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Shape shifter shifts twice

5:51pm, December 18, 2006

Certain plastics known as shape-memory polymers switch to predetermined shapes when triggered by heat or light. Now, researchers have developed more-versatile versions of such polymers. When heated, each of the new triple-shape polymers switches to a second shape. Then, at a higher temperature, the plastic changes to a third form.

"For some applications, [these] more-complex deformations are required," says chemist Andreas Lendlein of the GKSS Research Center in Teltow, Germany. He, chemical engineer Robert Langer of the Massachusetts Institute of Technology, and their colleagues have already made prototype devices from the new substances.

One such device is a tube that could force open partially blocked blood vessels. The tube, a removable stent, would start out with a squashed shape. Body heat would then expand the stent, which would push outward on the vessel walls. Later, further heating of the stent would shrink it for easy removal.

Each of the two new triple

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