Crystal Growth and Dissolution of Hydroxyapatite: The Role of Ascorbic Acid

Ascorbic Acid (AA), an important biomolecule present in relatively high concentrations in blood and other biological fluids, has been rarely investigated with reference to its effect on the biological mineralization–demineralization processes. To our knowledge, the present work is one of an extremely limited few found in the literature in which the effect of the presence of AA in mineralizing or demineralizing electrolyte solutions is addressed in a quantitative way. We have used the constant saturation method for the accurate measurement of the rates of crystal growth of hydroxyapatite (HAP, Ca5(PO4)3OH), the model compound of the inorganic component of the hard tissues of higher mammals. It was found that both crystal growth and dissolution were accelerated significantly. The increase in crystal growth rates showed stronger dependence on the solution supersaturation (120% increase for the highest and 460% for the lowest) in the presence of 0.1 mM of AA, pH 7.40, 37 °C, 0.15 M NaCl. The dissolution rate increase was less dependent (average of ca. 300% increase). It was concluded from the detailed characterization of the solid that the acceleration effect was due to the uptake of AA on the HAP surface.