Originally Published MDDI February 2005

R&D DIGEST

Heather Thompson

A diamond-like coating might offer a solution for infections caused by indwelling urinary tract catheters. Researchers at three institutions are conducting experiments with very thin coatings of carbon applied to urinary catheters that may help alleviate patients' discomfort and infection risk.

Despite state-of-the-art sterilization methods used in hospitals, catheterization remains a common cause of urinary tract infections. “Up to now, there has not been any effective way of preventing bacteria from entering the urinary tract via the catheter and thereby triggering a urinary tract infection,” says Norbert Laube, PhD, of Germany's University of Bonn. Also involved in the research are The Institute of Thin Film Technology of the Technical University of Kaiserslautern (Kaiserslautern, Germany) and New Technologies in Thin Films GmbH (Rheinbreitbach, Germany).

Furthermore, some species of bacteria alter urine's pH balance, which can cause salts and other substances in urine to precipitate and form a deposit on the catheter. The deposit forms a hard crust that protects the bacteria from antibiotic treatments and makes the removal of the catheter a painful process for the patient. If deposits form on a urinary stent or catheter that must stay in the body for months, an infection can become life threatening.

The team at Bonn used an extremely thin layer of diamond-like carbon (DLC) coating, applied in a plasma chamber, on urinary stents and catheters. After three months in the body, the devices showed virtually no incrustation. The team also noted that the coated catheters were easier to insert and remove than uncoated ones, and needed to be replaced less often.

Because of their high thermal conductivity and dielectric properties, DLC films have been used in laser diodes and microwave electronics. With the advent of mass production capabilities, DLC coatings are now being used in other sectors, including protective coatings for medical devices. Manufacturers that produce DLC coatings boast of its hardness, low friction, conformability to substrates, and biocompatibility. Thom Ozycz, marketing director for Applied Diamond Coatings (Durham, CT) says, “The most important thing about DLC is that it is biocompatible—that means it can be used for Class I, Class II, or Class III medical devices.” Even more encouraging, DLCs are inert in chemical environments. They do not react to acids, alkalis, solvents, salts, or water. This resistance to chemicals is integral to their success as indwelling urinary tract catheter coatings.

Nevertheless, using DLC as a coating for catheters does pose some complications.

“Diamond-like carbons are very hard,” says Lonny Wolgemuth of Specialty Coating Systems (Indianapolis), a Cookson Electronics company. “Any coating would have to be extremely thin to be flexible enough for use on a catheter.”

Indeed, most DLC applications are intended for harder products such as prosthetics and needles, according to Ozycz. “You couldn't apply it to a spring, for example,” he says, “because the coating would be too rigid and the spring wouldn't function.” But he agrees that, if applied correctly, the coating may be thin enough for a catheter. “We can get [DLC coatings] to a tenth of a micron if you want,” Ozycz says, “but most of our needs fall between 2- and 7-µm thicknesses.” Because it's applied in gas form, Ozycz explains, the coating is easy to apply to a substrate and then build up sublayers in a plasma chamber.

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