## 3 Wearable Electronics Based on Graphene Nanoplatelets  
Smart textiles are fibrous materials with numerous functionalities and applications compared to common fabrics [70]. It is predicted that the wearable device market will reach US$ 20.6 billion in the current year (2018) [71]. Electrical conductivity is the main promising feature of these garments, because it is highly sought after in fields such as flexible, wearable, and deformable electronics, and for the emerging Internet of Things [71; 72]. Miniaturization propelled by nanotechnology allows us to fabricate electronic components, even working on a single fiber [72]. However, direct functionalization of textiles is more often targeted by the incorporation of conductive nanoparticles inside/on fibrous networks [73; 74; 75; 76]. Using such an approach, remarkable results were achieved in applications related to generators [77], supercapacitors [78], and electrochemical sensors [79]. Nevertheless, further research is needed to create wearable conductive materials with stable electronic performance under mechanical stress and ambient conditions (e.g., sunlight, air etc.). In particular, wearable electronics require the creation of a new class of materials which are flexible, foldable, and washable, and which, at the same time, maintain a satisfactory level of electrical conductivity [48]. Polymeric nanocomposite materials, due to the intrinsic mechanical properties of polymers and ease of manufacturing, and to the large spectra of properties accessible with different nanoparticles, are suitable for conductive wearable technologies [80]. In this regard, promising approaches are: (1) the functionalization of fabric with Graphene Oxide (GO) [76; 81; 82; 83], (2) the employment of graphene-based materials to produce conductive fibers [84; 85; 86], and (3) the transfer of chemical vapor deposited graphene films onto textiles [87; 88]. All  these approaches present enhancements compared to metal functionalization [89]. However, some limitations can be identified [89]:  
1. Graphene oxide needs reduction steps, and the obtained sheet resistance is often high (i.e., in the order of thousands of \(\Omega\)/sq). 2. Graphene freestanding fibers have remarkable electrical properties, but difficult adaptability to the current garment industry. 3. Chemical vapor deposition of graphene is expensive, and the transferring procedure of the film is complicated. Recently, another promising procedure was reported to impart electrical conductivity to industrially produced fabrics through a functionalization based on GnPs. This method has the advantage of being adaptable to several commercially-available materials like cotton and polyesters, and since GnPs are already produced in amounts suitable for the textiles market (hundreds of tons), it is scalable. For example [PERSON] et al. [89] prepared a conductive GnP-infused poly(ethyleneterephthalate) fabric by dip coating and tip sonication in heptane and water. They reached a few k\(\Omega\)/sq sheet resistances at 15 wt % loadings. [PERSON] and coauthors [90] fabricated electroluminescent structures on textiles (paper and cotton), employing GnPs as transparent electrodes. They obtained a transmission of 70% of the incoming light, and sheet resistances in the order of 10 k\(\Omega\)/sq. [PERSON] and collaborators [91] produced a conductive fabric by layer-by-layer deposition of GnPs doped PEDOT:PSS-chitosan on cotton. Such fabrics featured ohmic I-V curves and could achieve an electrical conductivity of \(\sigma\approx 0.4\) S/m (see Figure 8a). Furthermore it was resistant to washing cycles, and simple circuitry could be realized, powering up LEDs, as shown in Figure 8b. The fabric also showed remarkable ultraviolet protective ability, i.e., approximately 300-fold higher than the control fabric. Printing and spraying were also employed in the context of wearable electronics. For example, [PERSON] et al. [92] screen printed a GnP-carbon nanotubes conductive paste onto cotton.