Fig. 1

Working principle and design strategy. a Schematic diagram of the working principle of the sensing and actuating layers, in which LCST means the lower critical solution temperature. b Schematic diagram indicating the structure design of the three-layer hydrogel muscle. c Images of the fabricating process and fabricated hydrogel muscle. d Cross-section SEM images of the actuating and sensing layer, and EDS images of the sensing layer. e FTIR image of the actuating layer with different HEMA content. f Deswelling (45 °C) and swelling (20 °C) process of the actuating layer with different HEMA content