WO2006088866A2

WO2006088866A2 - Biodegradable load-bearing carrier for bone regeneration

Info

Publication number: WO2006088866A2
Application number: PCT/US2006/005169
Authority: WO
Inventors: Tien-Min Gabriel Chu; Rena Lorraine Stewart
Original assignee: Indiana University Research And Technology Corporation
Priority date: 2005-02-14
Filing date: 2006-02-14
Publication date: 2006-08-24
Also published as: WO2006088866A3

Abstract

Implants for facilitating bone healing are provided. The implants comprise an osteogenic material and a structural carrier formed from a biodegradable material, wherein the structural carrier contains the osteogenic material.

Description

BIODEGRADABLE LOAD-BEARING CARRIER FOR BONE REGENERATION

PRIORITY

This application claims priority to United States Provisional Patent Application Serial

No. 60/652,537, filed February 14, 2005, entitled BIODEGRADABLE LOAD-BEARING CARRIER FOR BONE REGENERATION, and incorporated by reference herein.

BACKGROUND

Segmental defects of bone are often difficult to manage and often require multiple-phase surgery to achieve adequate union and function (Johnson, Urist et al. 1988). The causes for these large defects include the removal of tumors, massive trauma, congenital malformations, or nonunion of fractures (Gao, Lindholm et al. 1996). Most benign tumors of bone, including osteoma, chondroma, osteochondroma, and giant-cell tumors can be left alone as long as no discomfort, disability, or unsightliness occurs. In the event that removal is necessary, the stage of the tumor generally determines the surgical margins of removal, which in turn determines the magnitude of the defect. Treatment for malignant tumors such as osteosarcoma, Ewing's tumors, and metastatic tumors often include initially introducing cytotoxic drugs for chemotherapy prior to tumor removal surgery. The chemotherapy allows the prevention of spreading of the tumor so that only the segment of bone with the tumor itself may be removed as an alternative to amputation. In the event of an extreme high-energy trauma to a bone, a segmental defect may occur due to the large extent of fragmentation of the bone. To ensure union of the two ends of the defect, a support is needed for cells to proliferate across the gap.

Another common cause of segmental defects is that of nonunion. Nonunion occurs when there is either excessive motion, gap at the fracture site, poor nutrition, or significant comminution. A hypertrophic nonunion occurs when increased bone formation leads to an adequate healing process with lack of mechanical stability. Atrophic nonunion, however, occurs when bony resorption at the fracture site and vascular compromise leads to fibrous tissue occupying the fracture gap. When a nonunion has a lack of callus due to avascularity, appropriate immobilization, removal of the atrophic bone, and grafting of bone substitute material may be needed to ensure proper healing.

A. Current Methods of Regenerating Segmental Defects

Current treatment options to regenerate segmental defects include autografts, allografts, and distraction osteogenesis. When the above treatments options fail, alternative treatment may involve serious consequences of leg shortening or amputation. Bone replacement grafts taken from the patient under treatment are known as autografts. Both cortical and cancellous bones may be used as autografts. Some of the main advantages of autografts are that they provide a structural framework for bone formation and supply factors that stimulate bone formation. Further, autografts tend to incorporate into the surrounding tissue more quickly than allografts. Disadvantages to autografts include the limited number of places from which a graft can be taken, as well as the potential of donor site morbidity.

An alternative to autografts is allografts — bone grafts obtained from a donor other than the patient being treated. While allografts pose no risk of donor site morbidity, allografts do introduce the possibility of the disease transmission. Further, allografts include the potential of tissue rejection or a negative immune response, both of which are very unlikely in using an autograft. A decrease in the immunogenicity of bone allografts may result in better healing and mechanical strength, and while histocompatibility matching has been examined, it has not been clinically proven. An effective way of reducing the immunogenicity of allografts is to alter the individual grafts. Some methods of altering the allografts to prevent transmission of disease include sterile harvesting techniques, deep freezing, low level radiation, and freeze drying. While these techniques reduce the likelihood of disease transmission, they can reduce the osteoconductivity of allografts. Therefore, a method of conducting segmental defect repairs that does not have or greatly reduces the risks of disease transmission and negative immune response would be greatly appreciated in the art.

