The effect of alkali- and heat-treated titanium and apatite-formed titanium on osteoblastic differentiation of bone marrow cells.

This study was based on the hypothesis that osteogenesis is enhanced by growth of osteogenic cells on an apatitic surface. To test this hypothesis, the behavior of rat bone marrow cells on these surfaces was examined: commercially pure titanium (Cp Ti), alkali- and heat-treated titanium (AH Ti), and AH Ti incubated in a simulated body fluid to deposit crystalline hydroxyapatite on the surface (Ap Ti). The alkaline phosphatase (ALP) activity of the cells cultured on Ap Ti was significantly higher at day 7 and day 14 than the ALP activity observed for the other titanium surfaces. At day 14, the ALP activity on AH Ti was significantly increased compared with the ALP activity on Cp Ti. The amount of DNA per well increased nearly in parallel for each titanium. However, northern blot analysis at day 14 revealed that expression of osteocalcin and alpha1(I) collagen mRNA was higher in the cells cultured on Ap Ti than the cells cultured on AH Ti. The cells cultured on Cp Ti showed the lowest mRNA levels. After 7 days of cell-free culture in medium supplemented with 15% serum, X-ray photoelectron spectroscopy (XPS), and thin-film X-ray diffraction (TF-XRD) analysis showed that calcium phosphate had been deposited on the AH Ti (resulting in an increase in thickness with time). No phosphate was detected on the Cp Ti, even after day 14. This study indicates that Ap Ti provides the most favorable conditions for differentiation of bone marrow cells, and, at a later stage, AH Ti also provides favorable conditions, perhaps because of the formation of a surface layer of calcium phosphate. This potential for apatite formation may play an important role in osteoblastic differentiation.