Method of producing implantable bone replacement materials

Details Method of producing implantable bone replacement materials Method of producing implantable bone replacement materials

1986-07-18

1987-10-27

Lusignan, Michael R.

Coating processes

Medical or dental purpose product; parts; subcombinations;...

Particulate or unit-dosage-article base

427 38, 427309, 623 16, 623 18, A01N 102, B05D 306

Patent

active

047029307

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The invention relates to a method of producing implantable bone replacement materials by coating a metallic substrate (core) with a bioactive material on a calcium phosphate basis.
Implants of solid or porous, biocompatible metals or metal compounds are known, as well as bone replacement materials consisting of a plastics or metal matrix with incorporated calcium phosphate ceramic particles or of a dense aluminum oxide ceramic material.
The currently used methods and materials for producing a prosthesis-bone compound which is fully resistant to load are predominantly based on purely mechanical anchorages achieved by screwing or nailing, or on purely mechanically acting cementing, e.g., of a prosthesis shaft in an artificially produced cavity in the bone. These mechanical anchorages often cause inadmissibly high stresses in the bone bed which lead to atrophy of the bone region affected and thus to later loosening of the prosthesis.
The stability of the prosthesis anchorage is also dependent on the chemism of the materials used. The currently used biocompatible metals as well as the biostable oxide ceramics and the tissue-neutral polymer materials are, without exception, recognized by the bone as foreign bodies and thus remain encapsulated by tissue. This phenomenon, which is to be regarded as a first stage of rejection, in the case of permanently loaded prosthesis parts leads to widening of the connective-tissue membrane in the bone-implant boundary zone and to loosening and later rejection of the implanted material.
A different physiological behavior is shown by the bioactive implant materials, e.g. the bioactive calcium phosphate ceramics, which are more or less biodegradable, i.e. resorbable, depending on their composition. In the course of their chemical decomposition, these materials release materials to the surrounding tissue which do not disturb bone formation but, on the contrary, permit or even stimulate calcification of the bone tissue immediately on the alloplastic surface.
The term "bioactive" implies a specific chemical reaction of the material with the bone cells. Although this property is desirable for direct bone implant formation, it excludes the sole use of these materials for a permanent implant. An additional drawback consists in their relatively low mechanical strength, which is not sufficient for highly loaded endoprotheses. Therefore, the above-mentioned plastics were developed from resorbable plastic with incorporated bioceramic particles; the mechanical strength of these materials is, however, still insufficient, in particular after resorption of the ceramic component.
It is also known to coat a metallic prosthesis core with bioactive substances, e.g. with at least one enamel or enamel-like carrier layer into which the bioactive materials are then incorporated. In this case the serious drawback of the application of an enamel coating is accepted in order to achieve a satisfactory bond strength, although this enamel coating is incompatible with the bioceramic material and inavoidably results in tissue-incompatible decomposition products. It is not recognized that a firm bond between bioceramic and metal can also be achieved without enamel or enamel-like intermediate layers.
To produce bone or dental prostheses, it is known to apply a coating of a eutectoi of tricalcium phosphate and tetracalcium phosphate by means of a flame or plasma spraying device or to coat the entire metallic prosthesis with dense and porous ceramic material. For this pupose, tissue-incompatible bonding agents are required, as otherwise no sufficient bond between the coating and the implants can be reached.
In the case of a further known bone replacement material, calcium phosphate particles are incorporated into a solid metal core in the form of a single layer. These calcium phosphate particles have from the beginning a composition of CaO:P.sub.2 O.sub.5 between 3:1 and 4:1. The coating of prosthesis metals with such bioactive and biocompaticle materials is problematic, as bonding problems between

REFERENCES:
patent: 4623553 (1986-11-01), Ries et al.

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