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

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.