Shape shifter.

Scientists have created polymer rods that, even after being grossly deformed, will revert toward their original shape when exposed to ultraviolet (UV) light.

Andreas Lendlein at GKSS Research Center in Teltow, Germany, and his colleagues bestowed this shape-memory property on a polymer blend by adding photosensitive molecules. When exposed to UV light of a certain wavelength, these molecules link, cinching the polymer's own constituent chains in place. A dose of UV light of a different wavelength cleaves the bonds.

In a demonstration of the new material's capabilities, the researchers twisted a rod-shaped sample into a spiral and exposed it to UV light, fixing the shape. When they subsequently exposed the spiral to UV light of a different wavelength, the polymer and stretched out to almost its original form.

The material could find applications in minimally invasive surgery, the researchers suggest. A surgeon could thread a thin piece of plastic through a small incision and into a blocked blood vessel. A fiber-optic probe could activate the material with light, triggering the polymer to spring into a shape that would keep open the vessel.

The researchers describe their new material in the April 14 Nature.--A.G.