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Light makes plastic ping into shape


A new type of plastic can switch from a coil to a thread when a light shines on it (Image: iStockphoto)

A light-sensitive plastic that can be locked into a twisted form and then manipulated to snap back into its former self could be used for minimally invasive surgery or household staples.

An international team of researchers report the photosensitive shape-memory plastic in a recent issue of the journal Nature.

"It can be any shape you want," says team leader Professor Robert Langer, a chemical engineer at the Massachusetts Institute of Technology.

Researchers have previously developed shape-memory in metals and other plastics, but those materials require a change in temperature to work.

These latest shape-memory plastics represent a new family of materials that can bend and unbend in response to different wavelengths of light.

"Light as a stimulus will broaden the scope of applications for shape-memory polymers," says co-author Professor Andreas Lendlein, institute director of the GKSS Research Center in Berlin, Germany.

Sensitive to light

The key to the invention is a group of photosensitive molecules that binds to one another when exposed to a certain wavelength of light.

A film of these molecules is stretched over a scaffold of different molecules not sensitive to light. The initial shape of the scaffold represents the destination shape.

So, for example, if a researcher wants to build a stent, a coiled device used to keep blood vessels open, the scaffold would be constructed into the spiral shape and then the film of light-sensitive molecules would be grafted onto it.

Next, a special machine would be used to straighten the spiral into a thread. The molecules would then be exposed to light, causing the light-sensitive ones to bind to each other and lock the scaffold into the thread shape.

Later, a doctor would need only make a tiny incision to insert the thread, along with a fibre-optic probe, into a patient's artery.

A different wavelength of light from the probe would break the molecular bond and cause the stent to collapse back into its original corkscrew shape.

Clever and efficient

"That's very clever, in terms of concept and efficient in terms of execution," says biomedical engineer Professor Mark Saltzman of Yale University.

The challenge now, says Lendlein, is to tailor the technology for specific applications and upscale the reaction so that larger amounts of the plastics can be used.

Tags: science-and-technology, engineering, physics