Implants benefit from mussels

Medical implants may soon get better at preventing life-threatening clogs and bacterial infections thanks to an unusual coating that is being developed from mussels, according to researchers at Northwestern University.

They have developed a two-sided coating: one side is a sticky glue based on adhesive proteins secreted by mussels, the other is a special repellent. While the sticky side is designed to attach securely to the surface of the implant, the repellent side prevents the build-up of cells and proteins that typically foul implant devices such as cardiac stents, urinary catheters and dialysis tubing. Such contamination can lead to device malfunction, blood clots or fatal bacterial infections, the researchers say.

Their findings, which are based on laboratory studies, are scheduled to appear in the April 9 print issue of the Journal of the American Chemical Society.

Medical implant contamination, particularly that caused by bacterial infections, is a major medical challenge today. Although researchers have been developing anti-adhesive coatings and other anti-infective techniques for medical devices for years, no single approach works effectively for all types of implant surfaces, says Phillip B. Messersmith, a professor in the Biomedical Engineering Department at the university, located in Evanston, IL, and lead investigator in the study.

‘Our goal is to take advantage of the unique ability of mussels to attach to all types of surfaces, including Teflon, in order to develop a compound that will allow us to treat a variety of implant surfaces with a single approach,’ Messersmith says. Such a coating would be more versatile and cost-effective than those currently used, he predicts.

The foot of the common mussel (Mytilus edulis) produces a sticky glue that keeps the shelled organism anchored to rocks and other objects, allowing it to withstand the extreme pounding of waves. Chemical analysis of this natural, water-proof glue has shown that the key to its adhesiveness is a unique compound called mussel adhesive protein, which contains a high concentration of an amino acid, DOPA (dihydroxyphenylalanine), which can cling to wet surfaces with extraordinary strength.

While several researchers have focused their attention on developing these mussel adhesive proteins into a type of super-glue, Messersmith reasoned that the same compounds could be used to anchor a repellant component. He decided to attach the sticky DOPA molecule to a well-known repellent molecule, polyethylene glycol (PEG).

The result: A two-sided compound whose sticky side attaches to internal surfaces, but whose nonstick side can resist protein and cell attachment, such as that encountered by implanted medical devices.

In the current study, Messersmith and his associates demonstrated that the new compound could be easily attached to gold and titanium surfaces (common implant materials), rendering these surfaces resistant to cell attachment for up to two weeks. Although some antifouling coatings can fight contamination for a similar length of time, the researchers are optimistic that their compound can eventually be made to last much longer, perhaps permanently.

Just as mussel adhesive protein tends to bind to practically any surface it encounters, the researchers believe that the new compound can similarly attach to other surfaces used for medical devices, including stainless steel and plastic. Preliminary studies involving attachment of the compound to polymer surfaces appear promising, they say.

The new compound has not yet undergone animal or human testing, Messersmith says. If all goes well in future studies, the compound could be used in medical devices in 3 to 5 years, he predicts.

Besides implants, the compound could be used as a tooth coating to prevent dental plaque, which is caused by bacterial infection.

Ironically, the compound also shows promise in the shipping industry as an environmentally friendly alternative to toxic antifouling coatings currently used on boats to protect against mussels, barnacles and related organisms, Messersmith says.