October 04, 2005

Developed at SIUC's Center for Advanced Friction Studies New coating may extend life of artificial joints

by K.C. Jaehnig


Caption follows story

CARBONDALE, Ill. -- 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, a professor of mechanical engineering and energy processes from Southern Illinois University Carbondale believes.

Peter Filip, director of the University's Center for Advanced Friction Studies, has teamed up with physicist Samir M. Aouadi, orthopedic surgeons D. Gordon Allan and Per Freitag and post-doctoral fellow Manish Paliwal, and mechanical engineers Kambiz Farhang and Young W. Kwon— all from SIUC — to create a bio-friendly nanomaterial that when used as a coating on medical implants could reduce everyday wear and tear. The coating would prevent corrosion, one of the main reasons artificial joints fail.

Nowadays, increasing numbers of Americans are getting such joints. According to the National Center for Health Statistics, surgeons replaced some 220,000 hips and 418,000 knees in 2003. These implants typically last 15 to 20 years, Filip said.

"In the past, it was senior citizens who needed the replacements," he noted. "They weren't as active, so the implants lasted long enough.

"But today, more and more young people are getting implants because of athletic injuries or genetic problems. When these fail, it's a big problem."

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.

"When the implant modules move, they also makes the opening in the bone that houses them larger, which permits more movement, which further enlarges the opening," he said.

"A replacement implant has to be larger (to fit that larger opening), and that may not be possible, especially as micromotion also makes the bone very, very weak. If the implant can't be replaced, the person might wind up in a wheelchair. That's not a good prospect for a 35-year-old."

Filip's research focuses on the relationship between the structure and properties of metals, ceramics and composite materials. He decided to take a closer look at artificial joints after Allan, head of the University medical school's orthopedic surgery division in Springfield, asked him why implants removed from patients had failed.

"We analyzed them and saw what went wrong and what needed to be done to fix it," Filip said.

The research group's fix 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 said.

"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 cuts down on micromotion. But joints also have to move, and that's where the versatility comes in.

"We put two coats on an implant," Filip said.

"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."

With additional modification, the coatings also would prove useful for spinal disorders such as herniated disks, Filip said.

While the researchers have not yet tested the coatings on implants in actual use, Filip called preliminary laboratory results "encouraging."

"We found that the friction can be modified as we wish, and we found that wear resistance and corrosion resistance are as we expected," he said.

"We believe that the coatings should also help problems with infection and implant rejection because these are often due to corrosion."

The researchers already have applied for a patent on the materials and are searching for grant funds that would support further lab tests as well as work with animals and, down the line, humans.

Researchers elsewhere are laboring in this field, too. Scientists in Japan have developed a polymer coating for implants, and a Purdue University team is working on a coating made of DNA-based nanotubes, while a physicist from the University of Alabama is pressing industrial diamonds into nano-service, to name just a few. But Filip thinks the marketplace has room for them all.

"People are different — men and women, young and old, all have different needs," he said.

"I believe that rather than going to one solution for everyone, we will end up with an optimal solution for each. A wider spectrum of choice means that someday your physician may be able to take a tomographic look at your shape and your chemistry and design an implant just for you."

Leading in research, scholarly and creative activities is among the goals of Southern at 150: Building Excellence Through Commitment, the blueprint the University is following as it approaches its 150th anniversary in 2019.

(Caption: Slick — Peter Filip, director of the Center for Advanced Friction Studies at Southern Illinois Carbondale, explains how, when applied as a coating to an artificial hip joint, a new material engineered at the center can make an artificial hip joint “slippery” so that it moves more freely. This cuts down on the wear and tear that causes such implants to fail.)