Bioinspired layered hydrogel actuator via L-ascorbic acid-triggered interfacial self-growing from stiff hydrogel

Abstract

Stimuli-response layered hydrogel actuators are highly attractive in broad applications of soft robots, intelligent devices and etc., owing to softness, asymmetric responsiveness and deformability. However, current layered hydrogel actuators suffer from serious challenges such as tedious preparation, uncontrollable layer thickness and weak interfacial bonding force. Herein, we put forward a facile and highly efficient self-growing method to prepare layered hydrogel actuator from stiff hydrogel substrate by crafting L-ascorbic acid (Vc)-triggered interfacial radical polymerization. The redox reaction between Vc and confined Fe3+ in stiff hydrogel substrate could produce Fe2+ catalysts, resulting in surface catalytically initiated radical polymerization (SCIRP) at room temperature. Various layered hydrogels were prepared rapidly and the thickness of grown hydrogel layer can be accurately controlled. The obtained layered hydrogel exhibits asymmetric structural layers consisting of a dense layer and a porous layer, as well as strong interface bonding force of about 250 N/m between porous layer and stiff substrate. Furthermore, a thermo-responsive layered hydrogel actuator was developed, which showed reversible underwater bending ability in response to temperature and can also be designed as a smart manipulator to capture objects underwater. This work provides a novel and feasible approach for highly efficient and controllable preparation of layered hydrogel actuator, which will find promising applications in the field of soft robots, intelligent devices, sensors and so on.