Gel discs launch themselves upwards again and again, with no external power source needed.
A contact-lens-shaped device made of an elastic gel can jump repeatedly, all on its own — even up a flight of short stairs.
Gel devices that make a quick transition from one shape to another can exploit the power of this ‘snap’ to launch vertically into the air. Most such devices can snap only once, but organisms such as the Venus flytrap (Dionaea muscipula) use osmosis and water pressure to execute multiple snaps in a row.
Inspired by these biological examples, Alfred Crosby at the University of Massachusetts Amherst and his colleagues created a leaping device that harnesses the physics of evaporation. The researchers made a gel disc engraved with concentric grooves. When soaked in a volatile solvent, the disc swells into a concave shell.
As the solvent evaporates, the grooves deform in a specific pattern, causing the shell to snap from concave to convex. This launches the device into the air. The snap transition repeats up to 15 times, until the solvent has fully evaporated.
Such shape-shifting objects could be used to propel microscale robots, the authors say.