 2000 to 2020, reflecting a substantial increase in research activity and growing interest in hydrogel research across diverse scientific fields. However, a noticeable decline in citations is observed after 2020. This decline can be attributed to the typical citation lag, where newly published works require time to accumulate citations. As a result, publications from recent years have not yet reached their full citation potential, explaining the downward trend. Throughout the examined period, journal articles consistently represent the largest share of cited works, underscoring their dominant role as the primary channel for disseminating research findings within the academic community. Additionally, the dataset contains 101,264 publications that have collectively garnered 3,156,658 citations, highlighting the extensive scholarly attention hydrogel research has received. This pattern of growth, combined with the diverse publication types, emphasizes the expanding influence and interdisciplinary nature of hydrogel research. It also reflects the evolving dynamics of scientific communication, where rapid dissemination through preprints and comprehensive analyzes in reviews complement traditional journal articles in shaping the field’s impact.

Fig. 4.

Citation analysis of hydrogel research publications from 2000 to 2025. a Time series analysis of citation number along with main key metrics on the citation statistics. b Distribution of citations across various scientific fields categorized by citation percentiles (top 1%, top 10%, top 25%, top 50%, and below 50%). Biochemistry, Genetics, and Molecular Biology surpass Engineering in total citations, with ~210,000 citations coming from top 1% papers. The inset highlights that 20% of total citations are from the top 1% of publications, while only 2% are from the bottom 50%. c MaterSciMaterMed Percentage distribution of publications within each citation percentile across different fields, illustrating that fields like Materials Science have a higher proportion of highly cited publications, whereas Business, Management, Accounting, and Computer Science have a larger share of lower-cited works

The average number of citations per publication is 31.17, while the median is significantly lower at 8.00. This disparity suggests that a small subset of publications garners a disproportionately high number of citations, emphasizing the uneven distribution of research impact within the field. Additionally, only 1.03% of articles are ranked in the top 1% for citations, highlighting that a limited number of studies significantly influence the field. Expanding on this, Fig. 4b illustrates the distribution of citations across various research fields, segmented into citation percentiles (top 1%, top 10%, top 25%, top 50%, and below 50%). While Engineering leads in the number of publications, Biochemistry, Genetics, and Molecular Biology surpass Engineering in total citation counts. Remarkably, around 210,000 citations in Biochemistry, Genetics, and Molecular Biology come from papers within the top 1%, indicating that a small number of highly influential studies dominate citations in this domain. Furthermore, the inset shows that 20% of all citations—equating to 3.16 million—originate from the top 1% of papers, whereas only 2% are from publications in the bottom 50%. This trend underscores that while hydrogel research is growing, most publications have limited impact, with a few exceptional studies driving the majority of scholarly influence. Building upon this, Fig. 4c visually represents the percentage distribution of publications within each citation percentile across different fields. For instance, disciplines like Materials Science consistently have a higher proportion of publications in the top citation categories. In contrast, fields such as Business, Management, and Accounting, along with Computer Science, show a larger share of publications with fewer citations.

Collectively, these visualizations reveal notable disparities in citation patterns across scientific domains. Certain fields regularly produce highly cited research, while others show a lower concentration of impactful studies. These differences likely stem from varying research dynamics, innovation levels, societal relevance, and discipline-specific citation behaviors. Understanding these patterns provides deeper insights into how research impact is distributed across hydrogel-related studies and highlights areas with the potential for future growth and influence.

Author contributions analysis in hydrogel research (2000–2025)

Figure 5 offers a comprehensive analysis of author contributions and publication trends in hydrogel research across multiple scientific domains. Figure 5a illustrates the steady growth in author participation from 2000 to 2025 across four major scientific fields: Health Sciences, Life Sciences, Physical Sciences, and Social Sciences. Notably, the Physical Sciences consistently lead in the number of contributing authors, followed by Life Sciences, Health Sciences, and Social Sciences. This trend reflects an expanding and dynamic research landscape where increasing numbers of researchers are driving scientific advancements across disciplines. Complementing this observation, the inset pie chart reveals that Health Sciences accounts for the largest proportion of authors at 45.53%, followed by Life Sciences (28.08%), Physical Sciences (26.15%), and Social Sciences (0.24%). This distribution highlights the significant focus on Health Sciences within hydrogel research, likely fueled by pressing global health challenges and substantial biomedical research investments.

Fig. 5.

