A Conductive Hydrogel Based on GaIn and PVA/PAA/Fe³⁺ for Strain Sensor and Physiological Signal Detection

The conductive material used in traditional conductive hydrogels is inherently rigid, which makes the material’s mechanical properties poor. In addition, the use of chemical covalent bonds to form gels makes the hydrogel lack self-healing properties, which limits the conductivity and the application of gel. Based on the above reasons, we use the characteristics of the strong trivalent iron ion chelating ability to prepare a PVA/PAA/Fe3+ system three-dimensional network structure hydrogel and design a sandwich structure to encapsulate liquid metal gallium indium tin (GaIn) in the hydrogel. Inside, the strong conductivity of the liquid metal is used while protecting the liquid metal from being oxidized. In addition, we explore its mechanical properties, electrical conductivity, self-healing properties, adhesion properties, antibacterial properties, etc. and prove them by tensile stress–strain mechanic experiments, electrical impedance experiments, strain sensor signal detection, and biological signal detection experiments. The results show that the as-prepared hydrogel exhibited excellent self-healing performance and antibacterial ability and has mechanical properties that fit the elastic modulus of the skin. Compared with traditional Ag/AgCl electrodes, it can detect electrocardiogram and other biological signals very well as well as having long-lasting and repeated use.