A few years down the road, you may be able to get that scratch out of your car’s bumper simply by parking in a sunny spot. Researchers have created a polyurethane coating that heals itself when exposed to ultraviolet light.

"This new material will have a lot of practical applications," said study co-author Marek Urban, a chemist at the University of Southern Mississippi. “It could coat anything that can be scratched—electronics, aircraft, cars, you name it."

Self-healing coatings could minimize upkeep and repair on a variety of products, saving consumers money and reducing waste.

“Your car would last for a long time, and it would look new for a long time,” Urban said.

The new compound is not the first man-made self-healing material. In 2001, researchers at the University of Illinois embedded tiny liquid-filled capsules in a polymer coating. When the coating cracked, the capsules ruptured, spilling healing agents into the damaged area and repairing it.

One of the Illinois scientists, Scott White, founded a company based on this technology in 2005. Autonomic Materials, Inc. could have self-healing coatings on the market in the next couple of months, according to a recent article in the MIT Technology Review.

Other researchers have devised different methods. In 2002, scientists from UCLA and USC created a compound that heals itself quickly when exposed to high temperatures. The new coating is similar in that it requires an external stimulus to work. But the stimulus—UV radiation—should not be difficult to introduce. A few minutes in the sun would do the trick.

“It’s a new healing chemistry for polyurethane,” said Nancy Sottos, a materials scientist at the University of Illinois who was not involved in the new study.

Urban and co-author Biswajit Ghosh, also of the University of Southern Mississippi, created the compound by mixing chitosan—a derivative of chitin, the main component of arthropod exoskeletons—into polyurethane. They made tiny nicks in the new material, then exposed it to UV light about as intense as that given off by the sun. The radiation set off a series of reactions, causing damaged molecules to link up with each other again. The cuts healed in about 30 minutes.

This repair process, described Thursday in the journal Science, is not moisture-sensitive, meaning it should work in all climates. And making the new coating won’t break the bank, according to Urban.

“It’s very economical,” he said. “You can get chitosan for almost nothing.”

The mending reactions don’t seem to work a second time, so each part of the coating can repair itself only once. But Urban doesn’t see this as much of a drawback in the real world.

“Even if you try to hit the same spot, within a couple of microns, statistically the chances of it happening are very small,” he said.

*Citation: "Self-Repairing Oxetane-Substituted Chitosan Polyurethane Networks." By Biswajit Ghosh, Marek W. Urban. *Science Vol. 323, 13 March 2009.

See Also:

Image: Infrared (top) and optical views of a scratch after 0, 15, and 30 minutes of UV exposure. Courtesy of Marek Urban, via Science/AAAS.