Author Contributions and Publication Trends in Hydrogel Research (2000–2025). a Growth in the number of unique authors across four scientific domains—Health Sciences, Life Sciences, Physical Sciences, and Social Sciences—highlighting a significant increase in research collaboration, with Health Sciences accounting for the largest proportion of authors (45.53%). b Top 10 most prolific authors ranked by publication output, showing variations in total citation counts and emphasizing that research impact extends beyond publication volume. c Distribution of the top authors’ publications across citation percentiles, illustrating diverse citation impacts where some authors have a higher share of highly cited work, while others have more publications in lower citation categories. d Ribbon chart tracking the annual publication trends of the top five authors, revealing fluctuations in research productivity over time and reflecting evolving research priorities and collaborative efforts

Further emphasizing this collaborative research environment, the dataset features 269,440 unique authors. Among these, 8138 publications were single-author works, while the average number of authors per publication stands at five. Remarkably, some publications involve up to 100 authors, and 168 works include more than 20 contributors. This trend underscores the growing importance of large-scale, interdisciplinary collaborations in advancing hydrogel research.

Figure 5b shifts focus to the top 10 most prolific authors based on publication output, showcasing their substantial contributions to the field. These authors have published between ~150 and 260 articles each. However, the total citation counts vary significantly among them. For example, while Ali Khademhosseini and Jian Ping Gong have similar publication volumes, their citation impacts differ notably. This disparity underscores that research impact depends not only on productivity but also on the quality, relevance, and influence of the work within the scientific community.

Building on this, Fig. 5c presents a stacked bar chart detailing the distribution of these top authors’ publications across various citation percentiles. Authors like Kristi S. Anseth demonstrate a high concentration of papers in the top 10% and 25% citation categories, signaling a significant influence within the field. In contrast, authors such as Yang Li and Lyndon Jones show a greater share of their publications in lower citation categories. This variation highlights the multifaceted nature of research impact, where productivity does not always equate to influence, and the scholarly reach of publications can differ widely even among prolific authors.

Lastly, Fig. 5d employs a ribbon chart to track the publication trajectories of the top five authors over time. This visualization captures the evolving nature of research careers, revealing patterns of productivity. For instance, Ali Khademhosseini experienced a surge in publication output between 2013 and 2018, followed by a slight decline in recent years. This temporal analysis offers valuable insights into how researchers’ publication trends shift over time, reflecting changing research priorities, career stages, and collaborations.

Collectively, these visualizations provide a holistic view of author engagement, productivity, and research impact in hydrogel studies. They highlight not only the growing scale of collaborative research but also the complexity of measuring scientific influence beyond publication counts, emphasizing the importance of both quality and reach in academic contributions.

Global institutional participation and impact in hydrogel research (2000–2025)

Figure 6a illustrates the steady growth in the number of institutions involved in hydrogel research across four continents(Africa, the Americas, Asia, and Europe) from 2000 to 2025. All regions exhibit a clear upward trend, reflecting a significant expansion in research activity and institutional engagement in this field. Notably, Asia almost consistently leads with the highest number of participating institutions, highlighting the region’s strong and growing research presence. The Americas and Europe also demonstrate substantial growth, while Africa shows a steady but modest increase in institutional involvement. This trend emphasizes the dynamic and expanding global landscape of hydrogel research, with more institutions contributing to scientific advancements worldwide. Complementing this trend, the inset pie chart in Fig. 6a reveals the distribution of institutions by continent. Asia holds the largest share at 40.69%, followed by Europe at 28.41%, and the Americas at 24.16%. Africa and Oceania contribute 5.11% and 0.24%, respectively. This distribution underscores Asia’s dominance in hydrogel research, reflecting the region’s robust research infrastructure and increasing focus on scientific innovation. Key data points further highlight the scale of institutional participation in hydrogel research. A total of 14,343 institutions have contributed to hydrogel publications. Of these, 34,439 publications originated from a single institution, while the average number of institutions collaborating on each publication is 1.97. Moreover, 168 publications involved more than 20 institutions, underscoring a rising trend in large-scale, multi-institutional collaborations aimed at advancing hydrogel research.

Fig. 6.

