Bioplastic healed by water

According to a team of researchers at Penn State, a multiphase polymer derived from the genetic code of squid ring teeth can be healed by a drop of water. This material may someday extend the life of fibre-optic cables and other hard to repair in place objects.

"What's unique about this plastic is the ability to stick itself back together with a drop of water," said Melik Demirel, professor of engineering science and mechanics, Penn State. "There are other materials that are self healing, but not with water."

Prof Demirel and his team looked at the ring teeth of squid collected around the world and found that proteins with self-healing properties are ubiquitous. To produce a uniform material, the researchers used biotechnology to create the same proteins in bacteria. The polymer can then either be moulded using heat or cast by solvent evaporation.

The two-part material is a copolymer consisting of an amorphous segment that is soft and a more structured molecular architecture. The structured portion consists of strands of amino acids connected by hydrogen bonds to form a twisted and/or pleated sheet. This part also provides strength for the polymer, but the amorphous segment provides the self-healing.

The researchers created a dog-bone shaped sample of the polymer and then cut it in half. Using warm water at about 45°C and a slight amount of pressure with a metal tool, the two halves reunited to reform the dog-bone shape. Strength tests showed that the material after healing was as strong as when originally created.

"If one of the fibre-optic cables under the ocean breaks, the only way to fix it is to replace it," said Prof Demirel. "With this material, it would be possible to heal the cable and go on with operation, saving time and money.”

Tom Austin-Morgan

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