Scratches in car paintwork could become a thing of the past thanks to research that has made self-repairing paint a realistic possibility.

Scientists in the United States have developed a type of polyurethane coating that mends itself in less than an hour when exposed to sunlight. They plan to develop it as a paint for cars and other surfaces that are subjected to heavy wear and tear, as well as in new forms of packaging, clothing and biomedical products such as bandages.

Marek Urban and Biswajit Ghosh, of the University of Southern Mississippi in Hattiesburg, created the material using a natural substance found in the shells of crabs and shrimps.

The coating consists of a network of ring-shaped molecules known as oxetanes, which split open when damaged, exposing two reactive ends. When this is exposed to ultraviolet light from the Sun, a chemical reaction allows a material called chitosan, which is found in crab shells, to repair the broken rings.

In a paper published in the journal Science, the researchers wrote: “An ideal automotive coating would mend itself while a vehicle is driven.”

Tests showed that brighter sun-light speeded up the repair process. During summer, scratch healing would be three to four times faster in the sunny southern US compared with the same level of exposure in the north.

“Because cross-linking reactions are not moisture-sensitive, dry or humid climate conditions will not affect the repair process,” the researchers wrote.

“The . . . networks exhibit the ability to self-repair upon exposure to UV light, but if exactly the same previously repaired spot is damaged again, the ability for further repair may be limited by the thermosetting characteristics of these networks.”

Howell Edwards, of the University of Bradford, said: “Clearly, there are future applications of this work in the repair of automotive components, which extensively use polyurethane polymers, that have suffered minor damage, although the authors note that subsequent damage at the same site is not repairable.”

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