Abstract:
An osteoimplant is disclosed and includes a plurality of partially demineralized fibers. Each fiber has an elongated, thin body having a length of about 1 centimeter to about 3 centimeters. Further, the plurality of fibers engages to establish a matrix of material. The disclosure is further directed to a method of making the above-mentioned osteoimplant.

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to orthopedics and orthopedic surgeries. More specifically, the present disclosure relates to materials and methods for treating bone voids. 
     BACKGROUND 
     Grafts that aid in the healing of damaged bone are a relatively old technology that has undergone substantial growth in light of recent advances in medicine and biology. Improved understanding of osteoinductive and osteoconductive properties of certain materials has enabled the design of implants of ever-increasing efficacy. Recent examples include U.S. Pat. No. 7,045,141 to Merboth et al., entitled “Allograft Bone Composition Having a Gelatin Binder”; U.S. Pat. No. 6,808,585 to Boyce et al., entitled “Osteogenic Implant Derived From Bone”; U.S. Pat. No. 6,548,080 to Gertzman et al., entitled “Method for Partially Demineralized Cortical Bone Constructs”; and U.S. Pat. No. 6,776,800 to Boyer, II et al., entitled “Implants Formed with Demineralized Bone”. Absorbable Collagen Sponge (“ACS”), by Integra LifeSciences Corporation (Plainsboro, N.J.), and Mastergraft® Matrix, by Medtronic Sofamor Danek (Memphis, Tenn.), are specific examples of grafts currently available on the market. 
     Many of these implants do not provide any structural support at the implant site. Structural support ranges from the ability to resist the tendency for compression of the graft by local tissues (space maintenance) to the ability to be weight bearing. There exist numerous situations in which it is desirable to have an implant that both aids in the re-growth of the bone at the implant site while also providing structural support, which are so-called structural implants. However, not all structural implants have the properties, such as compression resistance, necessary for certain applications. 
     Accordingly, it is desirable to provide an osteoimplant that provides structural capabilities, yet which provides superior osteoinductive, osteoconductive and re-absorption properties. 
     SUMMARY 
     In a particular embodiment, an osteoimplant includes a plurality of partially demineralized fibers. Each fiber has an elongated, thin body having a length of about 1 centimeter to about 3 centimeters. The plurality of fibers engage to establish a matrix of material. 
     In an embodiment, a method of making an osteoimplant is provided. The method includes partially demineralizing a bone to form a plurality of fibers, wherein each fiber comprises an elongated, thin body having a length of about 1 centimeter to about 3 centimeters; and forming the plurality of partially demineralized fibers into a fiber matrix. 
    
    
     DETAILED DESCRIPTION 
     A matrix material is disclosed that can be used as an osteoimplant. In a particular embodiment, the matrix material includes a plurality of fibers. Typically, each fiber has an elongated, thin body. In an embodiment, the plurality of fibers engage to form the matrix material. In a particular embodiment, the plurality of fibers have a length of about 1 centimeters to about 3 centimeters, such as about 1 centimeters to about 2 centimeters. The length of the fibers enables the matrix material to form and, in an exemplary embodiment, the length of the fibers are spatially arranged in a random-orientation. In particular, the length and random-orientation of the plurality of fibers enable the formation of an osteoimplant with desirable physical and mechanical properties. For instance, the length of the fibers and random-orientation is advantageous to form a superior osteoimplant that is compression resistant, has a desirable degradation rate, and is osteoinductive. “Osteoinductive” as used here refers to fibers that promote bone growth throughout the internal structure of the implant. 
     In an embodiment, the source of the fibers can be allogenic, xenogenic, autogenic, recombinant, or any combination thereof. In a particular embodiment, the plurality of fibers are obtained from an allogenic source such as, for instance, an allograft bone segment. Any allograft bone segment is appropriate that may provide fibers of the length described above. In an exemplary embodiment, the allograft bone segment may be derived from long bone sites such as the humerus, radius, ulna, femur, tibia, fibula, the bones of the hands or feet including the metacarpals, metatarsals, or phalanges, or bones from the spine, pelvis or other location. In a particular embodiment, the allograft bone segment can be machined into strips. In another embodiment, the bone segment is partially demineralized and then the fibers are machined from the partially demineralized allograft bone segment. Any reasonable method is envisioned to machine the allograft bone segment. The strips may be of any length to provide fibers having a length as described above. 
     In an embodiment, the allograft bone strips or allograft bone segment are partially demineralized. The term “partial demineralization” means that from about 5% to about 90% of the original mineral content of the bone segment has been removed. The amount of demineralization of the bone segment typically depends upon the desired properties of the final osteoimplant. In a particular embodiment, the partial demineralization removes about 20% to about 90%, such as about 30% to about 90%, or even about 40% to about 90% of the original mineral content from the allograft strips. The partial demineralization provides a corresponding osteoinductive matrix that has greater compression resistance than a fully demineralized fiber matrix. In a particular embodiment, the osteoimplant of the present invention is free of any fully demineralized fibers or particles. 
