Check Out This Soft-bodied, Light-powered Swimming Robot

The team believes their new design could have some interesting applications in the future. It could, for example, open up opportunities for new designs of ocean-going robots, medical treatments, and autonomous ships. 

The robot was inspired by a natural phenomenon called phototaxis. Some creatures in nature, like jellyfish or moths, have this tendency to move towards a light source.

"OsciBot demonstrates that moving by oscillation can be directly powered [by] constant light, rather than relying on light energy that has been harvested and stored in a battery. It's made entirely of a soft material called a hydrogel that swells when placed in water and is responsive to light. The device does not require batteries or need to be tethered to another power source," notes the press release.

Using light to make hydrogel dance

To create their new soft-bodied, light-loving robot, the team first needed to develop a means of making an object oscillate in response to a constant energy source.

In order to do that, they first built a 2-centimeter flexible hydrogel long cylinder and anchored it to the bottom of a water tank. They found that when a beam of light was directed at the cylinder, it actually moved about 66 times per minute.

They were also astonished to find that by moving the light source, the cylinder actually bent left, right, up or down, in response.

By changing the length and thickness of the cylinder, they were also able to affect the speed at which the cylinder moved. Building on this, the team used the same hydrogel to build a rectangular surfboard-shaped robot with an extended underwater tail (as seen in the first video above).

According to the UCLA press article, "When light from a laser hits a spot on the tail, that spot heats up. The slight increase in temperature causes that part of the robot to eject some of its water and shrink in volume, which moves the tail toward the light source. After it moves up, the tail creates a shadow that cools the section where the laser originally made contact with the robot, which causes the tail to descend again."

So long as the light hits the target, this process can be repeated ad infinitum. Through further experimentation, the team found that they could make the tail flap about 35 times a minute.

That was enough, by their estimation, to move the robot about 1.15 times its body length per minute. 

Ximin He, a UCLA assistant professor of materials science and engineering, and the study's principal investigator explained that "typically, generating oscillation relies on intermittent energy input, such as pulsed light or alternating electric current."

"By contrast, this study shows a new way of generating oscillation, by using a constant energy input that is easily accessible from the ambient environment and inexpensive to harness," he added.

Just like the fixed cylinder in previous experiments, they could make the robot steer by repositioning the light source. It could even be directed around a bend.

"This is really a fundamental demonstration that direct and constant light can power and determine movement," said Yusen Zhao, the study's lead author.

"It could be a step toward a variety of robotic designs that are untethered and powered solely by the available light in their surroundings, rather than relying on heavy batteries or power cables," Zhao added.

What applications could this have in the real-world?

Theoretically, the design could be scaled up to provide new forms of underwater propulsion systems. It could even have applications for wind sails that use sunlight to maneuver. 

On a smaller scale, this technology could be used for some precision medical procedures. Of course, a direct light source would also need to be introduced into the patient's body to make this practical.

"The beauty of the gel-based photo-oscillator is its design simplicity," Zhao explained. "The interplay between the 'smart' soft material and the environmental light enabled its self-regulated motion."

Zhao even hinted that the technology could be adapted for energy generation —like acoustic waves, or electronic/magnetic signals, for example. 

The original paper was published in the journal Science Robotics.