Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1994-05-18
1995-11-07
Prebilic, Paul
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 11, 623 13, 623 15, A61F 228
Patent
active
054644402
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the field of medical technology and more specifically to the field of implantology, and relates to implants made of a porous, non-toxic material having a total open porosity exceeding 5% by volume but not exceeding 80% by volume within at least a portion of the implant.
BACKGROUND ART
When implant materials are used and are subjected to a substantial mechanical load, a high strength is the primary requirement. This is achieved by using essentially conventional construction materials--e.g. stainless steel, cobalt-chromium alloys, titanium and titanium-alloys, various ceramic materials such as silicon nitride and polymers. In order to fix implants, it is common practice to utilize a topographical surface or pores. In this connection special requirements as to holding and bone ingrowth must be met. A prior Swedish patent application No. 9101677-4 includes some important new aspects regarding primarily the pore size distribution. Thus, specific and complex pore size distributions can be utilized to accommodate bone ingrowth-promoting agents and to provide a satisfactory bone ingrowth in large pores.
BRIEF DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an improved implant as compared to the implant according to said Swedish patent application No. 9101677-4. The present invention relates more specifically to substantially limiting the porosity of micropores by adding bone ingrowth-promoting agents through carriers, which completely or partially fill micropores as well as pores or cavities in the surface layer, which makes the need of a large available surface less important. Thus, another object of the invention is to improve the bone ingrowth and the healing not only by creating geometrical opportunities for a satisfactory ingrowth but also by allowing a time control of the bone ingrowth, through different concentrations and release of active agents.
Generally, the purpose of the invention is to provide implants having the following characteristics: high strength, excellent biocompatibility by using bone ingrowth-promoting agents deposited in pores or in surface areas for time controlled bone ingrowth in order to achieve an improved reproduceable holding of the implant.
These and other objects of the invention can be achieved therein that communicating micropores, having a size of 10 .mu.m or less, preferably less than 5 .mu.m, most preferably less than 2 .mu.m, make up not more than 10% of the total pore volume, preferably not more than 5% of the total pore volume in said at least one portion of the implant, and that at least 5% of at least one section of the surface of the implant is covered by substantially evenly distributed pores having a pore size exceeding 50 .mu.m preferably in the range of 50-500 .mu.m, more preferably in the range of 75-400 .mu.m, or in the range of 100-300 .mu.m, or in the range of 150-250 .mu.m.
The term pore size is defined, as far as pores having pore sizes smaller than or equal to 50 .mu.m are concerned, as sizes calculated by means of conventional Hg-porosimetry, the relation between the pressure and the pore diameter (2r) being obtained through the expression: ##EQU1## p=the pressure s=the surface tension of Hg for a certain temperature; and Drake, Ind. Eng. Chem. 17 782 (1945))
Pore sizes exceeding 50 .mu.m are defined as sizes obtained through an optical measurement in a light microscope on a cross section of the specimens in a section made at a depth of 0.1 .mu.m and in a section perpendicular to the surface of the specimen, respectively.
The larger pores preferably are limited to, i.e. exist essentially only in the surface layer, more particularly are limited to a surface layer having a thickness of 3 mm, preferably 2 mm and suitably 0.3 mm. If for the rest the porosity is limited to a microporosity, i.e. to pores not larger than 10 .mu.m in diameter and having a total volume of micropores of not more than 10%, a high strength can be maintained.
In the pores one or several of those agents
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patent: 4440750 (1984-04-01), Glowacki et al.
patent: 4542539 (1985-09-01), Rowe, Jr. et al.
patent: 4629464 (1986-12-01), Takata et al.
patent: 4713076 (1987-12-01), Draenert
patent: 4778471 (1988-10-01), Bajpai
patent: 4957509 (1990-09-01), Tamari et al.
patent: 5073114 (1991-12-01), Detsch
patent: 5164187 (1992-11-01), Constantz et al.
LuCoCer Aktiebolag
Prebilic Paul
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