Hydroxyapatite crystal growth

Eanes, E.D. and Posner, A.S. 1970 A note on the crystal growth of hydroxyapatite precipitated from aqueous solutions. Materials Research Bulletin 5 377-384. 

Calcium phosphate precipitation may also be involved in the fixation of phosphate fertilizer in soils. Studies of the uptake of phosphate on calcium carbonate surfaces at low phosphate concentrations typical of those in soils, reveal that the threshold concentration for the precipitation of the calcium phosphate phases from solution is considerably increased in the pH range 8.5 -9.0 (3). It was concluded that the presence of carbonate ion from the calcite inhibits the nucleation of calcium phosphate phases under these conditions. A recent study of the seeded crystal growth of calcite from metastable supersaturated solutions of calcium carbonate, has shown that the presence of orthophosphate ion at a concentration as low as 10-6 mol L" and a pH of 8.5 has a remarkable inhibiting influence on the rate of crystallization (4). A seeded growth study of the influence of carbonate on hydroxyapatite crystallization has also shown an appreciable inhibiting influence of carbonate ion.(5). 

Humic substances. Analogous to the reactions described above, humic substances (the polymeric pigments from soil (humus) and marine sediments) can be formed by both enzymatic and non-enzymatic browning. High concentrations of free calcium and phosphate ions and supersaturation with respect to hydroxyapatite can sustain in soil, because adsorption of humic acids to mineral surfaces inhibits crystal growth (Inskeep and Silvertooth, 1988). A similar adsorption to tooth mineral in a caries lesion can be anticipated for polycarboxylic polymers from either the Maillard reaction or enzymatic browning. 

Lower et al. (1998b) can shed more light on this phenomenon. They again used AFM, SEM, TEM, SEM-EDS, electron diffraction, and XRD to study the reactions between 0.5 and 500 mg/L of Pb with hydroxyapatite at pH 6 and a reaction temperature of 22 °C. A commercial hydroxyapatite was used at sorbent concentrations of 0.5 g/L. Reactions were observed over a 2 h period. At high initial Pb concentrations, Pb solution concentrations dropped from 500 mg/L to <100 mg/L. At concentrations of 0.5-100 mg Pb/L, after reaction, Pb levels dropped to less than 15 pg/L. In both cases, hydroxyapatite dissolved and hydroxypyromorphite formed. The authors applied some nucleation and crystal growth theory developed... 

Eanes, E. D., Gillessen, I. H., Posner, A. S. Mechanism of conversion of non-crystalline calcium phosphate to crystalline hydroxyapatite. In Crystal Growth, pp. 373. Peiser, H. S. (ed.). Oxford Pergamon Press Inc. 1967... 

FrancjS m D. The inhibition of calcium hydroxyapatite crystal growth by polyphos-phonates and polyphosphates. Calc. Tiss. Res. 3, 151 — 162 (1969). 

Eanes, E.D., Gillessen, I.H., and Posner, A.S. Mechanism of conversion of non-crystalline calcium phosphates to crystalline hydroxyapatite, p 373-375, "Proc. Int. Cong, on Crystal Growth, Boston, 1966. Pergamon Press, Oxford, 1967. Termine, J.D., Peckauskas, R.A., and Posner, A.S. Calcium phosphate formation in vitro. II. Effect of environment on amorphous crystalline transformation. Arch. Biochem. Bio-phys. 140. 318-325 (1970). 

Francis, M.D. The inhibition of calcium hydroxyapatite crystal growth by polyphosphonates and polyphosphates. 

T. (1996) Acceleration and deceleration of bone-like crystal growth on ceramic hydroxyapatite by electric poling. Chem. Mater., 8, 2697 - 2700. 

