Biomimicry for Energy-Efficient Building Design: A Bibliometric Analysis

With the development of the biomimicry approach, new and creative ideas have been established to solve problems in architectural design. In the designs based on this process, “nature” is used as a diverse data source for the transfer of these data to various processes, functions, materials, and structures. The primary purpose of this paper is to explore the development of biomimicry as an architectural approach, with a bibliometric review of research related to biomimicry and energy efficiency. Emphasis on the importance of the need for biomimicry in modern designs is another goal of this study. In this study, articles published in the Web of Science database (2010–2021) were analyzed. VOSviewer and SankeyMATIC software were used to represent the analysis results graphically. According to the results of this study, in addition to the inadequacy of biomimicry research, the need for further research became apparent. This review can serve as a reference for future studies to transfer natural phenomena to architecture in order to solve the problem of efficient energy consumption.


Introduction
Climate change throughout the world has increased concerns about ecological harm. Greenhouse gas emissions from this activity inflict permanent harm. Global advances in energy efficiency have been dropping since 2015 according to IEA2020. A decrease in energy costs arrived with the COVID-19 pandemic, resulting in a reduction in energy intensity improvement in 2020, less than the revised rates for 2018 and 2019. As a consequence of the analytical studies of energy institutions, buildings account for one-third of this consumption. Buildings are also responsible for 40% of direct and indirect emissions of The importance of construction in worldwide energy consumption has raised awareness of environmental degradation trends. This rising knowledge has sparked efforts to optimize energy efficiency while minimizing environmental impact. The use of efficient designs reduces the energy consumption of a building during its life cycle and helps solve these challenges by reducing the damage to the environment and human health.
Architects and designers have long been concerned with meeting the challenges of nature and architecture. Owing to advances in technology, nature-based design and construction techniques have led to designs based on biological approaches. These techniques, which appear with various terminologies such as bionics, bio-inspiration, biomimetics, and biomimicry, are mainly based on solving problems by inspiring/learning/developing innovative proposals based on the shape, structure, and systems of nature". It has been also argued that "designers can be inspired by nature in order to tackle building design challenges, and this has led to a connection between architecture and biomimicry" [2].
Biomimicry's goal, developing technical advancements and achieving sustainability, appears to be the best ideas of nature, and it imitates them in design processes to solve

