Medical Device & Diagnostic Industry Magazine
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Originally Published MDDI August 2005

R&D Digest



Maria Fontanazza

A two-sided coating appears to extend implant life. How? Through mussels.

Or something like them, anyway. The coating combines a buildup-resistant polymer and a molecule that imitates the sticky secretions characteristic of mussels. According to research at Northwestern University (Evanston, IL), it has several promising medical applications.

The coating was tested on titanium dioxide, which is often used in medical implants. During the five-month experiment, it showed resistance to cells and proteins. That means implants with the coating may be able to last longer than uncoated ones, without putting patients at risk for infection.

“For… permanent implants, it is desirable to maintain resistance [to coating breakdown] for the lifetime of the implant—years, perhaps,” says Phillip B. Messersmith, associate professor of biomedical engineering and materials science at Northwestern. The applications for the molecular compound could include dental implants and urinary catheters. It could prevent buildup on cardiovascular implants and implantable biosensor surfaces caused by proteins, cells, and blood clots, says Messersmith. He also believes it could limit bacterial accumulation on long-term indwelling catheters. “There is significant potential for use of these coatings to facilitate drug or therapeutic release from the surfaces of virtually all types of implants,” he says.

Messersmith and Annelise Barron, associate professor of chemical and biological engineering at Northwestern, designed a two-part coating. “There are two unusual aspects of the polymer, which, when combined, make the coating particularly innovative,” says Messersmith.

The polymer contains a short peptide, which is the synthetic form of an adhesive protein secreted by mussels. In nature, this protein enables the mussel to attach to underwater surfaces. Likewise, the peptide's job is to firmly anchor the antibuildup, or antifouling, polymer to device surfaces. “The resulting anchorage is water resistant and long lasting—important properties for medical device applications,” Messersmith says. Even when a device is immersed in a water solution, it's easy to apply the material to metal, ceramic, and polymer surfaces.

The second part, the antifouling polymer itself, is chemically similar to polyethylene glycol. The chemical structure resembles protein backbones but is enzyme resistant. It's also expected to be biocompatible.

In vivo experiments in animals need to be performed before testing for possible uses in humans. The National Institutes of Health funded the research.

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