Mapping Smart Materials’ Literature: An Insight between 1990 and 2022

Abstract

The field of smart materials (SMs) is an area of great interest in the scientific community and one that is growing considerably from year to year due to the features this field brings to the development of high-performance products and applications. Considering these aspects, researchers choose to contribute to this field, and every year, an increasing number of scientific publications appear in the databases. Based on this consideration, the present paper approaches the domain of SMs from a quantitative perspective by carrying out a bibliometric analysis to provide young researchers with a mapping of the most important aspects, as well as the evolution of the field. The bibliometric analysis was carried out in the time frame 1990–2022 in the Web of Science (WoS) database, finding only selected research and review articles based on the most relevant keywords used in the domain. Based on the large number of results identified (8998 publications), the authors designed a classification of the most important aspects of bibliometric analysis.

1. Introduction

The field of SMs is progressively attracting researchers from around the world as a consequence of the extraordinary properties and potential that this relatively new category of materials has to develop products and applications that meet today’s requirements and contribute to sustainable development in the years to come. At the same time, this is a young field, and further research and analysis of its characteristics and properties is vital. According to a retrospective analysis of the literature, the term “smart materials” was first found in the 1980s, when the foundations of the domain were laid, and increasingly more publications gradually appeared in the literature dealing with this area. The use of this term and the subsequent formation of the field of SMs was not coincidental, as a number of products offering smart behavior, such as photochromic glasses or shape memory materials (SMM), in particular Ni-Ti-based shape memory alloys (SMAs), had been available since the 1960s. All these have laid the foundations and prepared the formation of the field of SMs, emerging as a natural evolution based on previous research [1].

Also, an important aspect that needs to be considered to create a complete overview of the research domain is to provide a clear definition of what SMs or intelligent materials are. Since the field is a relatively new one in the growing area, has not yet reached maturity, and has not established a clear boundary in terms of manufacturing methods, fields of use, and specific characteristics, researchers in this domain have not reached a unanimously accepted definition [2,3]. This issue is also specific to other new and emerging fields such as soft robotics [4] or Industry 4.0 [5]. However, within the literature, a number of authors and entities have proposed several definitions that will be pointed out below. NASA defined them as “materials that can remember different forms and able to reconcile with particular stimuli, or it can be defined as highly engineered materials which can react smartly to their environment” [6,7]. Another definition proposed by several researchers claims that they are materials that can regain their original shape when they come into contact with stimuli from the external environment and have a smart response that can be controlled [1,7]. Another definition has also been proposed in the context of the field of chemical technology, which appeared in the Encyclopedia of Chemical Technology: “Smart materials and structures are those objects that sense environmental events, process that sensory information, and then act on the environment” [8]. From these definitions, it is, of course, possible to identify a number of common characteristics. It is certain that intelligent materials have an active response in the presence of environments with considerable specific characteristics compared to other materials. The intrinsic characteristics of these intelligent materials, which may be alloys, substances, or various compounds, are by virtue of and identifiable from within their molecular structure. In fact, we can affirm that they are materials that produce motion or create actions that can be in similarity to biological finite [7,8,9].

Although this field dates back more than 50 years ago, with achievements in different forms, characteristics, and applications, we can affirm that this field has become one of great interest and topicality among the scientific community as well as society approximately 10 years ago. The domain of intelligent materials has developed a natural path over the years as these technologies have proven their potential and have been accepted by the materials science community, progressively attracting scientists, researchers, and engineers to actively contribute. Such facts are identified in a growing number of publications, special conference sessions, research projects, research laboratories, international collaborations, Special Issues of specialist journals, as well as in social events and activities.

Analyzed from an applications perspective, with the development of the field of SMs and the emergence of new categories of materials, their applications have been integrated into a growing range with considerable potential. Various important smart materials such as shape memory alloys/polymers, magneto and electrorheological fluids, hydrogels, dielectric elastomers, or self-healing materials are materials that can produce motion similar to actuators; therefore, these have an important application in the field of soft robotics. Shape memory alloys, commercially called Nitinol, based on nickel–titanium alloys, contribute considerably to the medical field, namely in the realization of wearable exoskeleton-type devices in general for upper limb rehabilitation following brain trauma [10,11] or the use of alloys in combination with elastomeric mass to fulfill the purpose of a gripper [12]. Also, shape memory polymers possess applicability in various prehension or locomotion systems [13]. Electro or magnetorheological fluids encompass the ability to react to magnetic or electrical stimuli, and based on this principle, they are used as actuators in various locomotion or prehension systems [14], as well as making sensors with applications in the medical industry [15]. The field of hydrogels is attracting the attention of more researchers as a material with biocompatible properties intensively used in the medical field, more specifically in transport systems by delivering drugs into the body and also in their progressive release [16]. Dielectric elastomers are made from a thin polymer sheet coated with compliant electrodes. When supplied with electrical voltage, a voltage difference is produced, which induces an electrostatic pressure at the two electrodes, thus allowing a compression movement. Such materials are widely used as actuators in soft robotics for locomotion, gripping, or wearable device applications [17]. Self-healing materials are developing rapidly and attracting increasing interest from researchers. They have the ability to self-heal and are most widely used in the electronics, construction, and biomedical industries [18]. A number of applications are those of sensors, actuators, bio-inspired robots, skin electronics, shape memory composites, and drug delivery where self-healing materials are implemented [19]. Of course, only some of the applications of smart materials that have been implemented in applications in various fields have been analyzed, thus creating the multidisciplinary context of the field.

