Surface modification of biomaterials through noble metal ion implantation

Studies are described involving effects of noble-metal ion implantation on corrosion inhibition and charge-injection capabilities of surgical Ti-6A1-4V alloy. A major factor linked to excellent long-term biological performance is resistance to metal-ion release to tissues. The elements most resistant to corrosion in aqueous solutions are the noble metals. Disadvantages include expense and general inadequacy of mechanical properties. However, if small quantities can be used to surface-modify a surgical device in the last stage of manufacture, that device could possess an optimum combination of environmental integrity, biological response, mechanical properties, and charge-injection capability at minimum expense. Results for ion-implanted Ir are presented. Iridium has been described as the most corrosion-resistant element known, and its activated oxide as having the highest charge-injection capability of any material known. Ti-6A1-4V samples, ion implanted with 2.5 and 5.0 atomic % peak-maximum concentrations of Ir, were subjected to corrosion treatments to enrich the surface with Ir. Corrosion potential and cyclic voltammetry measurements indicated enrichment in H2SO4, and continued enrichment in isotonic saline, with corrosion potentials approaching that of pure Ir, and charge densities in isotonic saline exceeding that of pure Ir for the 5.0% peak-max Ir implanted material. X-ray photoelectron spectroscopy confirmed the high levels of Ir surface enrichment.