Conductive polyacrylamide/pullulan/ammonium sulfate hydrogels with high toughness, low-hysteresis and tissue-like modulus as flexible strain sensors

Conductive hydrogels have great potential for applications in flexible wearable sensors due to the combination of biocompatibility, mechanical flexibility and electrical conductivity. However, constructing conductive hydrogels with high toughness, low hysteresis and skin-like modulus simultaneously remains challenging. In the present study, we prepared a tough and conductive polyacrylamide/pullulan/ammonium sulfate hydrogel with a semi-interpenetrating network. Ammonium sulfate promoted the formation of low-energy-dissipating motifs between polymer chains, reinforcing the gel matrix and resulting in excellent mechanical properties, including a high stretchability of 2063 %, a high strength of 890 kPa, and a high toughness of 4268 kJ/m³. The hydrogen bonds formed within the network endowed the gels with low-hysteresis under deformation. The unique semi-interpenetrating network structure provided the gels with a tissue-like low modulus. Additionally, the resulting hydrogels exhibited a high conductivity of 2.39 S/m and excellent anti-freezing properties, making them suitable for flexible strain sensors. These sensors demonstrated high sensitivity over a broad strain window of 0.1-1500 %, enabling the detection of various human motions and the recognition of different languages. These findings emphasize the potential of the composite hydrogels as wearable strain sensors for flexible devices.