Some work has been reported on deposition of hydroxyapatite under hydrothermal conditions, that is much above 100 °C. This includes a study by Liu, Savino and Yates (2011) who coated hydroxyapatite on titanium, stainless steel, aluminium and copper substrates by a seeded hydrothermal deposition method. The deposition strategy included an electrochemical reaction to form quickly a thin layer of HAp seed crystals. Subsequent hydrothermal crystal growth from the seed layer resulted in dense and durable HAp films. In a typical hydrothermal synthesis, a solution of Na2EDTA (0.20 M) and Ca(NOs)2 (0.20 M) was prepared in 15 ml water and a solution of (NH4)2HP04 (0.12 M) in 15 ml water was prepared in a second container. The two source solutions were mixed together after the pH of each solution was raised to 10.0 with ammonium hydroxide. The resulting combined solution was stirred at room temperature for about 20 min and then transferred to a Teflon-lined stainless steel pressure vessel of 40 ml internal volume. 

Onuma, K. (2006) Recent research on pseudobiological hydroxyapatite crystal growth and phase transition mechanism. Prog. Cryst. Growth Charact. Mater., 52, 223-245. 

Brown JL (1981) Calcium phosphate precipitation Effects of common and foreign ions on hydroxyapatite crystal growth. Soil Sci Soc J 45 482-486 Bulka GR, Vinokurov VM, Nizamutdinov NM, Hasanova NM (1980) Dissymmetrization of crystals Theory and experiment. Phys Chem Minerals 6 283-293 Bums RG (1970) Mineralogical Applications of Crystal Field Theory. Cambridge University Press, Cambridge... 

Bres EF, Steuer P, Voegel J-C, Frank RM, Cuisinier FJG (1993b) Observation of the loss of the hydroxyapatite six-fold symmetry in a human fetal tooth enamel crystal. J Micros 170 147-154 Brown WE (1966) Crystal growth of bone mineral. Clin Orthopaedics 44 205-220 Brown WE, Eidelman N, Tomazic B (1987) Octacalcium phosphate as a prectrrsor in biomineral formation. Adv Dent Res 1 306-313... 

Fig.5 Classical (a) vs. non-classical crystallization (b,c). a Crystallization of hydroxyapatite (HAP) fibers from block copolymer aggregates [108], where the block copolymers adsorb to all faces parallel to the HAP c-growth axis resulting in whisker structures with occasional branches (see arrows). b,c Formation of single crystalline and defect-free BaS04 (210) oriented fiber bundles by the process of oriented attachment in experiments described in [109-111], Figure reproduced from [112] with kind permission of Editorial Universitaria, Universidad de Chile, Santiago, Chile...

A solution containing Ca and HPO4 " ions and having the same ionic product as serum (18 (mg per 100 ml) ) in a clean container can be kept indefinitely without the separation of crystals. If, however, apatite crystals are introduced into the solution, they grow in size at the expense of ions from solution and the ionic product of the solution falls until it is equal to the solubility product for hydroxyapatite, at which point crystal growth stops. 

Slosarczyk A. (1997) Hydroxyapatite ceramics, PAN, Ceramics 51, Krakow Sung Y.M., Kim D.H. (2003) Journal of Crystal Growth, 254,411 17 Subotowicz K. (2008) Ceramics for each, Elamed, Katowice... 

Murugan R, Ramakrishna S (2004) Aqueous mediated synthesis of bioresorbable nanocrystalline hydroxyapatite. J Crystal Growth 274 209-213 DOI 10.1016/j.jcrysgro. 2004.09.069. 

Kuriakose, T., Kalkura, S., Palanichamy, M., Arivuoli, D., Dierks, K., Bocelli, G. and Betzel, C. (2004) Synthesis of stoichiometric nano crystalline hydroxyapatite by ethanol-based sol-gel technique at low temperature. Journal of Crystal Growth, 263, 517-23. 

Sato, K. and Tanaka,). (2002) Influence of emulsion on crystal growth of hydroxyapatite. Solid State Ionics, 151, 321-7. 

Onuma, K., Yamagishi, K. and Oyane, A. (2005) Nucleation and growth of hydroxyapatite nanocrystals for nondestructive repair of early caries lesions. Jourmtl of Crystal Growth, 282,... 

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