Surface characterization of bioceramic coatings on Zr and its alloys using plasma electrolytic oxidation (PEO): A review

Abstract

Zirconium (Zr) and its alloys are widely utilized in orthopedic, dental and replacement of hard tissue implants owing to their high biocompatibility and corrosion resistance, and low elastic modulus. The low elastic moduli of zirconium alloys reduce stresses in joint and bone implants that results in higher bone growth and implant stability. High corrosion resistance is ascribed to the formation of an oxide layer (ZrO2) on the surface of these alloys; however, this oxide layer is thin and not sufficient for durable medical applications. Zirconia is also used as a neutral (Bioinert) material. It is known to limit the formation of bonds with bone tissue; thus, an adequate bond cannot be formed which makes surface modification an essential requirement. Various techniques have been utilized to amend surface properties. Among the various methods, plasma electrolytic oxidation (PEO) results in the production of a uniform, thick, hard, and sticky oxide coating on the surface of zirconium. By optimizing the PEO process parameters, most of the coating properties can be controlled. In this review article, first the biological applications of uncoated zirconium will be reviewed, an introduction of the coating procedure will be presented, and the bioactive and biocompatibility behavior of deposited coatings on zirconium using the PEO technique will be evaluated.