Over the years, several authors have sought to organize and systematize the technical content of achievements in the domain of intelligent materials, resulting in a series of review articles that provide a qualitative perspective on the field. However, the present paper aims to provide and treat a different perspective on the field of SMs by conducting a bibliometric analysis that provides a quantitative overview of this research area. One of our objectives is to scientometrically analyze via the Web of Science database the field of SMs and provide researchers with a map of the evolution of the field in terms of number of publications per year, characteristic words, regions, most productive institutions, representative authors, most important journals, and most cited research and review articles. Synchronously, this paper aims to provide information on the evolution, current, and future trends of the field based on current data analysis. All this valuable information designs an overall picture of the quantitative scientific status of the field of intelligent materials. From our analysis, this work is the first in the field of intelligent materials research to address this type of quantitative analysis.

2. Methodology

The bibliometric analysis is composed of three key components: (1) establishing a well-defined scope [20], (2) accessing library data [21], and (3) employing a designated technique model [22]. Based on these elements, the analysis started on 8 February 2023, (1) identifying the most relevant building blocks of the domain of SMs; these include the global contributions, leading nations, institutional influence, prominent research domains, eminent editors, and authors, as well as top-tier journals. Furthermore, the data were sourced (2) from the WoS (international multidisciplinary database), and (3) the chosen technique model [12] adheres closely to conventional bibliometric/scientometric methodologies [20,21,23,24]. Although this approach allowed for a focused search based on strict criteria, it is important to note that some related publications may not have been included. The search analysis is based on a number of six sub-datasets in WoS which are Science Citation Index Expanded (SCIE) 1900–present, Social Sciences Citation Index (SSCI) 1900–present, Arts & Humanities Citation Index (A&HCI) 1975–present, Emerging Sources Citation Index (ESCI) 2005–present, Conference Proceedings Citation Index-Science (CPCI-S) 1990–present and Conference Proceedings Citation Index-Social Sciences and Humanities (CPCI-SSH) 1990–present. Furthermore, the journal impact factor (JIF) data was extracted from Journal Citation Reports 2021, a resource available via WoS.

Additionally, the methodology approached in the bibliometric analysis is shown below (Figure 1).

3. Results and Discussion

3.1. Keywords Analysis

Figure 2 illustrates the number of articles published each year from 1990 to 2022, classified according to six keywords. Each keyword is represented by a bubbles which increase or decrease in size according with the number of publications per years. The starting year of 1990 was chosen because of the limitations of the WOS database related to old literature [25] and also because of a relatively small number of publications appearing in the starting period. Due to the large number of publications found and the considerable variety of materials, and applications with applications in various fields, the variety of keywords is also dense and diverse, making it necessary to select the most relevant keywords characteristic of the domain. The selection was made mainly according to the total number of publications on each keyword. Therefore, the first six keywords with the most articles found were selected to better cover the dozens of types of materials. Among the 8991 articles identified, “smart materials” was the most frequently used keyword, arising in 6193 articles, accounting for 68.826% of the total, followed by “stimuli-sensitive materials”, which was found in 1286 articles, accounting for 14.303% of the total, while “intelligent materials” appeared in 708 articles, namely 7.874% of the total. Moreover, the majority of articles, 8801 in total, were written in English, which accounted for 97.886% of all articles. In contrast, only 121 (1.345%) articles were written in Chinese and 24 (0.266%) articles were written in Japanese. Indeed, the predominance of articles written in English comes primarily from the objective of disseminating research results worldwide, thereby resulting in the growth of the intellectual and social systems.

3.2. Publications Evolution

The graph in Figure 3 highlights the upward trend in the field of SMs, as shown by the two curves that provide a comprehensive overview of the quantitative evolution of the production of scientific articles in this field. The green curve displays the evolution of the number of publications per year, while the blue curve represents the cumulative evolution of articles published each year; by summing them up, almost 9000 publications were found. An in-depth observation of the graph shows three development intervals in which the domain of intelligent materials has developed as the production of scientific articles. The first interval is from 1990 to 2010, in which the field experienced a relatively slow growth in the number of scientific publications (1445, cumulative). The second interval is from 2011 to 2017, where the number of publications increased with a higher frequency, reaching in 2017 a number of 537 publications. The third interval is from 2018 to 2022, during which the field of SMs has seen a spectacular year-on-year growth exceeding the threshold of 1200 publications in 2022, representing 56% of the entire domain.

The spectacular increase in the number of publications in recent years highlights the growing interest of researchers in this field, which has implications in domains such as soft robotics, a field that has developed in close connection with the development of the field of SMs. This dramatic increase in the number of articles is driven by the intensification of research in the field of intelligent materials due to the rapid evolution of related fields such as materials, chemistry, and physics on the one hand, and on the other hand due to the identification of new applications of SMs such as medical applications based on shape memory alloys [26], or various locomotion applications based on magnetic particles inspired by biological systems [27]. Growth trends in SMs will continue until the domain reaches maturity and then saturation.