Research and Methodology
The purpose of this study was to survey publications and research directions in biomimicry and architecture utilizing a scientific literature database and science survey analysis. Bibliometric analysis is an effective method for determining the growth and future possibilities of a study topic. Bibliometric methodologies have been used to investigate the growth of research topics, find relationships between logical progress and modifications to the approach, and identify expanding interdisciplinary alliances. The research methodology provides detailed quantitative and statistical scientific information regarding the processes of making decisions.
Today, detailed analyses can be conducted via numerous online databases such as Web of Science, Scopus, and Google Scholar. Additionally, different software tools such as VOSviewer, Citespace, Bibexcel, Gephi, Pajek, Publish or Perish, Ucinet, and Science of Science (Sci2) provide informative data and visualization [8]. The bibliometric data of the search results made with the relevant keywords in the WoS (Web of Science) database were analyzed and visualized with the VOSviewer and Sankey diagram mapping methods, and the relationships, trends, and collaborations between the subjects were revealed through network maps. In addition to primary databases such as WoS, Scopus, EBSCO, and ProQuest used in bibliometric searches, networks such as Google Scholar, ResearchGate, and Academia are also available. The search results in Google Scholar, despite the variety, are not comprehensive, and the results have a different quality load, so the classification of articles for bibliometric work is the responsibility of the researcher. In Google Scholar, updating information related to articles is not accurate, so a bibliometric review of the articles may not have acceptable results. Classification studies were carried out in this study using the Web of Science, which includes indexes such as Sci, Sci, and A&HCI, where the most recent and qualified publications are published.
The bibliometric analysis in this research is based on two mechanisms of functional analysis and scientific mapping. Scientific mapping is a visual representation of the conceptual, intellectual, and social structures of research fields [7]. In this method, bibliographic data analysis is possible based on the author, document, source, institution, country, and keywords. In this research, the analysis of co-occurring words was used to map the studies, which is a method used to measure the strength of relationships between publications' keywords [9]. By analyzing co-occurring words, keywords related to the subject of the articles were obtained. Performance analysis is a method that measures the number of articles and citations published by authors and institutions in this field. In this study, mapping and performance analysis were used together in an integrative way. Bibliographic data from the Web of Science database were analyzed in VOSviewer and SankeyMATIC software. Figure 1 summarizes the study's methodology. were analyzed and visualized with the VOSviewer and Sankey diagram mapping methods, and the relationships, trends, and collaborations between the subjects were revealed through network maps. In addition to primary databases such as WoS, Scopus, EBSCO, and ProQuest used in bibliometric searches, networks such as Google Scholar, Re-searchGate, and Academia are also available. The search results in Google Scholar, despite the variety, are not comprehensive, and the results have a different quality load, so the classification of articles for bibliometric work is the responsibility of the researcher. In Google Scholar, updating information related to articles is not accurate, so a bibliometric review of the articles may not have acceptable results. Classification studies were carried out in this study using the Web of Science, which includes indexes such as Sci, Sci, and A&HCI, where the most recent and qualified publications are published. The bibliometric analysis in this research is based on two mechanisms of functional analysis and scientific mapping. Scientific mapping is a visual representation of the conceptual, intellectual, and social structures of research fields [7]. In this method, bibliographic data analysis is possible based on the author, document, source, institution, country, and keywords. In this research, the analysis of co-occurring words was used to map the studies, which is a method used to measure the strength of relationships between publications' keywords [9]. By analyzing co-occurring words, keywords related to the subject of the articles were obtained. Performance analysis is a method that measures the number of articles and citations published by authors and institutions in this field. In this study, mapping and performance analysis were used together in an integrative way. Bibliographic data from the Web of Science database were analyzed in VOSviewer and San-keyMATIC software. Figure 1 summarizes the study's methodology. Web of Science is "a website that offers subscription-based access to several databases that contain detailed citation data for a wide range of academic subjects" [10]. With the help of such an advanced tool, it is possible to track ideas and disciplines over time, with over 1.9 billion citations from 171 million records in the database. Users can also obtain all of the data for entries in a certain field of research based on a provided query phrase [10]. Visualization of similarity (VOS) mapping is a topic-based approach that allows for a comprehensive and clear representation of advancing study disciplines. It can also draw clusters and cooperation networks using vortices connected by lines [8]. The Sankey diagram (SankeyMATIC) demonstrates a wide data relation to visualize multifaceted connections. It is a type of diagram used to visualize the quantities and flows of assets in proportion to each other. The width of the lines or nodes in the diagram is used to Web of Science is "a website that offers subscription-based access to several databases that contain detailed citation data for a wide range of academic subjects" [10]. With the help of such an advanced tool, it is possible to track ideas and disciplines over time, with over 1.9 billion citations from 171 million records in the database. Users can also obtain all of the data for entries in a certain field of research based on a provided query phrase [10]. Visualization of similarity (VOS) mapping is a topic-based approach that allows for a comprehensive and clear representation of advancing study disciplines. It can also draw clusters and cooperation networks using vortices connected by lines [8]. The Sankey diagram (SankeyMATIC) demonstrates a wide data relation to visualize multifaceted connections. It is a type of diagram used to visualize the quantities and flows of assets in proportion to each other. The width of the lines or nodes in the diagram is used to express the size of the data. In this context, the size of the line or node also expresses the size of the flow amount [11].
Biomimicry is an approach that is widely used in material science, architecture, and engineering, etc. In this work, we integrated the network, group, and bibliometric studies Who are the main authors, and who is working with whom?

Data-Gathering Method
The study used articles screened for "titles, abstracts, and keywords" in English from the WoS (Web of Science) database. "Biomimetic(s)", "biomimicry", or "bio-inspired" and "thermoregulation", "energy efficiency", or "envelope/façade" were used as keywords to analyze trends in biomimicry between 2010 and 2021.
A total of 732 items in the specified period were identified. The records were divided into eight classes: articles (569; 77%), review articles (94; 12%), proceedings papers (70; 9%), book chapters (15; 2%), and others such as early access papers, editorial materials, and meeting abstracts. A total of 251 of the items were 'open access' (34%); the remainder were available through subscription.
Articles (148) and review papers (30) under the categories of architecture, construction building technology, energy fuels, ecology, environmental science, interdisciplinary engineering, and multidisciplinary papers were selected for a detailed analysis. A total of 53 research and review articles about biomimicry and energy efficiency in architecture were obtained.

