Originally Published MPMN July/August 2005
|A sample of “smart” plastic (a) is elongated and irradiated on the right-hand side with ultraviolet light, forming a temporary shape (b). Photos (c) and (d) show the plastic recovering its original shape after exposure to UV light of a different wavelength. Scale is in centimeters.|
A family of biodegradable polymers has been designed to change shape when exposed to light. A research team led by MIT bioengineer Robert Langer and chemist Andreas Lendlein from GKSS Research (Teltow, Germany) published its findings in the April 14, 2005, issue of Nature magazine.
Langer and Lendlein began work in 1997 on developing shape-memory polymers. In 2001, the researchers published their findings on biodegradable plastics that changed shape in response to an increase in temperature. A year later, the team demonstrated one medical product application for heat-sensitive, biodegradable, shape-memory plastics: a smart suture that ties itself into a knot. Their work was described in the journal Science; mnemoScience GmbH (Aachen, Germany) was selected to commercialize the discovery.
Their recent findings take shape-memory technology one step further. “Now instead of heat, we can induce the effect in polymers [by using] light,” says Lendlein. The polymers are programmed by means of what the researchers refer to as “molecular switches,” or photosensitive groups that are grafted onto a permanent polymer network. External stress is used to stretch the resulting photosensitive polymer film. The film is then illuminated with UV light of a certain wavelength. This prompts the molecular switches to bind to one another. “This is really a new family of materials that can change from one shape to another by having light shined on them,” says Langer.
A variety of other temporary shapes can be produced in addition to elongated films. For example, a spiral can be created by exposing only one side of the stretched sample to light. “While the deformation is well-fixed for [the irradiated] side, the other side keeps its elasticity,” say the researchers. As a result, one side contracts much more than the other when the external stress is released, forming an arch or corkscrew shape. Results also indicate that the temporary shapes are very stable for long times, even when heated to 50°C.
One possible medical application of the technology is a string-like plastic stent, implanted via minimally invasive surgery, that takes on a corkscrew shape once exposed to light. Once the stent is no longer needed, it dissolves in the body.
Langer co-wrote the latest paper with Lendlein, Hongyan Jiang, and Oliver Jünger. Lendlein, a former MIT visiting scientist, is institute director at the GKSS Research Center in Teltow, Germany. With Jiang and Jünger, he is also affiliated with the Institute for Technology and Development of Medical Devices at Rheinisch-Westfälische Technische Hochschule (RWTH) at Aachen University in Germany.
The work was funded in part by a BioFuture Award from the Bundesministerium für Bildung und Forschung, Germany, and a fellowship from the Alexander von Humboldt Foundation.
Copyright ©2005 Medical Product Manufacturing News