A simple drop of warm water self-heals a multiphase polymer derived from the genetic code of squid ring teeth. The bonded material, which researchers say may someday extend the life of medical implants, fiber-optic cables and other objects that are hard to repair in place, can be cut and retains the same strength as unbroken bioplastic once it self-heals.

The researchers first noted that the important proteins with self-healing properties were found in the ring teeth of squid collected around the world. However, the yield and composition of the proteinaceous material varied among species. To ensure a consistent yield, secure a uniform material and avoid depleting global squid populations, the researchers used biotechnology to create the proteins in bacteria. The polymer can then either be molded using heat or cast by solvent evaporation.

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

The two-part copolymer material consists of a soft, amorphous segment that provides the self-healing properties and a structured molecular architecture that is formed of strands of amino acids connected by hydrogen bonds. The amino acid strands create a twisted or pleated sheet that gives the bioplymer its strength.

As a part of its research, the Penn State team created a dog-bone-shaped sample of the polymer and performed strength testing on it. Once its properties were measured, the team cut the part in half, then used warm water at approximately 113°F (45°C) and applied slight pressure using a metal tool. The two halves healed together to form a dog-bone-shaped part that testing showed was as strong as the uncut piece. 

Video courtesy of Demirel Lab / Penn State