     Methods that provide for the partial demineralization of bone segment are known, and broadly involve chemically processing the bone with hydrochloric acid, chelating agents, electrolysis or performing other treatments to remove all or a portion of the minerals contained within the natural bone, leaving behind fibers having the length as defined above which form into the randomly-orientated matrix. In an embodiment, the partially demineralized fibers may be entangled in the random-orientation by any reasonable means. In an example, the partially demineralized fibers may be mechanically entangled. 
     In an exemplary embodiment, the fibers are chemically crosslinked after partial demineralization. In a particular embodiment, the chemical crosslinking both stiffens and bonds the fibers together. Accordingly, the use of a chemical crosslinker may further increase the compression resistance of the resulting osteoimplant. Any reasonable chemical crosslinker may be used to crosslink the fibers. In a particular embodiment, the cross-linking agent can be glutaraldehyde, genipin, formaldehyde, 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide/N-hydroxysuccinimide (EDC/NHS), or any combination thereof. Further, the cross-linking agent can be another protein cross-linking agent. 
     In an embodiment, any number of additives may be included within the matrix. Any reasonable additive may be included that can be envisioned for an osteoimplant. For example, the additives can include radiocontrast media, drugs, cellular matters, biological factors, or any combination thereof. In a particular embodiment, the drugs can include, for example, antibiotics, analgesics, anti-inflammatory drugs, anti-TNF-alpha, steroids, or any combination thereof. Further, the cellular matters can include, for example, bone marrow derived stem cells, lipo derived stem cells, or any combination thereof. The biological factor can include, for example, bone morphogenetic protein (BMP), growth differentiation factor (GDF), cartilage-derived morphogenetic protein (CDMP), platelet derived growth factor (PDGF), insulin-like growth factor (IGF), LIM mineralization protein, fibroblast growth factor (FGF), osteoblast growth factor, or any combination thereof. The additives can also include additives to promote matrix formation. Additives may improve protein retention, reduce protein degradation, promote protein folding, promote water binding, promote protein-to-protein interaction, promote water immobilization, or any combination thereof. Additionally, the additives can include polysaccharides such as, for example, proteoglycans, hyaluronic acid, or combination thereof, which can attract or bind water to increase hydration of the osteoimplant site. Further additives can include osteoinductive agents. In a particular embodiment, the osteoinductive agents have bone morphogenic protein (BMP) binding capability to partially demineralized fibers, minerals, collagen, and the like. In an embodiment, the additives include demineralized bone matrix (DBM particles), ceramic particles, or combinations thereof. Any reasonable means or methods can be used to include the additive within the matrix. 
     In an embodiment, the matrix may be “remineralized” to precipitate mineral back onto the partially demineralized fibers. Any reasonable method may be employed to remineralize the matrix. For instance, a mineral bath can be used to provide precipitation of mineral back onto the partially demineralized fibers. The mineral and concentration thereof to remineralize the matrix can be determined based on the properties desired. In an embodiment, any appropriate mineral may be envisioned that increases the matrix stiffness, increases the osteoconductivity of the partially demineralized fibers, or combination thereof. In an exemplary embodiment, the crosslinked matrix is placed into a mineral bath of calcium salts, silicate, or combination thereof. 
     Once the matrix of partially demineralized fibers has been provided, the matrix may be impregnated with a slurry to provide an open porous structure throughout an internal structure of the matrix. In an embodiment, the slurry may include collagen, or any other natural or synthetic polymer envisioned. For instance, the slurry may include chitosan, hyaluronic acid, alginate, gelatin, silk, elastin, polylactic and/or lactic acid, the like, and combinations thereof. In an embodiment, the collagen may be in a solution of any reasonable concentration and particle/fiber size to provide the open porous structure of collagen throughout the internal structure of the matrix. For instance, the open porous structure creates an increase of the surface area for cell attachment and new osteoid formation once the matrix is placed at the site of the osteoimplant. Any reasonable solution may be used for the slurry. In a particular embodiment, water or a saline solution, for example, may be used to form the slurry. Materials which are sticky in texture may also assist in the adherence of the collagen to the matrix. 
     Any reasonable method may be employed to impregnate the matrix with the slurry. This slurry may be coated over the matrix or the matrix may be submersed partially or wholly into the slurry. The matrix may optionally be vibrated, rotated, centrifuged, or combination thereof to encourage the slurry to migrate into the matrix. In an embodiment, it may be desirable to subject the matrix to at least a mild vacuum to partially or wholly evacuate the air from the matrix. In an embodiment, the slurry further includes any reasonable ceramic or bone particles that have osteoconductivity properties. Exemplary ceramic particles include calcium phosphates, tricalcium phosphate, hydroxyapatite, silicate containing ceramics, and combinations thereof. 
