Stretchable, self-healable and anti-freezing conductive hydrogel based on double network for strain sensors and arrays

The application of hydrogels for flexible sensor is gravely hampered due to their poor freezing resistance and fatigue fracture associated with durable deformation, hence hydrogels that can operate correctly at sub-zero temperatures and sustain long-term deformation are urged for wearable electronics and implantable sensors. In this paper, we develop conductive hydrogel (HB-Hydrogel) based on multi-hydrogen-bonded double network of polyvinyl alcohol (PVA) and polyaniline (PANI) via in-situ polymerization and solvent conversion. Tannin in the ethylene/water (EG/H₂O) binary solvent induces multiple dynamic hydrogen bonding network that closely connect PVA and PANI together, enduring HB-Hydrogel with outstanding self-healing capability and remarkable mechanical properties. On the other hand, HB-Hydrogel retains good flexibility even at − 20 °C by exchanging the aqueous solvent with EG/H₂O binary solvent. In-situ polymerization of conductive PANI conquers the dispersion issue in PVA hydrogel to generate a homogeneous conductive network, resulting in very high sensitivity (GF =  ~ 3.52) at low strain and outstanding linear dependence of sensitivity on strain. The assembled strain sensor equipped with the HB-Hydrogel can efficiently collect data of human monitoring, including the joint movements, pulses and voice-prints. Furthermore, a prototype 2D sensor array is built to detect strains or pressures in two dimensions, which is promising for electronic skin, touchpads, biosensors, human–machine interfaces, biomedical implants, wearable electronic devices and other applications.