Shape memory plastics are about as close as materials scientists get to doing magic. Bend and twist them all you want, but at the right temperature they’ll bounce back to their original shapes. Now, for the first time, researchers have made shape memory polymers that are both compatible with the body and biodegradable-a potential breakthrough in the development of implantable therapeutic devices.
“You can envision a whole range of minimally invasive surgical products that you could insert through a small hole in the body and have snap into a desired shape,” says MIT bioengineer Robert Langer, who helped develop the new material with Andreas Lendlein, a chemist at the German Wool Research Institute in Aachen, Germany. Lendlein and his team made the material from two biocompatible polymers; tweaking the ratio of the two sets the temperature at which the material will change shape. To commercialize the new polymer, Lendlein and Langer cofounded mnemoScience in Aachen, which plans to produce scaffolds for engineering new organs and coronary stents, the mesh tubes used to prop open blocked arteries. Such stents could be compressed and fed through a tiny hole in the body into a blocked artery. There, the body’s warmth would trigger the polymer’s expansion into its original shape. And rather than requiring a second surgery for removal, the polymer would gradually dissolve in the body over time.
While these shape memory polymers could be important for medical devices, engineers also envision using nondegradable versions to make parts for robots and other machines-a ligament for a robotic limb, for example. Patrick Mather, a chemist at the University of Connecticut, sees another breakthrough around the corner: a polymer that could flip back and forth between two shapes at different temperatures, without having to be manually reshaped after every cycle. Engineers have already made these reversible shape memory materials with metal alloys, but they can only bend so much. “But, with a reversible shape memory polymer, we could make the robot jump instead of walk,” says Mather.