| Objective:To study the ability of porous silk fibroin as scaffold in repairing rabbit's critical size mandibular defect preliminarily, and to conform if porous silk fibroin scaffold can be used for in situ tissue engineering.Materials and Methods:1,The silk fibroin scaffolds with 190±15μm pore size and 96.6±0.1% porosity were prepared. Then the surface and inside of the scaffolds were observed with SEM.2,Prepared the critical bone defect model.18 New Zealand white rabbits were selected for this experiment. Then, prepared a hole with 0.8cm diameter throughout mandible at two sides using high-speed electric drill.3,All the animal models were randomly divided into two groups, experimental group and blank control group. The silk fibroin scaffolds were implanted in the bone defects as experimental group, and the blank control group with no material implanted.4,The rabbits in each group were sacrificed at postoperative weeks of 2,6,12, then resected the mandibulars completely as specimens. The specimens were assessed by gross observation, X-ray evaluation, bone density measuring, histopathological HE staining and immunohistochemical staining for BMP-2.5,The data was statistical analyzed by SPSS 14.0.Results:1,The gross specimen showed:there was no infection and secondary fracture in both experimental group and control group. Rabbits'bone defect cavities became smaller in experimental group, without materials out, while bone defect cavities were full of granulation tissues in blank control group.2,X-ray and bone density:As time after surgery on, both experimental group and control group had higher bone density, and 12 weeks> 6 weeks> 2 weeks (P<0.05); both new bone area and bone density of experimental group were higher than control group in 2,6,12 weeks after surgery (P<0.05); during 12 weeks, bone defects did not achieve complete healing in both two groups, and porous silk fibroin scaffolds had not fully degraded.3,HE stained histopathological slice:At 2 weeks after surgery, in experimental group, host bone margins integrated with materials closely, defect margins grown into the scaffolds, new blood vessels could be seen inside materials, and no new bone formed obviously; In control group, host bone margins showed a small amount of absorption of bone, defect cavities were filled with a lot of fibrous connective tissues, and no new bone formed obviously. At 6 weeks after surgery, in experimental group, the interfaces between host bone ends and materials were unclear, there were a large number of neovascularization, islands of new bone tissues and patches of trabecular bone; In control group, host bone ends were clearly visible, a small amount of new bone formed and no trabecular bone formed obviously. At 12 weeks after surgery, in experimental group, new bone and islands of trabecular bone increased significantly, became thicker and denser, and fused into films. New blood vessels decreased slightly. Materials were obviously loose inside, some areas'apertures became larger, some areas collapsed; In control group, there were scattered new bone tissues in edges of host bone, no coarse trabecular bone formed.4,BMP-2 immunohistochemical staining:as time on, numbers of BMP-2 positive cells in new bone trabecular increased of varied degrees after surgery in both experimental group and control group, and 12 weeks>6 weeks>2 weeks, the differences were statistically significant (p<0.05); at each time, numbers of BMP-positive cells in experimental group were higher than control group, the differences were statistically significant (p<0.05).Conclusions:Pure silk fibroin porous scaffold had excellent biocompatibility, It can promoted new bone regeneration, and was suitable for in situ bone tissue engineering; The scaffolds (The average pore of silk fibroin porous was 190±15μm, the average porosity was 96.6±0.1%)can not be completely degraded within three months after implanted into bone.
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