Abstract
The properties of calcium phosphate (CaPi) formed in supersaturated solution (prepared by mixing CaCl2 and K2HPO4 at neutral pH) were studied by means of a Coulter counter and a calcium ion-specific electrode. It was found that the mean particle diameter (φ) of CaPi formed initially increased and then levelled off with time. The rate of increase of φ, however, decreased with increase in the amount of sodium chondroitin-6-sulfate (Na2Chs) added to the mother solution, presumably because of the dispersing effect of Na2Chs. The number concentration of formed particles of CaPi increased at first but after a short period it decreased with time because of the formation and aggregation of secondary particles. Remarkable consumption of Ca2+ was observed at two points in the time course of the precipitation reaction : (1) immediately after mixing the reactants, and (2) after and induction period (ttrans required for the crystallization of amorphous CaPi as hydroxyapatite (HAP), as was confirmed by measurement of the X-ray powder diffraction pattern. The lag time, ttrans, was not affected by the amount of Na2Chs added, but decreased with increase in the amount of CaPi precipitated or of seed HAP inoculated. The physiological significance of the present work is briefly discussed.
