Hydroxyapatite biological

Blumenthal, N.C., Belts, F. and Posner, A.S. 1975 Effect of carbonate and biological macromolecules on the formation and properties of hydroxyapatite. Calcified Tissue Research 18 81-90. 

The collagen fibers leave small compartments where apatite nanocrystals are deposited during a controlled biomineralization process [20]. The collagen acts as a structural framework in which plate-like nanocrystals of carbonated hydroxyapatite (CHA) are embedded to strengthen the bone. The chemical formula of biological CHA can be represented as follows ... 

Fig. 12.3 Powder X-ray diffraction patterns of biological and synthetic hydroxyapatites.

Bisphosphonates bind to hydroxyapatite in bone and decrease resorption by inhibiting osteoclast adherence to bone surfaces. All bisphosphonates become incorporated into bone, giving them long biologic half-lives of up to 10 years. 

Hydroxyapatite and titania are also useful stationary phase materials for biological samples. Hydroxyapatite, Cai0(PO4)6(OH)2, as a hexagonal column... 

Interest in the nature of interactions between shortchain organic surfactants and large molecular weight macromolecules and ions with hydroxyapatite extends to several fields. In the area of carles prevention and control, surfactant adsorption plays an important role in the Initial states of plaque formation (1-5) and in the adhesion of tooth restorative materials ( ). Interaction of hydroxyapatite with polypeptides in human urine is important in human biology as hydroxyapatite has been found as a major or minor component in a majority of kidney stones ( 7). Hydroxyapatite is used in column chromatography as a material for separating proteins (8-9). The flotation separation of apatite from... 

R.Z. Legeros, Biological and synthetic apatites, in P.W. Brown, B. Constantz (Eds.), Hydroxyapatite and Related Materials, CRC Press, Boca Raton, 1994, pp. 3-28. 

Nevertheless, fluoride does lead to a reduction in the solubility of hydroxyapatite in aqueous solution, even in the absence of trace levels of fluoride in solution, and hence can be seen to have an effect in the solid state as well [57], Apatites are complex and diverse materials which have the general formula Caio(P04)eX2 (X = F, Cl, OH) and they represent a crystallographic system, in which there can be considerable replacement of species. Thus, with little or no change in the dimensions of the crystal lattice, there can be exchanges of OH for F, Ca + for Sr +, and PO4 for CO and all of these are known to occur in biological systems. Natural hydroxyapatite, for example, is often partially carbonate substituted [58]. 

R.A. Young, Biological apatite vs hydroxyapatite at the atomic level, Clin. Orthop. 113 (1975) 249-262. 

La is of interest in its relationship to biological hydroxyapatite because of their inhibitory effect on the demineralization of dental enamel. The form of La was not clear, namely surface adsorption or lattice incorporation. In an attempt to clarify it, laser-induced luminescence has been used (Mayer et al. 1999). La " is not luminescent, Gd-containing samples were prepared and studied. Figure 11.1 demonstrates Gd luminescence spectra with 266 nm laser excitation before and after heating at 800 °C. It is clearly seen that luminescence intensity is drastically stronger after thermal treatment. Thus precipitated samples must be heated to 800 °C to enable Gd " " to replace Ca and become luminescent and its incorporation form is surface adsorption. 

The biologically most relevant calcium phosphates are dahllite [carbonate hydroxyapatite, (Na,Ca)10(PO4,CO3)6(OH)2] francolite [carbonate fluoroapatite] hydroxyapatite [Ca10(PO4)6(OH)2]... 

Many biological and environmental processes involve the dissolution or precipitation of a sparingly soluble ionic compound. Tooth decay, for example, begins when tooth enamel, composed of the mineral hydroxyapatite, Cas PO OH,... 

Ideally, hydroxyapatite has the formula mentioned above. The synthetic material usually contains fewer than 10 Ca-ions and more than 2 OH-ions per crystal unit. Important differences in crystal structure, composition and specific surface exist between synthetic and biologic apatite. These differences result from the processing method of the raw materials and the synthetic method used. 

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