3.3. Global Contribution and Leading Countries

Table 1. The top 20 most productive countries in SM research during 1990–2022.

Rank	Countries	TAc 1	TC 2	ACPP 3
1	China	2837	95,654	33.72
2	USA	1851	107,577	58.12
3	Germany	649	25,583	39.42
4	India	546	12,334	22.59
5	Japan	478	21,397	44.76
6	Italy	441	13,156	29.83
7	United Kingdom	426	22,027	51.71
8	South Korea	384	12,842	33.44
9	France	344	14,299	41.57
10	Canada	320	11,544	36.11
11	Spain	292	10,327	35.37
12	Australia	260	11,119	42.77
13	Iran	224	5302	23.67
14	Singapore	191	11,292	59.12
15	Russia	171	4241	24.8
16	Poland	170	2823	16.61
17	Netherlands	157	10,614	67.61
18	Switzerland	143	8063	56.38
19	Portugal	133	3550	26.69
20	Brazil	132	2930	22.2

¹ TAc, total articles per country; ² TC, total citations; ³ ACPP, average citations per publication.

highlights the top 20 countries contributing to the research of SMs. It can be seen that the first position is occupied by China with an impressive number of 2837 articles, the second by the USA with 1851 articles, and Germany ranks third with 649 articles. There are several reasons why these countries are in the top positions, and one of them is related to the initiation of dedicated MS funding programs such as Horizon 2020—H2022-NMBP-2016–2017, funded by the European Commission. An additional reason may be related to the large population in these countries and thus the number of people involved in research, which allows them to publish a large number of papers in all fields, especially new and emerging ones.

In terms of total citations, the USA ranks first with 107,577 citations and a distributed average per article of 58.12%, and China ranks second with 95,654 citations and an average per article of only 33.72%; furthermore, Germany had 25,583 citations and an average per article was 39.42%. It should be noted that the impact of China per publication is relatively low compared to the USA and Germany, which have a lower number of articles. This cannot be explained exactly, but there may be a number of reasons related to the language barrier, a late entry of China into the field, and/or the quality of the research.

Figure 4 illustrates the global map, highlighting the top 20 countries in publication sharing from 1990 to 2022 on an orange scale intensity. At this point, China took the top spot, accounting for a significant 31.53% of the world, followed by the USA at 20.57%, and the third place is held by Germany at 7.21%. However, the population and size of these countries are important factors in their accounting, so Germany has less population and area compared to China and the USA. Still, their sharing publication rate of 7.21% is impressive. Then, summing up the share of publications by continent, we see Asia covering more than half with 53.69%, followed by Europe with 25.89% and North America with 24.14%. Additionally, the map presents a holistic representation of the international contributions and influence of various countries in the research of SMs over time, showcasing their global reach and impact.

Drawing upon data-driven insights from Figure 4, our investigation delved into the developmental trajectory of China, the USA, and Germany in the SM field from 1990 to 2022. Subsequently, Figure 5 below presents the evolving interest of these countries by their number of published articles and the trendlines for each. Upon careful analysis of the graph, we observed the emergence of the USA as the sole active country in 1990 and 1995, leading the way with a total of 13 published articles. This established the initial publications in the SMs field. In the years 2000 and 2005, the USA maintained its lead with a total of 47 articles, accounting for 58.02% of the combined publications by these countries. However, during this period, China entered the scene with 19 articles (23.46%), while Germany also made its mark with 15 articles (18.52%). The years that came, 2010 and 2015, emerged as particularly significant, witnessing substantial growth and evolution in the domain of SMs. Here, the USA held the lead until 2015 with 92 articles (38.49%), but China surpassed it in the same year with 112 articles (46.86%), marking a notable moment in the domain’s evolution. Furthermore, in the same year, Germany contributed 35 articles (14.64%) to the overall publication output. The subsequent years examined, 2020 and 2022, revealed an interesting development driven by China. In 2020, China published 359 articles, followed by an impressive 532 articles in 2022, totaling 891 articles and accounting for a substantial 65.08% of the published output. In contrast, the USA published a total of 335 articles, contributing 24.47%, while Germany published 143 articles (10.45%) during the same period. China’s significant growth in 2015 exemplifies its strong interest and investment in the domain, driven by the anticipation of the versatile applications of SMs across various domains, such as biomedical and healthcare, energy and environment, robotics, and automation, but are not limited to these. We also anticipate that the USA will continue to follow China in the coming years. Still, Germany’s position may face challenges as countries like India (6.07%), Japan (5.31%), and Italy (4.90%) display a keen interest in the domain. While China’s publication output continued to grow steadily during the SARS-CoV-2 pandemic, both the USA and Germany experienced a decline. This suggests China’s ability to adapt and prioritize research efforts, while the decrease in output for the USA and Germany can be attributed to various factors such as disruptions in research activities, resource constraints, and shifting priorities caused by the pandemic’s impact on global research institutions.

3.4. Contribution of Leading Institutions

Table 2. The top 20 most productive institutions in SM research.

