Shining a laser at a graphene-based hydrogel causes the material to bend — a response demonstrated in the video above, where the shape-shifting material is molded into the shape of a hand. Each finger responds to the laser by curling inward, a rapid and reversible effect caused by the material’s varying porosity.

Described May 6 in Nano Letters, the hydrogel could be useful in applications ranging from soft robotics to drug delivery and synthetic tissue engineering.

Scientists at the University of California, Berkeley created the light-responsive gel after considering how plants flex and orient toward or away from light, a property called phototropism. Plants orient toward a light source by elongating cells on the side of a shoot farthest from the light, thereby bending the shoot toward the source.

To mimic this process, the team built the hydrogel from genetically engineered, elastin-like proteins and sheets of graphene, the one-atom thick sheets of carbon that earned Andre Geim and Konstatin Novoselov the 2010 Nobel Prize in physics.

Normally, the flexible proteins cling to water molecules, producing a swollen polypeptide matrix. But exposing the graphene sheets to infrared light generates heat, causing the proteins to release the water they cling to when cooler. Because one side of the hand-shaped gel is more porous and swollen than the other, shining an infrared laser at it produces the curling reaction as proteins bend and dry out — a fast and site-specific reaction to the light that can be repeated more than 100 times.

Videos: E. Wang et al., Nano Letters and YouTube