Halloysite nanotubes as nano-support matrix for programming the photo/H₂O dual triggered reversible gel actuator

Gel actuators are a kind of soft intelligent material that can convert external stimuli into deformations to generate mechanical responses. The development of gel actuators with advanced structures to integrate multiple responsiveness, programmability, and fast deformation ability is urgently needed. Here, we explored a poly(7-(2-methacryloyloxyethoxy)-4-methylcoumarin-co-acrylic acid-co-glycol) ternary gel network as an actuator with reprogrammable photo/H₂O dual responsibilities. In such a design, [2 + 2] photodimerization and photocleavage reactions of coumarin moieties can be realized under 365 and 254 nm light irradiation, respectively, affording reversible photodriven behaviour of the gels. The abundant carboxylic acid in the backbone has the capacity to form additional crosslinks to assist and accelerate the photodriven behaviour. The incorporation and orientation of halloysite nanotubes (HNTs) in gel matrices support an axial direction force and result in a more controllable and programmable actuating behaviour. The synergistic response enables fast grasping-releasing of 5-times the weight of the object in water within 10 min by fabricating HNT-incorporated gels as a four-arm gripper.