Rank	Institutions	TAi 1	TAi/TAk 2 [%]	TC	ACPP	Country
1	Chinese Academy of Sciences	392	4.357	18,030	45.93	China
2	Centre National de la Recherche Scientifique	217	2.412	9609	44.28	France
3	Harbin Institute of Technology	149	1.656	7362	49.941	China
4	Indian Institute of Technology System	147	1.634	2980	20.27	India
5	Udice French Research Universities	146	1.623	7496	51.34	France
6	Tsinghua University	129	1.434	6257	48.5	China
7	University of California System	123	1.367	8388	68.2	United States
8	Sichuan University	122	1.356	4382	35.92	China
9	University System of Ohio	107	1.189	5403	50.5	United States
10	Swiss Federal Institutes of Technology	103	1.145	5403	52.46	Switzerland
11	University of Science Technology of China	102	1.134	3378	33.12	China
12	Zhejiang University	102	1.134	6644	65.14	China
13	Consiglio Nazionale Delle Ricerche	101	1.122	3118	30.87	Italy
14	Helmholtz Association	101	1.122	3926	38.87	Germany
15	University of Chinese Academy of Sciences	100	1.111	3487	34.87	China
16	Nanyang Technological University	97	1.078	6851	70.63	Singapore
17	Russian Academy of Sciences	95	1.056	2284	24.04	Russia
18	Shanghai Jiao Tong University	93	1.034	2593	27.88	China
19	Jilin University	88	0.978	3047	34.63	China
20	N8 Research Partnership	85	0.945	4396	51.72	United Kingdom

¹ TAi, total article per institution; ² TAk, total articles found by keywords.

analyzes the top 20 most productive institutions worldwide in the domain of SMs. As can be seen in Table 1, China is the most productive country in terms of the total number of publications; the most productive institution is the Chinese Academy of Sciences, with a total of 392 publications, representing a percentage of 4.357% of the whole field, totaling 18,030 citations. In second place is the National Centre for Scientific Research in France, with a total of 217 publications, representing 2.412% of the whole field. As far as citations are concerned, they are about half the number of citations of the first-place institution, with 9609 citations. In third position is an institution also from China, namely the Harbin Institute of Technology, with a total of 149 publications representing 1.656% of the field, while the number of citations is 7362. Within this ranking, China delivers nine institutions with an impressive number of articles, as well as citations. The ranking also includes institutions from countries such as India, the USA, Switzerland, Italy, Germany, Russia, and last but not least, Singapore, which is ranked 16th but has an average citation per publication of 70.63% and is ranked first by this criterion. This can provide insight into the quality and impact of the results achieved by Nanyang Technological University of Singapore.

3.5. Contribution of Leading Research Areas

The distribution of 8991 articles in 96 research areas illustrates the multidisciplinary domain of these intelligent materials; for this reason of spreading over many research areas, we listed in

Table 3. Contribution of the top 20 research areas in the SM domain.

Rank	Research Area on WoS	TAra 1	TAra/TAk [%]	TC	ACPP
1	Materials Science	4412	49.033	172,254	39.04
2	Chemistry	2905	32.285	141,909	48.85
3	Engineering	1818	20.204	54,257	29.84
4	Science Technology Other Topics	1480	16.448	81,638	55.16
5	Physics	1477	16.415	66,301	44.89
6	Polymer Science	1121	12.458	38,383	34.24
7	Instruments Instrumentation	542	6.024	16,814	31.02
8	Mechanics	455	5.057	10,445	22.96
9	Metallurgy Metallurgical Engineering	232	2.578	5254	22.65
10	Biochemistry Molecular Biology	165	1.834	5556	33.67
11	Energy Fuels	133	1.478	6516	48.99
12	Automation Control Systems	131	1.456	4785	36.53
13	Computer Science	127	1.411	2483	19.55
14	Optics	113	1.256	2158	19.1
15	Mathematics	101	1.122	1720	17.03
16	Pharmacology Pharmacy	94	1.045	5656	60.17
17	Electrochemistry	92	1.022	2997	32.58
18	Robotics	81	0.900	2739	33.81
19	Acoustics	74	0.822	1252	16.92
20	Biotechnology Applied Microbiology	69	0.767	2550	36.96

¹ TAra, total articles in the specific research area.

the contribution of the top 20 research areas. It was obvious and natural that the main field of intelligent materials research is related to materials research areas. Therefore, according to Table 3, the domain of materials science occupies the first position with a total of 4412 articles representing approximately half of the total publications, i.e., 49.071% of the publications found. In terms of citations, a considerable number of citations were accumulated, namely 172,254 citations, with an average per citation of 39.04%. The second domain was chemistry, with a total of 2905 articles representing 32.285% of the total publications and a total of 141,909 citations with an average per citation of 48.85%. The field of chemistry is relevant and representative of the domain of intelligent materials because the intelligence of the material comes from within the molecular structure of the material. The third area is engineering, where specific applications of SMs are predominantly addressed, the first two being mainly oriented toward the development of new materials. Furthermore, the research area of engineering contributes with 1818 articles representing 20.220% of the total publications and a total of 54,257 citations with an average of citation per publication of 29.84%.

