Ascorbate–apatite composite and ascorbate–FGF-2–apatite composite layers formed on external fixation rods and their effects on cell activity in vitro

Ascorbate–apatite and ascorbate–fibroblast growth factor-2 (FGF-2)–apatite composite layers were successfully formed on anodically oxidized Ti rods clinically used for external fixation by a one-step procedure at 25 °C, using a metastable supersaturated calcium phosphate solution supplemented with l-ascorbic acid phosphate magnesium salt n-hydrate (AsMg) and FGF-2. The AsMg–apatite and AsMg–FGF-2–apatite composite layers were evaluated in vitro using fibroblastic NIH3T3 and osteoblastic MC3T3-E1 cells. The AsMg–FGF-2–apatite composite layer markedly enhanced the NIH3T3 cell proliferation and procollagen type І gene expression. Without FGF-2, the AsMg–apatite composite layer whose ascorbate content was 3.64 ± 1.27 μg cm−2 obviously enhanced osteoblastic proliferation and differentiation. However, the AsMg–FGF-2–apatite composite layers whose FGF-2 contents were from 0.15 ± 0.03 to 0.31 ± 0.04 μg cm−2 inhibited osteoblastic differentiation in vitro. Thus, the AsMg–FGF-2–apatite composite layer should be precipitated on the surface of external fixators attached to skin and soft tissue. On the other hand, the AsMg–apatite composite layer should be precipitated at the part attached to bone tissue.