A polymer that can heal itself over and over again when exposed to ultraviolet light has been developed by materials researchers at Carnegie Mellon University and Kyushu University. The substance could potentially be used to create products that repair themselves when damaged, including self-healing medical implants or parts for vehicles such as aircraft.
When the polymer is cracked it can swiftly be prepared without the need for heat or glues by simply pressing both sides of the material together and applying UV light. Researchers found that they could break the material into pieces and then reassemble it at least five times. They believe that with further development they could create a material that could heal itself many more times. Other self-healing materials have relied on microcapsules containing a healing agent, which break open when a crack forms. However, once the healing agent has been used up, the material loses its self-healing ability. The new polymer is cross-linked with trithiocarbonate bonds -- carbon atoms bonded to three sulphur atoms, two of which use their second bonding position to attach to another carbon atom. When UV light is applied, one of the carbon-sulphur bonds is broken, producing two radicals -- molecules with a free, unpaired electron. These radicals then react with other thrithiocarbonate groups to form new carbon-sulphur bonds, while breaking others to form more free radicals.
The experiments were conducted in a pure nitrogen atmosphere because, so far, the polymer can only repair itself in an oxygen-free environment. But it is hoped that other polymers could be developed that would heal themselves under normal atmospheric conditions.
25-Jan-11 
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