A Little Zap To Help Hip Implants Last

WITH SOME OF TODAY'S cementless hip replacements, the portion of the implant that meets bone is encased in a titanium wire mesh coated with hydroxyapatite (HA). This calcium compound encourages natural bone to grow into the implant. The trouble is, coating the mesh requires high-temperature spraying. It's like trying to spray-paint a pile of chains: The HA doesn't get into all the nooks and crannies. And the heat can cause the metal and the coating to degrade.

Researchers at the University of Nebraska-Lincoln are attacking the problem with a technique akin to electroplating. First, they use electricity to form brushite crystals evenly on the mesh. The brushite can then be changed to pure HA by a simple chemical reaction. This avoids the adverse effects of a hot spray. All it requires is adding one step to the implant-manufacturing process. So the technique should cost as little as one-tenth as much as conventional HA coating. "In principle, it could be done with a couple of batteries," says chemist Jody G. Redepenning, who invented the process. Several companies have expressed interest in creating a product.