Poly(vinyl alcohol), Tannic Acid, and Silver-Based Hydrogel Strain Sensors with "Fish Scale-Like" Surfaces

Skin-like soft conductive hydrogels with intrinsic mechanical flexibility exhibit promising potential as flexible electrical sensors. However, dilemmas remain regarding their electrical conductivity and fragile nature. Herein, a method including freeze-drying and rehydration of hydrogels to optimize the abovementioned properties is proposed. Poly(vinyl alcohol) based conductive hydrogels are fabricated by freeze-drying and rehydration of prehydrogels in AgNO3 solution, which results in densified polymer networks along with a "fish scale-like" surface consisting of inorganic materials originating from spontaneously interconnected Ag nanoparticles (AgNPs) on the exterior surface of hydrogels. The densified polymer networks dramatically improve the mechanical properties, while the AgNPs serve as electron transfer carriers for high electrical conductivity. Consequently, the prepared hydrogels realize 20 times improvement in both strength (3 MPa) and toughness (2.12 MJ/m3) along with ideal electrical conductivity (3.98 mS/cm) and strain sensitivity (GF = 4.12). The obtained conductive hydrogels can serve as strain sensors to monitor human motions and exhibit desirable antibacterial properties.