Conductive Hydrogels: Bioelectronics and Environmental Applications

Flexible multimodal sensors have garnered continued attention due to their tunable structural performance and sensitivity to electric signals, adaptability to various environments, and outstanding mechanical properties. However, the limited self-healing capabilities, degradation, and reversible self-adhesion of sensors made from rubbers, elastomers, and other polymers have hindered their widespread application. Flexible sensors based on hydrogels, which offer exceptional stretchability, flexibility, and biocompatibility, could provide a solution. However, their reliance on external energy sources limits their potential. Thus, efforts have been made to develop conductive hydrogels by incorporating functional groups, additives, or nanofillers into the hydrogel network, which has led to multifunctional wearable sensing capabilities. This review discusses recent advancements in the use of hydrogels in self-powered sensors, including strain/pressure sensors, electronic skin sensors, pressure/strain sensors, temperature monitoring and humidity monitoring applications. Moreover, it focuses on the mechanisms of energy conversion in self-powered sensors. It also provides a concise overview of the various synthesis methods used in developing conductive hydrogels. The current review also outlines the present challenges, besides suggesting potential pathways ahead for future advancement.