"What's
unique about this plastic is the ability to stick itself back together with a
drop of water,"
said Melik
Demirel. Image: Demirel Lab/Penn State
(September 1, 2015) A
drop of water self-heals a multiphase polymer derived from the genetic code of
squid ring teeth, which may someday extend the life of medical implants,
fiber-optic cables and other hard to repair in place objects, according to an
international team of researchers.
"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."
Demirel and his team 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, as they note in a recent issue of
Scientific Reports, "the yield of this proteinaceous material from natural
sources is low (about 1 gram of squid ring teeth protein from 5 kilograms of
squid) and the composition of native material varies between squid species."
So as not to deplete squid populations, and to have a
uniform material, the researchers used biotechnology to create the proteins in
bacteria. The polymer can then either be molded using heat or cast by solvent
evaporation.
self-healing
polymer
The polymer can
either be molded using heat or cast by solvent evaporation.
Demirel Lab/Penn
State
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 113 degrees
Fahrenheit -- 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," said Demirel. "With
this material, it would be possible to heal the cable and go on with operation,
saving time and money.