Results and Discussion
The data collected from the WoS database were analyzed based on the year of publication, research area, geographical area, authorships, citations, and the transition of biological phenomena to the architectural products studied. Figure 2 presents the distribution of publications by year, demonstrating that research in the relevant subject has intensified, and the number of articles has increased in the last five years. In 2021, 17 articles with the specified qualities were published, and the highest number was reached. Based on the results, more comprehensive research on biomimicry and energy efficiency is needed. On the other hand, the increasing number of articles indicates a growing interest in this field.

Research Area Analysis
The pie chart in Figure 3 indicates the thematic classification of biomimicry and energy efficiency in buildings. According to the chart, "engineering" is the most researched topic (24%). Substantial studies were conducted in" building technology, energy studies,

Research Area Analysis
The pie chart in Figure 3 indicates the thematic classification of biomimicry and energy efficiency in buildings. According to the chart, "engineering" is the most researched topic (24%). Substantial studies were conducted in" building technology, energy studies, materials science, and environmental studies". Additionally, 10% of the total research area distribution consists of studies in computer science, robotics, thermodynamics, urban studies, physics, and chemistry.

Research Area Analysis
The pie chart in Figure 3 indicates the thematic classification of biomimicry and energy efficiency in buildings. According to the chart, "engineering" is the most researched topic (24%). Substantial studies were conducted in" building technology, energy studies, materials science, and environmental studies". Additionally, 10% of the total research area distribution consists of studies in computer science, robotics, thermodynamics, urban studies, physics, and chemistry. The highest number of publications is in engineering (23), and construction and building technology (16) is in second place. Additionally, the input from the other areas has been shown clearly (Table 1).  The highest number of publications is in engineering (23), and construction and building technology (16) is in second place. Additionally, the input from the other areas has been shown clearly (Table 1).  Figure 4 shows the countries with publications in the relevant field. While 20 countries contributed to the 52 articles examined, only 5 countries published 6 or more, which shows the inadequacy of such research in many countries. In terms of the number of publications on biomimicry and energy efficiency, Australia, Germany, and the United Kingdom are at the top of the list, then Italy and United States follow them. These five countries account for more than 70% of the publications in this area.

