Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Having bio-absorbable component
Reexamination Certificate
1997-08-22
2001-03-27
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Having bio-absorbable component
C623S023710, C623S925000, C523S113000
Reexamination Certificate
active
06206931
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a medical structure and, in particular, to a graft prosthesis, materials, and methods therefor.
BACKGROUND OF THE INVENTION
Tissue implants in a purified form and derived from collagen-based materials have been manufactured and disclosed in the literature. Cohesive films of high tensile strength have been manufactured using collagen molecules or collagen-based materials. Aldehydes, however, have been generally utilized to cross-link the collagen molecules to produce films having high tensile strengths. With these types of materials, the aldehydes may leech out of the film, e.g. upon hydrolysis. Because such residues are cytotoxic, the films are poor tissue implants.
Other techniques have been developed to produce collagen-based tissue implants while avoiding the problems associated with aldehyde cross-linked collagen molecules. One such technique is illustrated in U.S. Pat. No. 5,141,747 wherein the collagen molecules are cross-linked or coupled at their lysine epsilon amino groups followed by denaturing the coupled, and preferably modified, collagen molecules. The disclosed use of such collagen material is for tympanic membrane repair. While such membranes are disclosed to exhibit good physical properties and to be sterilized by subsequent processing, they are not capable of remodeling or generating cell growth or, in general, of promoting regrowth and healing of damaged or diseased tissue structures.
In general, researchers in the surgical arts have been working for many years to develop new techniques and materials for use as implants and grafts to replace or repair damaged or diseased tissue structures, for example, blood vessels, muscle, ligaments, tendons and the like. It is not uncommon today, for instance, for an orthopedic surgeon to harvest a patellar tendon of autogenous or allogenous origin for use as a replacement for a torn cruciate ligament. The surgical methods for such techniques are known. Further, it has been common for surgeons to use implantable prostheses formed from plastic, metal and/or ceramic material for reconstruction or replacement of physiological structures. Yet, despite their wide use, surgical implanted prostheses present many attendant risks to the patient.
Researchers have also been attempting to develop satisfactory polymer or plastic materials to serve as such functional tissue structures and/or other connective tissues, e.g., those involved in hernia and joint dislocation injuries. It has been discovered that it is difficult to provide a tough, durable plastic material which is suitable for long term connective tissue replacement. The tissues surrounding the plastic material can become infected and difficulties in treating such infections often lead to the failure of the implant or prostheses.
As mentioned above, various collagen-based materials have also been utilized for the above-mentioned tissue replacements; however, these materials either did not exhibit the requisite tensile strength or also had problems with infection and other immunogenic responses, encapsulation, or had other problems when they may have been loaded with antibiotics, growth factors and the like. For example, U.S. Pat. No. 4,956,178 discloses a submucosa collagen matrix which is obtained from the intestinal tract of mammals; however, it is disclosed that the collagen matrix is loaded with antibiotics. In a related patent, U.S. Pat. No. 5,372,821, it is disclosed that a submucosa collagen matrix may be sterilized by conventional techniques, e.g., aldehyde tanning, propylene oxide, gamma radiation and peracetic acid. No specific processing steps are disclosed except that the submucosa layer is first delaminated from the surrounding tissue prior to sterilization treatment.
Therefore, there is a need to obtain improved purified forms of collagen-based matrices from tissue sources thereof. Also, there is a need to provide a process whereby the ease of removal of such matrices from tissue sources is enhanced so as to yield such improved, purified products. The present invention is addressed to these needs.
SUMMARY OF THE INVENTION
In accordance with one preferred embodiment of the present invention, provided is a graft prosthesis which includes a purified, collagen-based matrix structure removed from a submucosa tissue source, wherein the purified structure has a contaminant level making the purified structure biocompatible.
Another preferred embodiment of the invention provides a graft prosthesis which includes a purified, collagen-based matrix structure removed from a submucosa tissue source, wherein the purified structure has an endotoxin level of less than 12 endotoxin units per gram. The purified structure may have an endotoxin level of less than 1 endotoxin unit per gram, and even less than 0.5 endotoxin units per gram.
Another preferred embodiment of the invention provides a graft prosthesis which includes a purified, collagen-based matrix structure removed from a submucosa tissue source, wherein the purified structure has a nucleic acid content level of less than 2 micrograms per milligram.
Another preferred embodiment of the invention provides a graft prosthesis including a purified, collagen-based matrix structure removed from a submucosa tissue source, wherein the purified structure has a virus level of less than 500 plaque forming units per gram. The purified structure may have a virus level of less than 100 plaque forming units per gram, and even less than 1 plaque forming units per gram.
The present invention also provides a graft prosthesis which includes a purified, collagen-based matrix structure removed from a submucosa tissue source, wherein the purified structure has a processing agent level of less than 100,000 parts per million per kilogram.
A further embodiment of the invention concerns a method for obtaining a collagen-based matrix from a submucosa tissue source. The method includes treating the submucosa tissue source with a disinfecting agent to provide a disinfected submucosa tissue source, and removing the collagen-based matrix from the disinfected submucosa tissue source.
Another preferred embodiment of the invention provides a method for obtaining a collagen-based matrix from a submucosa tissue source, which includes providing a submucosa tissue source which has been treated with a disinfecting agent, and removing the collagen-based matrix from the submucosa tissue source.
The present invention also concerns a composition which includes a collagen-containing structure removed from a tissue source initially containing the structure and other tissue, wherein the collagen-containing structure has an endotoxin level of no greater than 12 endotoxin units per gram.
Also provided by the present invention is a purified collagen-containing matrix obtained from a mammalian tissue source, the matrix including mammalian tela submucosa and being obtainable by a process which includes disinfecting the mammalian tissue source then removing the structure from the resulting disinfected mammalian tissue source.
In preferred aspects, the invention provides purified forms of tela submucosa collagen matrices derived from the alimentary, respiratory, urinary or genital tracts of animals, the matrices having a bioburden level of substantially zero, and/or being essentially free of pyrogens. A preferred collagen matrix is capable of being implanted within a human or animal patient without causing a cytotoxic response, infection, rejection of the implant or any other harmful effect in a majority of patients. While a preferred implantable collagen matrix according to some aspects of the present invention comprises primarily tela submucosa, the collagen matrix in this instance may also comprise partial layers of laminar muscularis mucosa, muscularis mucosa, lamina propria, a stratum compactum layer and/or other such tissue materials depending upon the source from which it was derived.
Further in accordance with the present invention, a purified delaminated tela submucosa collagen matrix is provided which is derived
Cook William A.
Hiles Michael C.
Kozma Thomas G.
Patel Umesh H.
Cook Incorporated
Prebilic Paul B.
Woodard Emhardt Naughton Moriarty & McNett
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