Shape-Memory Polymer Trifecta

If shape-memory polymers were dancers, they'd be stuck doing the two-step: Mold them into one position, reshape them into another, and then use light or heat to make them snap back into their original shape. It's a neat trick, but hardly a showstopper. Now, a group led by Robert S. Langer of MIT and Andreas Lendlein of the Helmholtz Association Institute of Polymer Research, in Teltow, Germany, have created polymers with three steps in their shape-shifting repertoire (Proc. Natl. Acad. Sci. USA, 2006, 103, 18043). The researchers first "programmed" two different shapes into the polymer's memory before setting it into its initial position. As the material is heated, it takes on one of its programmed shapes. Increasing the temperature makes the polymer change into the other programmed shape. The new materials are suitable for applications such as hands-free fasteners and active medical implants.