# Recent Advances in Fiber-Shaped Electronic Devices for Wearable Applications
## 3 Device Applications
### Light-Emitting Fibers  
Fiber-shaped light-emitting devices have attracted great attention. Incorporating fiber LEDs into clothes is expected to maximize human-machine communication [15]. Therefore, fiber LED devices have been developed using inorganic LEDs, organic LEDs (OLEDs), light-emitting electrochemical cells (LECs), and phosphorescent electroluminescent devices (PELDs) [64]. [PERSON] et al. reported ultra-stretchable electroluminescent fibers (up to 400% stretch) that can display a pixel-based controllable light-emitting pattern (Figure 6a) [65]. A dip-coated zinc sulfide (ZnS) electroluminescent layer and a dielectric layer were sandwiched between two liquid metal-coated electrodes (eutectic gallium-indium, EGaIn) [65]. The cross-point of the ZnS-based fiber and the EGaIn-based fiber acted as an electroluminescent pixel that formed an electroluminescent fabric matrix when woven (Figure 6b) [65]. The pixel pattern on the fabric could be displayed using a direct-current (DC)-alternating-current converter connected to a Bluetooth switch in the electric circuit (Figure 6c) [65]. [PERSON] et al. developed continuous electroluminescent fibers using a one-step extrusion method (Figure 6d) [66]. The outer electroluminescent layer, containing ZnS particles with a silicone elastomer as a protecting layer, was simultaneously extruded with two inner parallel hydrogel electrodes [66]. Because of its unique single-fiber structure, the electroluminescent fibers emitted light in all directions [66]. The luminance of the light-emitting fiber was recoverable at 300% stretch, and retained after 100 stretching cycles [66]. These electroluminescent fibers were woven into a stretchable fabric to produce display patterns (Figure 6e) and applied to implement a brain-interfaced camouflage system (Figure 6f) [66]. The electroluminescent textile reacted to neuronal responses to decoder  
Figure 5: (**a**) Schematic illustration of the as-fabricated textile-based sensor. (**b**) Photographs of a wireless biomonitoring system based on a wearable textile sensor. (**c**) Schematic illustration of a 3D honeycomb-structured triboelectric nanogenerating fiber and working mechanism. (**d**) The textile-based wireless biomonitoring system and the acquired pulse wave signals when worn by a woman. (**a–d**) Reproduced with permission Ref. [47]. Copyright 2020, Elsevier. (**e**) Schematics of the fabrication process and a silk-based patch for diabetic wound healing. (**f**) A photograph of patches implanted as electrodes in a rabbit’s back (left image) and signals detected after breathing. (**e,f**) Reproduced with permission Ref. [61]. Copyright 2021, Wiley-VCH. lights [66]. The resulting textile display represents a promising wearable communication platform. [PERSON] et al. fabricated 1D cylinder-shaped red, green, and blue PELDs on a polyethylene terephthalate (PET) fiber substrate, using a multiple-dip coating method (Figure 6g) [15]. The PELD fibers exhibited excellent optoelectronic performance, including good brightness (4462, 11,482, and 1199 cd m\({}^{-2}\) for red, green, and blue, respectively), high current efficiency, and low driving voltages of \(<\) 8 V, compared with those of conventional OLEDs on glass substrates [15]. Specifically, they showed the highest values of current efficiency at 16.3, 60.7, and 16.9 cd A\({}^{-1}\) for red, green, and blue, respectively [15]. In addition, the proposed PELDs operated after repetitive flexural tests in multiple directions, as well as under 1.75% tensile strain [15]. The PELD fibers were used as independent pixels in an addressable structure and could be operated using a passive matrix scheme [15]. Letter information was successfully visualized on garments woven of the PELD fibers, indicating their potential to realize wearable textile displays (Figure 6h) [15].