Currently, flexible wearable hydrogel-based sensors have attracted considerable attention due to their promising applications in a variety of fields. However, concurrently integrating toughness, adhesiveness, self-healing ability, and conductivity into the hydrogel is still a great challenge. Here, casein sodium salt from bovine milk (sodium casein, SC) and polydopamine (PDA, inspired by mussels) were successfully introduced into the polyacrylamide (PAAm) hydrogel system to fabricate a tough and adhesive SC−PDA hydrogel. The hydrogel exhibits splendidly reversible adhesive behavioral bonding toward various materials and even human skin. Moreover, based on the dynamic cross-linking of SC and PDA in the system, the hydrogel has superstretching ability, excellent fatigue resistance, and rapid self-healing ability. In addition, the existence of sodium ions also endowed the SC−PDA hydrogel with sensitive deformation-dependent conductivity to act as a flexible strain and pressure sensor for directly monitoring large-scale human motions (e.g., joint bending) and tiny physiological signals (e.g., speaking and breathing). Therefore, the strategy would broaden the path of a new generation of hydrogel-based sensors for wide applications.

Breaking through the conventional way of conferring anti-icing ability on hydrogels with addition of organic solvents or inorganic salts, a novel anti-icing hydrogel driven by antifreeze proteins was successfully fabricated and applied as sensors.

Conventional hydrogels inevitably “swell” under liquid or physiological conditions, which drastically destroys their mechanical properties, severely limiting their practical applicability.