High‐Strength, Dual‐Responsive Conductive Hydrogels With Ionic Crosslinking for Flexible Strain Sensors

ABSTRACT Conductive hydrogels with dual responsiveness, such as temperature and deformation, demonstrate substantially broader application potential in flexible sensors compared to single‐responsive hydrogels. However, traditional temperature/deformation‐responsive hydrogels are often limited by their low mechanical strength, which restricts their practical utility. To address this limitation, this study develops a high‐strength, dual‐responsive hydrogel through free radical copolymerization of the temperature‐sensitive monomer N ‐isopropylacrylamide (NIPAM). The resulting poly(N‐isopropylacrylamide‐co‐acrylic acid)‐Fe 3+ /chitosan‐SO 4 2− ionically crosslinked double‐network hydrogel (PICDN) exhibits remarkable mechanical properties, achieving a maximum tensile strength of 1.10 MPa and an elongation at break of 225%. The hydrogel also demonstrates excellent self‐recovery and fatigue resistance under repeated cyclic strain. Furthermore, the PICDN hydrogel displays high sensitivity to deformation, enabling rapid detection of human motions, such as finger bending (0° to 30°), with a response time of only 0.608 s, as well as subtle muscle movements. Additionally, the hydrogel exhibits significant temperature responsiveness, with a lower critical solution temperature (LCST) of 25.41°C. Its transmittance decreases sharply from 41% at 20°C to 12% at 40°C, while its electrical signals vary correspondingly with temperature changes. Owing to its exceptional combination of mechanical, deformation, and temperature‐responsive properties, the PICDN hydrogel shows great promise for applications in flexible strain sensors.