Fibronectin adsorption on osteoconductive hydroxyapatite and non-osteoconductive α-alumina

The osteoconductivity mechanism of hydroxyapatite (HAp) has not been elucidated. It is hypothesized that specific proteins adsorb on HAp, promoting its osteoconductivity. To verify this hypothesis, we compared the adsorption behavior of fibronectin (Fn) on HAp powder and on alpha-alumina (alpha-Al2O3) powder, a material with no osteoconductivity. More Fn adsorbed on alpha-Al2O3 than on HAp, irrespective of the Fn concentration, and there was no significant difference in the secondary structure of Fn adsorbed on HAp and alpha-Al2O3. Further, it is possible that Fn did not adsorb on HAp and alpha-Al2O3 through the Arg-Gry-Asp motif of Fn. The amount of Fn adsorbed on HAp oriented to the a(b)-axis with very little decrease in carbonate and the adsorbed Fn had a smaller alpha-helix structure content. The results suggest that the secondary and/or higher-order structure rather than the amount of adsorbed Fn might affect the osteoconductivity of HAp, which might be electrostatically controlled by the crystal face orientation and/or carbonate content of HAp, although this should be confirmed by a cell culture test in the future.