Facile and fast preparation of stretchable, self-adhesive, moisturizing, antifreezing and conductive tough hydrogel for wearable strain sensors

With the rapid development of flexible wearable electronics, conductive hydrogels acting as flexible sensors have attracted increasingly extensive attention. Although significant progress has been made in designing and constructing hydrogel-based sensing devices, it is still a challenge to realize facile and fast preparation, long-term stability at extreme temperatures, high sensitivity and versatility at the same time in a conductive hydrogel. Herein, we report a facile metal ion catalytic strategy to quickly construct lithium chloride (LiCl)-doped conductive multiple-crosslinked (PSL) hydrogels, which are composed of a chemically crosslinked polyacrylamide network and interconnected long chains of polyethyleneimine and silk fibroin via physical crosslinking interactions. The obtained PSL hydrogels can achieve favourable tensile properties (141.75 kPa strength, 719.25% strain and 431.58 kJ m-3 toughness), high transparency (over 85%), outstanding adhesion behavior and repeatability towards various substrate materials. Interestingly, the introduction of LiCl can notably accelerate hydrogel formation at room temperature (within 30 s). Meanwhile, hydrogen bonds between LiCl and water molecules evidently elevate the moisturizing and antifreezing abilities of the hydrogel. Importantly, PSL hydrogel-based wearable strain sensors show high sensitivity, broad detection ranges and the capability to monitor human movements of elbows, wrists, fingers, knees and throats, demonstrating its application potential in the new generation of flexible wearable electronics. Stretchable, self-adhesive, moisturizing, antifreezing and conductive tough hydrogels for wearable strain sensors were conveniently and quickly prepared based on the catalytic mechanism of metal ions.