Compositions: ceramic – Ceramic compositions
Patent
1997-05-07
1998-07-07
Marcheschi, Michael
Compositions: ceramic
Ceramic compositions
623 16, 623 66, C04B 3500, A61L 2700
Patent
active
057768439
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for producing spongiosa bone ceramic.
BACKGROUND OF THE INVENTION
It has been known for a relatively long time that mineralized bone which has been sintered to form a ceramic is ideally suited as bone replacement material. With bone ceramic there is naturally a very great degree of correspondence in chemical composition, structural composition and mechanical strength with natural bone. In addition, spongiosa bone ceramic is found to be particularly osteoconductive. The open, interconnecting, trabecular structure of spongiosa bone ceramic promotes the growth of new bone matrix onto and into the ceramic, so that in the course of incorporation there is intensive colonization and therefore integration of the ceramic implant. Bone ceramics produced from bones of animal origin are therefore being increasingly employed as bone replacement materials in osteosynthesis and in the reconstitution of bone defects caused by illness or accident.
The production of bone ceramic from animal bone is generally carried out by first of all freeing selected bones or bone pieces mechanically from all adhering soft parts, then cutting these bones or bone pieces roughly to size by sawing, to give pieces of suitable shape and size, which are then mineralized by the removal of all other organic components. The mineralization process begins first of all with the bones being boiled out several times in water. Subsequent treatment can be carried out, for instance, with fat-dissolving or protein-dissolving solvents, and/or with the aid of hydrogen peroxide, as described for example in EP 0 141 004. Methods which have proved to be particularly simple and effective are those of pyrolytic mineralization, in which the action of heat decomposes the organic component of the bone and the resulting carbon is subsequently burnt to completion in excess oxygen. For the bone pyrolysis, temperatures of between 500.degree. and 1000.degree. C. are common. Following the mineralization of the bone, it is sintered to give the ceramic, with temperatures of between 800.degree. and 1400.degree. C., being common. It is only through sintering that the material acquires the desired ultimate strength. In the course of the procedures mentioned, particular care must be taken to ensure that the porous structure of the original bone is retained as far as is possible. For the conversion of spongiose bone material to spongiosa bone ceramic, a preferred option is to proceed in accordance with a process set out in DE 37 27 606, in which a specific temperature regime and reductive or oxidative character of the atmosphere enables particularly gentle pyrolysis.
It has been found that bone ceramic has a tendency towards uncontrolled instability if the principal phase, hydroxyapatite, exists alongside notable quantities of calcium oxide, which can be detected, for instance, by X-ray analysis. This is the case when the content of calcium oxide is more than 5%. The ingress of water, for example in the form of atmospheric humidity in the course of unprotected storage or in the organism after the implant procedure, is accompanied by successive transformation of calcium oxide to calcium hydroxide, which entails a considerable increase in volume. Depending on the proportional content, this process may extend up to complete breakdown of the ceramic. The proportion of calcium oxide in the bone ceramic is a natural parameter and may vary with the individual nature and breed of animal. The calcium oxide is formed by the calcium carbonate which is naturally present in the bone undergoing conversion, in the course of pyrolysis and sintering, to calcium oxide.
DE 40 28 683 proposed treating the mineralized bone material, prior to sintering, with an aqueous solution of an organic acid, especially citric acid. This step leaches calcium oxide components out of the material, so that the bone ceramic obtained after sintering has, according to X-ray analysis, a hydroxyapatite apatite content of more than 99%.
Although this procedure is highly effective and
REFERENCES:
patent: 4919751 (1990-04-01), Sumita et al.
patent: 5133756 (1992-07-01), Bauer et al.
patent: 5306302 (1994-04-01), Bauer et al.
patent: 5405390 (1995-04-01), O'Leary et al.
Almeida Antonia
Eberle Wilhelm
Taubert Ilona
Wagenknecht Rolf
Weber Frank
Marcheschi Michael
Merck Patent Gesellschaft mit beschrankter Haftung
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