A robust, fatigue-resistant, self-healing, and recyclable κ-carrageenan-based ionic conductive hydrogel with synergistic K+/Ca2+ enhancement for multifunctional flexible sensor.

Conductive hydrogels have demonstrated great potential in flexible wearable sensors due to their excellent flexibility and conductivity. Nevertheless, traditional hydrogels suffer from limitations such as weak mechanical properties, inadequate fatigue resistance, and lack of recyclability, which have hindered their practical applications. In this study, a polyvinyl alcohol/polyacrylamide/κ-carrageenan-Ca2+/K+ (PPK-Ca2+/K+) composite hydrogel was developed by constructing a dynamic network structure involving hydrogen bonds, electrostatic interactions, and synergistic co-crosslinking of Ca2+/K+. The resulting ionic conductive hydrogel exhibited remarkable stretchability (~ 414 %), high tensile strength (1190 kPa), and excellent fatigue resistance. Benefiting from the negatively charged κ-carrageenan and the ion transport co-regulation by Ca2+/K+, the hydrogel achieved a high ionic conductivity of 7.26 mS/cm. Moreover, owing to the thermoreversible properties of κ-carrageenan and PVA, the hydrogel material could be recycled through high-temperature remolding processes. The flexible sensor assembled with PPK-Ca2+/K+ hydrogel demonstrated high sensitivity, a broad detection range (0-400 %), and rapid response time (152 ms), enabling precise monitoring of various human activities, ranging from large joint movements to subtle muscle contractions. The proposed fabrication strategy for robust, fatigue-resistant, self-healing, and recyclable conductive hydrogel provides new insights for developing high-performance wearable sensors and electronic skin.