From Sea Cucumbers to Soft Robots: A Photothermal-Responsive Hydrogel Actuator with Shape Memory

Abstract

Soft robotics has undergone considerable progress driven by materials that can effectively transduce external stimuli into mechanical actuation. Here, we report the development of a photothermal-responsive hydrogel actuator with shape memory capabilities inspired by the adaptive locomotion of sea cucumbers. This actuator is based on sea cucumber peptides (SCP) and a liquid metal (LM) hydrogel network that is responsive to near-infrared (NIR) light. Upon NIR irradiation, the hydrogel undergoes a phase transition from a swollen to a collapsed state, resulting in a controlled volumetric and shape change. Incorporating a shape memory polymer (SMP) into the hydrogel matrix facilitates the actuator's retention of its deformed configuration following stimulus removal, thereby enabling intricate, multiphase shape transformations. This SCP/LM hydrogel overcomes the limitations of traditional hydrogels and achieves good stretchability (3,000%) and enough adhesion (21 kPa), exhibiting no toxicity to human cells. Furthermore, the actuator exhibited significant bending and complex deformation within 100 s of NIR exposure. This photothermal-responsive hydrogel actuator offers new opportunities for soft robotics and biomedical applications, showcasing a potential pathway for incorporating shape memory and photothermal-responsive materials into the next generation of smart soft devices.