Enhanced cytocompatibility of Ti6Al4V alloy through selective removal of Al and V from the hierarchical micro-arc oxidation coating

To improve cytocompatibility of Ti6Al4V alloy, porous oxide coatings were prepared on its surface through micro-arc oxidation (MAO) in the Na2B4O7 electrolyte plus KOH. The morphology and composition of the coatings were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). We found that, besides improving hydrophily, both bio-unfriendly elements of Al and V in the coatings decreased quickly when KOH was added into Na2B4O7 electrolyte from 0.05 to 0.35 M. While the KOH reached 0.25 M, the values of Al and V in the coatings decreased to as low as 0.06 at.% and 0.3 at.%, respectively (compared with Ti6Al4V alloy, Al/Ti and V/Ti are reduced by 98.3% and 73.8%, respectively), which means selective removal of Al and V in MAO coatings happened. In the immersion test using simulated body fluid (SBF), the release of Al and V ions from the coatings with lower content of Al and V was much less than that of the MAO coating treated without KOH addition in the electrolyte. Cytocompatibilty tests confirmed that the hierarchical oxide coatings with lower Al and V were beneficial to the adhesion, spreading, as well as the proliferation of the MC3T3 osteoblasts.