# Smart Textiles: A Review and Bibliometric Mapping
## 3 Results and Discussion
### Clusters of KW as indicators of research areas
One of the great challenges for smart textiles research and development is sustained self-powered textile-based devices that can also be used as elements of the Internet of Things and the Metaverse as its emerging successor. Mechanical energy harvesting technologies such as triboelectric nanogenerators, piezoelectric nanogenerators, and electrochemical mechanical generators have been used to convert mechanical energy directly into electrical power [14]. Other energy sources have also been considered for conversion into \begin{table}
\begin{tabular}{c c c} \hline \hline
**Authors’ Keywords** & **Average Publication Year** & **Occurrence** \\ \hline liquid metal & 2021.45 & 11 \\ MXenes & 2020.94 & 33 \\ textile electronics & 2020.92 & 13 \\ self-powered & 2020.83 & 12 \\ EMI shielding & 2020.64 & 22 \\ self-powered sensors & 2020.53 & 15 \\ silver nanoparticles & 2020.47 & 15 \\ strain sensing & 2020.40 & 10 \\ sustainability & 2020.39 & 18 \\ artificial muscles & 2020.22 & 23 \\ joule heating & 2020.18 & 11 \\ washable & 2020.18 & 11 \\ thermoelectrics & 2020.18 & 11 \\ triboelectric nanogenerators & 2020.16 & 63 \\ gait analysis & 2020.07 & 14 \\ self-cleaning & 2020.06 & 17 \\ fabrication & 2020.00 & 16 \\ soft robotics & 2020.00 & 13 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Authors’ keywords with an average publication year younger than 2020 and occurrence of more than 10 that can be considered as new propulsive research areas for smart textiles. electricity, such as photovoltaics, thermoelectric generators, electromagnetic generators, magnetoelastic generators, and pyroelectric and photovoltaic systems [21; 40; 134]. Examples of achievements include highly integrated composite core/shell fibres for weaving triboelectric nanogenerators that can be used in self-powered smart textiles whose fibres are stretchable, conductive, with good pliability and high resistance-strain sensitivity [135]; washable smart textiles based on triboelectric nanogenerator arrays used as bedsheets for real-time and self-powered sleep behaviour monitoring [136]; self-powered smart gloves based on the triboelectric effect and electrostatic induction, which can be used for a variety of purposes, including gesture recognition, sign language translation, human-machine interfaces, advanced robotic control, user identification, and object recognition [137]. **EMI shielding**. Digital and electronic devices cause interference of electromagnetic waves that negatively affect nearby electronic devices, communication signals, and human health. Textile materials, such as cotton, silk, polyester, nylon, spandex, polyethylene terephthalate, etc., can be modified by various methods and techniques with conductive materials such as silver nanowires, liquid metals, Cu nanoparticles, CNTs, graphene, graphene oxide, MXene, polypyrrole, or PEDOT to perform the function of protection from EM waves to provide EMI shielding [138]. Examples of new research include durable EMI-shielding ramie fabrics with flame-retardant and self-healing properties consisting of an ammonium polyphosphate/polyethyleneimine layer, MXene sheets, and a polycaprolactone layer [139], highly conductive textiles with bark-like morphology composed of MXene microstructure and porous textile, with improved flexibility, durability, breathability, and EMI shielding performance [140], and the development of titanium carbide (Ti\({}_{3}\)C\({}_{2}\)Tx) MXene nanosheets with improved stability and enhanced connectivity, containing Ti\({}_{3}\)C\({}_{2}\)Tx/PANI composites with 3D nanoflower structures. With the addition of GaIn liquid metal nanoparticles and carbon fabric substrates, flexible, stable, conductive composite fabrics for EMI shielding were obtained [141]. **Self-powered sensors**. Self-powered sensors constitute an important sub-class of self-powered products. Based on innovative self-powering technologies, they harvest energy directly from the working environment to ensure long-term sustainable operation.