Properties of hydroxyapatite crystallized from high temperature alkaline solutions

doi:10.1016/0022-0248(96)00165-0

Journal of Crystal Growth

Volume 165, Issues 1–2, 2 July 1996, Pages 124-128

https://doi.org/10.1016/0022-0248(96)00165-0 Get rights and content

Abstract

Hydroxyapatite was prepared from alkaline solutions at 95°C by the method of slow titration in an atmosphere of nitrogen. The crystals were ripened under reflux for various periods of time, and then characterized by X-ray diffraction, infrared analysis, transmission electron microscopy, differential thermal analysis, thermogravimetric analysis, surface area measurements and chemical analysis. The obtained crystals are pure apatites with stoichiometric $Ca P$ ratio. The phase composition of the prepared powders remains unchanged after heating at 900°C during 2 h. The lattice constants of maturated powders were in excellent agreement with ASTM 9-432 diffraction file data for the hydrohxyapatite. Ripening under reflux improved lattice ordering but did not have a marked effect on the $Ca P$ ratio. Crystallite size and morphology significantly changed during the first day of refluxing following synthesis.

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Typical precipitated particles are spherical or rod-like, which depends on experimental conditions [17–20]. Stoichiometric and well-crystallized HA, however, can be achieved through high temperature synthesis and use of reactant solutions with a low concentration below the solubility limit of the precursors [21–23]. Synthetic HA with a high crystallinity can also form at a high pH above 10 [21,24].
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This method involves dissolving Ag2O in a solution of H3PO4, and slow addition to suspension of Ca(OH)2 was applied for the homogenous distribution of silver ions. Slow reactant addition was found to yield pure, well-crystallized HAP, due to low supersaturation and avoidance of local inhomogeneity [34,35]. The main reason for using the neutralization method to produce silver-doped hydroxyapatite materials in this study is the possibility of preparing pure products from relatively inexpensive chemicals, and the suitability for an industrial production.
Monophase silver-doped hydroxyapatite (Ag_xCa_10−x(PO₄)₆(OH)₂; 0.002 ≤ x ≤ 0.04) nanoparticles were prepared using a neutralization method and investigated with respect to potential medical applications. This method consists of dissolving Ag₂O in solution of H₃PO₄, and the slow addition to suspension of Ca(OH)₂ was applied for the purpose of homogenous distribution of silver ions. Characterization studies from XRD, TEM and FTIR spectra showed that obtained crystals are monophase hydroxyapatites and that particles of all samples are of nano size, with average length of 70 nm and about 15–25 nm in diameter. Antimicrobial studies have demonstrated that all silver-doped hydroxyapatite samples exhibit excellent antimicrobial activity in vitro against the following pathogens: Staphylococcus aureus, Escherichia coli and Candida albicans. The hydroxyapatite sample with the highest content of silver has shown the highest antimicrobial activity; killed all cells of E. coli and brought to more than 99% reduction in viable counts of S. aureus and C. albicans. The atomic force microscopic studies illustrate that silver-doped hydroxyapatite sample causes considerable morphological changes of microorganism cells which might be the cause of cells’ death. Hemolysis ratios of the silver-doped hydroxyapatite samples were below 3%, indicating good blood compatibility and that are promising as biomaterials.
Synthesis, characterization and antimicrobial activity of copper and zinc-doped hydroxyapatite nanopowders
2010, Applied Surface Science
Antimicrobial materials based on hydroxyapatite are potentially attractive in a wide variety of medical applications. The synthesis of copper and zinc-doped hydroxyapatite was done by neutralization method. This method consists of dissolving CuO or ZnO in solution of H₃PO₄, and the slow addition to suspension of Ca(OH)₂ for obtaining monophasic product. Characterization studies from XRD, SEM, TEM and FTIR spectra showed that particles of all samples are of nano size and they do not contain any discernible crystalline impurity. The quantitative elemental analysis showed that the copper and zinc ions fully incorporated into the hydroxyapatite. The antimicrobial effects of doped hydroxyapatite powders against pathogen bacterial strains Escherichia coli, Staphylococcus aureus and pathogen yeast Candida albicans were tested in solid and liquid media. Quantitative test in liquid media clearly showed that copper and zinc-doped samples had viable cells reduction ability for all tested strains.
