Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-03-01
2001-04-24
Pezzuto, Helen L. (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C264S042000, C264S049000, C264S227000, C264S321000
Reexamination Certificate
active
06221477
ABSTRACT:
The invention relates to a process for the preparation of a material comprising a framework consisting of shell-like structures and an interconnecting pore system, a process for the preparation of a material consisting of shaped bodies connected via webs, a process for the preparation of a material which comprises a framework of shell-like structures and whose interconnecting pore system is filled with shaped bodies connected via webs, material producible by means of these processes as well as their use as bone replacement material, artificial bone, implant, filter and drug delivery system.
Lost bone, for instance due to a trauma caused by an accident or after the resection of tumors, after infections or by idiopathically developing bone cysts, has been representing a serious problem for surgeons for a long time. It has, for example, been tried to replace bone artificially, to use animal bone, to process animal bone accordingly such that it is not rejected in humans after it has been inserted or also to preserve bone from humans in freezers and to insert it as frozen homologous bone.
There are various methods for processing animal bone for the use in humans. Ivory, for example, has been also used. A bone replacement which is particularly accepted in surgery is the so-called “Kiel bone chip”.
All chemically processed heterologous transplants from animals, however, are incorporated into the host bone incompletely or not at all. The bank bone very often leads to lethal infections, i.a. AIDS infections. Fresh homologous bone transplants are affected by such complications to a much greater extent. In this case, it is even possible to transplant tumors. Therefore, it has repeatedly been tried to develop bone replacement materials and methods by means of which the disadvantages of the immune reaction and the transmission of diseases can be avoided.
In DE-A-39 03 695, a process for the preparation of absorbable ceramics on the basis of tricalcium phosphate is described which can be used as a bone replacement material and in which natural bone material from which the soft tissue has been removed is used as a starting material. Residual organic substance is removed from the bone material by pyrolysis and the remaining bone material consisting of hydroxylapatite is subsequently treated with phosphate carriers and then subjected to sintering. This ignited bovine bone material also exhibits good incorporation properties.
The mentioned materials derived from animals, however, cannot fulfil the demands on bone replacement material with respect to reproducibility of the structure, in particular in view of the material strength and the standardizability of the manufacturing process, and additionally their production is very expensive. Therefore, in medicine it is desirable to produce the used materials, for instance bone replacement materials, fully synthetically. These materials should guarantee maximum strength at a minimum of material and should provide a variety of properties for a variety of indications. It is, for example, desirable to provide a process by means of which on the one-hand bone-like trabecular structures, i.e. a “positive” of the bone, and on the other hand a “negative” of the bone, i.e. shaping negative molds of the medullary cavities of the bone can be produced. By means of such a process, on the one hand the physiological structure of bone could be reproduced and, by means of the negative, on the other hand supporting and guiding frameworks could be provided around which bone grows and which are very rapidly able to take up high loads.
In DE-A-40 33 291, a process is described by means of which the aforementioned demands can be achieved in some respects. In this process, firstly preferably spherical shaped bodies are connected to one another to form a three-dimensional conglomerate of shaped bodies, thereafter a material different from the material of the shaped bodies is molded around the shaped bodies in order to form a three-dimensional framework, and subsequently the shaped bodies are removed so that only the three-dimensional framework is left. In subsequent process steps, the cavity system resulting from the removal of the shaped bodies can be again filled with a ceramic mass, for example, and subsequently the three-dimensional framework can be removed. Thus, by means of this process both a “positive” of the bone and the above described “negative” of the bone can be produced. The preparation of the conglomerate of shaped bodies (negative) serving as the starting material is, however, rather money- and time-consuming and not in any case reproducible.
DE-A-22 42 867 discloses a process for the preparation of implantable, porous, ceramic bone replacement, bone composite or prosthesis anchorage materials. In this process, firstly an “auxiliary framework” is prepared of spheres which approximately corresponds to the pores and pore connections of the finished material, and subsequently a castable ceramic mass is filled into the framework. After the ceramic mass has at least partially solidified, the auxiliary framework is decomposed and removed. The process for the preparation of the initial auxiliary framework made of spheres can be, however, at best standardized in a time- and money-consuming manner and is hardly reproducible.
SUMMARY OF THE INVENTION
Thus, an object of the invention consists in providing materials and processes for their preparation, by means of which it is possible to provide on the one hand a material with a three-dimensional framework of shell-like or trabecular structures as a positive, and on the other hand also its negative, i.e. a material consisting of shaped bodies connected to one another, as well as a combination of these two materials, wherein the porosity and the thickness of the supporting structures of the positive material as well as the configuration of the shaped bodies and their connections in the negative material can be exactly and reproducibly adjusted while taking into account the respectively required properties, such as dimensional stability and absorbability.
A further object of the invention consists in providing such materials and processes for their preparation which exhibit increased strength and/or permeability.
These objects are achieved by means of the present invention. The invention thus solves an old problem in material preparation, in particular in the preparation of materials for medicine. By means of the process according to the invention it is possible to simply and reproducibly prepare a porous material with a continuously porous framework having an adjustable porosity and an adjustable strength as well as material properties, such as solubility and absorbability, which are adapted to the respective requirements, wherein the pore system can optionally be filled with a different material.
As “positive”, i.e. as material imitating the bone, the material according to the invention comprises a three-dimensional framework consisting of load-bearing shell-like structures which enclose cavities communicating with each other and adjustable in a predetermined manner. These cavities are adjustable in a predetermined manner in particular in that the space taken up by the cavities in the finished material is during the production process of the material firstly taken up by shaped bodies as space retainers, wherein the shaped bodies are appropriately selected and arranged in a mold depending on the demands on the pore system. The material according to the invention as “negative”, which can be used, e.g., as an implant, comprises a three-dimensional composite of shaped bodies which are connected with one another via webs whose width and length are adjustable. The shape and structure of these “webs” will be explained hereinafter. The material as positive is producible in that the framework is formed around deformable shaped bodies which serve as space retainers for the cavities and form a “negative”, and in that said shaped bodies are subsequently removed.
The finished material as negative can be produced by filling the fram
Pezzuto Helen L.
Westerman, Champlin & Kelly, P.A.
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