Stretchable, self-adhesive, conductive, anti-freezing sodium polyacrylate-based composite hydrogels for wearable flexible strain sensors

The vigorous development of flexible sensors, wearable electronic devices, and human-computer interaction techniques has promoted the construction of flexible, stretchable, and conductive hydrogels. However, due to the lack of self-adhesion and environmental adaptability, these hydrogels still face huge challenges in accurately and stably monitoring human motions as flexible sensors. In this paper, a multifunctional hydrogel of poly(sodium polyacrylate-dopamine based methylacrylamide)/polyvinyl alcohol (i.e., P(AAS-DAAM)/PVA) with the properties of stretchable, self-adhesive, conductive, and anti-freezing was synthetized by introducing methacrylic acid modified dopamine into sodium polyacrylate crosslinked network, and combine with a physical cross-linked network of the polyvinyl alcohol. The hydrogel exhibits excellent stretchability (>1000%), the higher conductivity (0.038 ± 0.003 S·cm−1), good frost resistance (−30°C) and excellent adhesion (419.3 ± 5.95 N/m) and remarkable biocompatibility (relative cell viability up to 132 ± 2.63%). The results indicate that P(AAS-DAAM)/PVA hydrogel can be used as a flexible sensor. Moreover, P(AAS-DAAM)/PVA-based strain sensor not only can stably and repeatedly monitor the changes of different strains (50% ~ 200%) with high sensitivity (GF = 1.65), but also stable and accurate monitoring capabilities for large joint bending (fingers, wrists, elbows, knees) or small physical (swallowing, speaking) activities. This hydrogel preparation strategy strongly promotes the development of new multifunctional hydrogels and hydrogel-based flexible sensors and other equipment to a new step.