Light-Treated Graphene Creates Water-Powered Creepy Crawler

Small, squishy self-powered robots are on the rise, like the fully-soft Octobot developed last summer. Now, researchers have demonstrated two devices—an insect-shaped crawler that, when activated by light, inches its way towards humidity and a star-shaped claw that closes when exposed to humidity.

While the “robots” themselves are pretty simplistic, the mechanism that drives them holds promise for tissue engineering, drug discovery, biomedical testing, and automation. The self-powered action they demonstrate could enable organs-on-a-chip that mimic biological systems or endow tiny machines with gripping claws.

The crawlers and claws were made using graphene, a two-dimensional sheet of carbon atoms.  Graphene and its oxygen-containing variants—known as graphene oxides—are strong, flexible, and stable. They also conduct heat and electricity, and many can be safely embedded in our bodies.

These small crawlers move towards humidity without any external power.

To prep the crawler, researchers exposed one side of it to a camera flash from about 20-30 millimeters away, which removed some of the oxygen- and hydrogen atoms in a process called reduction. The reduction process turned the graphene oxide from a yellow-brown color to the black seen in the video.

The singed side’s ability to attract water molecules is significantly diminished, so the unexposed side absorbs more water and expands more. The different rates of expansion allow the crawler to bend and move in response to humidity without any external power sources.

To get the crawler moving, the researchers simply had to raise or lower the humidity around it. The crawler inched forward at up to 0.14 inches in 12 seconds, or about 0.0007 mph, or about ten-times slower than a typical snail.

The graphene claw closed within 12 seconds and reopened 56 seconds later, after drying.

The bending process is reversible in both and quick — changing the water levels causes the crawler or the claw to quickly alter its curvature. The researchers tested the crawler at humidity levels between 33% and 86%.

Right now, the prototype doesn’t have any obvious uses in its current form. But adding motion to organs-on-a-chip could help simulate something like a breathing lung or beating heart in a laboratory environment, allowing researchers to explore tissues under more lifelike conditions.