A new light-responsive material could help soft robots move around underwater without requiring bulky frames and on-board power systems. The material bends when light is shone on it, a reflex that can be manipulated to make it crawl, walk and even swim.

Light responsive polymers have been designed that can crawl and carry objects, with researchers hoping they will one day find use in robotic devices. But until now, it has been difficult to make a self-propelling material that works when immersed in water.

Now, a liquid-crystal gel material has been designed to perform a range of underwater motions. In dark conditions, the gel’s monomers take on a planar arrangement, but when light is shone on it, the molecules take on a disordered structure. This causes the material to flex, allowing it to mimic the swimming movements of species like the Spanish dancer sea slug.

The gel’s high energy efficiency and low density are key to its ability to move when submerged in water.