Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Ligament or tendon
Reexamination Certificate
2001-06-05
2003-05-27
Robert, Eduardo C. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Ligament or tendon
C623S023720
Reexamination Certificate
active
06569200
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides a plasticized dehydrated bone and/or soft tissue product that does not require special conditions of storage, for example refrigeration or freezing, exhibits materials properties that approximate those properties present in normal hydrated tissue, is not brittle and does not necessitate rehydration prior to clinical implantation. The invention replaces water in the molecular structure of the bone or soft tissue matrix with one or more plasticizers allowing for dehydration of the tissue, yet not resulting in an increase in brittleness of the plasticized product, and resulting in compressive and/or tensile properties similar to those of normal hydrated bone. Replacement of the chemical plasticizers by water prior to implantation is not required and thus, the dehydrated bone or soft tissue plasticized product can be placed directly into an implant site without significant preparation in the operating room. The present plasticized graft does not need rehydration, possesses adequate materials properties, and is not a potential source for disease transmission.
BACKGROUND OF THE INVENTION
Bone tissue is a homogeneous material comprised of osteoid and minerals. The osteoid is a viscous gel-like material comprised primarily of type I collagen (approximately 90%), proteoglycans, and various sulfated and non-sulfated mucopolysaccharides. The mineral component consists primarily of a crystalline form of calcium phosphate, hydroxy apatite, with amounts of calcium carbonate, tricalcium phosphate, and smaller amounts of other forms of mineral salts. This bone tissue is laid down around cells called osteocytes and these cells are found in small interconnected channels (lacunnae) which are interconnected through a series of channels comprising the Haversian canal system. At the level of the microscope, it is possible to observe that bone tissue is organized into osteons of compact bone made of concentric, perivascular layers of highly coaligned mineralized collagen fiber bundles. The predominant orientation within a single layer varies with respect to the vascular axis and various combinations of orientation in successive lamellae result in variable overall collagen orientation within each osteon. Differences in overall collagen orientation are directly reflected in differing mechanical behavior of single osteons. Transversely oriented collagen results in better resistance to compressive loading along the axis, whereas predominant longitudinal orientation results in better resistance to tensile stress. The predominant orientation of collagen within a cross-section of long bone is not random, but matches the expected distribution of mechanical stress across the section, and its rotational shift along the whole shaft. More transverse collagen is deposited at sites of compressive loading, and more longitudinal collagen is deposited at sites of tensile stress. These structural oriented bone tissues in a load bearing bone are presumed to be laid down by the osteocytes present in the bone and bone remodeling mediates mechanical adaptation in compact bone.
A bone is typically comprised of bone tissue in the form of cortical and trabecular bone. Cortical bone is frequently referred to as compact bone and is the major load-bearing part of a bone. Trabecular bone is present in what is typically referred to as cancellous bone where it appears as a densely interconnected structure of “spongy” bone. Spongy bone in a typical bone contains the hemotopoietic cellular elements which is called bone marrow. Trabecular bone can be described as forming a cross-bracing lattice between cortical bone in a bone. It is important to emphasize a need to differentiate between “a bone” and “bone” (as a tissue). A bone is comprised of bone tissue present as cortical and cancellous (spongy) bone.
The mineralized osteoid typical of bone tissue is hydrated along the organic molecular structure and is an essential element of the mineral structure. Hydrating molecules of water form complex molecular associations with these organic and non-organic elements of bone tissue and can be described as being tightly bound, loosely bound, and free. Free water and loosely bound water can frequently be removed from bone tissue with only minor changes in the overall mechanical characteristics of the bone tissue. Tightly bound water can be removed only under extreme conditions and results in significant changes in the physical and mechanical properties of bone tissue. In fresh bone, water serves a solvating function in bone tissue allowing proper orientation and molecular spacing of the collagen fibrils which maintain structural alignment of the mineral phase in association with the organic phase.
Bone tissue in the form of bone grafts for implantation into a patient, is typically preserved and provided in a dehydrated state. Dehydration of bone tissue through drying, whether by air drying or sublimation as in freeze-drying, results in alteration of the molecular structure of the bone tissue and as a result of the reorientation of the collagen fibrils and the crystalline mineral phase, stress accumulates in the bone tissue. This stress can be relieved by rehydration or by the occurrence of small or large dislocations of structure. Small dislocations are designated micro fractures and are not usually visible to the naked eye. Large dislocations are designated fractures and are usually visible to the naked eye.
In a long bone, for example a femur, tibia, fibula, or humerus, the shaft separates the proximal and distal ends of the long bone. The shaft serves to focus loads applied to the whole bone into a smaller diameter than found at the proximal and distal ends of the long bone and the shaft of a long bone is typically of a cylindrical shape and is comprised of compact (cortical) bone. Loads applied along the axis of the shaft require that the cortical bone maintain a constant circumference, i.e. the tendency to failure would distort the bone tissue perpendicular to the axis of load application. Thus, the orientation of the collagen fibers should be such that tensile stress is resisted along the axis of loading and compressive stress is resisted perpendicular to loading. Drying of shaft portions of long bones results in reorientation of collagen fibers and the mineral phase such that changes in the circumferential orientation create stress within the bone matrix which can be relieved only by rehydration or occurrence of a fracture which allows a reorientation approximating the original orientation. In dehydrated cortical ring grafts cut from shafts of long bones, this stress release can present as a fracture along the long axis of the bone shaft leaving a circumference which approximates the circumference of the cortical ring graft prior to drying. By rehydrating bone grafts prior to implantation, the potential for fracture formation which can compromise the function of the bone product can be reduced, but not eliminated. Fractures as discussed above can occur in dehydrated bone prior to rehydration and result in a graft having compromised biomechanical properties, which in turn can result in graft failure when implanted in a patient.
Load-bearing soft tissue grafts such as ligaments, tendons, and fascia lata are frequently provided in a freeze-dried state. Such grafts must be rehydrated prior to clinical implantation. Such soft tissue grafts typically contain collagen, elastin, and assorted proteoglycans and mucopolysaccharides. The collagens and elastins are the load-bearing component(s) of these soft tissue grafts and the assorted proteoglycans and polysaccharides serve to bind the fibrillar collagens into a matrix-like structure. The structural organization of fascia lata is similar to dura mater in being somewhat isotropic in load-bearing properties (Wolfinbarger, L, Zhang, Y, Adam, BLT, Homsi, D, Gates, K, and Sutherland, V, 1994, “Biomechanical aspects on rehydrated freeze-dried human allograft dura mater tissues, J. Applied Biomaterials, 5:265-270) whereas tendons (for example the
Anderson Billy G.
O'Leary Robert K.
Wolfinbarger, Jr. Lloyd
LifeNet
Priddy Michael B.
Robert Eduardo C.
LandOfFree
Plasticized soft tissue grafts, and methods of making and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plasticized soft tissue grafts, and methods of making and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plasticized soft tissue grafts, and methods of making and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3083783