SYNTHESIS OF APATITE

Calcium phosphate apatite formulations that are available commercially from different suppliers exhibit high chemical variability. Thus, manufacturers of apatite for biomedical applications often produce their own powder. Furthermore, synthesis enables a range of chemical substitutions, crystal sizes, shapes and forms (separate crystals or cements, as discussed in the next section). Various reviews cover synthesis methods (Narasaraju and Phebe 1996, Le Geros et al. 1995, Orlovskii and Barinov 2001). 

Precipitation from solution is the most common synthesis route and involves simultaneous addition of a calcium salt and a phosphate compound to water, or drop-wise addition of the phosphate into an aqueous solution of the calcium salt. Examples of calcium salts include calcium nitrate, calcium hydroxide, calcium chloride, or calcium acetate. The salts are reacted with a hydrogen phosphate or the phosphate ions are 

At lower pH values, a calcium deficient HAp can be formed (Silva et al. 2001, Raynaud et al. 2002a). Reactions conducted at pH = 7.4 are primarily aimed at understanding the crystallization of apatites in the body (Okazaki et al. 1992). 

Chemical elements not found in bone can be substituted for different effects. For example, addition of silver has been used for imparting antimicrobial properties (Kim et al. 1998). 

High-temperature synthesis was the first method of apatite production reported and involved passing phosphorus trichloride vapor over red-hot lime (Daubree 1851). This 

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L.M. Rodriguez-Lorenzo, J.N. Hart, K.A. Gross, Influence of fluorine in the synthesis of apatites. Synthesis of solid solutions of hydroxy-fluorapatite. Biomaterials 24 (2003) 3777-3785. 

Chaikina M.V. Mechanochemical synthesis of apatites and ortophosphates. In Mechanochemical Synthesis in Inorganic Chemistry, ed. Avvakumov E.G. Novosibirsk Nauka, 1991. 

Lucas J. and Prevot L. (1985) The synthesis of apatite by bacterial activity mechanism. Set Geol. Mem. (Strasbourg) 77, 83-92. 

Rodriguez-Lorenzo LM, Hart J, Gross KA (2003) Influence of fluorine in the synthesis of apatites. 

On the other hand, the scrambled model of carbon sourcing does not seem to be applicable when we consider the metabolic fate of fatty acids. We find that there are partial barriers to the movement of FA-derived carbon atoms into the synthesis of proteins. This partial restriction leads us to expect a trophic level effect in the fractionation between collagen and bone apatite or respired CO2 of which apatitic carbonate is a sample. The magnitude of the fractionation depends on two separate fractionation factors which cannot be disentangled by analyses of bone samples alone. 

Synthetic fluor-containing apatites are prepared and investigated for biomedical applications and serve also as models to understand the formation of biological fluorapatites and some of their properties. The synthesis of fluoridated apatites has been accomplished in various ways from simple ion exchange in solution to more elaborate techniques involving sol-gel routes or thermal processes. Two main classes of synthesis routes are presented in this chapter high-temperature routes and low-temperature solution routes. 

Control of the pH and temperature of the precipitating solution is important to provide optimised conditions for stoichiometric, homogeneous, fluorhydroxyapatite formation. Similar conditions and set-up can be used for the synthesis of fluoride-substituted apatite crystals with varying size, crystallinity and morphology depending on the preparation temperature [124] a purge of the synthesis system with nitrogen gas ensures the preparation of carbonate-free fluorhydroxyapatite at ambient temperature [125]. 

The synthesis of B-type carbonate-fluoroapatites was reported by Montel et al. with fluoride ions present in two kinds of sites in the apatitic structure [126]. Moreover, the correlation between the respective amounts of fluoride and... 

The synthesis of the title compositions has been selected as representative of compounds that can readily be prepared by the flux-reaction technique. In this technique, a halide melt serves both as a flux and as a constituent component of the basic reaction. The procedure has been described in the literature1 and has served for the preparation of a variety of ternary oxides, usually in the form of small, well-defined, single crystals. The halide phosphates and vanadates of strontium represent the apatite and spodiosite structures, both interesting compositions from a biochemical and solid-state point of view. 

Fowler, B. O. (1974). Hydrothermal synthesis of hydroxyl apatite. Inorganic Chemistry, 13(1) 191-214. 

The methods of synthesis of fluorapatite have been widely dis cussed (J ). It is for example possible to obtain fluorapatite by substituting the hydroxyl ion for the fluoride ion, either in a-queous solution at room temperature, or through a solid state reaction at 800°C. It can also be prepared by the action of 6-tricalcium phosphate on calcium fluoride at about 800°C. Its solubility and thermal stability have already been established. While much is known about fluorapatite, many questions still exist concerning the mechanism of their formation, their composition and the structure of some of them. Two of these problems are dealt with here. First, we discuss the formation mechanism of fluorapatite by a solid state reaction between calcium fluoride and apa-titic tricalcium phosphate. Then we present the preparation and the structure of a carbonated apatite rich in fluoride ions. 

Chaikina M.V. Mechanochemical synthesis of phosphates and apatites - a new way of preparation of complex materials. Phosphorus Research Bulletin 1997 7 35-8. 

Chaikina M.V. The features of chemical interaction in multicomponent system during mechanochemical synthesis of phosphates and apatites. Chem. Sustainable Development 1998 6 13544. 

There is a debate over whether the classical formose reaction [3-5] might have played a role in the prebiotic synthesis of carbohydrates. When a slurry of carbonate-apatite is boiled with 0.5 M formaldehyde at pH 8.5 a yield lower then 40% in sugars is reached after a few hours. 

Andersson,., Areva, S., Spliethoff, B., and Linden, M. (2005) Sol-gel synthesis of a multifunctional, hierarchically porous silica/apatite composite. Biomaterials, 26 (34), 6827-6835. 

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