There is a wide diversity of research areas contributing to this field; some of them are areas related to materials science and chemistry such as polymer science, metallurgical engineering, molecular biochemistry, electrochemistry, and applied biotechnology/microbiology; on the other hand, some are application-oriented research areas such as robotics, acoustics, optics, automatic control systems, mechanics, and computer science.

3.6. Leading Publishers

Table 4. The top 20 publishers in the SM field.

Rank	Publisher	TAp 1	TAj/TAk [%]	TC	ACPP
1	Elsevier	2348	26.095	93,821	39.96
2	Wiley	1369	15.214	67,568	49.36
3	Amer Chemical Soc	901	10.013	39,072	43.37
4	Royal Soc Chemistry	756	8.402	42,518	56.24
5	Springer Nature	596	6.624	25,866	43.4
6	MDPI	457	5.079	8694	19.02
7	Iop Publishing Ltd.	373	4.145	12,036	32.27
8	Sage	282	3.134	6458	22.9
9	Taylor & Francis	203	2.256	4349	21.42
10	IEEE	124	1.378	4340	35
11	Science Press	91	1.011	998	10.97
12	Frontiers Media Sa	72	0.800	1179	16.38
13	ASME	50	0.556	499	9.98
14	Amer Inst Physics	49	0.545	1493	30.47
15	Nature Portfolio	44	0.489	1820	41.36
16	Chinese Acad Sciences	41	0.456	221	5.39
17	World Scientific	39	0.433	541	13.87
18	Techno-Press	34	0.378	269	7.91
19	Emerald Group Publishing	30	0.333	654	21.8
20	Trans Tech Publications Ltd.	30	0.333	167	5.57

¹ TAp, total articles per publisher.

presents the top 20 publishers in the field of SMs, encompassing both multidisciplinary and technical publishers. Elsevier holds the first position with 2348 publications, accounting for 26.115% of the total publications identified using the initial keywords; these publications have received a total of 93,821 citations. Wiley ranks second with 1369 publications, representing 15.226%, and garnering a total of 67,568 citations. The third position is occupied by Amer Chemical Soc, with 901 publications accounting for 10.021% and accumulating 39,072 citations. Other notable publishers in the list include Springer Nature, MDPI, IOP, Sage, and IEEE, among others.

3.7. Contribution of Leading Authors

In terms of the most important authors contributing to the research of SMs (

Table 5. Contribution of the top 20 authors in SM research.

Rank	Author	Country	TAa 1	TC	ACPP	h-Index
1	Zhang Yu	China	69	2985	43.26	24
2	Liu Yu	China	67	1969	29.39	26
3	Leng Jinsong	China	66	4775	72.35	30
4	Wang Yong	USA	61	1398	22.92	19
5	Liu Yijun	China	59	4658	78.95	30
6	Lanceros-Mendez Senentxu	Spain	57	1819	31.91	22
7	Wang Li	China	57	2897	50.82	27
8	Wang Wen	China	49	2491	50.84	24
9	Wang Joseph	USA	47	1524	32.43	24
10	Zhang Jun	China	44	960	21.82	19
11	Zhang Lu	China	44	1036	23.55	18
12	Wang Hai	China	41	1619	39.49	20
13	Li Yi	China	40	1614	40.35	20
14	Li Jun	China	37	874	23.62	18
15	Li Li	China	37	1065	28.76	18
16	Chen Yu	China	36	787	21.86	17
17	Li Quan	China	36	2142	59.5	20
18	Kim Jungwook	USA	35	2072	59.2	23
19	Liu Jian	China	33	893	27.06	16
20	Zhang Qi	China	33	964	29.21	17

¹ TAa, total articles published by the author.

), the ranking is governed by authors from China. This is somewhat natural, as China ranks first by a significant margin among the top most productive countries, as evidenced by a number of recent studies confirming China’s supremacy in scientific research [28,29]. The top three authors in the ranking, Zhang Yu, Liu Yu, and Leng Jinsong, have published a close number of articles, respectively 69, 67, and 66 publications, but significant differences appear in citations, where Leng Jinsong (third place) leads with a total of 4775 citations, which can confirm the quality and interest of researchers in the results obtained by this author.

3.8. Leading Journals

Table 6. Top 20 journals in SMs domain.

Rank	Journal	TAj 1	TAj/TAk [%]	TC	JIF 2021 2	JIF5 3	JIF Quartile 4
1	Composites Science and Technology	238	2.645	11,852	9.788	8.788	Q1
2	ACS Applied Materials & Interfaces	235	2.612	8824	10.383	10.382	Q1
3	Smart Materials and Structures	230	2.556	6662	4.131	4.253	Q2
4	Composites Part B-Engineering	214	2.378	8280	11.322	10.133	Q1
5	Journal of Intelligent Material Systems and Structures	191	2.123	4968	2.774	2.734	Q3
6	Advanced Functional Materials	179	1.989	11,470	19.924	19.978	Q1
7	Advanced Materials	171	1.900	19,139	32.086	32.095	Q1
8	Angewandte Chemie International Edition	132	1.467	10,421	16.823	15.311	Q1
9	Composites Part A Applied Science and Manufacturing	118	1.311	4799	9.463	9.224	Q1
10	Polymers	95	1.056	2562	4.967	5.063	Q1
11	Journal of Materials Chemistry C	88	0.978	3415	8.067	7.642	Q1
12	Materials	88	0.978	1391	3.748	4.042	Q3
13	Soft Matter	80	0.889	3683	4.046	3.895	Q2
14	Journal of the American Chemical Society	72	0.800	3974	16.383	16.289	Q1
15	Polymer	69	0.767	1793	4.432	4.161	Q1
16	Polymer Chemistry	67	0.745	2467	5.364	5.056	Q1
17	Macromolecular Rapid Communications	66	0.733	2240	5.006	4.809	Q1
18	Chemistry A European Journal	65	0.722	1954	5.02	4.822	Q2
19	RSC Advances	65	0.722	1654	4.036	3.748	Q2
20	European Polymer Journal	58	0.645	1301	5.546	5.006	Q1

