Investigation of the in vitro corrosion behavior and biocompatibility of niobium (Nb)-reinforced hydroxyapatite (HA) coating on CoCr alloy for medical implants

In this study, a niobium-reinforced hydroxyapatite (HA-Nb) coating was developed on cobalt-chromium (CoCr) alloy by plasma spraying with three varied levels, i.e., 10, 20, and 30% of weight percent (wt%) of Nb content. The corrosion behavior and biocompatibility of the samples were analyzed through electrochemical corrosion testing and cytotoxicity studies, respectively. The results of corrosion testing revealed that the HA coating increased the corrosion resistance of the CoCr alloy, and with the incremental increase of Nb reinforcement in HA, corrosion resistance was further enhanced. The HA-30Nb coating demonstrated the finest corrosion resistance with the highest E-corr and lowest I-corr values, which were about one order of magnitude lower in comparison to the bare CoCr alloy. The surface hardness increased and the surface roughness decreased with the increase of Nb content in the coating. Wettability analysis revealed that HA and HA-Nb coatings had a hydrophilic nature. HA-Nb coatings demonstrated a significantly better cell proliferation than the CoCr alloy.