Distraction osteogenesis is yet another method of segmental defect repairs is currently used in the art. Distraction osteogenesis is the process by which an osteotomy is performed on a bone and the two ends are gradually separated to allow the mechanical induction of new bone growth in between the two bone segments. Distraction osteogenesis is a three part process, consisting of: latency, distraction, and consolidation. The latency period is the initial inflammatory phase of fracture healing, typically lasting from three to ten days. The periodic lengthening that follows is known as the distraction phase. The optimum distraction cycle is 1 mm/day in four increments of 0.25mm throughout the day. After the prescribed amount of lengthening has been established, the last phase of consolidation can occur, which is the stabilization of the bone. This final phase tends to last the same amount of time as the distraction phase. While distraction osteogenesis reduces the chance of cellular morbitity in the patient and greatly reduces the chance of disease transmission that occurs in allografts, distraction osteogenesis introduces the chance of infection caused by external fixation devices. Common infections from the external fixation devices include pin track infections and infections from loosening of the fixation pins. Another drawback of distraction osteogenesis is the length of time it takes for the process to be completed. Therefore, a method of conducting segmental defect repairs that does not have or greatly reduces the risks infection and reduces the time period to complete the repair would be greatly appreciated in the art. In addition to the current methods of regenerating segmental defects discussed above, tests have been conducted to used synthetic scaffolds or carriers along with demineralized bone matrix ("DBM"). DBM has been shown to stimulate hyaluronic acid accumulation and alkaline phosphatase activity, thereby increasing the rate of bone formation. DBM comprises type 1 collagen, fibronectin, BSP, and BMP -2, 4, and 7, and may be produced from human bone chips or obtained commercially, and has often been used as an adjunct factor to facilitate fracture healing. While DBM and other osteogenic compounds such as bone morphogenic protein (BMP) have been used in conjunction with marrow aspirates or allograft to facilitate bone healing in segmental defect repair or in spine fusion, DBM falls short in regenerating segmental defects. Specifically, DBM lacks mechanical properties and is easily displaced in the large, unconfined space commonly seen in segmental defects, making it a poor choice for any segmental defect that occurs on a load bearing joint.

Commercial products, such as Grafton^® by Osteotech, Inc., AlloMatrix^® by Wright Medical Tech, attempt to address this issue by combining DBM with various molecular carriers such as glycerol, hyaluronic acid, procine gelatin, calcium sulfate, and Pluronic-F127 (an ethylene oxide/propylene oxide block copolymer) However, tests have shown that the lack of mechanical integrity of DBM, even when using these molecular carriers. In order to make up for this drawback, some have used DBM supported with additional non-degradable metallic hardware. For example, DBM and bone chips have been used with a titanium mesh cage to fit outside of the treated regeneration site to provide mechanical support to the DBM implant site. However, the use of such permanent metallic hardware can cause immune response in the patient. Therefore, a method of conducting segmental defect repairs that does not have or greatly reduces the use of permanent SUMMARY OF THE INVENTION

The use of DBM, BMP, or other osteogenic compounds in treating segmental defects is combined with a high strength, load-bearing, and biodegradable carrier. When first implanted, the load-bearing carrier provides an initial biomechanically stable environment for bone formation across the bone scaffold junction. The osteogenic compound released from the biodegradable carrier then provides an osteoinductive enviromnent to attract stem cells and progenitor cells to migrate to, populate, and mineralize on the scaffold surface, illustratively to form a continuous bridge between the proximal and distal segments of the bone. Finally, the degradable carrier degrades and allow bone to fill in the space left by carrier and continue to remodel to the physiological geometry and mechanical properties.

Thus, in one aspect of the present invention an implant for facilitating bone healing is provided, the implant comprising an osteogenic material, and a structural carrier formed from a biodegradable material, the structural carrier comprising a body and having at least one recess therein, wherein the structural carrier contains the osteogenic material in the recess. In various non-limiting illustrative embodiments, the osteogenic material may be selected from the group consisting of demineralized bone matrix and bone morphogenic protein; the body may form generally cylindrical shape; the body may further defines a plurality of additional recesses; at least one of the additional recesses may be sized to receive a screw for plate fixation; a second osteogenic material may be provided in one of the additional recesses, optionally wherein the osteogenic material and the second osteogenic material are different, optionally wherein the first osteogenic material is provided in a first time release material having a first time release profile, the second osteogenic material is provided in a second time release material having a second different time release profile, and optionally wherein the first osteogenic material is VEGF and the second osteogenic material is BMP, and the first time release profile is a faster time release profile than the second time release profile; at least one of the recesses may comprises an antibiotic; the osteogenic material may be absorbed into an amount of dicalcium phosphate dihydrate (DCPD) cement that has been provided in the recess, the structural carrier may possess sufficient mechanical strength to be load bearing; and the biodegradable material may be poly(caprolacton) trimethacrylate /tricalcium phosphate ("PCLTMA/TCP")-

