# Breathable Materials for Triboelectric Effect-Based Wearable Electronics
## 3 Breathable Wearable Electronics Based on Triboelectric Effect  
### Woven-Structured Wearable Electronics  
Everything around us has friction characteristics. As textiles and fibers are believed to be the second human skin [46; 47], researchers have considered using fibers, the essential components of clothes, to fabricate triboelectric effect-based wearable devices. [PERSON] was the first to put this idea into action [48]. By weaving polyester and nylon fabric, the triboelectric effect-based wearable device is breathable, flexible, and washable, which is similar to commonly worn clothes. Figure 3 is the structure illustration and fabrication process of the woven-structured electronics. To realize the washability and flexibility, silver fabric was chosen to replace metal foils to act as the electrode of the device. A single component of the device was constituted through covering both sides of the silver fabric with nylon or polyester. Weaving the single component of the fabrics together finished the device. In this situation, nylon and polyester fabrics act as two friction materials of the device. The working mechanism of the device can be concluded to freestanding friction layer. Benefiting from the easy integration of the device into clothes such as shirts, trousers or shoes, the device can harvest different kinds of human motion energy and powers several LEDs effortlessly. This work opened a new approach for fabricating breathable and comfortable wearable electronics. Inspired by the components of clothes, the homemade woven-structured device is a great step forward in skin-friendly wearable devices. However, the fabrics were weaved by hand, which is time-consuming and relatively expensive. Therefore, a mass-production method is necessary to realize the commercialization of the wearable device [49]. To solve this problem, normal yarn-winding machine was introduced to fabricate wearable electronics. Figure 2: Applications of triboelectric effect-based wearable device, including energy harvesting, health monitoring and human–machine interfacing. Figure adapted from ref. [39; 40; 41; 42; 43; 44; 45]. Recently, a wearable triboelectric device (WTD) made of compound yarns, mass produced by a commercial yarn-winding machine, was put forward [50]. As presented in Figure 4a, the yarn has a core-shell structure, where silver-plated yarn and nylon-6 (PA6) or polytetrafluoroethylene (PTFE) acts as core and shell, respectively. During the contact-separation process, PA6 and PTFE will rub against each other and silver-plated yarn serves as an electrode to collect the induced electrons. Figure 4b is a simple illustration of the process of how the friction materials such as PA6 or PTFE covered the surface of the silver-plated yarn through the winding machine. The flexibility and washability of the WTD are shown in Figure 4c, which shows firm evidence for the practicability of the WTD when integrated with commonly worn clothes. Moreover, the cross-sectional and top view of the core-shell yarn was presented in the bottom of Figure 4c as well. When directly integrated into the garment, the WTD with a size of 4 \(\times\) 4 cm can easily charge a capacitor from 0 to 5 V within 100 s and, further, power an electric watch and scientific calculator. With the help of the commercial yarn-winding machine, a breathable, flexible, and washable WTD can easily be scaled up, which is a significant step forward for the mass fabrication and commercialization of wearable WTDs. Figure 4: Wearable device made up of compound yarns, mass produced by a commercial yarn-winding machine. (**a**) Structure and application of the wearable triboelectric device (WTD). (**b**) The schematic of the formation of one yarn. (**c**) The flexibility and washability of the WTD and cross-sectional view of one yarn (Scale bar, 2 cm (i–iii), 200 \(\upmu\)m (iv), 400 \(\upmu\)m (v)). Figure adapted from ref. [50]. Figure 3: Woven-structure wearable triboelectric devices. (**a**) Fabrication process of the wave structure device.