ION-IMPLANTED MATERIALS
Real Artificial Joints

An ion-implanted hip joint.

The remarkable discovery of ion channeling by purely theoretical means at ORNL ultimately led to accelerator-based programs to introduce ions into materials. Ion implantation was found to improve the surfaces of many materials, including alloys used to make artificial hips and knees. Research was performed by ORNL's Jim Williams in collaboration with Ray Buchanan, then at the University of Alabama and now at the University of Tennessee. They discovered in 1980 that implanting the titanium alloy used in artificial joints with nitrogen ions hardens the alloy and greatly improves its resistance to wear and corrosion.

Ion implantation was found to improve both the titanium and cobalt-chrome alloys used to make surgically implantable artificial joints, but different mechanisms are involved. The technique hardens the titanium alloy's surface so that it cannot be scratched by the alloy's own oxide coating (which reduces surface chemical reactivity). For the cobalt-chrome alloy, ion implantation improves its wettability so that the artificial joint slides more easily and makes the surface hardness more uniform. Thus, the alloy interacts better with its mating polymer component, extending its life. In the early 1990s the Food and Drug Administration issued guidance requiring that all newly submitted titanium orthopedic devices be ion implanted.

Ion implantation of orthopedic materials was first applied commercially by Spire Corporation and then by Implant Sciences Corporation. Combined sales of several hundred thousand devices per year amount to about $10 million annually to the orthopedics manufacturers for wholesale surface treatments. Williams estimates that cumulative sales for the treatments are well over $100 million. The more important benefit, however, lies in the improved lives and comfort levels for millions of Americans who have ion-implanted artificial hips, knees, and other joints.

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