Controlled growth of calcium phosphate using phosphatidylcholine-modified porous titania as reaction compartments

Phosphatidylcholine-modified porous titania was employed as reaction compartments for the controlled growth of calcium phosphate. The process of calcium phosphate precipitation was investigated in detail using in situ quartz crystal microbalance (QCM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The obtained results showed that the nucleation and growth of calcium phosphate could take place within porous titania modified by neutral phosphatidylcholine in simulated body fluid (SBF), and that two different stages were present in the process of calcium phosphate precipitation, indicating two different kinetic processes. At the nucleation stage, the Ca2+ ions in SBF solutions bound firstly into the phosphatidylcholine-modified porous titania, and then the free ions in SBF solutions were attracted to the reaction compartments, causing the formation of calcium phosphate nuclei. With the increase of immersion time, a large amount of Ca2+ and ions in supersaturated SBF solutions deposited spontaneously into the phosphatidylcholine-modified porous titania to form calcium phosphate precipitation. In terms of the in situ frequency shifts, the reaction rate constants of calcium phosphate (K1 and K2) were estimated, respectively, at two different stages, and the results were (6.20±0.31)×10−4 s−1 and (1.25±0.13)×10−5 s−1, respectively, in 2.0 SBF solutions, indicating that the reaction rate at the nucleation stage was higher than that at the growth stage, and that the growth stage was the rate-limiting step.