Experimental Study On The Principle And Expression Of VEGF In The Course Of Membrane Guided Bone Regeneration

Objective: To study the principle and expressed VEGF of membrane guided bone regeneratin and provide further experimental evidence for treating bone defect.Methods: Selecting 18 New Zealand rabbits(2~3kg) were used to produce GBR models with silicon membrane tubes. The rabbits were divided into 6 groops randomly and there were 3 rabbits in one groop. 10mm long segmental defects were created in the diaphses of both radii in 18 rabbits and the defect was bridged by silicon membrane tube with 20mm periosteum abscised as experimental sides,the other sides as control. Rabbits were killed at the lst,2nd,4th,6th,8th,12th weeks after CR-X ray checked, then the specimens in the fracture site were taken, fixed and decalcified. Ozokerite slices were made to detect the expression of VEGF and TAIMENG Scientific and Technical BI-2000 Immunohistochemistry analysis system was used to measure the expressed amount of VEGF in the segmental defects. Data were analyzed with SPSS11.0 software.Results: (l)The X-ray films show that callus could not be seen in both experimental sides and control sides at 1st and 2nd week,but could be seen at 4th week and increased in the following time. At 4th week, the broken ends of fractured bone in the control sides were indurascent, conbining with ulnar bone and at last the defect was irregular and filled by fibrous connevtive tissue. Bone defect disappeared at 8 weeks in the study group and the medullary cavity started to form. Cortical bone was continuous and the medullary cavity reconnected at 12 weeks in study group with incomplete moulding. external callus in experimental sides covered the outside rim of tube and began to shrink after 8 weeks.(2) Histological observation: On the experimental sides, hematoma could be seen inside the membrane tubes at 1st week ,At the meantime new callus formed in the medullary cavity of the broken ends,extending towards the center of tubes,and endosteum,myeloid matrix and periosteal cells under the membrane multiplied actively and grew into hematoma.The cells mentioned above entered the hematoma accompanied by blood vessels, at last the hematoma fiberized completely. A lot of multiplied osteoblasts grew into granulation tissue inside the membrane tubes and a great quantity of active osteoblasts,osteocytes and osteoclasts could be seen in primary callus. At 8th and 12th week bone formation in the membrane tubes was extensive and neoformative bone trabecula derived from the broken ends of fractured bone grew into the center of membrane tubes apparently, myeioid tissue growing into them with active neogenetic osteocytes. In the initial stage a great deal of fibroblasts multiplied in defects on the control sides, afterward chondrogenesis appeared near to the broken ends of fractured bone and a little neogenetic osseous tissue centered the broken ends. Step by step cartilaginous tissue degenerated and at 4th week osteanagenesis stoped with maturate fibrous tissue filling the defects, external callus in experimental sides grew through os cartilaginea and membranous bone and osteanagenesis switched to bone resorption after 8 weeks.(3) Immunohistochemistry Result of VEGF showed that proliferate periosteum, medullary matrix cell and osteocytes in the broken bone ends in tubes were positive against VEGF at 1st week on the experimental sides and a great many fibroblasts, endotheliocytes of neogenetic micrangium and periosteal cells were positively stained too.The sites near to external membrane fringe are the same as the control sides.At 2nd week and 4th week after operation the strong positive VEGF expression by immunohistochemistry staining of lively osteoclasts, osteoblasts, osteocytes and periosteal cells could be seen in tubes on experimental sides and the strong postive VEGF expression of lively osteocytes, osteoclasts, osteoblasts and hypertrophic chondrocytes in the broken ends on control sides. At 6th week osteoclasts and osteoblasts in membrane tubes and neogenetic osteocytes in the expanded Haverisan canals walls were strongly stained in tubes on the experimental sides. The postive VEGF expression was weaker than before and gradually became weak obviously on control sides after 4th week. Osteoclasts, active osteoblasts, lively osteocytes in callus and neogenetic osteocytes in the tubes were still stained positively on the experimental sides at 6th and 8th after operation.Neoformative bone matrix ,osteoclasts, active osteoblasts and lively osteocytes in the external callus were weakly positive against VEGF after 8th week and were nearly normal at 12th week. Conclusion:(1) The expression of VEGF is much obvious and expressive time in silicon membrane tubes is longer than in other bone regeneration sites.As indicates that VEGF takes part in bone regeneration and playes a considerable part.(2) The effect of silicon membrane guided bone regeneration is good.The key reason is that a relatively independent bone regenerative enviroment is founded to prevent near-by tissue from inteference,and to prevent VEGF and osteoinductors from diffusion.