A Flatworm‐Like Hydrogel with Surface Double‐Network Structure for Re‐Programmable Multimode Actuations

Abstract Programmable stimuli‐responsive hydrogels have rapidly developed for various complex biomimetic actuations, but they commonly can only be programmed once. Herein, a flatworm‐like hydrogel (FLH) with bi‐surface double‐network structure (photothermal‐responsive FLH‐1 and pH‐responsive FLH‐2) has been explored, through UV‐polymerizing sodium poly(methylacrylic‐acid) (PMAA‐Na) and poly (N‐isopropylacrylamide) (PNIPAM) second‐networks on two surfaces of polyacrylamide‐graphene (PAAm‐G) substrate hydrogel first‐network respectively. First, the graphene can both control the thickness of the UV‐polymerized surface second‐network and endow the FLH with high‐efficient photothermal conversion for near‐infrared light (NIR)‐responsive actuation. More importantly, different from common pH‐/photothermal bi‐responsive actuating hydrogels, one FLH can be designed as various original shapes by pH‐responsive FLH‐2, for reprogrammable NIR‐responsive multimode complex actuations via FLH‐1. Finally, the FLH‐1 and FLH‐2 can be strongly integrated together by the interpenetrating structure of flatworm‐like structure between second‐network and first‐network, to endow the FLH with excellent stability for enduring complex deformations. Consequently, the synergy of re‐programmable original shapes via FLH‐2 and NIR‐responsive actuation by FLH‐1, can endow one FLH with multimode actuations for high‐level biomimetic devices. This work can provide a general method by non‐touching design of re‐programmable hydrogel with two stimuli‐responsive layers for multimode complex actuations, which also will inspire explorations of other reprogrammable intelligent materials.