Self-Healing Polymer May Repair Broken Bones
A material that can instantly heal bones is closer to becoming a reality, as researchers from UC Santa Barbara have discovered a polymer that can heal itself in aqueous conditions, such as the human body.
"Since the late 1990s, there have been many papers that concentrate on self-healing polymers under dry conditions," said Kollbe Ahn, a researcher at UC Santa Barbara's Marine Science Institute. "What we wanted was to study a polymer that could heal under moist conditions, or underwater."
The research was inspired by a protein secreted by mussels, which has the ability to bypass the liquid surrounding an object and effectively adhere to the surface. "Much of the time, the presence of water limits the ability of an adhesive to stay tacky, so even polymers that can self-heal under dry conditions are frustrated from doing so underwater. In that particular protein, the percentage of catechol groups is high: up to a third of all residues," said Herbert Waite, a professor in the UC Santa Barbara Department of Molecular, Cellular and Developmental Biology. Catechol is a naturally occurring organic compound that acts as a medium for hydrogen bonds, and as a result is able to facilitate underwater bonds between two different objects when found in high quantities.
Upon finding that this protein contained such a high proportion of catechol, the researchers put their hypothesis to the test by cutting rods of polymers and attempting to re-attach the pieces by outfitting them with catechols, soaking each surface in buffer solutions of various acidities, and exposing them to light pressure. More acidic buffer solutions enhanced the adhering ability of the catechols, while more alkaline solutions inhibited it, but all of the polymers adhered to some degree. The researchers measured the adhesion forces between the polymer surfaces and tested the bonds by attempting to break the rods once more, and found that the strongest bonds were even able to resist re-breaking. "The rods broke in other areas after we joined them together and pulled them apart again," said Dong-Woog Lee, co-lead author and postdoctoral researcher.
From the paper: "The repaired and pristine samples show similar mechanical properties, suggesting that the triggering of complete self-healing is enabled underwater by the formation of extensive catechol-mediated interfacial hydrogen bonds."
This technology could have a wide variety of applications, from self-healing surfboards and boat hulls to reinforced hip and knee implants. The researchers also believe that this polymer could serve to repair brittle bones with hairline fractures and protect them from further breaks.