Surface modification of titanium alloy inmplants

Abstract

The initial events after implantation may be crucial in determining the long term development of the implant tissue interface; this in turn will be influenced strongly by the implant's surface condition which will govern blocompatibility, corrosion and o sse o integration. With regards to corrosion, the problem of metal ion release or dissolution is important as the release of potentially harmful ions can lead to adverse local and systemic effects, and may lead to revision surgery. Hip replacement stems manufactured from Ti-6AI-4V titanium alloy have been surface treated to modify the natural and protective surface oxide. The metal ion release from these stems into bovine serum has been monitored using atomic absorption spectroscopy. A combination of transmission electron microscopy, x-ray photoelectron spectroscopy and atomic force microscopy have provided a method for fully characterising the nature and chemistry of the surface oxide. The kinetics of metal ion dissolution have been interpreted in terms of oxide surface chemistry and its interaction with the bioenvironment. Those stems either heated in air or aged in boiling distilled water were found to have significantly lower metal ion release compared to those receiving standard commercial treatments. This was maintained for both polished and corundum blasted implants. The improved dissolution behaviour is associated with a change in the surface oxide structure from mixed titanium oxides to a more stable homogeneous rutile structure. Kinetically, the dissolution reaction showed two stages were occurring for the aged and air-heated samples and a single stage was associated with the standard samples. The onset of the second stage was associated with the formation of a protemous biolayer on the implant surface. The unique implant surface chemistry resulting from thermal treatment facilitated the formation of a biolayer. The incorporation of these simple thermal treatments as standard into clinical procedures should reduce considerably metal ion release from the implant and its associated effects.

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