PubMed · 8529154
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F Codère. 1995. Hydroxyapatite implants: a rational approach.. https://pubmed.ncbi.nlm.nih.gov/8529154/
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Hydroxyapatite crystals were formed on a titanium electrode using the hydrothermal-electrochemical method in an autoclave with two electrodes. The electrolyte dissolving NaCl, K2HPO4, CaCl2.2H2O, trishydroxyaminomethane, and hydrochloric acid was maintained at 80 degrees - 200 degrees C. After loading of a constant current at 12.5 mA/cm2 for 1 h, the deposited amounts were measured through the weight gain of the electrode. The deposits were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, field emission-type scanning electron microscopy, field emission-type transmission electron microscopy, and energy dispersive X-ray spectroscopy. The deposited amount increased with electrolyte temperatures up to 150 degrees C and slightly decreased above that temperature. The deposits were identified as hydroxyapatite crystal rods grown along the c axis and perpendicular to the substrate. The crystallinity of the deposited hydroxyapatite increased continuously with the electrolyte temperature and closed to stoichiometric hydroxyapatite. At 150 degrees - 160 degrees C, the hydroxyapatite rod grew very homogeneously perpendicular to the substrate, and the edge of the needle had a flat hexagonal plane.
Hydroxyapatite nanocrystals synthetized in the presence of different concentrations of magnesium and fluoride ions in solutions--1, 5 and 10 at.% have been submitted to a structural and chemical characterization. The syntheses were carried out in the presence of low molecular weight polyacrylic acid, which has been verified to inhibit hydroxyapatite crystallization. The polyelectrolyte is adsorbed into the crystals during the synthesis and provokes a reduction of the mean crystal sizes. The reduction is greater along the direction orthogonal to the c-axis, suggesting a preferential adsorption of the polyelectrolyte on the crystalline faces parallel to the c-axis. Both magnesium and fluoride can be incorporated into the hydroxyapatite structure. On the basis of the values of the lattice constants and of the magnesium relative content of the solid phase, it can be suggested that probably just a part of magnesium is substituted for calcium, the remainder being adsorbed on the crystal surface. However, magnesium destabilizes the apatitic structure favouring its thermal conversion into beta-tricalcium phosphate, and displays an inhibiting effect on the crystallization of hydroxyapatite. This last effect is enhanced by the simultaneous presence of polyacrylic acid. Fluoride substitution for hydroxyl ions into hydroxyapatite structure induces a slight increase of the crystal sizes along the c-axis direction. The data indicate that the experimental approach can be successfully used to prepare nanoapatite with crystallinity, crystal dimensions, composition, structure and stability very close to those characteristics of biological apatites.