Materials use nitric oxide to kill bacteria

Bacteria that grow on implanted medical devices can wreak havoc. Now, a novel coating may offer a new way to fend off microbial buildup on catheters, artificial hips, and replacement cardiac valves.

Recently, chemists have been creating materials that emit nitric oxide (NO), an antibacterial chemical that the body produces. Much of the research has focused on using polymers containing NO-releasing chemical groups called diazeniumdiolates to prevent blood clotting. A drawback to those materials is that the loosely associated NO donors can leach out of the material and go elsewhere in the body.

Mark H. Schoenfisch and his colleagues at the University of North Carolina in Chapel Hill have made a different type of NO-emitting films by covalently bonding diazeniumdiolates to a siloxane-based polymer.

“It appears that these films can be formulated in such a way as to prevent any leaching of the chemicals,” says Mark Meyerhoff of the University of Michigan in Ann Arbor, who has made NO-releasing materials for preventing implant-induced blood clotting. Schoenfish’s work provides “a very important element to the potential practical application of this type of coating.” Using NO to prevent bacterial adhesion “is really exciting,” he adds.

Schoenfisch’s team tested its films in solutions containing the common bacterium Pseudomonas aeruginosa. Microscope images revealed that about one-quarter as many bacteria adhered to slides coated with the new materials as to uncoated slides. The group reports the results in an upcoming issue of the Journal of the American Chemical Society.

Schoenfisch now plans to test the films against other bacteria, look for the optimal amount of NO release, and try to extend NO emission from days to weeks. His team also intends to develop ways to make sure that the films don’t release NO before they’re used in a patient.

Robert S. Langer of the Massachusetts Institute of Technology calls Schoenfisch’s approach “a reasonable avenue to pursue.” Yet he cautions that it’s too early to know how the materials will behave in the body.

Schoenfisch agrees. He plans to examine whether the short-lived NO has toxic effects. “We speculate that [such effects] might be minimal,” he says.

Bacterial infections at implants are often treated with drugs, but antibiotic resistance is becoming a problem, says Harvard University’s George Whitesides. Sometimes, physicians must remove a device to save a person. Not only is such treatment expensive but it’s “very hard on patients,” he says.

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