Shape-Shifters; May 2001; Scientific American Magazine; by Steven Ashley; 2 Page(s)

Special plastic materials able to change shape in response to temperature may soon find applications in a variety of extreme climes-from the warm, moist environs of human blood vessels to cold, wet and windy mountaintops. These plastics have a "memory" that allows them to be deformed into a temporary configuration and then be restored to the original parent geometry by applying heat. Shrink-wrap is perhaps the most familiar example of a shape-memory polymer (SMP). But since the mid-1980s chemists, materials scientists and engineers have been working to develop SMPs as a kind of "smart" material-a substance that can respond to environmental changes as desired.

Shape-memory substances are not new: certain metallic compounds exhibited the effect in the 1930s, and alloys such as nickel-titanium (Nitinol) have since found use in actuators and medical devices such as dental braces and endovascular implants. These metals switch from a temporary to a parent shape above a certain transition temperature. Below that temperature, the shape-memory alloy (SMA) can be bent into various configurations.