In another aspect of the invention an implant for facilitating bone healing is provided comprising an osteogenic material, and a structural carrier formed from a biodegradable material, the structural carrier comprising a wall extending from a first end to a second end and defining a central channel extending from an opening in the first end to an opening in the second end, wherein the structural carrier contains the osteogenic material. In various non-limiting illustrative embodiments the osteogenic material may be selected from the group consisting of demineralized bone matrix and bone morphogenic protein; the wall may form generally cylindrical shape; the osteogenic material may be provided in the central channel; the wall may further define a plurality of windows extending from the central channel through the wall to an exterior surface of the wall; the osteogenic material may be provided in one or more of the windows, optionally wherein the osteogenic material is provided in one of the windows and a second osteogenic material is provided in another of the windows, wherein the osteogenic material and the second osteogenic material are different; at least one of the windows may comprise an antibiotic; the osteogenic material may be absorbed into an amount of dicalcium phosphate dihydrate (DCPD) cement that has been provided in one of the windows; the structural carrier may possess sufficient mechanical strength to be load bearing; and the biodegradable material may be PCLTMA/TCP.

In yet another aspect of this invention methods for repairing a bone defect are provided. The methods comprise the steps of placing a structural implant comprising an osteogenic material into the defect site, and fixing the implant to surrounding bone tissue. The methods optionally may include the step of leaving the implant in place and allowing the implant to degrade. Optionally, the fixing step may comprise using an intramedullary pin or may comprise using a plate and at least one screw.

Additional features of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments.

BRIEF DESCRIP TION OF THE DRAWINGS

Fig. 1 is a perspective view of one embodiment of an osteogenic compound carrier of the present invention.

Fig. 2. is a cross-sectional view of the osteogenic compound carrier of Fig. 1.

Fig. 3 is a chart showing the compressive strength of PPF/NVP/TCP and PCLTMA/TCP after in vitro degradation in PBS.

Figs. 4a-h are a series of X-rays of femurs, each of which has had an osteogenic compound carrier of Fig. 1 implanted therein. Figs. 4a-d are X-rays of plain carrier at 1, 3, 6, and 9 weeks (Sl, S3, S6, S9) and Figs. 4e-h are X-rays of carrier loaded with BMP at 1, 3, 6, and 9 weeks (Bl, B3, B6, B9).

Fig. 5 is a chart showing the X-ray scores of implant sites treated with BMP and non- BMP containing carrier at 1, 3, 6, and 9 weeks. Fig. 6 is a chart showing normalized cross section area (CSA), normalized volumetric bone mineral density (vBMD), normalized pQCT bone mineral content (BMC) and normalized DXA bone mineral content (BMC) of the femurs treated with BMP, non-BMP containing carriers and DBM carrier at 6 weeks.

DETAILED DESCRIPTION

A biodegradable, load-bearing carrier for delivery of an osteogenic compound illustratively is made from high strength biodegradable composites. When first implanted, the carrier provides an initial biomechanically stable environment for bone formation across the interface between bone and carrier. The osteogenic compound-carrying biodegradable carrier then provides an osteoinductive environment to attract stem cells and progenitor cells to migrate to, populate, and mineralize on the carrier surface, illustratively to form a continuous bridge between the proximal and distal segments of the bone. Finally, the degradable carrier degrades and allows bone to fill in the space left by carrier. The bone will then continue to remodel to physiological geometry and mechanical properties.

As used herein, the term "carrier" or "structural carrier" refers to this high strength structural carrier to be used in conjunction with an osteogenic compound such as DBM. The DBM may be supplied in a molecule carrier (i.e. hyaluronic acid, glycerol, calcium sulfate hemihydrate, etc). When referring to such molecule carrier, the term "molecule carrier" is used. While many of the examples use DBM, it is understood that other materials that provide for an osteoinductive environment may be used as well. Such materials include, but are not limited to, bone morphogenic protein (BMP) (including bone morphogenetic protein-2, bone morphogenetic protein-4, and bone morphogenetic protein-7), tissue growth factor beta (TGF-β), platelet- derived growth factor (PDGF), fibroblast growth factor (FGF), insulin-like growth factor, and vascular endothelial growth factor (VEGF). Moreover, the substances carried by the structural carrier is not limited to proteins. The structural carrier can include antibiotics or antiinflammatory drugs. Suitable antibiotics include, but are not limited to, benzylpenicillin, cefazolin, clindamycin, vancomycin, nafcillin, and ciprofloxacin. The structural carrier can also include other substances to promote an osteoinductive environment.

