Collagen modulating crystallization of apatite in a biomimetic gel system

Apatite crystals were formed at 37 °C in a biomimetic gel system with the presence and absence of collagen under pH 6.5, 7.0 and 7.5 respectively. X-ray diffraction, transmission electron microscope and selected area electron diffraction pattern were applied to characterize the crystals. The results indicated that collagen modulate crystallization of apatite both in composition and morphology. With the absence of collagen, the obtained crystals were ribbon-shaped octacalcium phosphate (OCP) at pH 6.5, the mixture of OCP and nanosize rod-shaped hydroxyapatite (HAP) at pH 7.0 and 7.5 respectively. OCP would be a precursor of HAP with the absence of collagen. With the presence of collagen, collagen acted more effectively in controlling crystallization of HAP than pH did in the system. Ribbon-shaped HAP was the main phase at pH 6.5, kept a very thin structure at pH 7.0 while the needle-shaped HAP with several nanometers in diameter was obtained at pH 7.5. It was discussed amorphous calcium phosphate would be an intermediate phase of HAP with the presence of collagen. Such understanding of collagen and pH control on biomineralization gives new insights on the controlled synthesis of apatite.