Anti-Freezing, Conductive Triple-Network Hydrogel for Wearable Sensing and Stable Biopotential Recording over 24 Hours.

Hydrogel-based sensors face two persistent challenges: freeze-induced performance failure at sub-zero temperatures and an inherent trade-off between mechanical robustness and electrical conductivity. To address these issues, a triple-network hydrogel composed of polyacrylamide, gelatin, and carboxymethyl cellulose was designed, synergistically integrated with LiCl, CaCl2, and glycerol. In this design, glycerol serves as the primary cryoprotectant, Li+ ions provide ionic conduction, and Ca2+ crosslinks reinforce the polymer network. The optimized hydrogel achieves high tensile strength (576 kPa), ultra-high stretchability (938%), outstanding toughness (233.4 kJ/m3), and high conductivity (2.95 S/m), while completely suppressing ice crystallization down to -80 °C. As a strain sensor, it delivers a gauge factor of 3.53 after freezing; as a bioelectrode, it records high-quality EMG, ECG, EOG, and EEG signals comparable to or surpassing commercial Ag/AgCl electrodes, and maintains reliable performance over 24 h at -20 °C. This work demonstrates a durable material candidate for long-term wearable sensing and biopotential recording in sub-zero environments.