# Smart Textiles: A Review and Bibliometric Mapping
## 3 Results and Discussion
### Clusters of KW as indicators of research areas
Actively heating textiles are made by modifying, coating, or embedding the textile fibre with electroactive materials such as CNTs, graphene, silver nanoparticles, MXene, or PEDOT:PSS [207; 208; 209; 210; 211; 212; 213]. The application of Joule heating in smart textiles has applications in personal warming in cold environments and medical thermotherapy. **Washable. ** Washing is one of the most important processes to ensure the hygiene of textiles and, thus, protect people's health. Therefore, smart garments should be washable. The first studies and produced electronic textiles were based on rigid conventional electronics integrated into textiles, which did not correspond to the stretchability, flexibility, and washability of textiles, so the removal of electronic devices before washing was strongly recommended. Nowadays, new technologies and new materials allow researchers to develop flexible, stretchable, and washable electronics integrated into textiles without losing comfort and wearability. The latest studies show that coating thread material with polydimethylsiloxane [214] and filling hollow silicon fibres, including conductive yarn, with a mixture of silicone rubber and a curing agent [143], coating triboelectric yarn containing conductive CNTs with PVDF fibres deposited by a tailored electrospinning process [215], increase the washability of smart textiles. Thus, encapsulating conductive yarns with polymers or coating textile sensors with superhydrophobic compounds makes smart textiles washable. **Thermoelectric materials generate electricity through the thermoelectric effect when a temperature gradient is applied. In new smart textiles, thermoelectric generators are used as flexible, self-powered solid-state modules that passively harvest energy from the heat of the human body. They operate on three principles: the Seebeck coefficient, the Peltier effect, and the Thomson effect [134]. Examples of inorganic thermoelectrics include metals (silver, copper), chalcogenides (bismuth telluride, antimony telluride), and metal oxides (zinc oxide), while among organic materials, conductive polymers are used, such as polyacetylene, polypyrrole, PANI, PEDOT, and PEDOT:PSS [40; 134]. Dopants can be incorporated into a base material such as graphene, graphene oxide, and CNTs to dope conductive polymers and increase the overall electrical conductivity of the system [134]. **  
**Triboelectric nanogenerators. ** Triboelectric energy harvesting is based on mechanical rubbing and electron transfer [40]. Triboelectric nanogenerators are nanodevices that harvest biomechanical energy from human body movement [216; 217]; they couple the triboelectric effect and electrostatic induction to convert mechanical energy into electricity [41]. Proper choice of materials and structures enhances performance [216; 218; 219]. Many designs and combinations of materials have been developed and fabricated. In general, triboelectric nanogenerators consist of substrates, electrode layers, and triboelectric layers [220]. Flexible substrates for triboelectric nanogenerators can be selected from polyimide, polydimethylsiloxane (PDMS), polyurethane, polyethylene terephthalate, or silk fibres. The electrode layer is a conductive material selected from carbon-containing materials (carbon particles, CNTs, graphene, carbon fibres), conductive polymers (polypyrrole, PANI, poly(P-phenylene-vinylene), polyetheretherketone (PEEK), PEDOT:PSS), metallic nanowires (silver, gold, copper nanowires), or conductive fibres, yarns, or fabrics. Negative triboelectric layers include PVDF, polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), and PDMS, while positive triboelectric materials are mainly nylon 66, silk, and cellulose [40; 220]. The main principle of the design of textile triboelectric nanogenerators is to suitably fit two friction surfaces with different properties into a textile.