Anisotropic Liquid Crystalline Hydrogel Actuators with Multi-Stimuli-Responsive Actuation and Multimodal Locomotion
Anisotropic hydrogels have attracted significant attention for applications in actuators, soft robotics, and artificial muscles due to their ability to undergo shape morphing and generate anisotropic responses under external stimuli. Here, we report a novel strategy for fabricating anisotropic hydrogels using liquid crystal polymers (LCPs). A series of liquid crystal polyester-polyethylene glycol (LCP-PEG) multiblock copolymers with varying PEG block molecular weights were synthesized via one-pot melt-polycondensation. Upon stretching, LCP-PEG forms a stable, oriented microphase-separated lamellar structure, which enables reversible shape changes driven by 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. The oriented microphase-separated lamellar structure confers 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 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. These results demonstrate the potential of LCP-based anisotropic hydrogels for advanced soft robotic applications.