# Smart Textiles: A Review and Bibliometric Mapping
## 1 Introduction  
### Definition and Characteristics of Smart Textiles  
The interdisciplinary research of textile technology with materials science, chemistry, physics, microelectronics, computer science, biomedicine, optics, and other technologies has led to the development of technologically advanced textiles and garments based on advanced smart materials [1; 2]. The concept of intelligent or smart materials was defined in 1990 by [PERSON] [3] as \"materials which respond to environmental changes at the most optimum conditions and manifest their own functions according to the changes\". The same author set a clear differentiation of structural and functional materials versus intelligent materials. Various definitions of smart textiles appear in the literature, and different terms have been used for similar textile products, such as smart textiles, smart fabrics, smart clothing, smart garments, as well as functional textiles, functional clothing, intelligent textiles, interactive textiles, etc. [1; 4; 5]. For instance, one definition of smart fabric from NASA [4] was \"a traditional fabric with integrated active functionality\". Some authors even equated the terms smart and functional textiles, such as \"smart textiles or functional textiles are demarcated as textile constituents that are capable of changing their characteristic behaviour with response to the inspiration of peripheral features or technical stimuli from the surrounding environment\" [6]. [PERSON] et al. [7] defined smart textiles as fabrics derived from intelligent or responsive materials that sense stimuli and enable information transmission. However, most authors agreed that smart textiles can sense the environment (sensing function), act upon it (actuating function), and adapt their behaviour accordingly(adaptive function) [2; 8] and that they have evolved from simpler to more complex over the three generations [2; 8; 9; 10]:  
* The first generation of smart textiles are referred to as **passive smart textiles**, with a sensing function only--their materials perceive external stimuli;
* The second generation is called **active smart textiles**, with an actuating function--they sense a stimulus from the environment and respond to it;
* The third generation is called **advanced**, **very smart**, or **ultra-smart textiles**--they perceive, respond, and adapt to changes in the environment. In 2020, the terminology, technical definitions, categorisation, and applications of smart textile products were finally defined by the International Standard organisation. The Technical Report ISO/TR 23383 [11] provided a better understanding of new terms and a clear differentiation between functional and smart textiles. In functional textiles (Figure 1), the functionality is over and above the normal textile function, is pre-defined [12], and is added by means of material, composition, and construction of finishing [11]. Smart textiles (also named intelligent or interactive textiles) interact reversibly with their environments or respond/adapt to stimuli or changes in the environment (Figure 2) [11]. Examples of some specific relationships between environmental stimuli and corresponding response effects in smart textiles are presented in Figure 3.  
Figure 1: Functional textile products, data from [11; 12]. Figure 2: Smart (intelligent) textile types, properties, and products as described by technical report ISO/TR 23383, data from [11]. Two aspects need to be considered when designing smart textiles: the selection of a suitable smart material and the technology to incorporate the smart material into the textile structure, e.g., by braiding, chemical treatments, coating/laminating, embroidering, knitting, printing, sewing, spinning, or weaving [2].