Scientists have devised a coating that when scratched heals itself upon exposure to sunlight.
The secret of the material lies in using molecules made from chitosan, which is derived from the shells of crabs and other crustaceans.
In the event of a scratch, ultraviolet light drives a chemical reaction that patches the damage.
The work by University of Southern Mississippi researchers is reported in the journal Science.
They designed molecules joining ring-shaped molecules called oxetane with chitosan.
The custom-made molecules were added to a standard mix of polyurethane, a popular varnishing material that is also used in products ranging from soft furnishings to swimsuits. 
Scratches or damage to the polyurethane coat split the oxetane rings, revealing loose ends that are highly likely to chemically react.
In the ultraviolet light provided by the sun, the chitosan molecules split in two, joining to the oxetane's reactive ends.
"In essence you create a scratch, and that scratch will disappear upon exposure to the sun," said Professor Marek Urban, director of the university's school of polymers and high-performance materials.
Professor Urban and graduate student Biswajit Ghosh found that their coatings were able to fully heal themselves in just 30 minutes.
