Frontal Polymerization-Oriented Self-Healing Hydrogels and Applications toward Temperature-Triggered Actuators

Hydrogels that are capable of autonomous healing upon damage have attracted wide attention in recent years. The design and fabrication of hydrogels possessing both excellent self-healing and high strength is highly desired. Herein, we report the facile synthesis of self-healing poly(MAH-beta-CD-co-AA) hydrogels (MAH-beta-CD = beta-cyclodextrin grafted vinyl carboxylic acid groups; AA = acroleic acid) via frontal polymerization (FP) for the first time. When ignited by a soldering iron, frontal polymerization occurred to fabricate poly(MAH-beta-CD-co-AA) hydrogels within 10 min. The as-fabricated hydrogels exhibited pH sensitivity and high mechanical strength and could repair themselves autonomously without any external stimuli. In addition, we reinforced poly(MAH-beta-CD-co-AA) hydrogel through further cross-linking with N-isopropylacrylamide to form a double network (DN) hydrogel. Benefiting from the excellent self-healing property, a Janus bilayer hydrogel toward temperature-triggered actuator was achieved by simply sticking poly(MAH-beta-CD-co-AA) and DN hydrogel together. This hydrogel actuator was very sensitive to thermal stimulus, which showed a rapid response in several seconds. This work might promote the development of diverse functional self-healing hydrogels via a facile and flexible pathway.