Figs. 1 and 2 illustrate one embodiment of the present invention, hi this illustrative embodiment, a structural carrier 10 is a cylindrically-shaped structure. A wall 12 forms the cylindrical shape, defining body 18 and central channel 28. Central channel 28 extends through the structural carrier 10, from a first opening 24 at a first end 23 to a second opening 26 at a second end 25. A plurality of windows 20 are provided in wall 12, extending from an outer surface 14 of wall 12 to an inner surface 16 of wall 12. The windows 20 communicate with central channel 28.

An osteogenic material 30 may be provided in one or more of the windows 20, and/or in the central channel 28. Optionally, one osteogenic material may be placed in one of the windows, and another placed in another window. The various osteogenic materials may have different time release profiles, to provide for an osteoinductive environment over a sustained period of time.

The illustrative structural carrier 10 is shown as a cylindrically-shaped tube having a generally circular cross-section. As such, the illustrative structural carrier is well suited for implantation in a large defect of a long bone. Other shapes may be better suited for other defects. For example, structural carriers having generally ovoid or trapezoidal cross-sections, in the shape of spinal cages or similar shapes, may be better suited for use in spinal surgery. While it is desirable for the wall to form a closed shape, due to the presence of the windows, it is understood that the cross-section of wall 12 at any one location along the structural carrier may not provide a closed shape. Further, depending on the particular application, the wall may not completely enclose the central channel. For example, if some native bone tissue remains in the space, it may be desirable to provide a slot or groove along the structural carrier to accommodate the remaining bone. Other shapes are contemplated within the scope of this invention. The requirements for the shape of the structural carrier are to provide suitable structural support and to retain the osteogenic material at the site of the defect for a period of time.

The device of Figs. 1-2 is well suited for intramedullary pin fixation. However, the device of Figs. 1-2 could be used with plates and screws or any other fixation device, as are known in the art. Any number of windows 20, may be provided in structural carrier 10. If plates and screws are used for fixation, optionally, one or more of the windows 20 may be sized to receive screws. Alternatively, screws may be tapped directly into wall 12. Additionally, if fixation other than an intramedullary pin is used, then it is understood that central channel 28 would not be necessary. In such an embodiment, windows 20 could extend all the way through body 18 or each window could simply provide a recess for receiving the osteogenic material 30.

The body 18 of the structural carrier is designed to serve as a temporary structural support for immediate load-bearing after implantation. The body of the device can be manufactured from any biodegradable polymers, including thermal plastic polymers or thermal setting polymers, as long as they possess sufficient mechanical strength of the intended application. The range of appropriate mechanical property can be obtained through in vivo implantation and in vitro degradation study. Illustratively, the compressive strength of the device should be at least 45% of that of the bone segment that the device is replacing in the first three weeks of implantation. In one embodiment, a device with compressive strength of 23 MPa was sufficient to allow bone regeneration in gap left by a bone segment of 53 MPa in compressive strength.

When using thermal setting polymer, in one illustrative embodiment, the device can be manufactured through an indirect casting technique, as described in U.S. Patent Application No. 10/178,292, herein incorporated by reference, although it is understood that other manufacturing techniques are within the scope of this invention. Illustrative choices for the thermal setting biodegradable polymer include, for example, poly(propylene fumarate)-co-vinylperrolidinone, or poly(caprolacton)-trimethacrylate. When using thermal plastic polymers, illustratively the device can be manufactured through standard injection molding process. The polymer may contain 10-50 volume percent of ceramic fillers to increase the strength and reduce the amount of polymers. The ceramic filler illustratively is a calcium phosphate based material such as tricalcium phosphate or hydroxyapatite. Such materials are found to facilitate bone formation and are incorporated into human bone tissue without causing inflammation reaction when implanted. The ceramic filler can be incorporated into the thermal setting polymer at room temperature before polymerization reaction with or without the use of appropriate surfactants. The surfactant can be non-ionic, anionic, or cationic. The ceramic filler can be incorporated into the thermal plastic polymer at elevated temperature, preferably at the melting temperature of the polymer. In one illustrative embodiment, the thermal plastic biodegradable polymer powder, for example, poly-lactic-acid-co-poly-glycolic-acid, can be blended with tricalcium phosphate powder and heated to 160° C to allow the polymer powder to melt and bond the ceramic powder together. The molten polymer/ceramic is then molded in die into desired device shape under pressure, illustratively between 10-1,000 psi.