¹ TAj, total articles published by the journal; ² JIF2021, journal impact factor in 2021; ³ JIF5, journal impact factor in five years; ⁴ JIF quartile, journal impact factor quartile.

provides an overview of the prominent journals that publish papers in the domain of SMs and related areas; thus, “Composites Science and Technology” takes the lead, with 238 articles accounting for 2.647% of the total publications identified. These articles have received a cumulative number of 11,852 citations and fall under category quartile 1. The next journal “ACS Applied Materials & Interfaces” secures the second position, with 235 articles representing 2.613% and a total of 8824 citations, similar to the first journal; it is also classified under category quartile 1. “Smart Materials and Structures” claims the third spot, with 230 publications accounting for 2.558% and 6662 citations, placed in quartile 2. Although these specialized journals exhibit similar publication numbers, their citation counts differ. In terms of impact factor, the journal “Advanced Materials” holds a significantly higher ranking compared to other journals, with an impact factor of 32. Despite ranking seventh in terms of publication count, it acquires the top position in terms of citations (19,139) and falls under category quartile 1. This highlights the substantial research interest in papers published within this journal.

3.9. Most Cited Articles

Also, in mapping a field, an important component is to identify the most important and referenced publications in the domain. In the case of SMs, such a table has been produced to provide researchers with the most relevant publications. This classification can be found below in

Table 7. The top 20 most cited publications during the period of 1990–2022 in the SM field.

R 1	Title	Author	Journal	Year	Country	TC	Ref.
1	Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials	Holtz, JH and Asher, SA	Nature	1997	USA	1745	[30]
2	Nanostructured Tungsten Oxide—Properties, Synthesis, and Applications	Zheng, HD et al.	Advanced Functional Materials	2011	Australia	1074	[31]
3	Mechanically induced luminescence changes in molecular assemblies	Sagara, Y and Kato, T	Nature Chemistry	2009	Japan	1012	[32]
4	MR fluid, foam and elastomer devices	Carlson, JD, Jolly, MR, and	Mechatronics	2000	USA	986	-
5	A reversibly antigen-responsive hydrogel	Miyata, T; Asami, N and Uragami, T	Nature	1999	Japan	945	-
6	A model of the behavior of magnetorheological materials	Jolly, MR; Carlson, JD and Munzo, BC	Smart Materials & Structures	1996	USA	682	-
7	4D Printing: multi-material shape change	Tibbits, S	Architectural Design	2014	USA	673	-
8	Mechanoresponsive Luminescent Molecular Assemblies: An Emerging Class of Materials	Sagara, Y et al.	Advanced Materials	2016	Japan	663	-
9	Synthesis, properties, and applications of graphene oxide/reduced graphene oxide and their nanocomposites	Simth, AT et al.	Nano Materials Science	2019	USA	650	-
10	Non-medical applications of shape memory alloys	Van Humbeeck, J	Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing	1999	Belgium	585	-
11	Large-scale MR fluid dampers: modeling and dynamic performance considerations	Yang, G et al.	Engineering Structures	2002	USA	575	-
12	Rapid self-healing hydrogels	Phadke, A et al.	Proceedings of the National Academy of Sciences of the United States of America	2012	USA	565	-
13	Covalent Adaptable Networks (CANS): A Unique Paradigm in Cross-Linked Polymers	Kloxin, CJ et al.	Macromolecules	2010	USA	553	-
14	Nanofabricated media with negative permeability at visible frequencies	Grigorenko, AN et al.	Nature	2005	England	539	-
15	Advances in piezoelectric finite element modeling of adaptive structural elements: a survey	Benjeddou, A	Computers & Structures	2000	France	529	-
16	Recent advances in mechanochromic luminescent metal complexes	Zhang, XQ et al.	Journal of Materials Chemistry C	2013	China	527	-
17	A hallow fibre reinforced polymer composite encompassing self-healing and enhanced damage visibility	Pang, JWC and Bond, IP	Composites Science and Technology	2005	England	518	-
18	Fast-moving soft electronic fish	Li, TF et al.	Science Advances	2017	China	509	-
19	Formation of asymmetric one-sided metal-tipped semiconductor nanocrystal dots and rods	Mokari, T et al.	Nature Materials	2005	Israel	475	-
20	Cradle-to-cradle design: creating healthy emissions—a strategy for eco-effective product and system design	Braungart, M, McDonough, W, and Bollinger, A	Journal of Cleaner Production	2007	Germany	472	-

¹ R, rank.

