Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles
Patent
1994-08-26
1998-02-03
Engel, James
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
264113, 264125, 623901, A61F 228, B29C 6702, B29C 3502, B22F 702
Patent
active
057141037
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the production of shaped articles having a predetermined pore structure. This process can preferably be used for the production of shaped articles having a three-dimensionally interconnecting pore system, and in particular for the production of shaped implants having the pore system of natural bones.
The production of shaped articles, regardless of from what substance and material, having a predetermined pore structure of course presents problems. This is the case above all if, instead of a material- and processing-related statistically uniform porosity or instead of a monodimensional pore alignment, a locally different structuring and/or a defined pore system in several dimensions is desired. Thus, known techniques for the production of porous materials or bodies, such as, for example, foaming of suitable materials or incorporation of soluble or gas-forming substances into corresponding matrix materials, lead to essentially statistically uniform pore structures. In extrusion operations on plastic or plasticizable materials, essentially monodimensionally aligned pore systems can at best be produced.
These generally applicable problems will now be illustrated in more detail by the example of shaped implants for bone replacement and the decisive requirements in this context.
Bone replacement materials for the production of shaped implants can be classified into the two main groups of bioinert and bioactive materials. Bioinert materials include physiologically acceptable metals, oxide ceramics and certain plastics. Bioactive materials, which cause a positive physiological effect of whatever type in the organism, include materials based on calcium minerals, biopolymers and composite materials based on the materials mentioned. Bioabsorbable materials form a subgroup of these.
Bioactive implant materials enjoy preferred interest, since they cause stimulation of bone growth and thereby improved healing of the implant into the bone and the endogenous tissue.
Shaped articles of ceramic material are primarily employed for replacement of load-bearing bone structures which must withstand high mechanical stresses. Examples of these are bone prostheses and bone connecting elements, such as, for example, medullary nails, bone screws and osteosynthesis plates.
Because it is related chemically to the mineral phase of natural bone, bone replacement materials based on calcium phosphate ceramics are regarded as bioactive. The mineral phase of natural bone comprises chiefly the calcium phosphate compound hydroxyapatite. Hydroxyapatite of synthetic or organic origin, for example from natural bone material, is therefore a raw material which is often used for production of implants for bone replacement.
Experience shows that the strength of the fusion of compact calcium phosphate ceramic with existing bone is mostly unsatisfactory. Porous calcium phosphate ceramics show more favorable growing-in properties.
The ceramic implant materials based on calcium phosphate which are currently available are divided into two basic groups.
The first group uses synthetically prepared calcium phosphates, which are shaped to compact or porous bodies and then sintered to give the ceramic. The advantage of these materials of course lies in the fact that the synthetic build-up allows selected chemical compositions to be obtained with a high accuracy and reproducibility without problems. The standardizability of the composition is essential for medical uses.
A decisive disadvantage of synthetic materials is that porous bodies can be produced only with great difficulty and with great effort. There has therefore been no lack of attempts to produce porous shaped articles from calcium phosphate ceramics by a procedure in which, for example, organic fibers, woven fabric or braided fabric or a body of spongy structure of organic material are embedded in a mineral matrix, and this is then baked thoroughly before or during sintering to give the ceramic. Such a process is described, for example, in EP 253 506. Because o
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Bauer Andrea
Bauer Jorg
Engel James
Jones Kenneth M.
Merck Patent Gesellschaft mit beschrankter Haftung
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