Light-driven autonomous swing of multi-layered hydrogel

Light-driven self-oscillators without electronic circuits or conventional heat engines are carbon-emission-free systems and hold promise for developing autonomous transmission pumps and self-swimming micromotors. Thermosensitive hydrogels as self-oscillators can be used in the exploitation of low-temperature heat sources and in medical applications since the driving temperature is close to body temperature. Here, the autonomous swinging of the hydrogel was achieved by irradiating a constant light beam onto a head laminated with two thermosensitive hydrogels with different transition temperatures. Hysteresis resulting from the transition point difference between the two hydrogels allowed the light-driven self-oscillation without self-shadowing from the irradiation. The proposed theoretical model and numerical simulations explain this light-driven continuous swing, and the results agree qualitatively well with the experiments.