Ultrastretchable\nWearable Strain and Pressure Sensors\nBased on Adhesive, Tough, and Self-healing Hydrogels for Human Motion\nMonitoring

Abstract

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