Tough double network gelatin-based hydrogel sensor via polyelectrolyte-induced Hofmeister effect for human-machine...

The development of hydrogel-based sensors for human-machine interaction (HMI) is often hindered by the trade-off between mechanical robustness and multifunctional responsiveness. Herein, a polyelectrolyte-induced Hofmeister effect strategy is proposed to construct the gelatin-based double network hydrogel (Gelatin-PAANa hydrogel), avoiding the salt leakage and cytotoxicity issues associated with conventional approaches. Localized salting-out of gelatin chains is electrostatically triggered by the incorporation of sodium polyacrylate (PAANa), leading to enhanced polymer crystallization and the formation of densely crosslinked network. The optimized hydrogel achieves high toughness (1.9 MJ/m³), ionic conductivity (1.05 S/m), and dual strain-temperature sensing. It exhibits fast strain response (329 ms, 10-400% range, gauge factor (GF) = 0.42) for motion detection, and a linear temperature response (temperature coefficient of resistance (TCR) = -1.16%/°C) suitable for fire warning. Integrated the Gelatin-PAANa hydrogel sensor with a microcontroller, it enables gesture recognition, Morse code transmission, and robotic control, while showing excellent biocompatibility. This work provides a biofriendly to design hydrogels for next-generation wearable electronics and intelligent interactive systems.