The influence of anionic chitin derivatives on calcium phosphate crystallization

The influence of two water-soluble anionic chitin derivatives, sodium carboxymethyl–chitin (CM-chitin) and phosphoryl-chitin (P-chitin) on the crystallization of calcium phosphate by seeded growth and turbidimetry were studied. The adsorption of these derivatives onto hydroxyapatite obtained at 37°C, fitted the Langmuir isotherm. The affinity constant and number of adsorption sites were measured at 2.9 and 1.69 μmol m -2 for CM-chitin and 11.85 and 4.23 μmol m -2 for P-chitin. P-chitin exerted a potent inhibitory effect on the seeded growth of hydroxyapatite from a supersaturated solution, reducing the initial rate of crystallization by more than 90% at a solution concentration of 10 -4 m. Both chitin derivatives also retarded the rate of spontaneous calcium phosphate precipitation. The type of calcium phosphate precipitated was poorly crystallized, calcium-deficient apatite. The chitin derivatives were found to be incorporated into the precipitate and influenced both the phase and morphology of calcium phosphate formed.