There are various ways for the osteogenic material such as demineralized bone matrix to be incorporated into the device. The space in central channel provides space for easy DBM incorporation during surgery. This is particularly suitable when the osteogenic compound is provided as a gel or paste. The gel or paste can also be inserted into one or more of the windows. An alternative way to provide the osteogenic substance is to fill one or more of the side windows with a delivery medium such as dicalcium phosphate dihydrate (DCPD) cement and then allow the osteogenic material to be absorbed onto the cement. The DCPD cement is a precipitation product from mixture of equi-molar of mono calcium phosphate monohydrate (MCPM) and tricalcium phosphate (TCP) with appropriate amount of water, preferably in the range of a liquid to powder ratio of 0.5 to 1.5. Various osteogenic compounds are available as a liquid and the liquid may be absorbed easily into the DCPD cement. Other examples of a delivery medium include polyvinyl alcohol hydrogel, alginate, or any degradable polymer used in drug delivery device. The release kinetics of the osteogenic component can be controlled by the releasing medium. Also, since the structural carrier can be provided with multiple windows and the protein releasing component can be incorporated into each window independently, there can be multiple factors loaded on the same device. The time release kinetics of the multiple factors can be controlled to mimic the protein cascade in nature wound healing. Thus, multiple factors, each with its own releasing kinetics, may be incorporated onto the structural carrier. In one example, a structural carrier is provided with one window loaded with VEGF in a degradable polymer that will provide early release to encourage blood vessel formation, and with other windows loaded with BMP for later release to facilitate bone formation. Optionally, another window can be loaded with antibiotic with early releasing profile to eliminate or prevent infection, while one or more of the other windows can be loaded with proteins to facilitate bone regeneration. The design of the drug releasing compartment is thus highly versatile.

Optionally, the structural carrier can be used to carry cells, illustratively stem cells. Some patients, illustratively elderly patients lack the necessary stem cell and progenitor cells to respond to the osteoinductive substance incorporated in the carrier. A possibility is to supply them with the stem cells that they need for regeneration. Current technology allows one to isolate mesenchymal stem cells from bone marrow which can be expanded and implanted back to patients. Due to the lack in mechanical rigidity in currently available scaffolds, these therapies typically require culturing cells in bioreactors for extended amount of time to allow primitive bone and cartilage to grow before they can be implanted. Isolated mesenchymal cells or other stem or progenitor cells can be encapsulated in hydrogels or in other materials and incorporated into the central channel or windows of the structural carrier. The structural carrier provides the protective environment for the cells to differentiate and grow into primitive bone and/or cartilage. The cells in the channels can serve as a supplement cell source to respond to the osteogenic factors also provided by the carrier. Reducing or eliminating the need for extended culturing in bioreactor can potentially reduce the risk of infections, reduce or eliminate the cost for cell culturing, and reduce or eliminate the waiting period for cell cultures before implantation.

When the osteogenic material is incorporated into the central channel 28, the central channel 28 functions as a reservoir and restricts movement and premature loss of the material due to tissue movement or irrigation after implantation. Furthermore, since the openings 24, 26 of the central channel will be in connect with the marrow cavity after implantation, this configuration allows for a guided diffusion direction for drugs to contact with the progenitor cells in the marrow cavity of the adjacent distal and proximal segment of the fractured bone. When drugs are incorporated into the windows 20, the windows 20 of the structural carrier 10 allow drugs to diffuse through the openings and to attract progenitor cells from the periosteum on the adjacent bone segments. The external and internal surfaces of the structural carrier provide the attachment surfaces for incoming progenitor cells and osteoblasts to lay down extracellular matrix and initiate the mineralization process. Finally, the configuration of the carrier will allow the use of intramedullary pin fixation. The intramedullary fixation technique is less traumatic to the periosteum compared to plate fixation, causes less soft tissue envelop disruption, and allows for load sharing and better biomechanical stimulation during healing. However, it is understood that plate fixation may be preferred in certain patients, and plate fixation is within the scope of this invention.

