Hypersensitized Strain Sensors Based on Conductive Hydrogels with Excellent Conductivity and Good Mechanical Properties

As the essential substrates for the manufacture of flexible electronic devices, conductive hydrogels have shown great potential in the fields of flexible strain sensors, wearable devices, and electronic skin. However, their application is greatly limited by the poor mechanical properties, low conductivity, and sensitivity. In this work, we present a facile approach for preparing sensitive hydrogel-based sensors with stretchability, excellent conductivity, and suitability for detecting small strains by reducing silver particles through aqueous in situ reduction on the surface of lignosulfonate/polyvinyl alcohol composite hydrogels. The resulting hydrogel shows an excellent conductivity of 3300 S·m^–1 and the tensile stress and strain at a break are 0.91 MPa and 380%, respectively. Furthermore, the conductive hydrogel exhibits high sensitivity (a gauge factor of 33.81 at 0–20% strain), linearity (R² = 0.9952), fast response (<20 ms), and good durability (100 cycles). The sensing mechanism of a conductive hydrogel is analyzed to be the generation and recovery of microcracks in the silver layer. The strain sensors composed of conductive hydrogels demonstrate superior sensing performance by detecting subtle vibrations, human pulses, and tiny phonations of different persons. Therefore, it is believed that the conductive hydrogel has great potential applications in human activity monitoring and soft robotics.