Biological responses of neonatal rat calvarial osteoblasts on plasma-sprayed HA/ZrO₂ composite coating

Plasma-sprayed hydroxyapatite (HA) coating, applied to metal substrates, can induce a direct chemical bond with bone and hence achieve a biological fixation of the implant. However, the poor bonding strength between the HA coating and the substrate has been a concern for the orthopedists. In a previous study, the zirconia-reinforced hydroxyapatite composite coatings (HA/ZrO₂) could significantly improve the mechanical strength before and after soaking in simulated body fluid. This study aims to investigate the biological responses of osteoblasts on plasma-sprayed HA/ZrO₂ coating. The osteoblasts derived from neonatal rat calvarial were cultured in Dulbecco's modified Eagle medium (DMEM) with fetal bovine serum (FBS) on the surface of plasma-sprayed HA coating, HA/ZrO₂ coating, and ZrO₂ coating, respectively. The biological responses were investigated by the cell growth (1, 3, 5, and 10 days) and the cell morphology under scanning electron microscopy (SEM) (3, 6, 12, 24 and 48h). Examination by SEM revealed that osteoblasts on HA coatings exhibit less spreading during the medium phase (6 and 12 h), while, better morphologies were observed at the latter phases (24 and 48h). This should be derived by the dissolution of HA coating in the culture medium. On HA/ZrO₂ coating, the cells showed the poor morphologies at the latter phases (24 and 48h). This could be explained by the no apatite formed at the surface HA/ZrO₂ coating after soaking in simulated body fluid. The lower contents of ZrO₂ coating in HA coating and the addition of other solid solution (ZrO₂-MgO, CaO-ZrO₂, ZrO₂-CeO₂) in HA coating are the two possible methods to improve the cytocompatibility of HA/ZrO₂ coating.