This invention relates generally to medical devices and procedures and more particularly to devices and methods for treating defects in the tissue of a living being.
To better treat our aging population, physicians are looking for new and better products and methods to enhance the body's own mechanism to produce rapid healing of musculoskeletal injuries and degenerative diseases. Treatment of these defects has traditionally relied upon the natural ability of these types of tissue to repair themselves. In many instances the body is unable to repair such defects in a reasonable time, if at all. Advances in biomaterials has allowed for the creation of devices to facilitate wound healing in both bone and soft tissues defects and injuries. Such devices are used in tissue regeneration as tissue (e.g. bone) graft scaffolds, for use in trauma and spinal applications, and for the delivery of drugs and growth factors.
Bone and soft tissue repair is necessary to treat a variety of medical (e.g. orthopedic) conditions. For example, when hard tissue such as bone is damaged as a result of disease or injury, it is often necessary to provide an implant or graft to augment the damaged bone during the healing process to prevent further damage and stimulate repair. Such implants may take many forms (e.g. plugs, putties, rods, dowels, wedges, screws, plates, etc.) which are placed into the tissue. Typically, such implants can be rigid, flexible, deformable, or flowable and can be prepared in a variety of shapes and sizes. For rigid implants (e.g. bone screws), the defect site is typically preconditioned by forming a depression, channel, or other feature (e.g. pre-tapped hole) therein in preparation for the application of the implant. For non-rigid structural repair materials (e.g. putties and pastes) to be conveniently used, they must be capable of being formed into a variety of complex shapes to fit the contours of the repair site. An accurately configured implant that substantially fills the defect site will enhance the integration of natural bone and tissue to provide better healing over time. For example, when repairing defects in bone, intimate load carrying contact often is desired between the natural bone and the bone substitute material to promote bone remodeling and regeneration leading to incorporation of the graft by host bone.
Current bone graft materials include autografts (the use of bone from the patient), allografts (the use of cadaver bone), and a variety of other artificial or synthetic bone substitute materials. Autografts are typically comprised of cancellous bone and/or cortical bone. Cancellous bone grafts essentially provide minimal structural integrity. Bone strength increases as the implant incorporates surrounding cells and new bone is deposited. For cortical bone, the graft initially provides some structural strength. However, as the graft is incorporated by the host bone, nonviable bone is removed by resorption significantly reducing the strength of the graft. The use of autograft bone may result in severe patient pain and other complications at the harvest site, and there are limitations to the amount of autograft bone that can be harvested from the patient. Allografts are similar to autografts in that they are comprised of cancellous and/or cortical bone with greater quantities and sizes being typically available. Disadvantages of allografts include limited supplies of materials and the potential for transmission of disease. The disadvantages of the existing products creates a need for a better devices and methods for treating defects in the tissue of a living being.
Collagen is the most abundant protein found in the body. The unique chemistry of collagen makes it an ideal material for structural and hemostatic applications in both clinical and diagnostic settings. Collagen, like all proteins, is comprised of amino acids linked covalently through peptide or amide linkages. The sequence of the amino acids, or the primary structure, outlines the three-dimensional structure of the protein which in turn dictates the function and properties of the molecule. Collagen is composed of three peptide chains associated in a triple helical orientation. These triple helices associate to form fibrils which ultimately make up connective tissue and other structural member.
Collagen has been used in a number of applications in the art. For example, one application is for use in hemostatic devices for the stoppage of bleeding, such as is described in U.S. Pat. Nos. 5,310,407 (Casal) and 4,890,612 (Kensey). However, neither teaches the use of native insoluble fibrous collagen. In U.S. Pat. No. 5,425,769, Snyders, Jr. discloses a biocompatible and bioresorbable bone substitute with physical and chemical properties similar to bone, consisting of reconstituted fibrillar collagen within a calcium sulfate di-hydrate matrix. The ratios of calcium sulfate and collagen are adjusted for each application and the bone substitute is molded in situ to form a solid phase. Similarly, U.S. Pat. No. 5,425,770 (Piez, et. al.) discloses a composition made from a calcium phosphate particulate mineral such as hydroxyapatite or tricalcium phosphate mixed with atelopeptide reconstituted fibrillar collagen for conductive bone repair. U.S. Pat. No. 5,904,718, (Jefferies) describes a process and invention comprising demineralized bone particles and collagen. Examples of medical implants that utilize reconstituted fibrous collagen include U.S. Pat. Nos. 4,642,117 (Nguyen™, et al.), 4,795,467 (Piez, et al.), and 5,997,896 (Carr, et al.). The '718, '769 and '770 patents, all require the use of reconstituted collagen.