Crystalline behaviors of hydroxyapatite in the neutralized reaction with different citrate additions
2009, Powder Technology
Ca(OH)₂ and H₃PO₄ were used to synthesize nano-sized hydroxyapatite. In the process of acid–base reaction, citric acid or sodium citrate was added to influence the crystallinity of hydroxyapatite. Formation of Ca-citrate complex resulted in variations of ionic concentrations and ionic activity products for solutions with different citrate additions. The degree of supersaturate was found higher for solutions with less citric acid or more sodium citrate addition. Consequently, hydroxyapatite particles with smaller size were gained. These crystalline behaviors were investigated and explained by mechanism of crystal nucleation and growth in solutions.
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Calcium phosphate powders with nano-sized crystallinity were synthesized by neutralization using calcium hydroxide and orthophosphoric acid with the assistance of citric acid. The influence of processing parameters, such as free or additive citric acid, synthetic temperature and ripening time, on the crystallinity of hydroxyapatite were investigated. The results of X-ray diffraction and microstructure observations showed that the crystallinity and morphology of nano-sized hydroxyapatite particles were influenced by the presence or absence of citric acid. It was found that the crystallinities and crystallite sizes of hydroxyapatite powders prepared with the additive citric acid increased with increasing synthetic temperature and ripening time. Especially, the crystallinities of (h k 0) planes were raised and more homogeneously grown particles were obtained with increasing synthetic temperature.
Electrochemical synthesis of silica-doped high aspect-ratio titania nanotubes as nanobioceramics for implant applications
2009, Electrochimica Acta
The preparation of silica-doped high aspect-ratio TiO₂ nanotubes and their apatite-forming ability were demonstrated in this study. The high aspect-ratio TiO₂ nanotube layers were produced by electrochemical anodic oxidation of Ti in chloride-containing electrolytes. Nanotubes were doped with different concentrations of silica particles through anodization in NaCl electrolyte containing different concentrations of water glass (24 g/L or 48 g/L Na₂SiO₃). The biomimetic apatite deposition behavior was evaluated under simulated body fluid (SBF) with an ion concentration nearly equal to human blood plasma. The experimental results collectively demonstrate the successful silica doping of the resultant nanotube layers with significant abundant OH groups on their surfaces. The results of hydroxyapatite (HA) growth on nanotubes clearly show that the silica doping greatly enhances the fast nucleation and growth of HA, especially for the tubes in their “as-formed” amorphous state, which usually require a long time for apatite induction. The nanotubes doped with high silica content combined with an anatase or a mixture of anatase and rutile led to the formation of very thick and continuous apatite layers with a thickness of ∼7 μm in 21 days. In contrast, to the tubes doped with a low concentration of silica (grown in an electrolyte containing 24 g/L Na₂SiO₃), the HA deposited in the form of closely packed spheroid particles and never developed into continuous films. This effect could be attributed to the critical active-site density (silanol groups, >Si–OH), which provides the sterochemical match for apatite growth. Finally, the results of this study provide, for the first time, evidence for the dependence of HA morphology/microstructure on the crystallographic structure and the density of active sites (>Si–OH groups).

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Solution growth; industrial, biological and molecular crystallizationProperties of hydroxyapatite crystallized from high temperature alkaline solutions

Abstract

Biomaterials

J. Chromatography

J. Chromatography

J. Chromatography

Water Res.

J. Crystal Growth

J. Crystal Growth

J. Crystal Growth

J. Colloid Interface Sci.

J. Colloid Interface Sci.

J. Colloid Interface Sci.

J. Crystal Growth

J. Crystal Growth

Solution growth; industrial, biological and molecular crystallization
Properties of hydroxyapatite crystallized from high temperature alkaline solutions