Concern continues over the possible long-term biological effects of corrosion products released by degradation of metallic surgical implant materials in the human body. One approach to improve long-term biological performance involves surface modifications to significantly reduce degradation rates. Fundamentally, the elements with lowest driving forces (lowest ΔG functions) for corrosion in aqueous solutions over a wide pH range are the noble metals. With regard to surface-modifications, one of the most effective methods is through ion implantation.
In the present on-going study, static in vitro corrosion properties of noble-metal ion-implanted surgical Ti-6Al-4V and commercially-pure(CP) Ti are being investigated in nonpassivating acid and passivating saline solutions. It was postulated that during the early stages of corrosion (or during a corrosion pretreatment) the implanted noble metal would enrich at the surface and significantly reduce subsequent corrosion rates. Thus far, the effects of ion-implanted Au and Rh have been studied, with mixed results. The Au implanted material yielded early benefits, but the enhanced corrosion resistance deteriorated with time, probably because the Au, during the enrichment stage, was not adequately adherent to the substrate. On the other hand, the observed behavior for the Rh implanted material appeared to follow the postulated mechanism, with both initial and time-dependent improvements in corrosion resistance.