Bioinspired swelling enhanced hydrogels for underwater sensing

Hydrogel-based wearable electronics are of great interest due to the potential applications such as artificial intelligence, electronic skins, and healthcare management. But their underwater sensing properties have been hindered owing to the high swelling ratio and weak mechanical strength in the aqueous solution. Inspired by the physiological enhanced muscles, herein, we report a novel kind of swelling induced enhanced hydrogel with underwater sensing properties. The resultant nanocomposite hydrogel, comprised of two acidic comonomers of acrylic acid (AA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) in the presence of acidic Al(OH)₃ NPs aqueous solution, exhibits relatively weak coordination crosslinking due to the partially prohibiting aluminum-carboxylate complexation. After the water immersion, the increased pH value leads to strong coordination crosslinking from full complexation of aluminum-carboxylate. As a result, the swollen hydrogel exhibited the significant increase in the mechanical properties compared to those of the as-prepared sample. Moreover, the hydrogel could sense human motions in air and underwater, even detecting the subtle motions like pulse beating in the aqueous solution. Thus, such enhanced hydrogel is a potential candidate in the field of biomedical robots and biosensors in aquatic environment.