Light-Powered Robot Decontaminates on Water’s Surface

Researchers at the University of California, Riverside have devised a sustainable solution to clean contaminants in open waters. The researchers have introduced a light-powered, floating, autonomous, soft robot that is fueled by vaporized water.

The robot is called Neusbot, after “neustons,” a category of organisms that float on the top of water or live right under the surface.

Neusbot can generate adjustable, mechanical oscillating movements — a capability that is essential for the robot to function in a controlled way. To achieve controllability, the researchers based the design of their sunlight-powered robot on the steam engines that powered the first locomotives.

“There aren’t many methods to achieve this controllable movement using light,” researcher Zhiwei Li said. “We solved the problem with a tri-layer film that behaves like a steam engine.”

The researchers built a steam-driven photothermal oscillator that operates under constant light irradiation. The oscillator can perform continuous or pulsed mechanical oscillations. The key component of the oscillator, which makes up the middle layer of the robotic film, is a hydrogel containing hybrid iron oxide and copper nanorods. Nanorods convert light into heat and generate steam bubbles that power the robot’s motion across the surface of water. The thermomechanical equilibrium of the oscillator can be disrupted to enable continuous or pulsed oscillation.

A robotic film developed by researchers at UC Riverside could be trained to vacuum oil spills at sea or remove contaminants from drinking water. The robot, called Neusbot, is depicted on the open ocean with a secondary light source. Courtesy of Zhiwei Li/UCR.

The design of Neusbot, an untethered, biomimetic robot, is based on this soft steam engine. Neusbot can adapt its locomotion mechanics between uniform and recurrent swimming to changes in light intensity and perform on-demand turning under continuous light irradiation. The self-adaptive Neusbot can actively adjust its body functions and working modes in response to environmental changes. Li and professor Yadong Yin, who developed Neusbot, controlled the robot’s direction by changing the angle of its light source.

Neusbot’s bottom layer is hydrophobic, or water-repelling. Even if an ocean wave were to overpower the film, it would float back to the surface. Additionally, the nanomaterials that comprise Neusbot can withstand high salt concentrations without damage.

The current version of Neusbot features three layers. The researchers plan to test future versions with a fourth layer that could absorb oil or other chemicals. “Normally, people send ships to the scene of an oil spill to clean by hand,” Li said. “Neusbot could do this work like a robot vacuum, but on the water’s surface.” The floating, robotic film could be deployed indefinitely for cleanup in remote areas, where recharging by means other than sunlight would be a challenge.

Superimposed images show Neusbot’s bending process. Neusbot can adapt its locomotion mechanics between uniform and recurrent swimming to changes in light intensity and perform on-demand turning under continuous light irradiation. Courtesy of Zhiwei Li/UCR.

The researchers also plan to work on controlling the robot’s oscillation mode more precisely and on enhancing its capability for complex motion.

Fueled by water and remotely powered by light, the multimodal, environment-driven oscillator that is the basis of Neusbot could offer an effective approach to other self-adaptive soft robots and solar steam engines. While other scientific teams have created robotic films that bend in response to light, they have not been able to generate the adjustable, mechanical oscillation of which Neusbot is capable. The soft robotic film is also reusable.

“Our motivation was to make soft robots sustainable and able to adapt on their own to changes in the environment. If sunlight is used for power, this machine is sustainable, and won’t require additional energy sources,” Li said.

The research was published in Science Robotics (www.science.org/doi/10.1126/scirobotics.abi4523).