Like the hips and knees they replace, artificial joints won't last forever. But with a little tweaking, they could last at least as long as their owners, an SIUC research team believes.

Peter Filip, director of the Center for Advanced Friction Studies, is coordinating the team's efforts to create a bio-friendly nanomaterial that could be used as a coating on medical implants to reduce everyday wear and tear.

The coating also would prevent corrosion, which can cause infection and implant rejection.

Joint implants typically last 15 to 20 years, Filip says. With seniors living longer and staying more active, and with more and more younger people getting implants because of athletic injuries or genetic problems, implant failure is of growing concern.

In modular implants (those with two or three parts), failures generally happen because of what Filip calls "micromotion"—the imperceptible movement of even the most perfectly machined and fitted modules as they rub against each other. That motion enlarges the opening in the bone that houses the implant. Replacement implants to fit that larger opening aren't always feasible, especially because micromotion weakens the bone, Filip explains. "If the implant can't be replaced, the person might wind up in a wheelchair."

Filip's research focuses on how the structure of metal and ceramic composite materials affects their properties. He decided to take a closer look at artificial joints after D. Gordon Allan, who heads the SIU medical school's orthopedic surgery division in Springfield, asked him why implants removed from patients had failed.

The research team's solution involves stopping both micromotion and corrosion by applying an infinitesimal layer of "noble metals" (such as gold, silver, and platinum) mixed with salt-like nitrogen compounds.

"These are all known materials, but they are combined in different ways to make totally new materials on a nanoscale (just a few atoms thick)," Filip says. "They are highly resistant to corrosion and have a high degree of friction, and they're very versatile. Different arrangements (of the components) will influence those two properties."

Friction acts like glue—the more there is, the stronger the bond, which reduces micromotion. But joints also have to move, and that's where the versatility comes in.

"We put two coats on an implant," Filip says. "The first coat is slippery to allow the movement. Then we change the chemistry, and we change the current and the voltage we use to deposit the coating on the implant, and we put the second coat on in a different place where it can act like a glue to hold the parts together."

Physicist Samir Aouadi's expertise with coatings allowed the team to develop these new nanocomposite materials with biocompatible ingredients. Early lab tests showed that "the friction can be modified as we wish, and wear resistance and corrosion resistance are as we expected," Filip says.

The researchers are applying for a patent on the materials. They've begun testing to confirm that the formulations aren't toxic to cells, and chemist Punit Kohli is investigating how two key proteins found in blood plasma interact with the coatings.

If all continues to look good, the team will use a hip simulator to assess friction and wear in implants coated with various nanocomposite formulations. These are the first steps toward testing in lab animals and people.

Researchers elsewhere are laboring in the implant field, too, trying things such as polymer coatings and DNA-based nanotubes. But Filip thinks there's room for many approaches.

"A wider spectrum of choice means that someday your physician may be able to look at your shape and your chemistry and design an implant just for you."

—by K. C. Jaehnig, Media & Communication Resources