Formation of the hierarchical porous structure and surface morphology in the micro-arc calcium phosphate coatings

Abstract

The study of the formation of the hierarchically organized porous structure and surface morphology, as well as phase and elemental compositions of the calcium phosphate (CaP) coatings deposited by the micro-arc oxidation (MAO) method under varied applied voltage (200-300 V) was performed. The increase of the MAO voltage led to the linear increase of the coating thickness (50-100 µm), surface average roughness (3.0-7.5 µm), surface porosity (20-35%) and sizes of the structural elements (spheres and pores). In addition, the increase in the voltage led to the structural-phase transformation in the coatings from the amorphous state to the amorphous-crystalline state with incorporation of CaHPO4 and β-Ca2P2O7 phases. The elemental composition of the CaP coatings did not significantly depend on the applied voltage value, however, the Ca content and Ca/P atomic ratio increased with increasing of the voltage. Thus, the MAO technique allows to form on the metal substrate the CaP coatings with specific physicochemical, and structural properties influencing the behavior of stromal stem cells and bone tissue regeneration.