U.S. Pat. Nos. 4,563,350 and 4,888,366 describe the use of lyophilized and preformed collagen carriers of osteoinductive factors in bone repair, respectively. When used as preformed solid implants, these carriers consist generally of ceramic materials which are held together by collagen. Similarly, U.S. Pat. No. 4,776,890 describes non-crosslinked collagen/mineral implants, which can be moistened and molded into a desired shape before implantation. Therein, crosslinking is described as being undesirable because of its inhibitory effects on bone in-growth. U.S. Pat. Nos. 4,795,467, 5,035,715 and 5,110,604 describe porous collagen-containing implants for use in bone repair and/or wound healing. U.S. Pat. No. 4,948,540 (Nigam) describes a type of fibrous native collagen for use as a hemostatic dressing. These references do not teach or suggest the solution to the ubiquitous problem of high porosity and excessive resilience in a collagen-containing implant material for bone defect repair.
Devices made from compressed collagen matrices include Robinson et al. (Cardiovasc Intervent Radiol 1990; 13:36-39), who described the use of compressed collagen plugs prepared from Gelfoam™ (manufactured by Pharmacia & Upjohn Company, Kalamazoo, Mich.) to repair biopsy tract defects in lungs. Armstrong et al. (Arch Dermatol 1986; 122:546-549) described the use of compressed collagen plugs prepared from Helistat™ (manufactured by Integra LifeSciences) to repair cutaneous biopsy wounds. All of these references teach the use of collagen but none teach the use of the multi-phasic composition of the present invention, furthermore the function of these devices is for stopping the bleeding from a puncture and not for regenerating tissue.
Accordingly, a need remains for a defect filling material, prepared primarily of collagen, which has improved mechanical stability and is adequately dense and sufficiently conformable for medical or surgical utility.
U.S. Pat. No. 6,110,484 (Sierra) describes an implant formed in situ, that contains a biodegradable porosifying agent; however the embodiment is a pre-formed solid plug and porosity is not rapidly created following implanting, to form an osteoconductive structure. Therefore, a need exists for an implant that rapidly becomes porous following implantation.
Various embodiments of these devices include polysaccharides in the construct. Polysaccharides are a key component of the extracellular matrix component of bone and related tissue, since they provide hydrophilicity and important structural aspects. When incorporated into medical implants, polysaccharides also impart hydrophilicity and help to regulate the wound healing response associated with the implant, as well as improve cell attachment. The combination of Polysaccharides and collagen has been described by U.S. Pat. Nos. 4,614,794 (Easton, et. al.) and 5,972,385 (Liu, et. al.). '794 is limited to fabrication from a hydrolytic degradation process, and the '385 device must be crosslinked. Therefore, a need exists for a polysaccharide that is not limited to fabrication from a hydrolytic degradation process, and the that does not require cross-linking.
Demineralized bone alone may be useful for repair of bony defects, there is much inconsistency because bone is a natural material. Some approaches to harvesting these minerals include defatting, grinding, and calcining or heating the bone. However, the resulting mixture of natural bone mineral is chemically and physically variable. Additionally, allogenic bone from cadavers must be harvested carefully under rigid conditions and then properly stored in tissue banks to prevent possible immunologic complications or possible transmission of viral or bacterial pathogens. Sterilization of demineralized bone may alter the physiochemical properties critical for bone induction when methods such as gamma radiation employed. It is recognized that irradiation of demineralized bone powder before implantation weakens the osteogenic response by approximately 20%. It is therefore extremely difficult to use natural bone as an implant, thus there remains a need for a synthetic bone replacement material.
In U.S. Pat. No. 5,425,769, (Snyders, Jr., et al.) teaches that there have been many attempts to enhance the handling and osteogenic ability of calcium phosphate implants by incorporation of calcium phosphate granules into a binding matrix such as plaster of Paris or soluble or reconstituted fibrous collagen. This will improve the workability of the implant and encourage bony in-growth through partial resorption of the implant. Disadvantages of this conjugate include the inability of the malleable collagen matrix to attain a solid state in vivo and the resistance of solidifying plaster matrices to molding. The is overcome by the present invention with a unique blend of soluble and native fibrous collagen which maintains its strength following implantation, while still remaining somewhat compliant, without the need for ceramic additives; although, the present invention contemplates the potential improvement of their use.
In U.S. Pat. No. 4,394,370, Jefferies describes an implant made of reconstituted collagen and either demineralized bone or else bone morphogenic protein, and which when implanted into bone, will cause osteogenesis. The collagen may be chemically cross-linked. The physical properties of these sponges is not specified in the disclosure, however, reports of the handling of similar collagen sponges indicates these materials to be very weak and quickly resorbable (no wet tear strength and resorption in 1 to 2 weeks).
Additionally, in U.S. Pat. No. 4,430,760, Smestad describes an implant consisting of demineralized bone or dentin inside of a container made from either fibers such as collagen or a microporous membrane. The pores of the implant are sized so that it selectively allows osteocytes and mesenchymal cells to pass, but does not allow the particulate demineralized bone or dentin to pass through. The problem concerning this patent is that it can not be used in load-bearing locations. Therefore, a need exists for an implant that will maintain structural or mechanical integrity following implant.
