Summary
The maturation of calcium phosphate crystals formed by the conversion of spontaneously precipitated amorphous calcium phosphate (ACP) was studied in aqueous media at temperatures ranging from 20° to 37°. Reaction pH was kept at 7.4 with either Hepes buffer or by the pH-stat addition of base. Reaction kinetics were followed by monitoring solution calcium and total phosphate, and, in the pH-stat controlled reaction, by recording the amount of KOH needed to maintain pH. Reaction products were examined chemically and by X-ray diffraction and transmission electron microcopy. The first crystals to form deviated markedly from apatite in morphology, composition, structure, and solubility. They were extremely thin and flaky in appearance, had a low Ca/P molar ratio (1.4), contained an appreciable amount of acid phosphate (16%), and had an exceptionally largea-axis (10.5 Å vs. 9.4 Å for apatite). With maturation, the crystals became thicker but smaller in lateral dimensions, more apatitelike in structure and composition, and less soluble. However, this ripening of the crystals was accompanied by unusual inflections in the solution Ca and total PO4 curves, and, in the case of the pH-stat experiments, in the OH consumption profiles as well. These anomalous post-ACP solution changes suggest that a phase change had taken place during crystal maturation. Although the observed structural and compositional changes are not inconsistent with the perfection of an initially defective apatite, the changes in crystal morphology and the anomalous behavior of the reaction solution may more accurately reflect a conversion of the ACP first into an OCP-like crystalline phase which subsequently hydrolyzes into apatite.
Similar content being viewed by others
References
Blumental, N.C., Betts, F., Posner, A.S.: Nucleotide stabilization of amorphous calcium phosphate. Mat. Res. Bull.10, 1055–1060 (1975)
Boskey, A.L., Posner, A.S.: Conversion of amorphous calcium phosphate to microcrystalline hydroxyapatite. A pH-dependent, solution-mediated, solid-solid conversion. J. Phys. Chem.77, 2313–2317 (1973)
Boskey, A.L., Posner, A.S.: Magnesium stabilization of amorphous calcium phosphate. Mat. Res. Bull.9, 907–916 (1974)
Boskey, A.L., Posner, A.S.: Formation of hydroxyapatite at low supersaturation. J. Phys. Chem.80, 40–45 (1976)
Brečević, L., Füedi-Milhofer, H.: Precipitation of calcium phosphates from electrolyte solutions. II. The formation and transformation of the precipitates. Calcif. Tiss. Res.10, 82–90 (1972)
Brown, W.E.: Crystal growth of bone mineral. Clin. Orthop.44, 205–220 (1966)
Chughtai, A., Marshall, R., Nancollas, G.H.: Complexes in calcium phosphate solutions. J. Phys. Chem.72, 208–211 (1968)
Davies, C.W.: Ion association. London: Butterworth 1962
Dunning, W.J.: Ripening and ageing processes in precipitates. In: Particle growth in suspensions, (Smith, A.L., ed.), pp. 3–28. London: Academic Press 1973
Eanes, E.D.: The interaction of supersaturated calcium phosphate solutions with apatitic substrates. Calcif. Tiss. Res.20, 75–89 (1976)
Eanes, E.D., Gillessen, I.H., Posner, A.S.: Intermediate states in the precipitation of hydroxyapatite. Nature (Lond.)208, 365–367 (1965)
Eanes, E.D., Posner, A.S.: Kinetics and mechanism of conversion of noncrystalline calcium phosphate to crystalline hydroxyapatite. Trans. N.Y. Acad. Sci.28, 233–241 (1965)
Eanes, E.D., Posner, A.S.: Intermediate phases in the basic solution preparation of alkaline earth phosphates. Calcif. Tiss. Res.2, 38–48 (1968)
Eanes, E.D., Posner, A.S.: A note on the crystal growth of hydroxyapatite precipitated from aqueous solutions. Mat. Res. Bull.5, 377–384 (1970)
