Tunable Thermoresponsive and Antifreezing Hydrogels Enhanced by LiCl for Health Detection and Information Encryption

Temperature-stimulus-responsive hydrogels with outstanding mechanical and electrical properties have attracted extensive attention in the field of health detection and information encryption due to their unique environmental responsiveness. In this work, a flexible, conductive, tunable thermoresponsive, and antifreezing poly(acrylic acid-acrylamide)/gelatin/lithium chloride (P(AA-AM)/Gelatin/LiCl, PGL) hydrogel was fabricated via a simple one-pot approach. Functional regulator LiCl effectively enhances the mechanical properties of the PGL hydrogel through salting-out effect and phase separation. Also, the transparent-to-opaque transition is reversible and repeatable, and the phase transition temperature can be sensitively adjusted by LiCl mass in the PGL hydrogels. Especially, the PGL_0.8 hydrogel with a strength of 180 kPa, a strain of 620%, and a conductivity of 2.16 S m^-1 can serve as the strain sensor (gauge factor of 1.95) and temperature sensor (temperature resistance coefficient of 2.05%/°C at 25-45 °C). Benefiting from its excellent performance, the as-prepared PGL hydrogels can capture real-time electrical signals, including human joint motions, subtle physiological movements, and temperature fluctuations, when utilized as wearable multifunctional sensors. Therefore, the tunable thermoresponsive and antifreezing hydrogel holds promise for human health monitoring and information encryption, meeting theoretical and practical application requirements of flexible wearable sensors.