Ultraviolet shifts plastic's shape

Materials that change shape are potentially very useful, especially if the shape change is easy to control and takes place quickly.

Researchers from German organizations GKSS Research Center, Rhine-Westphalia Institute of Technology (RWTH Aachen) and MnemoScience GmbH, and the Massachusetts Institute of Technology have concocted a polymer material that can be switched from one shape to another in the presence of the right wavelengths of ultraviolet light.

The material could eventually be used in industrial and medical applications, including intelligent stents and sutures. An intelligent stent could begin as a string that could be threaded into a blood vessel through a tiny incision, then activated with ultraviolet light via a fiber-optic probe to change into a corkscrew-shaped stent that would keep a blood vessel open. An intelligent suture would form a knot when activated.

The material can be manipulated into a new shape, which is fixed when the material is illuminated with ultraviolet light with a wavelength longer than 260 nanometers. The material changes back to the original shape when illuminated with ultraviolet light below a wavelength shorter than 260 nanometers. The material can be fixed into many types of shapes, including elongated films, tubes, arches and spirals. Existing light-activated shape-memory polymers are limited to expanding, shrinking and bending.

The material is a mix of two polymers. The first forms the material's original shape, and the second forms cross-links in the presence of ultraviolet light longer than 260 nanometers. Exposing the material to the shorter wavelength breaks the cross-links, which allows the material to recover its original shape.

The polymers hold the second shape even when heated to 50 degrees Celsius, according to the researchers.

The ultraviolet shape-memory polymers could be used for non-medical applications in less than five years, and medical applications in five to ten years, according to the researchers. The work appeared in the April 14, 2005 issue of Nature (Light-Induced Shape-Memory Polymers).