BACKGROUND: Nearly 1 million people undergo a hip, knee or shoulder replacement every year, according to the American Academy of Orthopaedic Surgeons, and in about 1 to 2 percent of those cases, an implant gets infected. The most common cause of these infections is a type of bacteria Staphylococcus epidermidis, which is found on the skin and mucous membranes.

The bacteria can enter through a surgical wound and apply itself to an implant. Then, the bacteria multiply and create a layer called biofilm.

The biofilm forms around an implant and acts as a physical and chemical barrier that resists antibiotics. The most common treatment for this type of infection is surgery to clean the implant or replace it altogether.

Orthopaedic implant surgeries are on the rise, with a current market valued at more than $16 billion and a projected value exceeding $23 billion by 2010, according to the Stevens Institute of Technology.

With the increasing number of procedures comes an increasing risk for implant infections, and researchers are working on solutions.

Some researchers are working with substances called hydrogels, polymers that absorb large amounts of water.

Most bacteria -- including the Staph strains common to implant infections -- can't adhere to most hydrogels.

Researchers at the Stevens Institute of Technology have created hydrogel particles that can be deposited onto an implant surface. The goal is to design implants with these gel particles on the surface in an arrangement that repels bacteria but allows other harmless cells to grow over the implant.

NANO-SIZED INFECTION FIGHTER: Researchers at Brown University are working on another solution for implant infections. Thomas Webster, Associate Professor of Engineering at Brown, and his team developed on the idea that microscopic bumps on implants aid in bone growth and may prevent bacteria from attaching. The researchers made discs out of zinc and titanium oxide. Some discs had bumps that measured .023 microns in diameter, while others had bumps 5 microns in diameter. They then applied Staphylococcus epidermidis bacteria to the discs. After an hour, the discs with the smaller bumps -- or the nanostructured discs -- hosted 1,000 times less bacteria than the discs with larger bumps.

Similar experiments revealed twice as many bone-forming cells grew on nanostructured discs, and indicators of healthy bone growth like collagen synthesis were stronger on the nanostructured discs. Dr. Webster says the next step in his research is animal studies.

FOR MORE INFORMATION, PLEASE CONTACT:
Thomas Webster
Brown University
Thomas_webster@brown.edu