Structural characteristics and barrier properties of anodic zirconium oxides for biomedical applications

Abstract

Although originally used almost exclusively in the nuclear energy industry due to its low neutron absorption section, zirconium and some of its alloys are currently being considered as a high-quality alternative to titanium as permanent implant materials. Zirconium as a valve metal is characterized by the rapid irreversible formation in oxygenated media of a surface oxide film which behaves as a barrier against corrosion in many aggressive media including living tissue fluids. Anodization represents an inexpensive and efficient route to re-design the surface of zirconium in the micro and nanoscale. In acidic media, the thickening of zirconium oxide layer may be controlled by the anodic potential. When fluorides are present in the anodizing electrolyte, ordered nanotubular structures may be formed. Thus, the carefully selection of anodization conditions lead to a wide range of morphologies including nanopores and high aspect ratio nanotubular structures. Some difficulties, however, are still unsolved, as the adhesion of thick nanotubular oxide layers to the metal substrate, or homogeneous coverage on complex geometries. In this chapter, current results regarding structure and surface features influence on the in vitro and in vivo performance of anodized zirconium and its alloys will be reviewed and some trends for further research will be stated.