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Coating process may give implants longer life
A process that bonds the stuff from which bones are made onto the surface of artificial bone and joint implants has the potential of giving longer life to as many as 600,000 implants a year.
"These kinds of implants generally have a five- to ten-year lifetime," said Dr. Dwain Coble, an associate professor of chemistry at The University of Alabama in Huntsville. "On a hip transplant, for instance, the surgeon cuts off the knob of the thigh and drills a hole down into the remaining bone. The implant has a peg that fits down into that hole. They put a 'super glue' on the implant and stick it down in there.
"Unfortunately, none of the glues like that are permanent. They slowly dissolve in the body. And the metal surface of the implant is made of an inert material, either a titanium or a cobalt alloy, so the bone doesn't bond to the implant. Eventually they can come loose.
"Implant surfaces are chemically inert (so the body doesn't react with or dissolve the metal), making them difficult to coat with materials to which the bone might attach itself.
The new process uses electrodeposition to bond hydroxyapatite (the material that covers teeth and makes up about 70 percent of our bones) in a matrix of an inert cobalt alloy on the surface of the implant. The implant is electroplated in a solution containing particles of cobalt alloy and hydroxyapatite. As metal particles are drawn to and bond with the implant, they trap the much larger hydroxyapatite particles. The hydroxyapatite sticks out of the matrix like tennis balls trapped in a net. Because the new surface is up to 70 percent hydroxyapatite, it is hoped that the bone could form a permanent bond with the implant.
Patents on the process are held jointly by scientists at UAH, McDonnell Douglas, The University of Alabama at Birmingham, and the three institutions.
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