Bioactive Scaffold Preparation And Repair Of Bone Defects

In clinic, the bone defects often occur because of trauma, tumor excision, infection, developmental abnormalities and other reasons. Traditional methods of bone defect repair mainly invovle autologous and allograft, bone cement, ceramics and metal transplantation, etc. fewer sources and complications of bone-supply parts in autogenous bone graft often brought patients some suffering. The immune reaction, the spread of diseases and other issues existed in allogeneic bone graft also limited its clinical application. At present, there were three kinds of bone substitutes including inorganic materials, polymeric organic materials and natural biological material. Single material can't meet the needs of bone tissue engineering beacause of poor absorption and slow degradation of inorganic material, cell toxicity of polymeric organic materials, low intensity and excessive degradation in natural biological material. In the meantime, the function of cells must rely on the presence of extracellular matrix, so matrix materials should possess three-dimensional structure and which promote cell adhesion and differentiation and provide a certain degree of mechanical strength. Therefore, in the bone tissue engineering, the scaffold material choice is an important aspect. This study was designed to use the characteristics of gelatin easy to hole in the process of freeze-drying to prepare nHA /gelatin porous scaffold, and increase osteoblast activity by combination with rhBMP-2. we wish our study can provide experimental basis for clinical application.Objective1,To prepare nHA /gelatin scaffold and optimize the preparation conditions.2,To study the biocompatibility of porous scaffold material.3,To increase osteoinduction of porous scaffold material.Materials and methods(1) Prepare the porous scaffold: three different kinds of porous scaffolds were prepared by gelatin in combination with 10wt%, 20wt%, 30wt% Nano-hydroxyapatite. The differences among three kinds of porous scaffolds in porosity, pore size, connectivity, degradation, PH value, mechanical strength and XRD was deteced. The preparation methods were optimized by comparing their respctive characteristics with the ideal needs of bone tissue engineering scaffold. (2) The biocompatibility of porous scaffold: Hemolysis,cytotoxicity,pyrogen and in vivo implantation tests were undertaken respectively to detect the biocompatibility of the optimized porous scaffold in accordance with the country's standards. (3) Improving osteoinduction in vitro of the optimized porous scaffold: fibrin glue carrying with rhBMP-2 was infused into the porous scaffold and processed vacuum drying to prepare the compoud porous scaffold. The inner structure,the release of rhBMP-2 and the effects of compoud scaffold on human marrow stromal cell proliferation and differentiation was detected. (4) observing the osteogenesis in vivo of the compoud scaffold: We used general observation,X-ray,bone densitymeasures, histological observation, mechanical experiments to investigate the osteogenesis of the compound scaffold on ectopic bone formation and critical radial bone defects.Resuts(1) Three of porous scaffolds prepared with gelatin and 10wt%, 20wt%, 30wt% nHA had good porosity, pore size and connectivity, physical and chemical properties stability. Among of these, the porous scaffold with 20 wt% nHA meet the needs of bone tissue engineering more.(2) The Optimized porous scaffold which was non-toxic, non-thermal,no hemolytic reaction and can degradate in rabbit muscle possessed good compatibility with the surrounding tissue.(3) Compared with the original scaffold, the compoud porous scaffold which was prepared by the method of fibrin glue with rhBMP-2 infused into optimized porous scaffold and second freeze-drying had no obvious changes in porosity and inner structure.the release of rhBMP-2 from the scaffold was slow, human bone marrow stromal stem cells were easy to differentiate to osteoblast under the stimulation of rhBMP-2 from the compound scaffold. (4) The compoud porous scaffold had good osteogenesis. Ecotopic bone foemation in muscle occurred in 6 weeks and critical rabbit radial bone defects were repaired completely in 12 weeks.Conclusion(1) The scaffolds which were prepared by the method of freeze-drying had good porosity, water absorption.they possessed the characteristics of about eight weeks degradation rate and stable PH value. In comparison,we thought the scaffold material including 20% nHA components was more suitable for the needs of bone tissue engineering.(2) The porous scaffold which was non-toxic, non-thermal,no hemolytic reaction and could degradate in rabbit muscle possessed good compatibility and met the needs of bone tissue engineering.(3) The compound porous scaffold possessed the ability of osteoinduction and it had good osteogenesis in vivo and in vitro test.