Polyethylene Glycol-Based\nConductive Hydrogels with\nAnti-Freezing, Water Retention and Self-Adhesion for Flexible Sensors

Conductive hydrogels are characterized by their extraordinary\nstretchability,\nflexibility, and biocompatibility, making them ideal materials for\nflexible wearable sensors. However, they often encounter challenges\nsuch as freezing and water loss, which can adversely affect their\nconductivity and stretching performance. In this study, we introduce\na conductive hydrogel incorporating polyethylene glycol (PEG), acrylic\nacid (AA), acrylamide (AM), and lithium chloride (LiCl), which exhibits\nlow-temperature tolerance, resistance to drying, self-adhesion, and\nmechanical robustness. The hydrogel’s excellent mechanical\nproperties, including an elongation at break of 1120% and a toughness\nof 2.9 MJ m<sup>–3</sup>, are attributed to the formation of\na tight polymer network between P(AA-AM) and PEG through hydrogen\nbonding. The multiple hydrogen bonding system between PEG and the\npolymer networks, combined with the hydration of LiCl and electrostatic\ninteractions between the carboxyl group and Li<sup>+</sup>, significantly\nenhances the hydrogel’s freezing resistance (down to −60\n°C), water retention (with only 20% water loss after 15 days),\nand self-adhesion (with an adhesion strength to pig skin of up to\n55.08 kPa). When employed as a flexible sensor, the P(AA–AM)/PEG/LiCl\nhydrogel exhibited excellent sensing properties for monitoring various\nhuman motions, with an impressive gauge factor of 1.91 and electrical\nconductivity of 4.50 S m<sup>–1</sup> Moreover, it maintained\na high electrical conductivity (3.82 S m<sup>–1</sup>) even\nat −20 °C. The conductive hydrogel consistently produced\nstable and reliable electrical signals in response to external mechanical\nstimuli, making it a preferred material for human motion monitoring.