Global Institutional Participation and Impact in Hydrogel Research (2000–2025). a Growth in the number of institutions involved in hydrogel research across Africa, the Americas, Asia, and Europe, showing a consistent upward trend globally. The inset pie chart displays the distribution of institutions by continent, with Asia leading at 40.69%, followed by Europe (28.41%), the Americas (24.16%), Africa (5.11%), and Oceania (0.24%). b World map visualization highlighting the geographical distribution of research institutions, with the United States and China exhibiting the highest concentration of institutional participation. c Bar chart ranking the top 10 countries by the number of institutions engaged in hydrogel research, led by the United States (2432) and China (2105), followed by other major contributors such as India, France, and Japan. d Comparative bar charts of the top 10 institutions based on research impact (total citations) and productivity (total publications). Harvard University leads in citations (117,000), while the Chinese Academy of Sciences ranks highest in publication output (2137). e Number of publications for Top10 institutions

Figure 6b offers a global perspective through a world map visualization, where the size of circles represents the number of institutions involved in hydrogel research per country. The visualization reveals a dominant research presence in the United States and China, indicated by larger circles reflecting a high concentration of research institutions. Europe also demonstrates considerable research activity, whereas Africa, South America, and Oceania show comparatively lower institutional participation. This global overview highlights regional disparities in research engagement and the concentration of hydrogel research institutions in leading economies.

Further detailing the geographical distribution, Fig. 6c presents a bar chart ranking the top 10 countries by the number of institutions involved in hydrogel research. The United States leads with 2432 unique institutions, followed closely by China with 2105 institutions, underscoring their leadership in global research capacity. Other top contributors include India, France, Japan, Great Britain, Germany, Italy, Russia, and Spain, reflecting a broad and diverse global research landscape. While this chart highlights the number of institutions, it is important to note that it does not directly measure the research output or impact of these countries.

Figure 6d provides a more nuanced analysis through two bar charts comparing the research output and impact of the top 10 institutions. The first chart ranks institutions by citation count, with Harvard University leading at 117,000 citations, followed by the Chinese Academy of Sciences (103,000) and the Massachusetts Institute of Technology (102,000). The second chart ranks institutions by publication volume, where the Chinese Academy of Sciences tops the list with 2137 publications, followed by Sichuan University (1455) and Shanghai Jiao Tong University (1099). This comparison reveals that while some institutions, such as Harvard University, excel in research impact, others, like the Chinese Academy of Sciences, demonstrate high productivity. These findings highlight the multifaceted nature of research success, where both publication volume and citation impact are critical for evaluating institutional performance.

Additionally, the annual publication trends for the top 10 institutions from 2000 to 2025 provide further insight into their research productivity (Figure 6e). The Chinese Academy of Sciences shows a consistent upward trend, reaching 313 publications in 2023 and contributing to its overall total of 2137 publications. Similarly, Sichuan University and Shanghai Jiao Tong University have exhibited strong growth, reflecting sustained increases in research output. This data underscores the dynamic and evolving research productivity of leading institutions, driven by continuous investments in scientific innovation and collaboration.

Together, these visualizations present a comprehensive overview of the global institutional landscape in hydrogel research, highlighting the growth, distribution, and impact of research institutions across regions. The analysis reflects how global collaboration and regional strengths continue to shape the advancement of hydrogel science.

Country participation in hydrogel research (2000–2025)

Figure 7a presents bar charts comparing the top 20 countries based on their research output and impact in hydrogel research. The first chart ranks countries by total citations, with the United States leading at over 1 million citations, followed closely by China with 770,000 citations. In contrast, the second chart ranks countries by the number of publications, where China surpasses the United States with 27,931 publications compared to 18,373. This contrast highlights distinct strengths: the United States leads in research influence, while China demonstrates higher research productivity, reflecting differing priorities and strategies in advancing hydrogel research. Figures S2–S4 present the publication and citation data for the top three countries in hydrogel research by publication volume (USA, China, Japan). These figures summarize key findings from a bibliometric analysis of hydrogel research, including publication trends, institutional contributions, research output by field, and author productivity and impact. In addition, rates of progression from 2000 to 2024 in terms of number of publications, number of citations, number of institutions, and number of authors are presented in Figure S5.

Fig. 7.

Global Comparative Analysis of Research Output and Impact in Hydrogel Research (2000–2025). a Bar charts comparing the top 20 countries by total citations and publication counts in hydrogel research. The United States leads in total citations (>1 million), indicating higher research impact, while China leads in publication output (27,931), reflecting greater research productivity. b World map visualization showing the global distribution of hydrogel research output, with larger representations for countries producing more publications. The United States, China, and several European nations (United Kingdom, Germany, France) demonstrate significant research activity. c Bar chart comparing the research output of the United States and China across scientific fields. China leads in Engineering and Materials Science, while the US excels in Medicine and Biochemistry, Genetics, and Molecular Biology. Both countries show competitive outputs in Chemistry, Environmental Science, and Energy. d Sankey diagram illustrating the distribution of citations from the United States and China across impact categories (Top 1%, Top 10%, Top 25%, Top 50%, and Below 50%). The US has a higher share of publications in the top 1% citation category, while China demonstrates broader citation distribution, reflecting differing research impact profiles

Building on this, Fig. 7b offers a world map visualization that illustrates the global distribution of hydrogel research output. The size of each country’s representation is proportional to its number of publications, reinforcing the dominant research presence of the United States and China. Additionally, several European countries—particularly the United Kingdom, Germany, and France—exhibit substantial research activity. This global perspective highlights the varying levels of scientific engagement across regions and emphasizes the widespread and growing interest in hydrogel research worldwide.

