Plastic inspired by squid teeth self-heals with water
Scientists derived the genetic code of squid ring teeth to develop a polymer that self-heals with a single drop of water. The material potentially could extend the life of medical implants, fiber-optic cables, and other hard-to-repair objects, researchers say. “What’s unique about this plastic is the ability to stick itself back together with a drop of water,” says Melik Demirel, professor of engineering science and mechanics at Pennsylvania State University, College Park. “There are other materials that are self-healing, but not with water.” Demirel and colleagues looked at the ring teeth of squid collected around the world—in the Mediterranean, Atlantic, near Hawaii, Argentina, and the Sea of Japan—and found that proteins with self-healing properties are ubiquitous.
However, “the yield of this proteinaceous material from natural sources is low (about 1 g of squid ring teeth protein from 5 kg of squid) and the composition of native material varies between squid species,” researchers report. So as not to deplete squid populations, and to have a uniform material, researchers use biotechnology to create the proteins in bacteria. The polymer can then either be molded 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.
Healing wounds
Researchers created a dog-bone shaped sample of the polymer and then cut it in half. Using warm water at about 113°F—slightly warmer than body temperature—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 fiber-optic cables under the ocean breaks, the only way to fix it is to replace it,” Demirel says. “With this material, it would be possible to heal the cable and go on with operation, saving time and money.
“Maybe someday we could apply this approach to healing of wounds or other applications,” he says. “It would be interesting in the long run to see if we could promote wound healing this way, so that is where I’m going to focus now.”
Other researchers from Penn State and from Carnegie Mellon University and the Max Planck Institute at Stuttgart, Germany contributed to the paper. The Jenny and Antti Wihuri Foundation, Walter Ahlström Foundation, Academy of Finland, the National Science Foundation, and the Office of Naval Research supported this work.