EXAMPLE 1 : Degradation strength of PPF/NVP/TCP and PCLTMA/TCP

Poly(propylene fumarate) synthesized from diethyl fumarate and ethylene glycol was provided by Prof. Mikos at Rice University. The synthesized PPF has a Mn 1750 g/mol and Pl = 1.5. A thermal-curable PPF/TCP suspension was prepared by mixing PPF, N- vinyl pyrrolidinone, and TCP at a weight ratio of 1 :0.75:0.66. PCL300TMA and PCL900TMA were synthesized by Dr. Xie. PCLTMA/TCP slurry was prepared by adding PCL300TMA, PCLTMA900TMA, and TCP in a weight ratio of 2.625:0.875:1.5. The geometry of the BMP- carrier was first designed using commercial computer aided design software (Rhinos Software). The tube shaped structural carrier had an outer diameter of 4 mm and inner diameter of 2 mm, with four side windows of 800 micrometers in diameter on the side walls. The negative of the carrier design was then generated with Boolean operation on the computer and was used as the mold design to make the casting mold. The 3D mold design was first sliced into many 2D layers of 12.5 μm thickness by commercial software (SolidWorks^®, Solidscape Inc. NH). The processed file was then transferred to the 3-D InkJet Printing Machine (T66, Solidscape Inc. NH) and wax molds were built according to the sliced files. PPF/NVP/TCP composite slurry and PCLTMA/TCP slurry were combined with 0.5% Benzoyl Peroxide (thermal initiator) and 10 μl of dimethyl p-toluidine (accelerator) and cast into the wax mold. The slurry was allowed to solidify in air for one hour. The wax mold in the now hardened slurry was removed by acetone to reveal the PPF/NVPITCP and PCLTMA/TCP carriers. The structural carriers were immersed in physiologically buffered solution (PBS) for one hour, one (1) week, three (3) weeks, and six (6) weeks, and then tested on the material testing machine in uniaxial compression setting with a loading rate of 1 mm/min. After degradation, the strength of PPF/NVP/TCP was found to reduce from 23 MPa to 12 MPa and the compressive strength of PCLTMA/TCP was found to remain in the range between 7.25 to 12.35 MPa for the first six weeks (Fig. 3).

EXAMPLE 2: Long-term feasibility study of carrier as BMP carrier

In this study, PPF/NVP/TCP carriers were made as described above. The side windows were filled with dicalcium phosphate dihydrate (DCPD) cement. Ten micrograms of bone morphogenetic protein (BMP -2, generously provided by Wyeth Co.) was added aseptically to the porous DCPD cement.

Eight Long Evans rats of 450-550 grams were used. Five rats were implanted with BMP- containing carrier and three rats were implanted with non-BMP-containing carriers. Skin incision was made on the lateral aspect of the right thigh, followed by a blunt dissection between quadriceps to reach the right femur. A 5 mm osteotomy was created by a rotating cutting blade under copious irrigation and the carrier was placed in the gap. After implantation, the carrier was then fixed with a 1.25 mm diameter K-wire as intramedullary pin. The K-wire was drilled into the trochlear groove between the lateral and medial condyles to reach the femur marrow cavity. The wire was then allowed to pass through the central channel of the structural carrier to attach to the proximal end of the femur marrow cavity. After thorough irrigation of the operation field, the muscle layers were closed in layers with 3-0 Vicryl sutures. Skin was closed with 3-0 Prolene. The study is now at its 10 week time point and the femurs will be retrieved at 15 weeks.

X-ray results ~ For this study, x-rays were taken at 1, 3, 6 and 9 weeks after implantation. The x-rays showed no bone formation for all carriers at 1 week after surgery. At 3 weeks, the x-rays showed that a continuous callus had formed and bridged across the distal and proximal segment of the femurs in the BMP -treated group. In the control group, though some cortical bone thickening and callus formation was noticed next to the carrier, callus did not bridge the gap. At 6 weeks, the callus bridge in the BMP-treated group showed signs of consolidation and further thickening of the cortex next to the carrier. In the control group, isolated radiopaque spots were noticed, but there was still no sign of callus bridging. Further thickening of the callus was seen in the nine week x-ray in the BMP group and some questionable union was seen in the control group.

Radiographic scores of 0, 1, and 2 were assigned by three independent reviewers with experimental groups and time points blinded to the reviewers; 0 indicated no callus formation, 1 indicated positive callus formation but no bridging across the gap and 2 indicated positive bridging across the gap. All samples in the BMP-containing group were found to reach a score of 2 (radiographic evidence of union) at six weeks, while the non-BMP-containing group has an average score of 1 even at 9 weeks (Fig. 4). This difference was statistically significant (p<0.05).

EXAMPLE 3: Short-term feasibility study of carrier as BMP carrier

In this study, PPF/NVP/TCP carriers were manufactured and BMP incorporated as described above. Eight Long Evans rats of 450-550 grams were used. The same surgical procedures were performed and four were implanted with BMP-containing carrier and four were implanted with non-BMP-containing carriers. The femurs were retrieved at 6 weeks.