To further explore the research landscape, Fig. 7c compares the research output of the United States and China across various scientific fields. China demonstrates a significant lead in Engineering (7633 publications vs. the US’s 4652) and Materials Science (5325 vs. 2652), while the United States excels in Medicine (5196 vs. China’s 4673) and Biochemistry, Genetics, and Molecular Biology (5144 vs. 3824). In fields such as Chemistry, Environmental Science, and Energy, both countries maintain comparable publication volumes, highlighting a competitive and diverse research environment. This field-specific comparison underscores how each nation capitalizes on its scientific strengths, contributing to the dynamic global research landscape.

Complementing this analysis, Fig. 7d presents a Sankey diagram illustrating the distribution of citations from the United States and China across citation impact categories: Top 1%, Top 10%, Top 25%, Top 50%, and Below 50%. The thickness of the flow lines represents the proportion of citations in each category. The United States has a noticeably higher share of publications in the top 1% citation category. In contrast, China has a smaller proportion of highly cited papers. This comparison highlights the differing citation profiles of these two research powerhouses, emphasizing the United States’ research impact and China’s growing research productivity.

Collectively, these visualizations provide a comprehensive overview of global research performance in hydrogel research, revealing not only the leading contributors but also the nuanced dynamics of research output and impact across countries and scientific disciplines.

Influential journals in the hydrogel research (2000–2025)

Figure 8 provides a comprehensive analysis of the most influential journals and publications in hydrogel research, offering insights into publication output, citation impact, and the distribution of high-impact research across top journals.

Fig. 8.

Analysis of the most influential journals and publications in hydrogel research. a Bar chart of the top 20 journals ranked by publication output, segmented by citation categories (Below 50%, Top 50%, Top 25%, Top 10%, Top 1%). ACS Applied Materials & Interfaces leads in publication volume, with a significant portion of highly cited papers. b Bar chart of the top 20 journals by total citation counts, highlighting Biomaterials as the most cited journal with a substantial share of citations in the Top 1% and Top 10% categories. c Bar chart of the top 20 journals ranked by average citations per publication, with Choice Reviews Online demonstrating the highest average impact. d Table of the top 30 most highly cited publications in hydrogel research, dominated by influential review articles and high-impact research papers from leading journals such as Chemical Reviews, Advanced Drug Delivery Reviews, Nature, and Science

Figure 8a presents a bar chart showcasing the top 20 journals based on their publication output. Each bar represents the total number of publications for a specific journal, segmented by color to indicate the proportion of publications across different citation categories: Below 50%, Top 50%, Top 25%, Top 10%, and Top 1%. “ACS Applied Materials & Interfaces” leads with 1577 publications, followed closely by the International Journal of Biological Macromolecules with 1426 publications. Notably, “ACS Applied Materials & Interfaces” has 577 publications (36.6%) in the Top 50% category, highlighting its strong citation performance. In contrast, the “Journal of Biomedical Materials Research Part A” has a smaller proportion of highly cited papers, with only 230 publications (24.5%) in the Top 50% category. This visualization emphasizes the diversity in citation impact among high-output journals, reflecting both research productivity and scholarly influence. Table S1 provides a visual representation of the publication trends of top journals in hydrogel research, enabling a deeper understanding of the evolving publication landscape and the relative influence of different journals in shaping the field.

Building on this, Fig. 8b displays the top 20 journals ranked by total citation counts. “Biomaterials” emerges as the leader, surpassing 130,000 citations, followed by “Advanced Materials” and “ACS Applied Materials & Interfaces” with over 115,000 and 95,000 citations, respectively. The bars are segmented by citation categories, revealing that “Biomaterials” has a substantial portion of citations in the Top 1% and Top 10% categories. This chart deepens the understanding of citation dynamics across journals, highlighting which journals contribute most significantly to advancing hydrogel research.

