Calcium phosphate-based composite coating by micro-arc oxidation (MAO) for biomedical application: a review

Calcium phosphate (Ca-P) based composites have attracted great attention in the scientific community over the last decade for the development of biomedical applications. Among such Ca-P-based structures, carbonate apatite (CA) and hydroxyapatite (HA) materials have received much attention in the clinical and biomedical fields, mainly because of their unique biological characteristics. These characteristics can promote the biocompatibility of implant materials and osseointegration between the implant and host bone. Various studies have been carried out on the fabrication of Ca-P coatings on orthopedic and dental implants using the micro-arc oxidation (MAO) process; however, there has not been a comprehensive review of the control of MAO parameters to achieve an optimal coating structure. This article presents a critical analysis of the synthesis techniques that have been adopted for the fabrication of Ca-P-based coatings on both commercially pure titanium (CP-Ti) and biomedical grade Ti alloys. Moreover, this work elucidates the influence of MAO processing parameters such as electrolyte concentration, pH value, voltage, and time on the crystal structure and surface morphology of Ca-P coatings. It is shown that the surface thickness, crystal structure, and surface morphology of Ca-P coatings directly influence their biocompatibility.