Geographical Area Evaluation
Countries in the top ranks show that economically and technologically strong countries are more active in this field. Some countries' publications appear only as single-country publications. This shows that these countries do not collaborate with other countries. Because more than half of the publications are co-authored, multiple countries may enroll for an article. The authors' collaboration networks show that growth is occurring in a multi-institutional and international way, utilizing the infrastructures accessible in the authors' organizations and countries ( Figure 5). After analyzing the articles under the headings of biomimicry and energy efficiency, the results were obtained in the form of three clusters: the red cluster represents Australia, Chile, Greece, and Italy; the green cluster represents the United Kingdom, France, Spain, and Turkey; and the blue cluster represents Germany, the Netherlands, and the United States. Figure 6 shows the relation between countries and citations. The five countries with the most citations are Germany (304), the United Kingdom (205), the United States (132), Italy (120), and Australia (81), respectively.
Biomimetics 2022, 7, x FOR PEER REVIEW 6 of 15 Figure 4 shows the countries with publications in the relevant field. While 20 countries contributed to the 52 articles examined, only 5 countries published 6 or more, which shows the inadequacy of such research in many countries. In terms of the number of publications on biomimicry and energy efficiency, Australia, Germany, and the United Kingdom are at the top of the list, then Italy and United States follow them. These five countries account for more than 70% of the publications in this area. Countries in the top ranks show that economically and technologically strong countries are more active in this field. Some countries' publications appear only as single-country publications. This shows that these countries do not collaborate with other countries. Because more than half of the publications are co-authored, multiple countries may enroll for an article. The authors' collaboration networks show that growth is occurring in a multi-institutional and international way, utilizing the infrastructures accessible in the authors' organizations and countries ( Figure 5). After analyzing the articles under the headings of biomimicry and energy efficiency, the results were obtained in the form of three clusters: the red cluster represents Australia, Chile, Greece, and Italy; the green cluster represents the United Kingdom, France, Spain, and Turkey; and the blue cluster represents Germany, the Netherlands, and the United States. Figure 6 shows the relation between countries and citations. The five countries with the most citations are Germany (304), the United Kingdom (205), the United States (132), Italy (120), and Australia (81), respectively.   Countries in the top ranks show that economically and technologically strong c tries are more active in this field. Some countries' publications appear only as single-c try publications. This shows that these countries do not collaborate with other count Because more than half of the publications are co-authored, multiple countries may e for an article. The authors' collaboration networks show that growth is occurring multi-institutional and international way, utilizing the infrastructures accessible in th thors' organizations and countries ( Figure 5). After analyzing the articles under the h ings of biomimicry and energy efficiency, the results were obtained in the form of t clusters: the red cluster represents Australia, Chile, Greece, and Italy; the green clu represents the United Kingdom, France, Spain, and Turkey; and the blue cluster re sents Germany, the Netherlands, and the United States. Figure 6 shows the relation tween countries and citations. The five countries with the most citations are Germ (304), the United Kingdom (205), the United States (132), Italy (120), and Australia respectively.    Figure 7 shows the top 10 authors with the most citations of their articles related to biomimicry and energy efficiency in buildings. According to the results obtained from the cluster network, the greatest number of citations (199), with a total link strength of 21, belongs to "Achim, Menges". In this part of the analysis, the identification of the most influential authors was considered. The top 10 authors with the most citations and their link strength are shown in Table 2, and Table 3 shows the 10 most cited articles on biomimicry and energy efficiency. Ideas and processes related to biomimicry and energy efficiency in buildings are presented in these articles. The main focus of the articles is on the energy efficiency of building envelopes according to design approaches.  Figure 7 shows the top 10 authors with the most citations of their articles related to biomimicry and energy efficiency in buildings. According to the results obtained from the cluster network, the greatest number of citations (199), with a total link strength of 21, belongs to "Achim, Menges". In this part of the analysis, the identification of the most influential authors was considered. The top 10 authors with the most citations and their link strength are shown in Table 2, and Table 3 shows the 10 most cited articles on biomimicry and energy efficiency. Ideas and processes related to biomimicry and energy efficiency in buildings are presented in these articles. The main focus of the articles is on the energy efficiency of building envelopes according to design approaches.  cluster network, the greatest number of citations (199), with a total link strength of 21, belongs to "Achim, Menges". In this part of the analysis, the identification of the most influential authors was considered. The top 10 authors with the most citations and their link strength are shown in Table 2, and Table 3 shows the 10 most cited articles on biomimicry and energy efficiency. Ideas and processes related to biomimicry and energy efficiency in buildings are presented in these articles. The main focus of the articles is on the energy efficiency of building envelopes according to design approaches.

Analysis of Organizations
The performance of organizations with two or more publications in terms of biomimicry and energy efficiency is represented by the graph bar in Figure 8. The University of Stuttgart is the most productive research center with the most publications (6)

Analysis of Organizations
The performance of organizations with two or more publications in terms of biomimicry and energy efficiency is represented by the graph bar in Figure 8. The University of Stuttgart is the most productive research center with the most publications (6)

Citation by Sources
The relationship between publications and citations is presented in the form of a network visualization in Figure 10. The size of the node is proportional to the number of Figure 9. Visualization of organizations' citation network.

Citation by Sources
The relationship between publications and citations is presented in the form of a network visualization in Figure 10. The size of the node is proportional to the number of publications, so the more articles, the larger the size of the node. The highest number of publications (5) and citations (176) belongs to the Renewable and Sustainable Energy Reviews journal, with total link strength of 24. It is followed by Energy and Buildings, Buildings, and Sustainability. The distribution of articles classified as biomimicry and energy efficiency in the field of architecture are mostly published in the journals listed in Table 4.

