Tough and recyclable polyvinyl alcohol/carboxymethyl chitosan hydrogels with high strength, low modulus and fast self-recovery as flexible strain sensors

Fabrication of soft electronics using hydrogels is in high demand because of their biomimetic structures and favorable flexibility. However, poor mechanical properties of some developed hydrogels limit their use as stretchable sensors that require high strength, low modulus and suitable conductivity simultaneously. In this study, tough and conductive polyvinyl alcohol/carboxymethyl chitosan hydrogels were fabricated using a facile strategy, wherein an acid solution was employed to induce molecular structural transformation, thereby enhancing network interactions and mechanical strength. The resulting hydrogels, which had a high-water content of 83 %, exhibited excellent mechanical properties, with breaking stress of 1.81 MPa, breaking strain of 638 %, toughness of 5.01 MJ/m³, yet the tissue-like low modulus of 35-144 kPa. The hydrogel possessed a suitable conductivity, and fast recoverability after unloading and excellent recyclability after usage. These features made the hydrogels promising candidates for fabricating resistive strain sensors. The resulting sensors demonstrated a broad strain window, outstanding linear response with high sensitivity, and exceptional durability in long-term usage, enabling them to effectively monitor various physical movements as wearable electronics. This research offers a new approach to creating stretchable conductive hydrogels for smart technologies and flexible electronic devices.