Light-Powered Soft Steam Engines for Self-Adaptive Oscillators and Biomimetic Swimming Robotics

Oscillation plays a vital role in the survival of living organisms in changing environments, and its relevant research has inspired many biomimetic approaches to soft autonomous robotics. However, it remains challenging to create soft oscillators that can work under constant energy input and actively adjust the oscillation mode in response to environmental changes. Here, we present a steam-driven photothermal oscillator operating under constant light irradiation for continuous or pulsed, damped harmonic mechanical oscillations. The key component of the oscillator is a hydrogel containing Fe₃O₄/Cu hybrid nanorods, which can convert light into heat and generate steam bubbles. Controllable perturbation to the thermo-mechanical equilibrium of the oscillator can thus be achieved, leading to either continuous or pulsed oscillation depending on the light intensity. Resembling the conventional heat steam engine, this environment-dictated multimodal oscillator uses steam as the working fluid, enabling the design of self-adaptive soft robots that can actively adjust their body functions and working modes in response to environmental changes. We then developed an untethered biomimetic neuston-like robot (neusbot) based on this soft steam engine, which can adapt its locomotion mechanics between uniform and recurrent swimming to light intensity changes and perform on-demand turning under continuous light irradiation. Fueled by water and remotely powered by light, this unique hydrogel oscillator enables easy control over the oscillation dynamics and modes, offering a promising approach to self-adaptive soft robots and solar steam engines.