Strong and Tough Antifreezing Hydrogel Sensor via the Synergy of Coordination and Hydrogen Bonds

Abstract

Hydrogel sensors are fascinating as flexible sensors and electronic skin due to their excellent biocompatibility and structure controllability. However, developing conductive hydrogels possessing both excellent mechanical and antifreezing properties for environmental-adaptive sensors remains a challenge. Herein, a strategy of combining betaine and metal ions to construct poly­(acrylic acid) (PAA)-based high-conductive hydrogels has been reported. PAA-Al3+/betaine hydrogels with high toughness and antifreezing property were prepared by a one-step UV curing method. Their high toughness is attributed to the coordination of metal ions with the carboxylic groups in PAA, the interaction of betaine with PAA, and the formation of hydrogen bonds between them and water molecules. Moreover, the significant antifreezing property is due to the reduction of free water in the hydrogel. This, in turn, is attributed to the hydration of metal ions and the synergistic hydrogen bonding between betaine and water. The experiments demonstrate that the hydrogel has excellent mechanical property, high conductivity, superior transparency, antiswelling property, antipuncture as well as shape memory properties, and especially, low cytotoxicity. It can be used as a sensor for motion detection and information recognition. This work provides new insights into the application of flexible sensors and human–machine interfaces in multienvironmental conditions.

Anti-Freezing and Ultrasensitive Zwitterionic Betaine Hydrogel-Based Strain Sensor for Motion Monitoring and Human–Machine Interaction

“…As displayed in Figure 1c, massive hydrogen bonds were formed by the amino group, the hydroxyl group, BA, and water molecules, which dynamically built strength and durability. 28 Figure 1d demonstrates covalent bonds between PAM chains and PVA chains were also cross-linked, which effectively dispersed energy and enhanced toughness. 29 Besides, in Figure 1e, the electrostatic interaction of zwitterionic betaine attracted ammonium and sulfate, which enhanced hydrogel strength and conductivity.…”

“…During the formation of the hydrogel, there were multiple chemical interactions to enhance mechanical properties. As displayed in Figure c, massive hydrogen bonds were formed by the amino group, the hydroxyl group, BA, and water molecules, which dynamically built strength and durability Figure d demonstrates covalent bonds between PAM chains and PVA chains were also cross-linked, which effectively dispersed energy and enhanced toughness .…”