Studies on induction of L-aspartic acid modified chitosan to crystal growth of the calcium phosphate in supersaturated calcification solution by quartz crystal microbalance.

Acidic amino acids, such as aspartic acid (L-Asp) and glutamic acid, are the primary bioactive molecules of the glycoprotein on the organic/inorganic interface of biomineralized tissues. In this study, the induction of chitosan film modified with L-Asp on the crystal growth of hydroxyapatite (HAP) was investigated by a novel in situ analysis approach, quartz crystal microbalance (QCM), associated with the dynamically structural and morphological characterization of precipitation products on various phases by X-ray diffraction (XRD), Fourier-transformed infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The natural chitosan exhibited no inducing ability on the crystal growth of HAP. However, the growth rate of induced HAP was dramatically accelerated by the L-Asp modification of chitosan film and increased with the increase of the concentration of L-Asp in the chitosan substrate. It was shown that the chelation of calcium ion with L-Asp provided a nucleation centre and the cluster nuclei was formed by adsorbing further PO(4)(3-), Ca(2+), and then HAP deposited on the original HAP coating in the supersaturated calcification solution (SCS). The developed method allows a kinetic evaluation of the induction of organic film on crystal nucleation and the growth of HAP in vitro.