, where the top 20 research publications are ranked according to the number of citations, representing somewhat the impact and relevance of that publication accumulated over time and validated by various researchers. The most cited article in the ranking is that of the American authors Holtz, JH and Asher, SA, published in 1997 in the journal Nature entitled “Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials”, which has accumulated 1745 citations by 2022. The article deals with issues related to creating SMs with adjustable optical properties, offering responsiveness and visual indications in response to specific chemical signals. These adaptable materials can be used in diverse applications, including chemical sensing, biomedical diagnostics, and other fields that demand sensitive and versatile materials [30]. In the second position is an article published more recently in the year 2011 in the journal “Advanced Functional Materials” entitled “Nanostructured Tungsten Oxide—Properties, Synthesis, and Applications”, which addressed nanostructured tungsten oxides (WOx) known for their chromism, photocatalysis, and sensing capabilities, it also considered vital elements in advancing functional materials and smart devices. Moreover, its potential stands on unlocking new material functionalities, particularly in terms of adaptability and versatility [31]. Since 2011, on the WoS database, the article has been cited 1074 times. At a relatively small difference from the second position in terms of citations, the Japanese authors Sagara, Y and Kato, T are in third position with their article “Mechanically induced luminescence changes in molecular assemblies” on piezochromic luminescent materials; these materials exhibit changes in their luminescent color in response to mechanical stimuli. Their potential stands for being used in sensors, memory devices, and displays, and furthermore, their adaptability is vital for crafting novel SMs [32]. Published in 2009 in the journal “Nature Chemistry”, it managed to reach the top of the reference articles in the field of SMs with a number of 1012 citations. These articles underscore the complex nature of SM development. However, they also offer valuable insights into working with nanoscale materials and present intriguing applications for their utilization. As top articles in the field, they represent the core of the SM domain, likely to remain influential for a considerable period.

It is thought-provoking to note that from the above table a relatively large number of USA authors appear in this ranking compared to Chinese authors. One possible reason could be that the two countries (“Country” represents the country of affiliation of the first author’s institution) have approached the field of SMs at different time intervals, which provided the USA authors a substantial advantage (supported by Figure 4). This can be seen from the year of publication of the articles, that of the USA co-authors were published around 1996–2012, and that of the China author collective being published more recently (2013, 2017). In addition to these insights, it is worth noting that German authors are absent from the top rankings despite their third-place position among the top countries. Also, the ranking of the Japanese collectives is remarkable and at the top of the ranking.

3.10. Most Cited Reviews

Table 8. The top 20 most cited reviews during the period of 1990–2022 in SM domain.

R	Title	Author	Journal	Year	Country	TC	Ref.
1	Mesoporous materials for drug delivery	Vallet-Regi, M, Balas, F, and Arcos, D	Angewandte Chemie- international edition	2007	Spain	2096	[33]
2	Visible-light driven heterojunction photocatalysts for water splitting—a critical review	Moniz, SJA et al.	Energy & Environmental Science	2015	England	1736	[34]
3	Stable metal-organic frameworks: design, synthesis, and applications	Yuan, S et al.	Advanced Materials	2018	USA	1701	[35]
4	Using the dynamic bond to access macroscopically responsive structurally dynamic polymers	Wojtecki, RJ et al.	Nature Materials	2011	USA	1220	-
5	Biomimetic super-lyophobic and super-lyophilic materials applied for oil/water separation: a new strategy beyond nature	Wang, B et al.	Chemical Society Reviews	2015	China	1187	-
6	Making molecular machines work	Browne, WR and Feringa, BL	Nature Nanotechnology	2006	Netherlands	1145	-
7	Future perspectives and recent advances in stimuli-responsive materials	Roy, D, Camber, JN, and Sumerlin, BS	Progress in Polymer Science	2010	USA	1132	-
8	Flexible nanodielectric materials with high permittivity for power energy Storage	Dang, ZM et al.	Advanced Materials	2013	China	1086	-
9	Shape-memory polymers and their composites: stimulus methods and applications	Leng, JS et al.	Progress in Materials Science	2011	China	1079	-
10	Nanostructured functional materials prepared by atom transfer radical polymerization	Matyjaszewski, K and Tsarevsky, NV	Nature Chemistry	2009	USA	1039	-
11	Growth factor delivery-based tissue engineering: general approaches and a review of recent developments	Lee, K, Silva, EA, and Mooney, DJ	Journal of the Royal Society Interface	2011	USA	975	-
12	Programmable materials and the nature of the DNA bond	Jones, MR, Seeman, NC, and Mirkin, CA	Science	2015	USA	964	-
13	New directions in thermoresponsive polymers	Roy, D, Brooks, WLA, and Sumerlin, BS	Chemical Society Reviews	2013	USA	956	-
14	Recent advances in shape-memory polymers: structure, mechanism, functionality, modeling and applications	Hu, JL et al.	Progress in Polymer Science	2012	China	939	-
15	Recent progress in shape memory polymer: New behavior, enabling materials, and mechanistic understanding	Zhao, Q, Qi, HJ, and Xie, T	Progress in Polymer Science	2015	China	927	-
16	Bioresponsive materials	Lu, Y et al.	Nature Reviews Materials	2017	USA	884	-
17	Functional soft materials from metallopolymers and metallosupramolecular polymers	Whittell, GR et al.	Nature Materials	2011	England	828	-
18	Thermoresponsive Polymers for Biomedical Applications	Ward, MA and Georgiou, TK	Polymers	2011	England	806	-
19	Prussian Blue and its analogues: Electrochemistry and analytical applications	Karyakin, AA	Electroanalysis	2001	Russia	794	-
20	Magnetorheological fluids: a review	de Vicente, J, Klingenberg, DJ, and Hidalgo-Alvarez, R	Soft Matter	2011	Spain	762	-

