Visible-light-driven isotropic hydrogels as anisotropic underwater actuators

Abstract

Photo-driven hydrogel actuators have attracted tremendous attention due to their underwater photo-mechanical applications, but these critical limitations include reliance on harmful UV light, slow driving speed and limited transformation morphologies need to be further resolved. Here, the transparent polyurethane (PU) hydrogels containing dual networks of dynamic covalent crosslinked hexaarylbiimidazole (HABI) and permanent-crosslinked pentaerythritol units are fabricated and exhibit diversified anisotropic transformations in response to visible light. The underwater three-dimensional (3D) actuations including curling, twisting and folding can be spatiotemporally programmed and achieved within tens of seconds. The biomimetic flower and hydrogel wheel enable rapid photo-driven locomotion. The hydrogel actuators possess great fatigue resistance and reusability. Our work provides new insights to the design of underwater biomimetic intelligent actuators based on photochemically transformation. Isotropic polyurethane hydrogels containing the dynamic covalent units hexaarylbiimidazole (HABI) are designed as visible light-driven anisotropic underwater actuators, which exhibit simple bending, diversified three-dimensional (3D) movement including curling, twisting and folding and the blooming/closing of biomimetic flower as well as the rolling of hydrogel wheel upon directional 405 nm irradiation. • Dual-crosslinked biomimetic polyurethane (PU) hydrogels containing hexaarylbiimidazole (HABI) units are fabricated. • The cleavage of dynamic C‒N bonds in HABI units cause the photo-induced secondary swelling of hydrogels upon irradiation. • Diversified three-dimensional (3D) deformation can be spatiotemporally programmed and achieved within tens of seconds. • The covalent-crosslinked dual networks endow actuators remarkable mechanical stability and long-term repeatable utility.