Citation by Sources
The relationship between publications and citations is presented in the form of a network visualization in Figure 10. The size of the node is proportional to the number of publications, so the more articles, the larger the size of the node. The highest number of publications (5) and citations (176) belongs to the Renewable and Sustainable Energy Reviews journal, with total link strength of 24. It is followed by Energy and Buildings, Buildings, and Sustainability. The distribution of articles classified as biomimicry and energy efficiency in the field of architecture are mostly published in the journals listed in Table 4.  Applied Energy 2 6 5 10 Bioinspiration & Biomimetics 2 17 4 11 Biomimetics 3 0 5 Figure 10. Visualization of publication sources' citations. Table 4. List of journals with more than one publication in biomimicry and energy efficiency.

Co-Occurence of Keywords
The network diagram shows the keywords in the appropriate publications and their relationships to each other ( Figure 11). The keywords analyzed were words that were repeated at least three times in the selected articles. As a result, 39 keywords were obtained in 4 groups. Relating keywords to the main content of the publications is key to revealing trends in research topics. This study found that the authors preferentially used the keywords "Biomimicry" and "Biomimetics". It was also found that the focus of the studies is on different design strategies for thermal performance through building envelopes. relationships to each other ( Figure 11). The keywords analyzed were words that were repeated at least three times in the selected articles. As a result, 39 keywords were obtained in 4 groups. Relating keywords to the main content of the publications is key to revealing trends in research topics. This study found that the authors preferentially used the keywords "Biomimicry" and "Biomimetics". It was also found that the focus of the studies is on different design strategies for thermal performance through building envelopes.

Content Analysis of the Selected Articles
In nature-based research, adaptation mechanisms are explored to achieve quantitative and qualitative ideas, such as the transfer of information between scales, programs, processes, or partnerships, and, as a result, a design solution is established. Solving difficulties, such as form, materials, shape, processes, and systems, in this kind of study is confined to the biological knowledge of the designer. Support for such a study by a multidisciplinary team will significantly lessen the challenge of interdisciplinary information transmission.
A content analysis was performed in this part of the research for the articles to better comprehend and remark on biologically inspired studies that altered the energy performance of buildings in the architectural literature as a consequence of multidisciplinary investigations (Table 5). Table 5. Content analysis of articles.

Year
Description Reference

2012
"Biomimetic responsive material systems that do not require an external energy source or any mechanical or electronic control" [18] 2013 "A novel type of kinetic envelope design inspired by plant movements" [21] 2014 "Design of an adaptive responsive facade based on tracking the position of the sun inspired by shrimps' compound eyes" [22] 2015 "An approach for generating biomimetic design ideas and water-harvesting surface designs" [19] 2015 "Investigation of the effect of thermal energy on bio-inspired reflective building envelopes in dense urban areas" [16] 2015 "Building systems that adapt to their environment through the usage of hygromorphic materials" [14] 2015 "Building-shell design using smart materials that act similarly to human skin" [23] Figure 11. Co-occurrence of keywords.

Content Analysis of the Selected Articles
In nature-based research, adaptation mechanisms are explored to achieve quantitative and qualitative ideas, such as the transfer of information between scales, programs, processes, or partnerships, and, as a result, a design solution is established. Solving difficulties, such as form, materials, shape, processes, and systems, in this kind of study is confined to the biological knowledge of the designer. Support for such a study by a multidisciplinary team will significantly lessen the challenge of interdisciplinary information transmission.
A content analysis was performed in this part of the research for the articles to better comprehend and remark on biologically inspired studies that altered the energy performance of buildings in the architectural literature as a consequence of multidisciplinary investigations (Table 5). Table 5. Content analysis of articles.

Year
Description Reference

2012
"Biomimetic responsive material systems that do not require an external energy source or any mechanical or electronic control" [18] 2013 "A novel type of kinetic envelope design inspired by plant movements" [21] 2014 "Design of an adaptive responsive facade based on tracking the position of the sun inspired by shrimps' compound eyes" [22] 2015 "An approach for generating biomimetic design ideas and water-harvesting surface designs" [19] 2015 "Investigation of the effect of thermal energy on bio-inspired reflective building envelopes in dense urban areas" [16] 2015 "Building systems that adapt to their environment through the usage of hygromorphic materials" [14] 2015 "Building-shell design using smart materials that act similarly to human skin" [23] 2015 "Responsive biomimetic building envelope with hygrometric material properties" [12] 2015 "A novel type of kinetic envelope design inspired by plant movements for shading" [15] 2016 "Proposing a biomimetic building envelope to reduce energy consumption, conserve materials, and increase building sustainability" [24] 2016 "Design ideas for shape-morphing sunshades are examined, with a focus on energy-efficient smart materials and biomimetic principles" [25] 2016 "Biomimetic design for enhancing thermal energy performance in office buildings through the use of the biomimicry approach to building energy efficiency" [26]

