Silver nanowire/partially reduced graphene oxide-based nanocomposite hydrogel system for highly sensitive wearable strain sensor applications

We designed a conductive nanocomposite hydrogel system for flexible strain sensor materials with excellent strain sensitivity and electrical stability, high flexibility and stretchability, and rapid self-healing properties. Silver nanowires (AgNWs) with a high aspect ratio of 74.9 that can impart excellent electrical properties to the hydrogel and partially reduced graphene oxide (PRGO) with excellent electrical conductivity and water solubility were prepared. AgNW/PRGO-based (AN/PRGO) conductive nanocomposite hydrogels with a double network structure showed high stretchability greater than 1,051% and excellent self-healing properties. Particularly, poly(acrylic acid) (PA)-AN100/PRGO100 hydrogel showed 258.7 times better conductivity than those without AgNW components and 3.1 times better conductivity than those without PRGO. The conductivity of hydrogels could be controlled by varying the contents of AgNW and PRGO. The gauge factor (GF) of hydrogels increased with increasing conductivity, and GF showed higher values even in the low strain region of 0–75% than in the high strain region, indicating high sensitivity to small deformation. The PA-AN100/PRGO100 hydrogels were able to adhere well to the skin due to their excellent self-adhesion despite large and repetitive movements, and they maintained good sensitivity for both subtle muscle movements and large joint bending movements. In vitro cytotoxicity results showed a relatively high cell viability greater than 93%, indicating that the hydrogels had no significant cytotoxicity. Therefore, AgNW/PRGO-based nanocomposite hydrogels could be a promising material for wearable strain sensor applications.