Ultrastretchable and adhesive MXene-based hydrogel for high-performance strain sensing and self-powered application

Conductive hydrogels have been extensively explored for human movement and health monitoring. However, the poor adhesion of hydrogels to the skin hinders their performance in real-time monitoring with minimal loss of signal transmission. In this work, hydrogels composed of acrylic acid (AA), acrylic acid–N-hydrosuccinimide ester (AA–NHS), sulfobetaine methacrylate (SBMA), and cellulose nanofibers (CNFs) in the presence of initiators were rapidly gelated (within a few minutes) after adding Ti3C2TX MXene as a versatile crosslinking agent. AA and SBMA copolymerized to form the main network structure of the hydrogel and the introduced CNF improved the tensile strain of the hydrogels from 1737 % to 2240 %. By virtue of the combined zwitterionic-adhesion mechanism and NHS-activated ester bonds, the hydrogels conformally adhered to porcine skin with an adhesive strength of 11.6 kPa. When assembled as strain sensors, the hydrogel sensors exhibited high sensitivity (gauge factor = 4.98) and a fast response (95 ms). Next, the hydrogel was assembled as the electrode in a triboelectric nanogenerator (TENG) for mechanical-energy harvesting and self-powered sensing. The TENG exhibited good electrical output properties and could charge commercial capacitors with the mechanical energy harvested from walking. This work promises the design of wearable hydrogel devices with mechanical extensibility and self-adhesive properties.