The use of thin layer activation to evaluate ion beam surface treatments of orthopaedic implant materials

Abstract

The wear of metal and of polyethylene orthopaedic components used in hip and knee replacements creates several severe medical problems, due both to the wearing out of the prosthesis and to the body's reactions to submicroscopic wear debris. Conventional methods for measuring wear under realistic conditions are insensitive and inaccurate. We describe the use of thin layer activation (TLA) by high energy ion beams in order to monitor sensitively the wear rates of metallic and polymeric specimens treated by a variety of ion beam surface techniques designed to reduce wear. Polyethylene was activated by a recoil process, using 7Be + ions. Ion implanted species induced nitrogen, tin, aluminum, oxygen, carbon, iodine, and barium, and tin and silver were introduced by ion beam mixing. Four different nuclear particle accelerators, and energies from 50 keV to 35 MeV were utilized. Nitrogen or carbon ion implantation was shown to be effective in reducing metal erosion by up to 500× in titanium alloy and by 5× in cobalt–chrome. There are major differences, in some cases, between the wear rate in distilled water and that under bovine serum. The wear of the UHMWPE is also reduced by factors between 2 and 3 fold by ion implantation of the metal counter face. Thin layer activation is shown to be a versatile, rapid and accurate method for measurement of wear in orthopaedic materials during in vitro testing. It is shown that as little as 30 nm of wear is detectable.