shows the top most cited review articles this time. Mainly, these articles review a set of research-type articles addressing a specific topic. From the table below, somewhat naturally, these types of articles have appeared more recently but have seen a more accelerated increase in citations than the research-type articles. In this top list, the first position is held by a collective from Spain published in 2007 in the journal “Angewandte Chemie-international edition” entitled “Mesoporous materials for drug delivery”, which addressed silica-based materials like SBA-15 and MCM-48 that exhibit bioceramic properties, making them ideal for bone repair applications. Moreover, certain mesoporous materials have shown intelligent behavior, adjusting to changes in pH, temperature, magnetic fields, and specific light wavelengths. This breakthrough results from the synergy between material science and biomedical applications, holding a lot of promise for advancing medical treatments and improving patient outcomes [33]. From 2007 to 2022, this article has accumulated a significant number of citations (2096). In second position with 1736 citations is the article entitled “Visible-light driven heterojunction photocatalysts for water splitting—a critical review”, written by a team from England and published in 2015 in the journal “Energy & Environmental Science”, where a comprehensive exploration is undertaken to examine the feasibility of harnessing SMs for the development of efficient and eco-friendly energy production methods, moreover the study investigates how these advanced materials can propel the progress of semiconductor-based applications [34]. In third place is an article published in the journal “Advanced Materials” in 2018 with a rapid increase in citations written by a team from the USA. It is titled “Stable metal-organic frameworks: design, synthesis, and applications”, which describes metal-organic frameworks (MOFs) being another class of porous materials crafted with metal nodes and organic linkers. Their potential stands in practical applications, such as gas storage and separation, chemical sensing, and biomedical uses. An area of importance in MOF research is focused on improving their stability (particularly in harsh conditions), making them not only versatile but also durable for industrial-scale applications [35]. It is noteworthy that among these articles, two show significant potential for biomedical applications, while one focuses on green energy. Present growing interest in these materials is evident in countries such as China and the USA, where they are trying to provide solutions for evolving energy demand, as well as advances in medical treatments.

Likewise, in this classification, as in the table above, authors from the USA appear in large numbers, but this time, the appearance of articles by the Chinese authors’ collective was higher. In both Table 7 and Table 8, the articles address a wide variety of aspects of SMs.

4. Conclusions

This paper presents a bibliometric analysis of the scientific literature in the field of SMs. The authors have analyzed data retrieval from the WoS library, covering the period from 1990 to 2022. In recent years, from 2016 to 2022, there has been a consistent annual publication of over 100 research and review articles, signifying a robust growth trend in the domain; hence, the domain is on track to soon exceed 10,000 total publications. As the pioneering analysis of its kind, this study offers an overview of the most crucial bibliometric aspects, representing an important advance by enhancing the intellectual and social system in understanding the field of SMs. Via such a quantitative analysis and by providing a clear and relevant overview of the field, researchers, the academic community, policymakers, and others can help them comprehend the evolution of the field over time, the current status of the main contributors, and future opportunities.

The worldwide research interest in SMs is very distinct, with the production of scientific papers increasing year by year, especially in recent years, as shown in Figure 3, where the dynamics of the field can be observed. Of course, the motivation of researchers and funding institutions is based on the impact and potential that the development of this field has in the medical, social, defense, and other fields. Another aspect that made the development of the field as a synergistic and multidisciplinary field possible was mainly based on the development of materials science in general, chemistry, and engineering, which prepared the emergence of the SMs field as a natural and necessary evolution. This huge potential of the field was quickly understood by the Chinese researchers who expeditiously became the dominant force in terms of quantity in the field, although they joined the SMs field only very late. China has now overtaken the USA in terms of scientific publications output, productive institutions, and author contributions, followed by the USA and several other countries such as Germany, India, Japan, Italy, England, South Korea and France, which are actively involved in research and development in this field. This global involvement suggests a growing potential for collaboration between countries, fostering the accelerated development of SMs. The analysis also highlights prominent contributions by Chinese authors such as Zhang Yu, Liu Yu, and Leng Jinsong, who have obtained substantial citations. The research of their work can provide valuable insights for fellow researchers, lead to breakthroughs, and encourage collaboration among experts from different fields, including medicine, bioengineering, and beyond. However, the field of SM research is evolving and is an area of interest for more and more countries that are funding projects to develop this field with applications in the medical industry, defense, or commercial applications. This field is strongly influenced by the scientific contributions of authors from China, who joined relatively late (this can be seen in the most cited research/review articles) and have come to lead it today. Looking ahead, novel SMs and applications will drive further advancements, shaping the future of the field.