Polyethylene Glycol-Based Conductive Hydrogels with Anti-Freezing, Water Retention and Self-Adhesion for Flexible Sensors

Conductive hydrogels are characterized by their extraordinary stretchability, flexibility, and biocompatibility, making them ideal materials for flexible wearable sensors. However, they often encounter challenges such as freezing and water loss, which can adversely affect their conductivity and stretching performance. In this study, we introduce a conductive hydrogel incorporating polyethylene glycol (PEG), acrylic acid (AA), acrylamide (AM), and lithium chloride (LiCl), which exhibits low-temperature tolerance, resistance to drying, self-adhesion, and mechanical robustness. The hydrogel’s excellent mechanical properties, including an elongation at break of 1120% and a toughness of 2.9 MJ m^-3, are attributed to the formation of a tight polymer network between P(AA-AM) and PEG through hydrogen bonding. The multiple hydrogen bonding system between PEG and the polymer networks, combined with the hydration of LiCl and electrostatic interactions between the carboxyl group and Li⁺, significantly enhances the hydrogel’s freezing resistance (down to −60 °C), water retention (with only 20% water loss after 15 days), and self-adhesion (with an adhesion strength to pig skin of up to 55.08 kPa). When employed as a flexible sensor, the P(AA-AM)/PEG/LiCl hydrogel exhibited excellent sensing properties for monitoring various human motions, with an impressive gauge factor of 1.91 and electrical conductivity of 4.50 S m^-1 Moreover, it maintained a high electrical conductivity (3.82 S m^-1) even at −20 °C. The conductive hydrogel consistently produced stable and reliable electrical signals in response to external mechanical stimuli, making it a preferred material for human motion monitoring.