Mussels help researchers develop tougher restorative product

According to Dr. Kollbe Ahn, a materials scientist at UCSB’s Marine Science Institute who worked on the project, one of the primary reasons restorations fall out or crack is due to brittle failure of the bond to the surrounding tooth. “All dental composites have micro-particles to increase their rigidity and prevent their shrinkage during their curing process,” explained Ahn, “but there’s a trade-off: When the composite gets harder, it gets more brittle.”

Because of this, Ahn and his colleagues looked to nature to find a solution that not only maintained the strength and hardness of a restorative composite, but also improved durability. Enter the mussel. Being able to adhere to irregular surfaces under the variable conditions of the intertidal zone, as well as evolving to resist pounding waves, the blazing heat of the sun and cycles of salt water immersion and windy dryness, mussels presented the ideal model for more durable dental restorative materials.

Specifically, the researchers were interested in the byssal threads mussels use to affix to surfaces that allow them to resist the forces that would otherwise tear them from their moorings. “In nature, the soft collagenous core of the mussel’s byssal threads is protected by a 5-to-10 micrometer thick, hard coating, which is also extensible and thus, tough,” said Ahn.

This durability and flexibility allows the mollusks to stick to wet mineral surfaces in harsh environments that involve repeated push-and-pull stress. Key to its functionality is what scientists call dynamic or sacrificial bonding: multiple reversible and weak bonds on the subnanoscopic molecular level that can disperse energy without compromising the overall adhesion and mechanical properties of the load-bearing material.

This type of bonding occurs in many biological systems, including animal bone and teeth. However, the mussel’s byssus contains a high number of unique chemical functional groups called catechols, which are used to prime and promote adhesion to wet mineral surfaces. The new study has shown that using a catecholic coupling agent instead of the conventional silane coupling agent provides ten times higher adhesion and a 50 percent increase in toughness compared with current dental restorative composite resins.

According to Ahn, the next step in the research process is to increase the material’s durability even further. He estimates that a commercial product will be available within a couple of years.

The study, titled “Significant performance enhancement of polymer resins by bioinspired dynamic bonding,” was published online on August 18 in the Advanced Materials journal before inclusion in an issue.