Spiropyran based hydrogels actuators-Walking in the light

•Synthesis of a bipedal hydrogel walker is reported.•Hydrogel shrinking and swelling is controlled via light.•The hydrogel shows unidirectional walking when placed onto a ratcheted surface.•Direction of movement is determined by ratchet design.

Herein we report on the synthesis of a bipedal hydrogel walker, based on N-isopropylacrylamide-co-acrylated spiropyran-co-acrylic acid p(NIPAAm-co-SP-co-AA). Due to the presence of the photochromic spiropyran molecule in the polymer structure, these hydrogels reversibly shrink and swell in aqueous environments when exposed to different light conditions. When placed onto a ratcheted surface, the actuation of the bipedal gel produces a walking motion by taking a series of steps in a given direction, as determined by the optimised design of the ratchet scaffold. We anticipate that such biomimetic hydrogel walkers could form the basis of light-actuated soft robots capable of more advanced functions, such as autonomous migration to specific locations accompanied by triggered release of molecular cargo.

Graphical abstractHerein we report on the synthesis of a hydrogel walker. These hydrogels are able to reversibly shrink and swell in aqueous environments when exposed to different light conditions. When placed onto a ratcheted surface, the actuation of the bipedal gel can result in a walking motion by taking a series of steps in a unidirectional fashion.Download high-res image (104KB)Download full-size image