Conductive polymer based hydrogels and their application in wearable sensors: a review

Hydrogels have been attracting increasing attention for application in wearable electronics, due to their intrinsic biomimetic features, highly tunable chemical–physical properties (mechanical, electrical, etc.), and excellent biocompatibility. Among many proposed varieties of hydrogels, conductive polymer-based hydrogels (CPHs) have emerged as a promising candidate for future wearable sensor designs, with capability of realizing desired features using different tuning strategies ranging from molecular design (with a low length scale of 10−10 m) to a micro-structural configuration (up to a length scale of 10−2 m). However, considerable challenges remain to be overcome, such as the limited strain sensing range due to the mechanical strength, the signal loss/instability caused by swelling/deswelling, the significant hysteresis of sensing signals, the de-hydration induced malfunctions, and the surface/interfacial failure during manufacturing/processing. This review aims to offer a targeted scan of recent advancements in CPH based wearable sensor technology, from the establishment of dedicated structure–property relationships in the lab to the advanced manufacturing routes for potential scale-up production. The application of CPHs in wearable sensors is also explored, with suggested new research avenues and prospects for CPHs in the future also included.