Muscle-like self-strengthening poly(vinyl alcohol)/cellulose/MXene composite hydrogel by mechanical training for wearable electronics.

The development of mechanically tunable and self-strengthening hydrogels for advanced electronic applications is highly desirable but remains a challenge. Muscles, as force-bearing tissues, could autonomously grow to adapt to the surrounding environment through cyclic disassembly and reconstruction of muscle fibers by mechanical training. Inspired by this biological feature, we presented a mechanical training enhancement strategy for preparing self-strengthening conductive composite hydrogels. The polyvinyl alcohol (PVA) acted as the hydrogel matrix, MXene serving as conductive medium realized high conductivity (679.6 mS/m), and the incorporation of carboxymethyl cellulose (CMC) not only prevented MXene self-stacking but also strengthened hydrogen bonding interactions and chain entanglement density. During mechanical training process, the nanocrystalline domains of the PVA chain were reoriented into a highly ordered structure, while the decrease in average distance between neighboring nanocrystalline domains increased the density of nanocrystalline domains in the cross-section. As a result, the prestretched composite hydrogel demonstrated enhanced tensile strength of 1356.1 kPa and toughness of 2962.2 kJ/m, which were 4.4 and 6.4 times of the initial composite hydrogel, respectively. The composite hydrogels were successfully employed as strain sensors for monitoring human motions. This work demonstrated a promising approach to developing self-strengthening soft materials for advanced applications.