Complementing these insights, Fig. 8c presents a bar chart of the top 20 journals ranked by the average number of citations per publication. “Choice Reviews Online” leads with an impressive 4.7 K citations per publication, underscoring its exceptional research impact. Other high-impact journals include “Nature Reviews Materials” (0.8 K), “Neuron” (0.7 K), and “Advanced Drug Delivery Reviews” (0.7 K). This analysis reveals that while some journals have high overall output, others maintain influence through consistently high citation averages, reflecting deep engagement and influence in their fields.

Lastly, Fig. 8d features a table listing the top 30 most highly cited publications in hydrogel research. Review articles dominate the list, with standout works like “Hydrogels for Tissue Engineering” in “Chemical Reviews” (4963 citations) and “Hydrogels for Biomedical Applications” in “Advanced Drug Delivery Reviews” (4736 citations) leading the rankings. High-impact research articles from prestigious journals such as “Nature”, “Science”, and “Advanced Materials” are also prominently featured. This table highlights the pivotal research contributions that have shaped the field, offering a glimpse into key themes and influential studies driving hydrogel innovation.

Collectively, these visualizations provide a holistic view of the publication and citation landscape in hydrogel research, emphasizing the interplay between research output, citation impact, and scholarly influence across leading journals and publications.

Collaboration network analysis

Co- authorship network analysis

Co-authorship network analysis at international level

Figure 9a presents a global co-authorship network diagram illustrating international research collaborations in the hydrogel field. In this network, nodes represent individual countries, and edges connect countries that have co-authored research publications. The size of each node reflects the number of publications resulting from international collaborations involving that country. The visualization highlights a highly interconnected global research network, with extensive collaborations spanning continents. Notably, the United States and China emerge as major hubs, connected by a particularly thick edge that signifies a strong research partnership in hydrogel studies.

Fig. 9.

Global co-authorship networks at country level in hydrogel research. a The global collaboration network illustrating international research partnerships, where nodes represent countries and edges indicate co-authored publications. Node size reflects the number of publications, with the United States and China emerging as major hubs, highlighted by a thick edge denoting strong collaboration between them. b Evolution of international research collaboration networks in 2000, 2010, and 2020. The diagrams show increasing global interconnectedness over time, with a significant expansion in collaborations and the growing prominence of China–US partnerships by 2020. The rising number of nodes and edges underscores the dynamic and expanding nature of global research collaboration in the hydrogel field. c China’s international collaboration network highlights strong connections with the US, Australia, and Great Britain. d The US collaboration network shows prominent partnerships with China, Canada, and South Korea

Figure 9b further explores the evolution of international research collaboration in hydrogel studies across three distinct years: 2000, 2010, and 2020. In 2000, the United States dominated as the central hub in the global hydrogel research network, reflecting its leading role in fostering international collaborations. By 2010, the network had expanded significantly, with more countries engaging in collaborative research, although the US maintained its prominent position. By 2020, the collaboration between China and the United States became especially prominent, as indicated by the thickened edge between them. Additionally, the network exhibited increased interconnectedness, with numerous new connections forming between various countries, signaling the growing global engagement in hydrogel research.

Building on this global perspective, Fig. 9c, d provides a more focused comparison of international research collaborations for China and the United States, respectively. Figure 7c illustrates China’s collaboration network, showcasing its role as a central hub with strong connections to countries across Europe (Germany, France, and the UK), Asia (Japan and South Korea), and North America (the USA and Canada). In contrast, Fig. 9d depicts the US network, which also exhibits extensive global connections. The US maintains particularly strong collaborations with China, followed by Canada and South Korea, while China’s closest collaborators include the US, Australia, and Great Britain.

Together, these visualizations reveal a clear trend of increasing global interconnectedness in hydrogel research. The rise in both the number of participating countries (nodes) and collaborative links (edges) underscores a dynamic and evolving global research landscape. This growing network of international partnerships highlights the expanding trend of cross-border collaboration, emphasizing the collective effort in advancing scientific discovery in the hydrogel field. The comparative analysis of China and the US further demonstrates how both nations strategically engage with global partners to strengthen their leadership and innovation in hydrogel research.

Co-authorship network analysis at institution level

Figure 10 illustrates the evolution of co-authorship networks at the institutional level in hydrogel research for China, the USA, and Japan—the top three countries in publication output—across three key years: 2000, 2010, and 2020. These network diagrams visualize the connections and collaborations among research institutions within each country, revealing how collaborative structures have developed over time.

Fig. 10.