In U.S. Pat. No. 4,440,750, Glowacki et al. describe an aqueous dispersion of reconstituted collagen fibers mixed with demineralized bone particles for use in inducing bone formation. This graft material possesses little physical strength and mechanical properties and thus, its uses are limited. Furthermore, with time, the demineralized bone particle suspended within the aqueous collagen sol-gel begin to settle under gravitational forces, thus producing an non-homogeneous or stratified graft material; whereas the present invention provides strength, and does not utilize sol-gel processing thereby avoiding any settling of gel constituents, or other unintentional non-homogeneity. Additionally, U.S. Pat. No. 4,485,097 (Bell) describes a material composed of a hydrated collagen lattice, fibroblast cells, and demineralized bone powder. This material is in the form of a hydrated collagen gel, and therefore has minimal physical strength or mechanical integrity. Therefore, the material fails to meet the aforementioned shortcomings in the art.
In U.S. Pat. No. 4,623,553, Ries et. al. describes a method for producing a bone substitute material consisting of collagen and hydroxyapatite and partially crosslinked with a suitable crosslinking agent, such as glutaraldehyde or formaldehyde. The order of addition of these agents is such that the crosslinking agent is added to the aqueous collagen dispersion prior to the addition of the hydroxyapatite or calcium phosphate particulate material. The resultant dispersion is mixed and lyophilized. The '553 patent lacks any components which are known osteogenic inducers, such as demineralized bone matrix or extracted bone proteins. Similarly, U.S. Pat. Nos. 4,865,602 and 5,035,715, (Smestad, et. al.) describe a process for preparing a biocompatible bone implant composed of atelopeptide fibrillar reconstituted collagen and a mineral component which may be calcium phosphate, hydroxyapatite, or tricalcium phosphate. The implant is gamma sterilized with enough irradiation to cause cross-linking of the collagen in order to produce the desired handling and mechanical properties for the implant. The '602, '715, and '553 patents differ from the present invention in that they require crosslinking, which is suspected to be detrimental to in-growth, additionally, the '602 and '715 patents include a reconstituted collagen matrix.
In U.S. Pat. No. 5,071,436 Huc et. al. describe a new bone-substitute biomaterial which is a combination of collagen, hydroxyapatite, and glycosaminoglycans and in the form of a sponge. The concentration of the glycosaminoglycans is preferably between 1 and 2% per liter of 1% collagen gel. The concentration of the hydroxyapatite and the collagen to each other is preferably about equal, which is six times greater than the concentration of glycosaminoglycan component.
In U.S. Pat. No. 5,320,844, Liu et. al. describes a composite material for hard tissue replacement whose properties are similar to natural bone. The synthetically derived, homogenous composite contains a collagen component and a calcium phosphate-containing component precipitated from a liquid medium.
In U.S. Pat. No. 5,711,957, Patat et al. discloses an implant made of a porous calcium carbonate-based material as an external wall to support a growth factor. These authors also teach why they believe that the presence of collagen is neither necessary nor desirable in the case when the implant is intended to be used as a bone-formation implant, regardless the external wall of '957 is the only region housing a growth factor.
In U.S. Pat. No. 5,904,718, Jefferies describes a chemically cross-linked matrix of demineralized bone particles or collagen which may or may not contain a drug or mineral additive. The 718 patent discloses that the cross-linking enables the construct to have a mechanical strength. Further, the 718 patent discloses that the cross-linking can conjugate the drug or mineral to the organic matrix. Embodiments of the current invention do not rely on crosslinking for strength, nor does it rely on crosslinking for conjugation of drugs or other therapies; this is an important feature of the present invention, since crosslinking has been shown by others to inhibit tissue ingrowth.
The fabrication of and application of microspheres is known and as such the following examples are included herein as reference. U.S. Pat. No. 3,887,699 describes a solid biodegradable polymer spheroid implants which incorporate a drug for sustained release as the polymer naturally degrades in the human body. Many different methods of constructing this type of controlled release system have been developed. Although the uniform matrix of a polymer provides a simple and efficient structure for the controlled release of agents with microspheres, many advanced methods of containing and releasing the therapeutic agents have been developed. U.S. Pat. No. 4,637,905 (Gardner) discloses a method for encapsulating a therapeutic agent within a biodegradable polymer microsphere. U.S. Pat. No. 4,652,441 (Okada et al.) discloses a method of utilizing a water-in-oil emulsion to give prolonged release of a water-soluble drug. The patent describes a wide variety of drugs that can be delivered via prolonged release micro-capsules as well as suitable polymeric materials and drug retaining substances. It is conceived that the system of this invention could incorporate any of the drugs described to in this patent to generate a beneficial effect in the cardiac tissue. U.S. Pat. No. 5,718,921 (Mathiowitz et al.) discloses a method for constructing a multiple layer microsphere which can release two different drugs at controlled rates or a singe drug at two different rates. U.S. Pat. No. 5,912,017 (Mathiowitz et al.) also discloses a method of forming two layered microspheres by using an organic solvent or melting two different polymers, combining them with a desired substance and cooling. Microspheres are not limited to just water-soluble therapeutic agents. See, for example, U.S. Pat. No. 5,288,502 (McGinity et al.) which discloses a multi-phase microsphere which is capable of incorporating water-soluble and water-insoluble drugs.
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