Characterization and bioactivity of hydroxyapatite-based coatings formed on steel by electro-spark deposition and micro-arc oxidation

Abstract The hydroxyapatite (HA); a bioactive and biocompatible; was formed on steel by electro-spark deposition (ESD) and micro-arc oxidation (MAO). At the first stage, Ti6Al4V alloy was coated on steel by ESD method under argon atmosphere. And then, the HA-based ceramic coatings were directly fabricated on ESD coated surface by MAO in an aqueous electrolyte containing calcium acetate and β-calcium glycerophosphate-based electrolyte at 30 min. The phase structure, surface and cross-sectional morphology, surface topography and roughness, wettability, surface and cross-sectional elemental composition and functional groups of the coatings were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), surface profilometer, contact angle goniometer (CAG), energy dispersive spectroscopy (EDX-Mapping) and Fourier transformed infrared spectroscopy (FTIR), respectively. The highly crystalline HA structure was detected on ESD + MAO surface. The HA-based surface was rough and porous due to the existence of micro discharge channels through MAO. The elements such as Ca and P in the structure of HA were homogeneously distributed over the whole surface. The HA-based duplex coating had a low contact angle indicated a hydrophilic character due to the existence of porous and rough structure on the surface. The bioactivity of HA-based coatings was carried out by immersion test in simulated body fluid (SBF) at body temperatures up to 14 days. After 14 days, the HA-based surface was uniformly covered by secondary apatite structure. The HA-based coating on steel significantly contributed improving bioactivity.