Experimental Research On Repairing Mandibular Defect With RhBMP-2/nano-hydroxyapatite/collagen Bone Compsite

1.ObjectsEstablish the animal model of mandibular defects,to investigate the healing process of mandibular defects by human bone morphogenetic protein 2(rhBMP2) activated nano-hydroxyapatite/collagen(nHAC) transplantation,discuss the significance of"bone growth factor - scaffold" approach for the tissue engineering to repair mandibular defects,evaluate the capacity of mandibular defects repairment of the composite of recombinant human bone morphogenetic protein -2 in collagen-based bone(rhBMP-2/nHAC),and give a introduction for clinical application of this bioactive materials in repairing the craniofacial bone defects of plastic surgery and provide a theoretical basis for craniomaxillofacial surgery clinical use in the future.2.Methods18 New Zealand white rabbits for the experiment,using bone grinding operation to establish the rabbit model of bilateral mandibular defects,random selected one side of the mandibular defects filled with rhBMP-2/nHAC as experiment group,and the other side filled with nHAC as control group.All of groups were autogenous control. At postoperative weeks of 5,10 and 20,according to Lane-Sandhu X-ray and histological criteria,respectively,for each observation:the general observed,X-ray examination,histological sections by light microscopy and scanning electron microscopy.Score the results based on comprehensive evaluation of rhBMP-2/nHAC artificial bone repair material of the mandibular defects repair capacity and osteogenic effect.3.Results1.General observation:During the entire experiment in all animals entered the final analysis,no loss.In all experimental period,experimental animals grew well, weight increased steadily.Wound healed well without implant extrusion,no foreign body,the immune response and other row signs of infection,all animals did not occur secondary to fracture.2.General observation of specimens:in different periods after surgery,gross anatomy have not been occurred soft tissue graft degeneration or necrosis.Connective tissue fibers attached to the surface of plants,abundant angiogenesis.With the observation period,materials appearance and texture were gradually approaching to the mandibular bone,materials firmly connected the mandibular.3.X-ray observations:At 5^th week,experimental side defect can be seen partial cloudiness defect density shadow;Contrast side defect can be seen low-density implants,bone defects are clearly visible boundaries.At 10^th week,the experimental side bone defect area can be seen projective patchy resistance,bone defect boundaries are not clear,the bone-bed department density increased slightly,showing dense shadow cloudiness and new bone formation,bone graft is still visible;Contrast side defect bone defect gap clear,nearly no obvious bone-bed department to repair bone callus formation,bone clear boundaries.At 20^th week,experimental side defect was connected fuzzy gap bone defect,in order to stop the continuity of high-density projection,blurred bone;Contrast side and the relatively low bone density uneven density was patchy shadow,transplantation of bone and bone defects can be seen fuzzy space.Lane-Sandhu X-ray score results:In addition to 5 weeks after operation due to materials not in the X-ray film autoradiography led to no results,after 10 weeks and 20 weeks the experimental group and control group in the new bone formation,bone connectivity and bone remodeling were significant differences exist (t₁=3.162,P₁=0.025;t₂=4.568,P₂=0.006),experimental group than the contrast group display the more new bone formation,bone connected closier,a higher degree of bone remodeling.4.Histological observation by light microscopy:Experimental groups:At 5^th week,the host bone and a good combination of active materials,a large number of bone-like tissue ingrowth;At 10^th week,the bone tissue significantly increased,and more mature trabecular bone,a large number of bone cells and osteoblasts material part of the degradation.At 20^th week,the implantation defect activity materials for the mature bone tissue,and lamellar bone formation,bone tissue in a large number of bone pits and mature osteoblasts,showing Haversian system,complete degradation of the basic material,only a small amount of residue.Contrast group:At 5^th week,the simple material and host bone connective tissue for a large number of fibers;At 10^th week at the beginning of an increase in osteoid tissue,but still more loose and for the new organization,there is no obvious trabecular bone structure,material residues more slow degradation.At 20^th week,the bone-like tissue continued to grow,but the central area of bone tissue defects is still small and immature,bone matrix in the more immature collagen,the material part of the degradation.5.The results of scanning electron microscopy:Experimental groups:At 5^th week, the activity of combination of materials to work closely with the host bone,no obvious interface boundaries,materials area there are obvious bone tissue ingrowth; At 10^th week,the defect in the near interfacial region dense new bone tissue, morphology and similar to host bone,a small amount of residual material;At 20^th week,the defect-side and the defect-in with a good integration of new bone tissue, and central defects are dense border of bone-like tissue.Most materials degradation, only a small amount of new bone fragments wrapped in between.Contrast group:At 5^th week,combined with the host bone is not close,a clear interface slot,and to see the connective tissue fibers;At 10^th week when the defect-end materials and clear boundaries,there are a large number of material defects residues.A small amount of bone-like tissue along the porous material into the material;At 20^th week when the defect-side and the defect-in in integration of new bone tissue is relatively poor structural defects within the loose,a lot of porosity. Degradation of materials is only part of a large number of residues.Lane-Sandhu histological score Results:After 5 weeks,10 weeks and 20 weeks the experimental group and control group in the histology of bone connecting, cancellous bone and cortical bone were significant difference(t1 = 2.907,P1 = 0.034; t2 = 4.392,P2 = 0.007;t3 = 7.050,P3 = 0.001),the experimental group than the contrast group bone connected closier,the more bone trabeculae and cortical bone formation.4.Conclusion1.nHAC has a good role of osteoconduction and biocompatibility,the degradation of material absorption and new bone formation matches well,it is an ideal scaffold for tissue engineering.2.After activated by rhBMP-2,the nHAC has a certain role in osteoinduction, accelerate osteogenesis and reliable approach to the healing of bone,and the application method is simple,with a greater potential for clinical application.3.Application of "bone growth factor - scaffold" approach for the tissue-engineered mandible can be a more effective method of mandibular bone defect to promote regeneration and renewal,nHAC and rhBMP-2 can be used as a tissue engineering scaffold materials and growth factors for craniomaxillofacial bone defect.