A Superior Self-Adhesive, Self-Healing, and Anti-Freezing Gel toward Flexible Sensor Applications in Extreme Conditions

As an important part of flexible wearable electronics, hydrogel sensors have aroused great interest. However, two serious issues, low self-healing efficiency and terrible environmental adaptability, have largely limited the development of hydrogel sensors. Herein, a versatile gel elastomer (P(HEA-AA)/PEI/Gly) is synthesized via introducing polyethylenimine (PEI), 2-hydroxyethyl acrylate (HEA), and acrylic acid (AA) into a glycerin/water binary solvent system, which exhibits high stretchability (1427% elongation), outstanding self-healing efficiency (95%), and exceptional low-temperature adaptability (−35 °C) as well as robust self-adhesion. Meanwhile, the assembled P(HEA-AA)/PEI/Gly gel sensor possesses reliable sensitivity, wide strain range, and long-term cycling stability, which can not only precisely monitor different mechanical deformations (stretching, twisting, and bending) but also specifically distinguish the human activities in the opposite direction. In particular, even in an extremely cold environment of −35 °C, the gel sensor still can withstand large mechanical damages caused by external factors and restore its sensing capability. This feature inspires us to construct a wearable communication device with a low-temperature self-healing function that can accurately deliver various valuable information to the receiver under extreme conditions, such as "Warn", "Cold", and "Dangerous". This work provides a feasible method to construct excellent self-healing and temperature tolerant gel sensors and paves the way for versatile applications in electronic skin, artificial intelligence, and soft robotics.