Led by Prof. Dick Broer, scientists from the Netherlands' Eindhoven University of Technology and America's Kent State University have created what they claim is "the world's first machine to convert light directly into walking." It actually undulates more than walks, and could ultimately be used for applications such as the transportation of small objects within inaccessible spaces.
The paper clip-sized device consists of a strip of liquid crystal polymer, mounted lengthwise in a rectangular frame. Because that frame is shorter than the strip, the polymer ends up having a hump at one end and a dip at the other.
When violet light is shined on the device from the end that the hump is on, it's absorbed by the hump – the dip is shadowed by the hump, so it doesn't receive any light.
Light-sensitive molecules in the polymer cause the material in the hump to expand on one side, while contracting on the other. This causes the hump to deform downwards to become a dip. As a result, the other end of the strip (which was formerly a dip) bulges upwards into a hump, where it absorbs the light. It in turn reacts and deforms back to a dip, once again moving the hump to the previous end.
In this way, a wave is continuously passing through the strip, causing the device to move away from the light source at a rate of approximately half a centimeter per second – about the speed of a caterpillar. In order to get it to move towards the light source, the mechanism just has to be flipped over.
In lab tests, the device has been able to transport objects larger and heavier than itself, and going uphill to boot. That said, the polymer might also find use in solar panels, working as an undulating transparent surface layer that shrugs off dust and debris.
The device can be seen moseying along, in the video below.