     In an embodiment, the addition of the slurry to the matrix is followed by freeze-drying of the slurry in the matrix. Typical freeze-drying is achieved through the use of standard commercial freeze-drying equipment. In a particular embodiment, the freeze-drying of the collagen slurry in the matrix facilitates the formation of a porous structure throughout the internal structure of the matrix. The pores formed through the internal structure of the matrix may be of any reasonable size to facilitate cell attachment and new osteoid formation when the matrix is placed at the site of the osteoimplant. In an embodiment, the allograft fiber matrix can have pores of about 1.0 to about 5.0 mm diameter in size. In an embodiment, the addition of the collagen slurry provides a collagen matrix with pores large enough to allow cell migration in, such as having pores greater than about 0.01 mm diameter. In a particular embodiment, the collagen slurry after freeze drying can have pores about 0.01 mm to about 3.0 mm diameter in size. 
     The formation of the osteoimplant further includes cutting the matrix material into the final desired shape. The desired shape is dependent upon the site of implantation. In an embodiment, the osteoimplant may be pre-shaped for a specific target region or may be provided in a standard shape that may be later tailored by the physician for the particular requirements of the implant site. Any suitable method may be used to shape the osteoimplant and may be performed before or after the matrix is formed. Typically, the osteoimplant may be cut with any reasonable medical or surgical tool such as a saw, file, blade, and the like. 
     Processing of the matrix may be performed under aseptic conditions such that the final osteoimplant is sterile and does not require a terminal sterilization procedure. Alternatively, the matrix may be processed under less rigorous conditions and terminal sterilization is used to achieve sterility. Various methods of terminal sterilization may be used (such as gamma or electron beam irradiation, ethylene oxide, etc.), but should be controlled to ensure the final osteoimplant maintains appropriate biological characteristics for supporting bone growth. 
     Generally, the matrix, including the partially demineralized fibers and optional collagen and additives form the osteoimplant. The amount of partial demineralization and any optional additives may be chosen depending upon the properties desired for the osteoimplant. In some embodiments, the matrix consists essentially of the partially demineralized fibers as described above. As used herein, the phrase “consists essentially of” used in connection with the matrix of the osteoimplant precludes the presence of materials that affect the basic and novel characteristics of the osteoimplant, although, various additives as described above, such as chemical crosslinkers, collagen, and the above discussed additives, may be used in the osteoimplant. 
     It is expected that the matrix may be used as an osteoimplant that will have utility in a diverse array of procedures where bone grafting is desired. Exemplary procedures include posterolateral spinal fusion, interbody spine fusion, fracture repair, bone cyst filling, periodontal, cranial, containment of autograft, maxillofacial, and other procedures where bone grafting is desirable. In an embodiment, the osteoimplant may be used for long bone segmental defects, alveolar bone ridge grafting, repairing calvarial bone defects, and the like. 
     Once formed into a matrix, the matrix exhibits mechanical properties that advantageously enhance the performance of the osteoimplant formed of the matrix. In particular, the osteoimplant may exhibit desirable mechanical properties, such as compression resistance. In an exemplary embodiment, the hydrated matrix exhibits a compression resistance of at least about 2 MPa, for example, measured using standard compression test methods. In particular, the compression resistance may be at least about 5 MPa, such as at least about 10 MPa, or even at least about 15 MPa. In a particular embodiment, the compression resistance provides an osteoimplant that withstands drilling during a surgical procedure. For instance, any type of screws, spikes, and the like may be used to fasten the osteoimplant within the implant site. 
     In addition, the osteoimplant may be evaluated for performance in producing characteristics desirable for the osteoimplant such as, for example, the matrix retaining its shape and structure for several weeks after implantation. In an exemplary embodiment, the matrix exhibits a degradation rate of at least about 20% six months after implantation. In particular, the degradation rate may be at least about 30% six months after implantation, such as at least about 40% six months after implantation, or even at least about 50% six months after implantation. The degradation rate is desirable for providing structural integrity at the implantation site while bone growth occurs throughout the internal structure of the matrix. 
     Further, the osteoimplant is osteoinductive and is an ideal bone grafting matrix. For instance, bone growth replaces at least about 20% of the implant after six months implantation, such as at least about 30% of the implant after six months implantation. In a particular embodiment, the osteoimplant is osteoinductive, compression resistant, and has an exemplary degradation rate. For instance, the osteoinductive osteoimplant has a compression resistance of at least about 2 MPa, a degradation rate of at least about 20% six months after implantation, and bone growth replacing at least about 20% of the implant after six months implantation. Accordingly, the osteoinductive osteoimplant is highly compression resistant, retains its shape and structure, and promotes bone growth throughout the matrix. 
     The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments that fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.