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, Ti6A14V 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 (beta-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 Xray 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 Pin 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. (C) 2017 Elsevier B.V. All rights reserved.