Chemistry of inorganic compounds – Phosphorus or compound thereof – Oxygen containing
Patent
1988-11-22
1990-07-03
Doll, John
Chemistry of inorganic compounds
Phosphorus or compound thereof
Oxygen containing
423311, 4332011, 623 16, C01B 2532
Patent
active
049389386
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the preparation of a carbonaceous hydroxyl apatite material by means of hydrothermal conversion with the addition of an aqueous (NH.sub.4).sub.2 HPO.sub.4 solution. As starting material a hard tissue purified from organic substances in employed.
Hydroxyl apatite material of this kind is suitable for use as a biocompatible implant, for examle as hard tissue replacements for bones and teeth, since the inorganic portion of human hard tissue in essence is formed of a cryptocrystalline carbonaceous hydroxyl apatite.
A process is known from U.S. Pat. No. 3,929,971 according to which a hydroxyl apatite material is extracted from the aragonitic skeletons of living corrals and starfish by means of hydrothermal treatment. This known process has the disadvantage that the hydrothermal treatment must be carried out at a relatively high temperature under very high presure.
The use of the hydroxyl apatite material as implants has the disadvantage that, with the known process of production, as a result of the temperature, the pressure and the chemical potential of the participating components, high defect densities do not occur, which results in a bone-like difference of the material from the ideal structure of a dense material of the formula Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2 with apatite structure. These defect densities can occur for example by the substitution of carbonate CO.sub.3.sup.2- for phosphate PO.sub.4.sup.3- or by stray ions, in particular alkali in cation sublattice form, as well as halogenides in the anion sublattice. Moreover, the products obtained by means of the known process do not attaine desired requirements for deviation of the bone-like cryptocrystallinity with respect to the use as implants.
It is an object of the present invention to provide a process of the above type which, as a result of reduced energy requirements and relatively low pressure, can be carried out in a relatively short time and afford the desired bone-like defect density and cryptocrystallinity. desired bone-like defect density and crypytocrystallinity.
Accordingly, the invention provides a process for the preparation of a carbonaceous hydroxyl apatite material by means of hydrothermal conversion with the adddition of aqueous (NH.sub.4).sub.2 HPO.sub.4 solution, whereby as starting material an organic substance-free hard tissue is employed, characterized in that the conversion takes place in an autoclave at saturation steam pressure of the respective fluid phase.
Thus, the object is attained by the hydrothermal conversion in an autoclave at saturation stream pressure of the respective fluid phase being employed. The saturation steam pressure is reached if the pressure vessel is not completely filled. Already with operating times of less than 24 hours and a temperature of 200.degree. C., an optimum conversion can be attained.
In a preferred embodiment of thke invention, by means of a controlled adjustment of the pH value of the substitution solution, preferably to at least about 8.5, the formation of other phases than hydroxyl apatite can be suppressed.
In addition, it can also be of advantage to suppress the influence of Mg.sup.2+ ions by appropriate addition of fluoride ions. This measure has the advantage that the content of magnesium ions compensates for and thereby hinders the formation of undesired .beta.-tricalcium phosphate (.beta.-Whitlockite). Furthermore, the crystallinity and defect density of the materials, i.e. the real structure of the material and thus the adaption of the material to the implant area, is attained during the synthesis by the addition of fluoride. This leads to an artifical aging or hardening of the material.
Preferably the process is continued by after-treatment of the hydroxyl apatite material by tempering. Also through these measures can the artificial aging or hardening of the materials be attained. As a result of the temperature, the defect density is influenced, while the crystallite size increases with the tempering time.
In particular, for the prepar
REFERENCES:
patent: 3929971 (1975-12-01), Roy
patent: 4861733 (1989-08-01), White
Della M. Roy, "Hydroxyapatite Formed From Coral Skeletal Carbonate by Hydrothermal Exchange", Nature, vol. 247 (Jan. 25, 1974), pp. 220-222.
Hydrothermal Synthesis of Various Carbonate Containing Calcium Hydroxyapatites, D. M. Roy et al., Mat. Res. Bull., vol. 9, pp. 35-40, 1974, Pergamon Press, Inc.
Petrologic Phase Equilibria, W. G. Ernst, Univ. of Calif., Los Angeles, pp. 27-29, W. H. Freeman and Co., 1976.
Experimental Petrology-Basic Principles and Techniques, Alan D. Edgar, 106-109, Clarendon Press, Oxford, 1973.
Bremen
Ewers Rolf
Kasperk Christian
Simons Bruno
Doll John
Ewers Rolf
Lange Wayne A.
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