Evolution of institutional co-authorship networks in hydrogel research for China, the USA, and Japan in 2000, 2010, and 2020. The network diagrams illustrate the growth and structure of research collaborations within each country over two decades. In 2000, the USA exhibited a more interconnected network compared to China and Japan. By 2020, China experienced rapid expansion, with the Chinese Academy of Sciences emerging as a central hub, while the USA showed steady growth and Japan demonstrated moderate expansion centered around the University of Tokyo. These visualizations highlight the increasing importance of collaborative research and reveal distinct national patterns in network evolution

In 2000, the US co-authorship network was noticeably more active and interconnected than those of China and Japan, indicating a well-established collaborative research environment. However, over the next two decades, China’s research landscape underwent a remarkable transformation. By 2020, China’s network had expanded significantly, marked by a substantial rise in both the number of participating institutions (nodes) and the volume of collaborative links (edges). The Chinese Academy of Sciences emerged as a dominant hub, playing a pivotal role in fostering and coordinating research collaborations nationwide.

In contrast, the US network, while continuing to grow, expanded at a slower pace compared to China. The growth was steady but lacked the rapid, centralized expansion seen in China. Japan’s network exhibited moderate growth during this period, with the University of Tokyo consistently serving as a central connector among research institutions, though the overall network remained less expansive than those of China and the US.

These visualizations collectively highlight the dynamic and evolving nature of institutional research collaboration within the hydrogel field. The increasing density of networks and the rise of prominent research hubs emphasize the growing importance of collaboration in advancing scientific innovation. Furthermore, the distinct national patterns of network development reflect different research strategies: China’s rapid, centralized expansion contrasts with the US’s steady growth and Japan’s more moderate, institution-focused collaboration.

Co-authorship network analysis at individual level

Figure 11a showcases the evolution of research collaborations for Ali Khademhosseini, a leading figure in hydrogel research, particularly recognized for his exceptional citation count, which positions him as a top contributor in the field. The network diagram illustrates the connections between Dr. Khademhosseini and his co-authors from 2000 to 2025. Nodes represent individual researchers, with the size of each node reflecting their publication output in collaboration with Dr. Khademhosseini. The thickness of the edges connecting the nodes indicates the frequency and strength of these collaborations. Notably, the network’s significant growth from 2000–2010 to 2010–2020 reflects a marked increase in both the number of collaborators and the density of these connections, underscoring Dr. Khademhosseini’s expanding influence and his pivotal role in advancing hydrogel research.

Fig. 11.

Research collaborations and publication strategy of Dr. Ali Khademhosseini, a leading figure in hydrogel research. a Network diagram illustrating the evolution of Dr. Khademhosseini’s research collaborations from 2000 to 2025, with nodes representing co-authors and edges indicating the frequency of collaboration. b Publication output across various journals, with nodes sized according to the number of publications. Advanced Healthcare Materials stands out as the most significant journal

This expanding network of collaborations is further mirrored in Dr. Khademhosseini’s publication strategy, as illustrated in the network diagram of his publication output across various high-impact journals (Fig. 11b). The size of each journal node is proportional to the number of publications authored by Dr. Khademhosseini in that particular journal. A standout observation is the central role played by Advanced Healthcare Materials, where Dr. Khademhosseini has published 29 papers, the highest of any journal, reflecting his focus on disseminating key research findings. In addition to Advanced Healthcare Materials, prominent journals such as Advanced Materials (15 publications), ACS Nano (5 publications), and others further highlight his strategic approach to publishing in influential outlets. This diverse portfolio of journals not only illustrates Dr. Khademhosseini’s widespread academic influence but also reinforces his commitment to advancing research in hydrogel-related fields through reputable platforms.

In conclusion, these visualizations collectively offer valuable insight into Dr. Khademhosseini’s research trajectory, revealing both his expanding collaborative network and strategic publication choices, which have significantly contributed to his standing as a top researcher in the field of hydrogel research.

Co-concurrency analysis

The word cloud provides a glimpse into the evolution of hydrogel research from 2000 to 2025 (Fig. 12a). Throughout this period, “biocompatibility” emerges as a dominant keyword, underscoring the critical importance of ensuring hydrogels are safe and well-tolerated within biological systems. Between 2000 and 2015, the research focus was predominantly on fundamental material properties and the exploration of various hydrogel types. Prominent keywords such as “polymer,” “hydrogel,” and “acrylic acid” suggest an emphasis on understanding the basic principles of hydrogel formation and characterization. However, a significant shift towards biomedical applications becomes evident from 2015 to 2025. Terms like “regeneration,” “tissue engineering,” “drug delivery,” and “bioprinting” gain prominence, highlighting a growing interest in translating hydrogel research into clinical applications. In addition, the emergence of keywords such as “bioprinting,” “3D printing,” and “nanotechnology” signals the increasing integration of advanced technologies into hydrogel research. These innovations enable the design and fabrication of complex, customized hydrogels with tailored properties and functionalities. Based on this evolving keyword landscape, future hydrogel research is likely to focus on developing materials for complex tissue regeneration, personalized medicine, and enhancing the clinical translation of hydrogel-based technologies.

