Lumbar Interbody Fusion With Porous Biphasic Calcium Phosphate Enhanced By Recombinant Bone Morphogenetic Protein-2/Silk Fibroin Sustained-released Microsphere: An Experimental Study On Sheep Model

Object:To investigate the osteogenic efficacy of porous Biphasic Calcium Phosphateenhanced by Recombinant Bone Morphogenetic Protein-2/Silk Fibroin sustained-Releasedmicrosphere in a sheep lumbar interbody fusion model.Methods:The microspheres were prepared by a water-in-oil emulsion solvent diffusionmethod.And the β-sheet content of the microspheres was changed by the water-vaportreatment. Dissolution of the microspheres was modified thus the release properties ofthe SF/rhBMP-2microspheres was changed. The shapes of the microspheres wereobserved by scanning electron microscope(SEM). The concentration of rhBMP-2wasmeasured by ELISA at different time points in the phosphate buffer (PBS), calculate thecumulative release of rhBMP-2and microsphere drug loading rate in vitro.16healthy adult sheep were divided into two groups randomly. Anteroposterior andlateral films were routinely obtained preoperatively to ensure the lumbar spine werenormal sequence and normal bone structure.All sheep were operated on the leftextraperitoneal approach and intervertebral discs of L1-L2、L3-L4、L5-L6were exposedrespectively. Uniform-sized graft material transplant bed was made at the midpoint of eachside of the disc with the depth of12mm, the diameter of8.0mm.Each transplant bed wasperpendicular to the sagittal plane and parallel to the lumbar endplate.The opposite side ofthe annulus remained intact, the nucleus was removed entirely, and the endplate wasprocessed to capillary bleeding.Three graft bed in each animal were randomly implantedthree of the following four materials: autologous iliac、 BCP/SF/rhBMP-2、BCP/rhBMP-2or BCP/SF.The two groups sheep were sacrificed respectively at12and24weeks postoperation. Subsequently, the spine segments of interest were evaluated by grossexamination, manual palpation, X-RAY, computed tomographic scans, non-destructivebiomechanical testing and histology.Results：The microspheres had a spherical and smooth surface. The drug loaded microspheresstill had a spherical but rough surface. The morphology of the non-treated and the treatedSF microspheres were similar. The dissolution of the drug loaded SF microspheressignificantly decreased.And the solution of non-treated SF microspheres slightlydecreased. The treated SF microspheres showed slow release over the whole period oftime compared to the non-treated SF microspheres.Surgery went smoothly. An animal model of anterior interbody fusion hadsuccessfully established.Graft materials have been successfully implanted. The group ofBCP/SF/rhBMP-2had received a similar fusion rate compared with the group ofautologous iliac at12and24weeks after operation. Fusion intensity was significantlyenhanced at24weeks postoperatively compared with the situation at3months.Radiographic scores, histological scores, biomechanical testing were close to or higherthan the group of autologous iliac at the same time point, and they were significantlybetter than the other two groups.Conclusion:1. The performance of the controlled release SF/rhBMP-2microspheres wasimproved with more drug loading, more slower drug release,and lower solubility. Todevelop a new drug delivery vehicle,further study should be done.2. The novel new artificial bone has the properties of osteoconductive, osteoinductiveand osteogenic potential. It’s degradation rate also match the osteogenesis rate in vivo.We can obtain a similar lumbar fusion results compared with autologous iliac. It isexpected to be applied to clinical practice in the future by further improving its properties.