Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Having bio-absorbable component
Reexamination Certificate
1999-10-25
2003-01-28
Isabella, David J (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Having bio-absorbable component
C623S016110
Reexamination Certificate
active
06511511
ABSTRACT:
BACKGROUND OF THE INVENTION
The potential repair of articular cartilage in human using porous scaffolds has been described. Mears in U.S. Pat. No. 4,553,272 describes a method for osteochondral repair focusing on the use of starter cells, specific pore sizes in a porous scaffold, and providing a barrier between the two pore sizes. There is no mention of the use of biodegradable scaffolds or the necessity of providing a scaffold that can withstand physiological loads. Hunziker in U.S. Pat. No. 5,206,023 teaches a method for articular cartilage repair involving pretreating the defect area with enzymes to remove proteoglycans, then providing a biodegradable carrier (scaffold) to provide proliferation agents, growth factors, and chemotactic agents.
Vert et al. in U.S. Pat. No. 4,279,249 describe a solid biodegradable osteosynthesis device made of a fiber-reinforced composite. The fibrous component is a biodegradable polymer high in glycolide content and the matrix component is high in lactide units. There is no mention of porous devices and the favorable mechanical properties achieved through fiber reinforcement are obtained through typical stacking and layering techniques known in the art. Uniform distribution of fibers throughout the matrix is not disclosed.
The prior art does not appear to teach how to optimize mechanical properties by reinforcing highly porous materials (50%-90% porous). Nijenhuis et al. in Eur.0,277,678 describe a biodegradable, porous scaffold preferably incorporating biodegradable reinforcing fibers. The scaffold has a bi-porous structure (bimodal pore distribution) made using a combination of solution-precipitation and salt-leaching techniques. Although the fibers are incorporated to “reinforce” the scaffold, no evidence is presented to verify that the mechanical properties are actually improved through such reinforcement and the fibers appear to be randomly aligned.
Stone et al. in U.S. Pat. No. 5,306,311 describe a prosthetic, resorbable articular cartilage composed of a dry, porous, volume matrix of randomly or radially oriented, allegedly biocompatible and bioresorbable fibers. Stone's patent speaks mainly of natural polymeric fibers, such as collagen and elastin, which are harvested and purified from xenogenic sources. The fibers are then cross-linked to provide a cohesive scaffold. The ability of the scaffold to support articulating joint forces is not shown.
All publications and patent applications referred to herein are fully incorporated by reference to the extent not inconsistent herewith.
SUMMARY OF THE INVENTION
This invention provides a fiber-reinforced, polymeric implant material useful for tissue engineering, and method of making same. The implant material preferably comprises a polymeric matrix, preferably a biodegradable matrix, having fibers substantially uniformly distributed therein in predominantly parallel orientation as shown in
FIGS. 1 and 2
. In preferred embodiments, porous tissue scaffolds are provided which facilitate regeneration of load-bearing tissues such as articular cartilage and bone.
The material of this invention is used to prepare porous, fiber-reinforced, biodegradable tissue scaffolds whose fibrous supports are oriented predominantly in a single direction. The scaffold may be implanted into humans or animals to provide support for physiological loads applied parallel to the predominant direction of orientation of the fibers. For example, in an osteochondral site on the femoral condyle, the primary direction of loading is perpendicular to the surface of the cartilage. The oriented fibers act like struts in a bridge support to provide strength and stiffness to the pore walls of the scaffold and provide a characteristic columnar pore architecture especially suitable for cell in growth. The orientation of the fibers also causes the mechanical properties of the scaffold to be anisotropic, i.e., the higher strengths provided by the fibers is maximal in the direction parallel to the fibers, thus providing primary support for physiological loads where they are highest.
Orientation of the fibers is achieved through a dissolution-precipitation process combined with a novel kneading and rolling process. Using various amounts of fiber reinforcement, the mechanical properties of the scaffold may be tailored to the host tissue environment for optimal performance.
Alternatively, the polymer used may be non-biodegradable, and/or the implant may be made non-porous (fully dense) for use as a permanent implant, such as a bone plate in locations requiring load bearing.
The fibers are substantially uniformly distributed throughout the polymer matrix, that is the number of fibers present in a selected portion of the matrix which is large enough to contain several macropores should be substantially the same as (within at least about 20% of) the number of fibers present in any other such selected portion of the matrix. “Macropores” are the larger, columnar-shaped voids formed in the process of manufacturing the material as shown in
FIGS. 1 and 2
.
The invention may be used for a variety of tissue engineering applications, including osteochondral defect repair, partial and full thickness cartilage defect repair, bone graft substitute, bone graft onlay, ligament or tendon augmentation, oral/maxillofacial surgery, and other reconstructive surgery. The invention is particularly useful for, but not limited to, applications where the implant is to be placed in a defect in a load-bearing tissue, i.e., where stresses applied to the implant once placed in the defect are high in one direction compared to relatively perpendicular directions. One example is in an osteochondral or full thickness cartilage defect, where during such activities as normal walking, there are very high compressive stresses perpendicular to the surface of the cartilage, whereas the stresses parallel to the surface are much less. Another example is alveolar ridge augmentation, where primarily one-directional compressive stresses are due to biting or chewing.
The reinforcing fibers may be made of any suitable biodegradable material by methods known to the art or may be commercially available fibers. Polyglycolide (PGA) fibers are currently available from several sources including Albany International, Sherwood Davis & Geck and Genzyme Surgical Products. Fibers from sutures may also be used, e.g., Vicryl® (90:10 poly [glycolide:lactide]) from Ethicon (Johnson & Johnson). They are preferably synthetic fibers, and are preferably of a length short enough not to interfere with processability, e.g., less than about 1 cm. They can be chopped to the desired length from longer fibers, preferably they have a length between about 0.5 mm and about 1.0 cm and more preferably between about 0.5 mm and about 4.5 mm. The fibers preferably have a diameter between about 5 &mgr;m and about 50 &mgr;m, more preferably between about 5 &mgr;m and about 25 &mgr;m.
The reinforcing fibers preferably have mechanical properties that are not substantially compromised when tested in a physiological (aqueous, 37° C.) environment. Any biocompatible material can be used to make the fibers. The fibers are preferably insoluble in the solvent used to dissolve the matrix polymer. For articular cartilage repair, the fibers are preferably made from polyglycolide (PGA) or a glycolide-lactide copolymer with a glycolide content above 80%. For bone repair, the fibers may be made of a biodegradable glass such as calcium phosphate orbioactive ceramic. The volume fraction of fibers within the composite scaffold is preferably between about 5% and about 50%, and more preferably between about 10% and about 30%.
The reinforcing fibers used in this invention may alternatively be hollow fibers known to the art. The hollow fibers provide channels to aid in cell and tissue infiltration and can additionally be filled with bioactive agent for delivery to the tissue.
Biodegradable polymers or other biodegradable materials known to the art may be used for the biodegradable matrix. Some examples of suitable biodegradabl
Kieswetter Kristine
Leatherbury Neil C.
Niederauer Gabriele G.
Slivka Michael
Greenlee Winner and Sullivan P.C.
Isabella David J
OsteoBiologics, Inc.
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