2.1.3. Nanofibers

For the fabrication of nanofibers, different techniques are used, like electrospinning (Figure 2), self-assembly, force spinning, melt blowing, and island-in-sea (bicomponent nanofiber) (Almetwally et al., 2017, [69]), (Nayak et al., 2019, [70]), (Naeem et al., 2019, [71]). Out of these techniques, the electrospinning is considered the most convenient one due to its low cost, higher rate of production, higher porosity, and ability to control nanofiber morphology and diameter. A stretchable piezo-resistive carbon nanotube-incorporated nanofiber sensing yarn (Figure 3) was first designed as well as prepared by a facile electrospinning technique by (Qi et al., 2020, [72]). Moreover, the nanofibers are unique with high capability as active layers in face masks, to protect people against diseases such as coronavirus (Tebyetekerwa et al., 2020, [73]).

**Figure 2.** Electrospinning design. Reproduced from (Montazer et al., 2018, [74]).

**Figure 3.** Schematic of the fabrication processes of carbon nanotube-incorporated nanofiber sensing yarn. Reproduced from (Qi et al., 2020, [72]).