Year Description
When the 47 directly related articles were examined, innovative designs for the built environment, such as energy efficiency, reductions in energy consumption, water harvesting, thermoregulation, and sensitive and responsive façades and materials, were found to be produced without the help of motors, computerized devices, or external energy sources. The common feature of all these studies is that they aim to minimize the damage to nature, reduce energy consumption, and produce energy-efficient, zero-energy buildings. In this context, it is seen that biomimetic design offers many opportunities for energy-efficient buildings. The main reason why the examined studies mostly focus on the building envelope is that this has properties that require the control of various environmental factors such as ventilation, humidity, heat, light, and mechanical stress, just like shells, the skin, and surfaces in nature. Nature has the potential to provide unlimited examples for the production of sustainable, adaptive, adaptable, and energy-efficient buildings.
According to the Sankey diagram ( Figure 12), more than 70% of the approaches to solving the energy problem in buildings are problem oriented. Concepts such as simulations, parametric models, kinetic mechanisms, and computational design are used to transfer the solutions found in nature to architectural designs. The data obtained by analyzing the biomimicry approach, the biological phenomena of nature, and the architectural research based on these phenomena and what topics they cover in energy efficiency are presented through data visualization. In this paper, "information analysis techniques" were used. It can be observed that the architectural studies interact with nature in the framework of a technological perspective and that architecture, biology, and technology are closely linked.
Biomimetics 2022, 7, x FOR PEER REVIEW 12 of 15 sources. The common feature of all these studies is that they aim to minimize the damage to nature, reduce energy consumption, and produce energy-efficient, zero-energy buildings. In this context, it is seen that biomimetic design offers many opportunities for energy-efficient buildings. The main reason why the examined studies mostly focus on the building envelope is that this has properties that require the control of various environmental factors such as ventilation, humidity, heat, light, and mechanical stress, just like shells, the skin, and surfaces in nature. Nature has the potential to provide unlimited examples for the production of sustainable, adaptive, adaptable, and energy-efficient buildings.
According to the Sankey diagram ( Figure 12), more than 70% of the approaches to solving the energy problem in buildings are problem oriented. Concepts such as simulations, parametric models, kinetic mechanisms, and computational design are used to transfer the solutions found in nature to architectural designs. The data obtained by analyzing the biomimicry approach, the biological phenomena of nature, and the architectural research based on these phenomena and what topics they cover in energy efficiency are presented through data visualization. In this paper, "information analysis techniques" were used. It can be observed that the architectural studies interact with nature in the framework of a technological perspective and that architecture, biology, and technology are closely linked.

Conclusions
Biomimicry is a novel approach, and there has been very little research carried out in this area. The increased number of recently published articles demonstrates that there has been notable research in this area. Challenges in energy and climate change have led researchers to establish nature-based designs that demonstrate the importance of biomimicry in today's world. The analysis of the WoS database revealed that, in recent years, there has been notable growth in the number of publications on this topic. Germany, the United Kingdom, and Australia have the most significant influence on biomimicry research. The University of Stuttgart has the greatest number of publications and citations. According to the detailed analysis of the papers, it was found that most of the studies Figure 12. Sankey diagram of the biomimetic approach, biological phenomena, transition to architecture, and issues to be solved.

Conclusions
Biomimicry is a novel approach, and there has been very little research carried out in this area. The increased number of recently published articles demonstrates that there has been notable research in this area. Challenges in energy and climate change have led researchers to establish nature-based designs that demonstrate the importance of biomimicry in today's world. The analysis of the WoS database revealed that, in recent years, there has been notable growth in the number of publications on this topic. Germany, the United Kingdom, and Australia have the most significant influence on biomimicry research. The University of Stuttgart has the greatest number of publications and citations.