Anti-freeze hydrogel-based sensors for intelligent wearable human-machine interaction

As human-machine interaction (HMI) is inseparable from our daily life, it drives people to pursue a more convenient and intelligent way of life. Most of the traditional HMI devices are manufactured with rugged materials, accompanied by disadvantages such as being fragile and not being bent at random. Hydrogels with good mechanical properties, excellent biocompatibility, and ultra-high sensitivity have been used in HMI systems and received wide attention from researchers. However, due to the high water content of hydrogels, freezing inactivation happens in low-temperature environments. Therefore, it is necessary to develop a new generation of antifreeze gel materials that can withstand harsh cold environments and be used to expand the practical applications of wearable HMI devices. Here, we systematically classify antifreeze hydrogels based on the antifreeze mechanism of inhibiting ice crystallization and inhibiting ice nucleation, and summarize the representative antifreeze agents in antifreeze hydrogels as well as the corresponding preparation methods. Meanwhile, the main properties of antifreeze hydrogels are introduced in detail. Furthermore, we highlight representative applications of antifreeze hydrogels in wearable HMI, including healthcare, touch monitoring, and intelligent control. Finally, we outline the critical challenges currently faced in the field and a view of future trends.