Fig. 12.

Evolution and interconnectedness of keywords in hydrogel research from 2000 to 2025. a Word cloud illustrating the progression of key themes, highlighting the sustained importance of “Biocompatibility” and the growing prominence of biomedical applications such as “Regenerative Medicine” and “3D Bioprinting.” b Quantitative analysis of keyword frequency over time, showcasing trends in material diversification and technological integration. c Co-occurrence network of keywords in 2010, emphasizing central hubs like “Biocompatibility,” “Acrylic Acid,” and “Gelatin,” and early exploration of emerging fields such as “Nanoparticles” and “Drug Delivery.”

Beyond qualitative insights, Fig. 12b offers a quantitative analysis of keyword frequency over time, providing a more precise understanding of research trends. For example, the rapid rise of terms like “Regenerative Medicine” and “3D bioprinting” in recent years is particularly noteworthy. The data aligns with and expands upon the findings from the word cloud analysis. One of the most significant trends is the sustained and substantial increase in the frequency of the term “biocompatibility,” reaffirming its vital role in ensuring hydrogel safety and biological compatibility. In addition, it also indicates a diversification of materials, with increased mentions of terms such as “gelatin,” “acrylic acid,” “polyvinyl alcohol,” and “biopolymer.” This trend mirrors the word cloud’s suggestion of a broader exploration of materials in hydrogel research. Additionally, the rising frequency of keywords like “3D bioprinting,” “decellularization,” and “cell encapsulation” confirms the integration of advanced technologies into the field. Furthermore, terms related to characterization and modification, such as “characterization,” “surface modification,” and “thermogravimetric analysis,” show steady growth, emphasizing the increasing focus on understanding and enhancing hydrogel properties.

Figure 12c provides valuable insights into the co-occurrence of keywords in hydrogel research for the year 2010, highlighting key themes and emerging trends. The diagram reveals several central hubs with extensive connections to other keywords, illustrating the foundational concepts in hydrogel research during this period. Notably, “biocompatibility” stands out as a major hub, emphasizing its critical role in ensuring that hydrogel materials are safe and biologically compatible. This hub is closely connected with terms related to material properties, biological interactions, and testing methods. Similarly, “acrylic acid” emerges as a central node, reflecting its widespread application in hydrogel synthesis and structural modifications. Another significant hub is “gelatin,” a natural biopolymer, which connects to keywords associated with biomaterials, biocompatibility, and biomedical applications.

The co-occurrence network further underscores the interconnectedness of various aspects of hydrogel research. “Biocompatibility” is strongly linked to terms such as “viability assay,” “MTT assay,” and “cell encapsulation,” indicating a focus on evaluating the biological responses to hydrogel materials. “Acrylic acid” is associated with terms like “cationic polymerization,” “ammonium persulfate,” and “swelling capacity,” highlighting its integral role in creating diverse hydrogel structures. Likewise, “gelatin” is connected to terms like “biomaterial,” “biocompatibility,” and “cell encapsulation,” emphasizing its potential in biomedical and therapeutic applications.

Topic modeling of hydrogel research with latent dirichlet allocation

LDA is a topic modeling method that automatically uncovers hidden thematic structures within large text datasets [39, 40]. By classifying documents into a set number of topics—each defined by a distribution of words—LDA enables each document to be represented as a mixture of these topics. This probabilistic framework is especially valuable for identifying patterns and relationships in unstructured data, making it highly effective for exploring complex research fields such as hydrogel studies. Through this approach, researchers can systematically analyze vast amounts of scientific literature to reveal emerging trends and dominant research areas. However, the effectiveness of LDA largely depends on selecting the optimal number of topics, as this choice directly influences the model’s ability to produce meaningful and interpretable results. To address this challenge, the coherence score serves as a critical evaluation metric by measuring how semantically related the top words within each topic are. A higher coherence score indicates that the topics are logically connected and well-defined, enhancing their interpretability.

