A Stretchable Electroluminescent Skin based on Microcracked Electrodes for Wearable Sensors

Conductive hydrogels are commonly used in wearable devices and electronic skin as flexible strain sensors. However, the existing hydrogel sensors have limitations in reflecting the strain distribution accurately in space. To overcome this challenge, we have successfully developed a microcracked silver nanosheets composite polyacrylamide/hydroxypropyl cellulose framed hydrogel electrode. The mechanical, electrical, and optical properties of the silver nanosheet composite hydrogel have been significantly improved. The microcracked silver nanosheet composite hydrogels showed an enhanced fracture stress of 391.1 kPa, which is 1.5 times that of the hydrogel without silver nanosheets. Their fracture strain can reach 1160%. W e have discussed the microcracks mechanism and found that the microcracks in the hydrogel electrode act like a light shield, which can dynamically map the applied strain and deformation distribution in space with corresponding 3D luminescent signals. We also prepared a sandwich-structured stretchable electroluminescent device that consists of an upper hydrogel electrode-ZnS: Cu/Ecoflex phosphor layer-bottom hydrogel electrode. The upper and bottom electrode layers were made of microcracked silver nanosheet composite hydrogels. The stretchable luminescent behavior of the device was studied. Finally, we demonstrated its ability to monitor the finger joint movements at bending angles of $0^{\circ}, 45^{\circ}$, and 90°. The results could pave the way for investigating smart photonic artificial skin in advanced sports training and sports injury rehabilitation, human-machine interfaces, intelligent robots, and others.