Novel Anti-Bacterial Implant Coatings

Orthopedics This Week
Biloine Young • Thu, Dec 16th, 2010
Copyright 2009-2010 RRY Publications

Call it the 1% solution. For a hospital, an infection rate of 1% for knee and hip replacement surgery may not sound like much, but for the infected individual, the infection rate is 100%. Of course, for second surgeries the data shows that infection rates rise to 3-5%.

Post operative infections can be tough. Too often infected tissue and the hardware must be surgically removed and replaced with an antibiotic block. In those cases, patients are treated with intravenous antibiotics to eliminate all traces of infection and, often, are not able to walk for six to eight weeks. The price tab can balloon from around $30,000 to nearly $150,000.

Infections are costly, deadly and, perhaps, preventable with a novel anti-bacterial coating for orthopedic implants from a team of MIT researchers.

A team of Massachusetts Institute of Technology (MIT) researchers led by Paula Hammond, PhD., the Bayer Chair Professor of Chemical Engineering, is tackling the problem of infections that enter the body with an implant, as well as those that can occur years later when bacteria are introduced into the bloodstream, with a unique set of orthopedic coatings that have permanent antibacterial properties.

While antibiotic coatings have been developed for many devices, such as stents, joints present special problems because they have to move The coating cannot be too thick and the joints must be able to move freely.

As reported on December 13 in MIT’s Technology Review, Hammond is using a polymer-coating technique to load large concentrations of drugs into implant coatings without making them too thick. Her group drops an implant alternately in solutions of negatively and positively charged molecules such as polymers and drugs. The difference in surface charges holds each layer tightly to those above and below it, leading to very thin layers of materials—on the order of tens of nanometers thick. The drugs are released when the polymers biodegrade within the body.

This drug-releasing film was previously developed by Alexander Klibanov, a professor of chemistry at MIT said, "When these polymers are present on a surface, bacteria will die on impact."

His work was published online in the Journal of American Chemical Society in November 2010.

“What distinguishes this technology is the promise of being able to release different drugs sequentially, in a controlled way,” said Myron Spector, professor of orthopedic surgery at Harvard Medical School. Other patients, such as those with a poor vascular system that can compromise bone growth, might also benefit from coatings that release drugs to stimulate bone formation or blood-vessel growth, in addition to antibiotics.