Lendlein says the key to the new structures was developing two types of polymers that have distinct melting points. At room temperature, the material holds its first shape. But when heated above a certain temperature, areas throughout the material soften, allowing it to change to an intermediate shape. At a yet higher transition temperature, the rest of the material softens, allowing the structure to take its final shape.

Although the researchers designed polymers specifically for this project, Lendlein says that the results demonstrate a general principle that could work with a variety of polymers. Indeed, he says that for specific applications researchers may need to change materials to make them compatible for use in the body and to decrease costs for use in manufacturing. Lendlein is working with mNemoscience, based in Aachen, Germany, a spin-off of MIT and RWTH Aachen University, to commercialize the new technology.

Richard Vaia, a researcher at the Air Force Research Labs, says the work is part of a trend in shape-memory research toward more-complex, higher-performance materials. While early applications, such as shrink-wrap, were simple, researchers are using nanoparticles to increase the amount of force the materials can apply as they change shape, and they're developing new ways of triggering the changes, Vaia says. Another major goal would go beyond Lendlein's multishape materials to those that can change shape reversibly, returning to the original shape for applications that require repeated movements.