The application of niobium and tantalum oxides for implant surface passivation

Abstract

Despite the advantages of ceramics, with their high corrosion$\$nstability in vivo, most medical implant constructions$\$nare still made from metals [1]. To increase the$\$ncorrosion stability of metals, different coatings are applied$\$nto the implant surfaces, typically such coatings are the$\$noxides of the metals in the implants [2].$\$nFor an oxide film to have protective properties it$\$nmust satisfy the following requirements:$\$n• to be unbroken and pore-free;$\$n• to have good adhesion with the metal;$\$n• to have a thermal expansion constant near to the$\$nvalue for the metal;$\$n• to be chemically inert in different environments;$\$n• to be hard and have minimal wear under load.$\$nThe oxides of metals such as Al, Ti, Zr, Nb and Ta$\$nsatisfy all these properties to some degree [3–5]. Indeed,$\$nsome of these metal oxides are used in medicine$\$nindependently without a metal substrate, such as implant$\$nconstructions from sapphire (a single-crystal modification$\$nof Al2O3) [6, 7].$\$nTitanium is the most widely used material for$\$nmedical implant manufacture [8]. Its chemical passivity is$\$nprovided by the oxide film (TiO2), covering the entire free$\$nsurface; a result of titanium contact with air. But titanium$\$nis unable to satisfy all the requirements necessary for an$\$nimplant material because of its insufficient corrosion$\$nstability [9–11]. The application of combined implants$\$nconsisting of a metal base and a ceramic coating also does$\$nnot give a complete solution to the problem, because of$\$nthe low adhesion strength and fragility of ceramic$\$ncoatings [12, 13].