Hydrogen-Bonded Liquid Crystal Elastomers Combining Shape Memory Programming and Reversible Actuation

Materials that undergo shape morphing in response to external stimuli have numerous applications, e.g., in soft robotics and biomedical devices. Shape memory polymers utilize kinetically trapped states to, typically irreversibly, transfer between a programmed morphed shape and an equilibrium shape. Liquid crystal elastomers (LCEs), in turn, can undergo reversible actuation in response to several stimuli. This study combines the irreversible and reversible shape morphing processes to obtain LCEs that undergo shape-programming via the shape memory effect and subsequent reversible actuation of the programmed shape. This is enabled by an LCE crosslinked via dynamic hydrogen bonds that break at high temperatures and reform upon cooling, endowing the shape memory effect, while mild thermal or photothermal stimulation yields the reversible actuation. Through this combination, proof-of-concept robotic application scenarios such as grippers that can adjust their shape for grabbing different-sized objects and crawling robots that can morph their shape to adapt to constrained spaces, are demonstrated. It is anticipated that this work adds new diversity to shape-programmable soft microrobotics. A liquid crystal elastomer (LCE) actuator that can be programmed into multiple temporary shapes while maintaining reversible actuation capability is designed by incorporating hydrogen-bond crosslinks into a chain-extended LCE. The shape programming is enabled via the shape memory effect, while reversible actuation is obtained via mild thermal or photothermal stimulus. Potential applications in light-controlled grippers with adjustable shapes to grab different-sized objects, and locomotors that can be shape-programmed to fit into tight spaces, are anticipated.image