Eanes, E.D., Termine, J.D., Nylen, M.U.: An electron microscopic study of the formation of amorphous calcium phosphate and its transformation to crystalline apatite. Calcif. Tiss. Res.12, 143–158 (1973)
Fleisch, H., Russell, R.G.G., Bisaz, S., Termine, J.D., Posner, A.S.: Influence of pyrophosphate on the transformation of amorphous to crystalline calcium phosphate. Calcif. Tiss. Res.2, 49–59 (1968)
Francis, M.D.: The inhibition of calcium hydroxyapatite crystal growth by polyphosphonates and polyphosphates. Calcif. Tiss. Res.3, 151–162 (1969)
Gee, A., Deitz, V.R.: Pyrophosphate formation upon ignition of precipitated basic calcium phosphates. J. Amer. chem. Soc.77, 2961–2965 (1955)
Gregory, T.M., Moreno, E.C., Brown, W.E.: Solubility of CaHPO4.2H2O in the system Ca(OH)2−H3PO4−H2O at 5, 15, 25, 37.5°C. J. Res. Nat. Bur. Stand.74a, 461–475 (1970)
Madsen, H.E.L.: Ionic concentrations in calcium phosphate solutions. I. Solutions saturated with respect to brushite or tetracalcium monohydrogen phosphate at 37°C. Acta chem. scand.24, 1671–1676 (1970)
McDowell, H., Wallace, B.M., Brown, W.E.: The solubilities of hydroxyapatite at 5, 15, 25 and 37°C. Program and abstracts, 47th General Meeting IADR, Abstract No. 340, 1969
Meyer, J.L., Eick, J.D., Nancollas, G.H., Johnson, L.N.: A scanning electron microscopic study of the growth of hydroxyapatite crystals. Calcif. Tiss. Res.10, 91–102 (1972)
Meyer, J.L., McCall, J.T., Smith, L.H.: Inhibition of calcium phosphate crystallization by nucleoside phosphates. Calcif. Tiss. Res.15, 287–293 (1974)
Meyer, J.L., Nancollas, G.H.: The influence of multidentate organic phosphonates on the crystal growth of hydroxyapatite. Calcif. Tiss. Res.13, 295–303 (1973)
Moreno, E.C., Patel, J.M., Gregory, T.M., Brown, W.E.: Solubility of Whitlockite, β-Ca3(PO4)2. Program and abstracts, 48th General Meeting IADR, Abstract No. 183, 1970
Murphy, J., Riley, J.P.: A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta27, 31–36 (1962)
Nancollas, G.H., Mohan, M.S.: The growth of hydroxyapatite crystals. Arch. oral Biol.15, 731–745 (1970)
Nancollas, G.H., Tomažič, B.: Growth of calcium phosphate on hydroxyapatite crystals. Effect of supersaturation and ionic medium. J. Phys. Chem.78, 2218–2225 (1974)
Robertson, W.G.: Factors affecting the precipitation of calcium phosphate in vitro. Calcif. Tiss. Res.11, 311–322 (1973)
Strickland-Constable, R.F.: Kinetics and mechanism of crystallization. London: Academic Press 1968
Termine, J.D.: Mineral chemistry and skeletal biology. Clin Orthop.85, 207–241 (1972)
Termine, J.D., Conn, K.M.: Inhibition of apatite formation by phosphorylated metabolites and macromolecules. Calcif. Tiss. Res.22, 149–157 (1976)
Termine, J.D., Lundy, D.R.: Hydroxide and carbonate in rat bone mineral and its synthetic analogues. Calcif. Tiss. Res.13, 73–82 (1973)
Termine, J.D., Peckauskas, R.A., Posner, A.S.: Calcium phosphate formation in vitro. II. Effect of environment on amorphouscrystalline transformation. Arch. Biochem. Biophys.140, 318–325 (1970)
Tomažič, B., Nancollas, G.H.: The seeded growth of calcium phosphates. Surface characterization and the effect of seed material. J. Colloid Interface Sci.50, 451–461 (1975)
Tomažič, B., Tomson, M., Nancollas, G.H.: The growth of calcium phosphates on natural enamel. Calcif. Tiss. Res.19, 263–271 (1976)
Walton, A.G.: The formation and properties of precipitates. New York: Interscience 1967
Walton, A.G., Bodin, W.J., Füredi, H., Schwartz, A.: Nucleation of calcium phosphate from solution. Canad. J. Chem.45, 2695–2701 (1967)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Eanes, E.D., Meyer, J.L. The maturation of crystalline calcium phosphates in aqueous suspensions at physiologic pH. Calc. Tis Res. 23, 259–269 (1977). https://doi.org/10.1007/BF02012795
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02012795