The incidents are rare, but the repercussions can be grave: Every year, about 1 to 2 percent of people undergoing hip and knee replacements in the U.S. end up with surgery-related bacterial infections. In a worst-case scenario, the infection continues for months and the patient requires a new prosthesis.

Now, Johns Hopkins researchers have designed a thin, biodegradable plastic coating for metal implants that can release multiple antibiotics to diminish the chance of such infections.

In studies on mice, dermatologist Lloyd Miller and bioengineer Hai-Quan Mao found that knee joints possessing the special antibiotic-coated implants showed no detectable infection after a strain of staph bacteria was introduced to mimic an infected implant. Meanwhile, most of the mice who had received implants without antibiotics in the coating were found to have abundant bacteria on the surface of the implant and in the infected tissue around the knee joint.

The coating is composed of nanofibers embedded in a thin film, both of which are made of the same materials used in degradable stitches.

Antibiotic-coated implants are not new. In this case, however, the researchers paired fast-acting rifampin with one of several longer-acting broad-spectrum antibiotics to completely eliminate the infection.

Miller says ensuring the coating released each antibiotic at the correct rate proved to be challenging.

“The hardest part of this project was optimizing how to have a dual-component coating that can independently release the right levels of both antibiotics for enhanced efficacy,” says Miller. “It’s very critical to the enhanced effectiveness of the coating.”

The team received funding from a Johns Hopkins Institute for Clinical and Translational Research Nexus Award and is planning on additional preclinical testing in animals. The study has been published online in Proceedings of the National Academy of Sciences.

Bioluminescent bacteria from the infected mouse knee joint that did not receive an antibiotic-coated implant.