What began as pure research--numbers in a computer model--has ended up, decades later, in artificial joints that replace some 100,000 crumbling hips and knees every year.
In the early 1960s, ORNL physicists had used computers to model the way impurities turned into crystalline solids during ion implantation, the blasting of charged atoms into materials. Their research helped pave the way for today's semiconductor chips, whose electrical properties arise from carefully controlled impurities (called dopants) deposited in silicon or other insulators.
In 1980, physicist Jim Williams began seeking new ways to use ion implantation. Ion-implanting even a thin layer near a material's surface, Williams and his colleagues knew, could radically alter the surface properties, imparting hardness, say, or corrosion resistance far beyond that of the base material or dopant.
It was just those properties, in fact--hardness and corrosion resistance--that were needed in materials for artificial joints. They combined stresses of wear and corrosive body fluids take their toll on implants; a titanium-alloy knee could wear out in only a few years, for example, necessitating another painful operation. But working with a materials scientist at the University of Alabama in Birmingham--home to a large medical center--Williams found that implanting the titanium's surface with nitrogen ions made a remarkable difference in its resistance to wear and corrosion. The technology was rapidly adapted for commercial use by Spire Corp., a Boston company specializing in high-tech surfaces for aerospace, electronics, and biomedical components.
By 1993, Spire expects to be ion-treating nearly 50,000 artificial knees a year, plus a similar number of artificial hips (in hip prostheses, ion-treating the cobalt-chromium ``ball'' makes the metal even harder--but kinder and gentler to the joint's polyethylene ``socket'').
A decade ago, Jim Williams figured out something that now helps tens of thousands of artificial joint recipients every year: Sometimes, making things a little harder makes them a log easier.
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Date posted 5/10/94 (cel)