Dual energy X-ray absorptiometry (DXA) results ~ AU femurs (BMP and non-BMP treated) were scanned by DXA using a PIXImus mouse densitometer (Lunar Corp., Madison, WI.) with ultra high resolution (0.18 x 0.18 mm/pixel). For scanning, bones were placed on their posterior surface on a soft tissue equivalent. A scanning window of 7.2 x 6 mm was used to enclose the 5 mm section of the implant site. Total mineral content in the scanned window was measured. Due to the limitation of the software, the contribution from tricalcium phosphate in the structural carrier was not excluded in the calculated total mineral contents in the scan. It is expected the contribution from the carrier will be constant from each specimen and will not alter the trend of the results. An averaged mineral content of 0.075 ± 0.015 g was found in segmental defect implanted with non-BMP containing carrier group, while a mineral content of 0.108 ± 0.003 g was found in the defects implanted with BMP-containing carriers, The mineral content in the BMP group was significantly higher (p<0.005) than the non-BMP group. The total mineral content of the treated femurs was then normalized by the mineral content of the contra lateral intact femur scanned with the same window size. The mineral content of the group with non- BMP carrier reached 84 ± 12% of that of the contra lateral side, while the BMP group reached 121 ± 10% of that of the contra lateral side. This difference was significant (p<0.005) (Fig. 5).

Peripheral computed tomography (pQCT) results — The treated femurs were assessed by peripheral computed tomography (pQCT) to determine implant site volumetric bone mineral density (vBMD; g/cm³), bone mineral content (BMC, mg/cm) and cross sectional area (CSA; mm²). Bones were fixed in a plastic tube and centered in the gantry of a Norland Stratec XCT Research SA+pQCT (Stratec Electronics, Pforzhiem, Germany). A 0.46 mm thick slice was taken at the center of the carrier as determined from the scout view. A 0.07 mm voxel size was used. Contouring mode 1 with a threshold of 400 mg/cm³ was used to separate bone from soft tissue. The non-BMP-containing carrier group had an averaged volumetric bone mineral density of 444.48 ± 18.17 mg/cm³. The BMP-containing carrier group had a volumetric bone mineral density of 473.98 ± 71.74 mg/cm³. The difference was not statistically significant (p>0.5). The non-BMP-containing carrier group had an averaged cross sectional area of 11.74 ± 5.31 mm². The BMP group had an averaged cross sectional area of 26.13 ± 3.87mm². This difference was statistically significant (p<0.005). The measurements were then normalized by that of the intact femurs in the contra lateral side. The femurs treated BMP containing carrier reached 180% in the cross section area compared to the contra lateral side, while non-BMP group had 85%. The femurs treated with BMP-containing carriers reached 94% in bone mineral content, while the non-BMP group reached only 40% (Fig. 6). The results show that BMP increases the cross sectional area of bone in the segmental defect, but not the mineral density. As a result, an increase in the total mineral content was found in the segmental defect in the BMP group. EXAMPLE 4: Feasibility of construct as DBM carrier

In this in vivo study, structural carriers were made from poly(caprolacton) trimethacrylate

/tricalcium phosphate (PCLTMA/TCP) composites carrier as described in Example 1. One Long Evans rat of 450 grams was used. Skin incision was made on the lateral aspect of the right thigh, a blunt dissection between quadriceps to reach the right femur. A 5 mm osteotomy was created by a rotating cutting blade under copious irrigation. Putty type demineralized bone matrix (Grafton^® DBM Putty, Osteotech, Inc. NJ) was used in this preliminary study. DBM putty of 0.25 ml was incorporated into the central channel of the PCLTMA/TCP carrier. The putty type DBM attached to the carrier well and, while the putty substantially filled the central channel, the putty showed very little displacement by pin insertion. After implantation, the structural carrier was fixed with a 1.25 mm diameter K- wire as the intramedullary pin and the animal was sutured as described above.

X-ray results ~ X-rays were taken at 1, 3, and 6 weeks after implantation. The x-rays show similar results as that of BMP-containing carrier. No bone formation was observed for all carriers at 1 week. At three weeks, a continuous callus has formed and bridged across the distal and proximal segments of the rat femur. This initial result shows union at 3 weeks with a DBM- loaded carrier, comparable to BMP-containing carriers.

