Comparison of Osteoconduction, cytocompatibility and corrosion protection performance of hydroxyapatite-calcium hydrogen phosphate composite coating synthesized in-situ through pulsed electro-deposition with varying amount of phase and crystallinity

Abstract

In order to improve the surface biocompatibility, a composite coating of hydroxyapatite and calcium hydrogen phosphate was synthesized over 316 L grade of stainless steel through pulsed electro deposition. It was observed that relative phase composition and corresponding crystallinity vary with the deposition current density. Thus a detailed study with the help of simulated body fluid and MG63 cell line was carried out in order to compare their respective biocompatibility in terms osteoconduction and cytocompatibility. A detailed electrochemical behavior study was carried out to assess the corrosion behavior under contact with body fluid.Cell proliferation studies indicate that the coating deposited with a current density of 10 mA/cm2, which is having the highest weight percentage and crystallinity of hydroxyapatite phase, is the most preferable one for continuous, faster and interconnected cell growth. Also cell cytoskeletons spread in bigger areas around their nucleus with a strong interconnection between each other. The bio-mineralization study shows that on immersion of these coatings in simulated body fluid, coating obtained through 10 mA/cm2, trends to build up hydroxyapatite on its surface with 200 nm pores at initial 1–3 days. After 14 days of immersion, hydroxyapatite deposition trends to form a spherical shape of around 2 micron in radius which can accommodate larger surface area for tissue growth vis-à-vis better bonding, as compared to other coating surfaces. The polarization resistance of 10 mA/cm2 coating is almost 10 times higher than the others and thus indicates its slower rate of corrosion under contact with simulated body fluid.