Nanofiber Coating Prevents Prosthetic Joint Infections

A novel coating made with antibiotic-releasing nanofibers has the potential to prevent some of the serious bacterial infections related to total joint replacement surgery.

Developed by researchers at Johns Hopkins University (JHU; Baltimore, MD, USA), the thin, biodegradable plastic coating is composed of a nanofiber mesh embedded in a thin film, both made of biodegradable polymers. The coating is loaded with multiple antibiotics, including rifampin and combinations of vancomycin, daptomycin or linezolid. Vancomycin, daptomycin, or linezolid are released for seven to 14 days, and rifampin over three to five days, thus deploying two antibiotics against a potential infection and ensuring rifampin was never present as a single agent.

This was necessary, since rifampin, while demonstrating excellent anti-biofilm activity, cannot be used alone, as bacteria rapidly develop resistance. The researchers tried different combinations of drugs for coating titanium Kirschner wires – a pin used in orthopedic surgery to fix bone in place after wrist fractures – and inserted them into the knee joints of anesthetized mice. They then introduced a strain of phospholuminent Staphylococcus aureus in order to noninvasively track infection over time.

The results showed that after 14 days of infection in the mice that received an antibiotic-free coating on the pins, all had abundant bacteria present in the infected tissue around the knee joint, and 80% had bacteria on the surface of the implant. In contrast, after the same time period in the mice that received pins with either linezolid-rifampin or daptomycin-rifampin coatings, none of the mice had detectable bacteria, either on the implants or in the surrounding tissue. The study was published on October 24, 2016, in Proceedings of the National Academy of Sciences (PNAS).

“We were able to completely eradicate infection with this coating. Most other approaches only decrease the number of bacteria, but don’t generally or reliably prevent infections,” said co-senior study author Lloyd Miller, MD, PhD, an associate professor of dermatology and orthopedic surgery at the JHU School of Medicine. “We can potentially coat any metallic implant that we put into patients, from prosthetic joints, rods, screws and plates, to pacemakers, implantable defibrillators, and dental hardware.”

An estimated 1-2% of hip and knee replacement surgeries are followed by infections linked to the formation of biofilms that adhere to the surface, forming a dense, impenetrable matrix of proteins, sugars, and DNA. These infections are very difficult to treat and, in many cases of chronic infection, prostheses must be removed and patients placed on long courses of antibiotics before a new prosthesis can be implanted.

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