DXA and pQCT results ~ The femur treated with DBM showed a normalized total mineral content of 123% in the scanned window. The total mineral content is in the range of that found for the BMP group (121%) and is 34% higher than that for the non-BMP carrier (84%). The DBM carrier had a normalized cross sectional area of 187%, in the same range as that for the BMP group (180%) and 134% larger than that in the non-BMP carrier (85%). The results indicate that DBM is capable of inducing a similar bone regeneration effect in these large segmental defects as BMP at the dose level studied in the present examples (Fig. 6).

Both PCLTMA/TCP and PPF/NVP/TCP structural carriers can provide biomechanical stability to segmental defect repair. Using the designed PCLTMA/TCP and PPF/NVP/TCP carriers with BMP and DBM is effective in inducing bone formation. There is radiographic evidence of bone bridging at 3 weeks and consolidation at 6 weeks in both the BMP groups and DBM group. The total mineral content and the cross-sectional bone area were both significantly higher in defects treated with BMP-containing carrier than the defects treated with non-BMP- containing carriers. The total mineral content and cross-sectional bone area in defects treated with DBM-containing carrier were similar to that of the defects treated with BMP-containing carriers.

Although the two biomaterials tested in the examples above both showed promising results, N-vinyl pyrrolidone, a component in the PPF/NVP/TCP composite was not degradable. For this reason, PCLTMA/TCP will be used as the carrier material for the following example.

The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.

All references cited herein are incorporated by reference as if fully set forth.

Claims

CLAIMSWhat is claimed is:

1. An implant for facilitating bone healing comprising a. a first osteogenic material, and b. a structural carrier formed from a biodegradable material, the structural carrier comprising a body and having at least one recess therein, wherein the structural carrier contains the first osteogenic material in the recess.

2. The implant of claim 1, wherein the first osteogenic material is selected from the group consisting of demineralized bone matrix and bone morphogenic protein.

3. The implant of claim 1, wherein the body forms a generally cylindrical shape.

4. The implant of of claim 1 , wherein the body further defines a plurality of additional recesses.

5. The implant of claim 4, wherein at least one of the additional recesses is sized to receive a screw.

6. The implant of claim 4, further comprising a second osteogenic material wherein the first osteogenic material and the second osteogenic material are different.

7. The implaint of claim 6, wherein the second osteogenic material is provided in one of the additional recesses.

8. The implant of claim 6, wherein the first osteogenic material is provided in a first time release material having a first time release profile, and the second osteogenic material is provided in a second time release material having a second time release profile differing from the first time release profile.

9. The implant of claim 8, wherein the first osteogenic material is a vascular endothelial growth factor and the second osteogenic material is a bone morphogenic protein, and wherein the first time release profile is a faster time release profile than the second time release profile.

10. The implant of claim 9, wherein at least one of the recesses comprises an antibiotic.

11. The implant of claim 10, wherein the first osteogenic material has been absorbed into an amount of dicalcium phosphate dihydrate cement that has been provided in the recess.

12. The implant of claim 11 , wherein the biodegradable material is poly(caprolacton) trimethacrylate /tricalcium phosphate.

13. ' An implant for facilitating bone healing comprising: a. a first osteogenic material, and b. a structural carrier formed from a biodegradable material, the structural carrier comprising a wall extending from a first end to a second end and defining a central channel extending from an opening in the first end to an opening in the second end, wherein the structural carrier contains the first osteogenic material.

14. The implant of claim 13, wherein the first osteogenic material is selected from the group consisting of demineralized bone matrix and bone morphogenic protein.

15. The implant of claim 13, wherein the wall forms a generally cylindrical shape.

16. The implant of claim 13, wherein the first osteogenic material is provided in the central channel.

17. The implant of claim 16, wherein the wall further defines a plurality of windows extending from the central channel through the wall to an exterior surface of the wall.

18. The implant of claim 17, wherein the first osteogenic material is provided in one or more of the windows, and the implant further comprises a second osteogenic material provided in another of the windows, wherein the osteogenic material and the second osteogenic material are different.

19. The implant of claim 19, further comprising cells provided in the central channel, and wherein the biodegradable material is poly(caprolacton) trimethacrylate /tricalcium phosphate.

20. An implant for facilitating bone healing comprising: a. a first time release material operable to release a vascular endothelial growth factor in a first time profile; b. a second time release material operable to release a bone morphogenic protein, and c. a structural carrier formed from poly(caprolacton) trimethacrylate /tricalcium phosphate, the structural carrier comprising a wall extending from a first end to a second end and defining a central channel extending from an opening in the first end to an opening in the second end, wherein the structural carrier contains the first time release material and the second time release material, and wherein the structural carrier contains an antibiotic.