Robust hydrogel sensor with good mechanical properties, conductivity, anti-swelling ability, water tolerance and biocompatibility

Versatile PVA/SG (polyvinyl alcohol/sodium glycinate) hydrogel sensors have been successfully developed using SG and PVA as cost-efficient and biocompatible starting materials. The mechanical properties significantly increase with increasing F-T (freezing-thawing) times and SG content in the PVA/SG hydrogel. The strengthened mechanical properties mainly result from the abundant hydrogen bond interactions of PVA with SG and the enhanced hydrogen bond crosslinking density endowed by F-T cycles and increased SG content. Moreover, the PVA/SG hydrogel shows excellent electrical conductivity (4.85 S m-1), realizing the excellent combination of high mechanical properties and electrical conductivity. Interestingly, as well as wonderful cytocompatibility, the hydrogel displays excellent swelling resistance and water tolerance, and the mechanical properties remain almost unchanged after immersion in water for 6 months. Most importantly, the hydrogel has high strain sensitivity with a gauge factor of 1.76, stable signal repetition monitoring, very good elasticity, fatigue resistance and recovery, and thus can be assembled into flexible sensors to monitor bending changes in human Knuckles, wrists and knees, and also be used to simulate manual control of a mobile phone screen for writing text. This study provides valuable information for the design and construction of wearable hydrogel sensors with high performance for practical applications. Versatile PVA/SG conductive hydrogel with robust mechanical properties, high conductivity, excellent anti-swelling ability, water tolerance, biocompatibility and sensitivity can monitor human joint motions and simulate human skin for writing text on a mobile phone screen.