Poly (vinyl alcohol)/Pullulan/NaCl Conductive Hydrogels for Wearable Strain Sensors

Ionic conductive hydrogels have emerged as promising candidates for wearable sensors thanks to their stretchability and conductivity. However, it is still challenging to fabricate hydrogels simultaneously with balanced mechanical strength, ionic conductivity, and sensitivity. In this work, PVA/Pullulan/NaCl ionic hydrogels were prepared by soaking frozen-thawed PVA/Pullulan hydrogels in NaCl solutions. Due to the synergy of the semi-interpenetrating network between PVA and pullulan as well as the salting-out effect due to NaCl, the hydrogels exhibited a large tensile strength of 2.72 MPa. The presence of Na+ and Cl− ions endowed the hydrogels with superb ionic conductivity (up to 10.44 S/m). The hydrogel was assembled as a strain sensor, which displayed good sensitivity (up to 5.98) and was utilized for the detection of human joint movements. Additionally, hydrogel sensors can provide efficient information transmission through Morse code. As such, the presented PVA/Pullulan/NaCl hydrogels suggested a promising prospect for the next generation of wearable sensors.