Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1998-01-16
2001-04-17
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023720, C623S919000, C623S923000
Reexamination Certificate
active
06217614
ABSTRACT:
The present invention relates to a process for treating bone tissue and corresponding implantable biomaterials.
In particular such a process enables bone tissue to be treated with a view to its being implanted into a human. Such a tissue must not cause rejection (or at least as little as possible), and must have a good osteoconductive capacity, ie it must allow the formation and migration of bone tissue which has been newly formed by the recipient.
The grafting of bone tissue is a technique used daily in most orthopaedic surgery departments throughout the world. These grafts may be of three types, namely;
allografts,
autografts,
xenografts.
Bone allografts consist in implanting bone tissue from a donor into a recipient of the same species, but different from the donor. Bone autografts consist of removing bone tissue and grafting it into the same individual. Bone xenografts consist of implanting bone tissue from an animal (often a pig or a bovine) into a human individual.
To carry out these grafts, the starting point is bone tissue which is treated to clean it mechanically and purify it of all materials which would adversely affect its implantation. In doing this, it is found, with the treatments used in the prior art, that the mechanical properties of the bone tissue are impaired. This is because the organic substances extracted influence the mechanical properties of the bone. However, the grafting of a bone implant is generally carried out for the purpose of restructuring the skeleton, in a part which is subject to problems of strength in which the mechanical properties are of the utmost importance. It would therefore be advantageous to have available bone grafts with mechanical properties which are equivalent, or even superior, to those of natural bone.
For example such grafts would be indicated in orthopaedic applications and in particular when the graft is put under load, ie in particular: spinal surgery (cervical fusion, replacement of lumbar discs, etc), reconstruction of the base of the cotyle, arthroplastic surgery, osteotomy, pseudoarthrosis, arthrodesis, etc.
Thus, when the graft is used to restore a part of the skeleton which supports an implanted artificial prosthesis (joint prosthesis, dental prosthesis, etc), the use of a graft whose mechanical strength, particularly under compression, would be greater than that of the original deteriorated bone, would be a decisive advantage from the point of view of the life and functioning of the prosthesis. Furthermore, the graft inserted between the prosthesis and the natural bone would make the variations in mechanical properties more gradual and would improve the quality of the transmission of stresses by avoiding excessively steep localised gradients in strength. Furthermore, if the graft has, from the time it is implanted, strengths equivalent to those of the bone, all risk of deterioration during the resorption of the graft by a newly formed bone tissue is eliminated.
The aim of the invention is therefore to propose an implantable biomaterial whose mechanical properties, particularly strength under compression, are at least equivalent to those of natural bone. In particular, the invention aims to propose an implantable biomaterial whose strength under compression can be between one and two times that of natural bone.
Furthermore, the invention also aims to propose a biomaterial which improves the efficacy of bone grafts both from the mechanical and from the biological point of view.
Indeed, allografts have numerous drawbacks. First of all the risks of infection related to the transmission of bone tissue from one individual to another are many. Such is the case in particular where the transmission of the AIDS HIV virus is concerned. Given the large increase in this illness, such a risk of infection has increased considerably in recent years. Apart from these risks of infection, which also concern other viruses, the main complications related to the use of allografts are fractures, an unsuccessful recolonisation of the implanted bone tissue (grafts) and rejection of the implant. The unsuccessful recolonisation of the grafts today poses a significant problem. This is because the tissues of the graft are supposed to be resorbed, invaded and then replaced by newly-formed bone tissue. But until now this rehabilitation has been somewhat weak.
One of the aims of the present invention is therefore to produce an implantable bone tissue which is safe from the point of view of infection and the immune system.
Another aim of the invention is that a bone tissue of this kind should have a good osteoconductive capability (ie one that facilitates a successful recolonisation of the grafts).
Autografts are often preferred to allografts because they are more successfully recolonised and likely to contribute bone cells at the site of a graft. The result of this is that the risks of infection and to the immune system are considerably reduced, but this type of practice is not completely satisfactory. This is because it is painful, often meets with an unfavourable response from the patient, and involves a risk of complications at the donor site. In addition, numerous operations require large quantities of bone tissue, which is incompatible with autografts.
Bone xenografts also have many drawbacks. Generally, these grafts cause strong immune reactions (rejections). To mitigate this drawback, various attempts aiming to reduce or eliminate these reactions have been made. They are generally based on the principle of extracting the protein from the bone tissue before implantation. This is because the proteins contained in the bone tissue are the cause of some of the rejection reactions. These rejection reactions are also related to the presence of cell debris in the medullary tissue and to other elements of this tissue.
The use of organic solvents for extracting proteins from bone tissue is known. The most commonly used solvents are: ethylene diamine, hydrogen peroxide, various chlorinated solvents such as chloroform or dichloromethane, and also ethanol and acetone. With the protein thus extracted most bone tissues present little or no immune reaction. They are generally revascularised successfully and are invaded by osteogenic cells from the recipient. However, they do not themselves have osteoinductive properties. Their mechanical strength is generally lower than or similar to that of natural bone.
It will however be noted that the solvents used for protein extraction are often highly toxic. Because of this, the bone tissues have to be carefully rinsed (which is not easy, given their porosity) to avoid any pollution of the recipient site.
The patent FR-A-2.654.625 describes a protein extraction process using such toxic solvents combined with a selective urea-based extraction agent. However, such a process results in very variable extraction of lipids, because according to this patent 0.5 to 5% of lipids may remain.
Fluids in the supercritical state are already known for extracting various substances such as lipids, proteins, nucleotides, and saccharides from animal tissues or organs. However, these known processes are considered to be complex and costly to use, without having any decisive advantages compared with other extraction processes.
Thus the prior art does not disclose the possibility of extracting organic matter when treating bone tissue as a result of which extraction the mechanical strength of the bone tissue is improved.
The aim of the present invention is to mitigate all the drawbacks of the prior art and in particular to propose an implantable bone tissue with improved strength compared with that of natural bone, which is safe with respect to infection and the immune system, which has a good osteoconductive capability and which does not use toxic products. The present invention has the particular aim of proposing a process enabling such bone tissue to be treated.
For this purpose, the present invention concerns a process for treating animal or human bone tissue in order to obtain biomaterial which can be implanted in a human and is
Combes Didier
Condoret Jean-Stephane
Fages Jacques
Marty Alain
Bioland
Isabella David J.
Kok Choon P.
Shlesinger & Arkwright & Garvey LLP
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