A skin-mimetic MXene-loaded silk-textile composite anisotropic hydrogel for programmable complex, powerful and fast light-responsive actuations

Stimuli-responsive actuating hydrogels, with “soft and wet” state, are most important intelligent materials, which have been widely applied in more and more fields. However, the natural isotropic structure and high water-content of hydrogels leads to relatively simple actuating mode and weak mechanical performance respectively, which severely limit further applications of actuating hydrogels. To solve these problems, this study has developed a new actuating hydrogel with skin-mimetic anisotropic structure. Based on supramolecular interaction, monolayer MXene nanosheets can be loaded on the surface of silk-textile that can be embedded in the N-isopropylacrylamide (NIPAM) precursor solution to obtain as-prepared skin-mimetic anisotropic hydrogel (SMAH) with MXene-loaded silk-textile/poly(N-isopropylacrylamide) (PNIPAM) composite hydrogel layer and the pure PNIPAM hydrogel layer. First of all, the MXene-loaded silk-textile layer of the SMAH (just like the epidermis layer of the skin) not only can provide high strength for powerful actuating force, but also can be embedded into the PNIPAM layer (just like the dermis layer of the skin) to obtain anisotropic structure for various programmable complex actuation. Furthermore, the SMAH can achieve remotely-controlled near-infrared light (NIR)-responsive fast actuation owing to the high-efficiency of photothermal-conversion caused by the MXene-loaded silk-textile. As a result, this SMAH has been designed for several intelligent biomimetic devices with programmable complex, powerful (it can lift up ≥ 60 mass times of itself) and fast (71o/s of average bending speed) actuations under remotely-controlled NIR-irradiation, including biomimetic “claw”, “snake” and even “octopus”. This study provides a skin-like anisotropic intelligent actuating hydrogel for biomimetic deformations and movements, which also will inspire the new research of other smart materials and devices.