Medical implants that naturally resist infection could someday be made using a new method for attaching antibiotics to Teflon.

Teflon is commonly used to make medical implants, like heart patches and vascular grafts, as it is well tolerated by the body and its surface is not normally chemically reactive.

However, like any other implant material, Teflon can sometimes harbour bacteria. Even if the implant is not contaminated during surgery, bacteria from an infection in another part of the body may sometimes attach to it. The bacteria can then form a slimy biofilm that protects them from normal antibiotics.

Researchers at the University of Southern Mississippi, US, decided that treating implants with antibiotics before implantation could perhaps prevent bacteria from taking hold. They attached penicillin to the surface of Teflon in a clever three-part chemical process.

Sticky surface

Because things tend not to stick to Teflon surfaces, the researchers first had to make the surface chemically reactive. They did so by exposing it to microwaves in the presence of maleic anhydride – a reactive organic compound. This created acid groups on the surface, capable of interacting with other molecules.

The next step was to attach "spacer" molecules of polyethyleneglycol to these acid groups. And finally, the penicillin was attached to the spacer molecules.

"The effectiveness of this approach comes from the fact that we utilised a spacer between the material and the antibiotic," says Marek Urban, a polymer scientist at the University of Southern Mississippi. "If you attach the antibiotic directly to the surface, it's less effective."

The spacer molecules allow the penicillin to attach to the surface at varying depths. This means a bacterium that settles on the surface of the Teflon will be surrounded by penicillin. Since penicillin works by attaching to the wall of a cell, increasing the surface area in contact with a target makes it more effective.

Time trouble

In vitro, the penicillin-coated Teflon prevented Staphylococcus aureus – the organism that causes staph infections – from growing.

"It's very nice to show you can put it on Teflon. I think that's going to serve as an example," says Eric Wickstrom, a biochemist at Thomas Jefferson University in Philadelphia, US. But he says that a penicillin coating will eventually be used up as it reacts with bacteria, and that another antibiotic could perhaps be more effective.

Wickstrom and others at Thomas Jefferson are working on an alternative solution: bonding an antibiotic called vancomycin to titanium beads. If these can then be used to coat an implant, it would not lose its effectiveness over time, Wickstrom claims.

Journal reference: Biomacromolecules (DOI: 10.1021/bm061050k)