Applying this evaluation, the coherence score analysis reveals that selecting 17 topics is optimal for capturing meaningful and interpretable themes within the dataset (Fig. 13a). The LDA analysis successfully identifies these 17 distinct topics, which encompass a wide range of themes in hydrogel research, including material properties, fabrication techniques, biomedical applications, and emerging trends. For example, a “Material Focus” emerges through frequent mentions of gelatin, acrylic acid, polyvinyl alcohol, and biopolymers, highlighting their crucial role in hydrogel development. Simultaneously, “Biomedical Applications” is strongly represented, with topics concentrating on tissue engineering, wound healing, drug delivery, and regenerative medicine. Moreover, the presence of keywords such as nanotechnology, bioprinting, and advanced materials points to “Emerging Trends” that signal ongoing innovation and evolution within the field.

Fig. 13.

a Coherence score analysis determining the optimal number of topics for the LDA model, identifying 17 distinct and interpretable themes within hydrogel research. b Distribution of publications and citations across the 17 topics, highlighting the dominance of certain topics—particularly Topic 6—in research output and academic impact

Building on this thematic breakdown, Fig. 13b further illustrates the number of publications and citations associated with each of the 17 topics, providing valuable insight into the distribution and impact of research themes within hydrogel studies. A key observation is the highly uneven distribution of both publications and citations across topics. While certain topics dominate in research output and academic attention, others receive comparatively less focus, indicating varying levels of interest and exploration within the field. In particular, Topic 6 stands out as the most prominent, with the highest number of both publications and citations. This suggests that Topic 6 represents a significant and influential area of hydrogel research, potentially encompassing cutting-edge advancements or widely explored applications. Furthermore, the citation distribution closely mirrors the publication trends, as topics with more publications generally accumulate more citations. The dominance of Topic 6 highlights the need for a deeper exploration of its specific themes to understand the factors contributing to its substantial academic impact and influence.

Conclusion

This comprehensive bibliometric analysis of hydrogel research from 2000 to 2025 reveals several significant trends and patterns that characterize the field’s evolution. The analysis demonstrates remarkable growth in research output and impact, with publication volumes increasing from 350 in 2000 to nearly 11,000 in 2024, reflecting the expanding interest and investment in hydrogel science. The study highlights three key developments that have shaped the field’s trajectory.

First, the analysis reveals significant transformations in global research collaboration networks. While the United States maintains the highest citation impact with over 1 million citations, and China leads in publication volume with 27,931 publications, the most striking development is the evolution of collaborative partnerships. The co-authorship network analysis reveals increasingly complex international collaborations, with institutional partnerships growing from an average of 1.97 institutions per paper to some publications involving more than 20 institutions. Particularly noteworthy is the strengthening collaboration between Chinese and US institutions, as evidenced by the thickened network edges between these countries from 2010 to 2020. The Chinese Academy of Sciences has emerged as a central hub in the global network, while Harvard University maintains the highest citation impact, demonstrating how different institutions contribute distinct strengths to the collaborative ecosystem.

Second, the study identifies distinct patterns in research impact and dissemination across collaborative networks. The analysis of institutional co-authorship networks reveals three distinct patterns: China’s rapid, centralized expansion around key institutions like the Chinese Academy of Sciences; the United States’ more distributed network with multiple strong nodes including Harvard, MIT, and Stanford; and Japan’s moderate growth centered around the University of Tokyo. These different collaboration models have implications for research productivity and impact, with the finding that 20% of all citations originate from the top 1% of papers suggesting that certain collaborative structures may be more effective at producing high-impact research.

Third, the application of Latent Dirichlet Allocation topic modeling reveals 17 distinct research themes, highlighting how collaborative networks influence research directions. The evolution of these themes corresponds with changes in collaboration patterns, particularly evident in the growing emphasis on interdisciplinary applications such as tissue engineering, drug delivery, and regenerative medicine. This diversification reflects the impact of cross-institutional and international collaborations in driving innovation.

Looking forward, this analysis suggests several promising directions for enhancing research collaboration. There is a clear opportunity for increased partnership between established research centers in North America and Europe with emerging hubs in Asia, particularly in areas where complementary expertize exists. The identified collaboration patterns point to the potential for more structured international research programs, especially in rapidly growing areas such as biomedical applications and smart materials. Additionally, the relatively lower representation of certain research areas, particularly in environmental applications and energy storage, suggests opportunities for new collaborative initiatives.

In conclusion, this bibliometric analysis provides valuable insights into the dynamic landscape of hydrogel research, with particular emphasis on the critical role of research networks and collaborative structures in driving innovation. The findings underscore the field’s increasing maturity and highlight how different models of collaboration contribute to scientific advancement. Understanding these collaboration patterns is crucial for informing future research strategies, policy decisions, and international research initiatives that can further accelerate progress in hydrogel science.

Compliance with ethical standards

Conflict of interest

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1007/s10856-025-06887-2.