Anisotropic liquid crystalline hydrogel actuators with multi-stimuli-responsive actuation and multimodal locomotion

Anisotropic hydrogels have garnered significant attention for their potential applications in actuators, soft robotics, and artificial muscles, owing to their ability to perform shape morphing and generate anisotropic responses under external stimuli. Herein, we present a novel strategy for fabricating anisotropic hydrogels with the aid of liquid crystal polymers (LCPs). A series of liquid crystal polyester-polyethylene glycol (LCP-PEG) multiblock copolymers with varying molecular weights of the PEG block is synthesized via one-pot melt-polycondensation. Upon stretching, LCP-PEG forms a stable, oriented microphase-separated lamellar structure, which endows LCP-PEG with reversible shape change from melting-induced contraction and crystallization-induced expansion of the oriented PEG crystals. This unique structure imparts anisotropic swelling behavior to the films when exposed to water or humidity. Thanks to the oriented microphase separated lamellar structure, the anisotropic liquid crystalline hydrogels have high fracture strength (11.2–14.7 MPa), fracture strain (1600%–2100%), fracture energy (1.7–2.8 MJ m−2), and Young’s modulus (51.2–139.9 MPa). Furthermore, the anisotropic LCP-PEG hydrogel actuators exhibit a range of versatile locomotion modes, including object grabbing and transfer between water and air, object gripping in rainy conditions, walking and somersaulting on ratchet-patterned bases under humidity stimuli, and slope climbing through somersault locomotion under salty water stimuli.