Preparation and cytocompatibility of brushite-hydroxyapatite coating on Ti by chemical conversion

In order to enhance the osseointegration of Ti implant, chemical conversion technology was used to prepare a calcium phosphate (CaP) coating on Ti. The alkali treatment was conducted to rise a secondary coating on the primary coated Ti. The phase composition, microstructure and corrosion resistance of the CaP coated Ti (Ti-CaP) samples were investigated using the XRD, field emission SEM and electrochemical measurements, respectively. The cytocompatibility was evaluated by the cell attachment, proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 cells. The results show that the primary coating formed on Ti is mainly composed of brushite (CaHPO₄·2H₂O) with a blocky structure. After alkali treatment, the brushite crystals are partly transformed to hydroxyapatite (HA) crystals with a coarser surface and some newborn crystals. The electrochemical measurements reveal that the corrosion resistance of the HA coated Ti is better than that of the brushite coated Ti. In vitro cell tests demonstrate that the surface of the coated Ti samples exhibit better cytocompatibility than that of pure Ti.