Skin-conformal MXene-doped wearable sensors with self-adhesive, dual-mode sensing, and high sensitivity for human motions and wireless monitoring.

Flexible sensors have attracted extensive attention due to their excellent flexibility, biocompatibility, and information acquisition accuracy. Therefore, it is desired to fabricate a flexible sensor with high toughness and sensitivity based on conductive hydrogels to monitor human movement. In this work, MXene-(Ti3C2Tx-)WPU/PAM dual-network hydrogels (PPM hydrogels) were successfully prepared. As the first network, waterborne polyurethane (WPU) plays the role of energy dissipation and enhancement. Polyacrylamide (PAM) and WPU polymer chains form interpenetrating networks (IPNs). MXene acts as a conductive material to enhance the conductivity and for nano enhancement. The PPM hydrogels exhibited excellent mechanical characteristics (tensile ratio >600%, tensile strength 639 kPa, 1000 stretching cycles, and self-recovery rate 93.7%). Moreover, based on these hydrogels, we fabricated flexible sensors. These sensors had high sensitivity and sensing durability, and could be assembled into a human body wireless monitoring device, which possesses great potential in facial micro-expression monitoring, all-around human motion detection, and wearable electronic products. In addition, these resulting hydrogels possessed outstanding reversible adhesion to various materials (human skin, wood, PDMS, etc.) and the maximum adhesion strength can reach 305.1 N m-1 when exposed to a PDMS substrate. Therefore, PPM hydrogels could provide new inspiration for the development of wearable flexible sensors in the domain of human movements and personalized physiological health monitoring.