Design And Manufacture Of A New-type Assembling Scaffold For Bone Repair And The Evaluation Of Ectopic Osteogenesis In Vivo

Trauma,infection,tumor,dysplasia and other disorders are prevalent,causing bone defects.Large or segmental bone defects are difficult to repair and require grafts.Autologous bone is the gold standard of bone graft material,but the source is limited,and it is easy to causing postoperative discomfort and other complications.Allogeneic bone materials have a relatively wide range of sources relative to autologous bone,but there is an immune rejection,which can lead to the spread of diseases and the formation of tumors.With the rapid development of bone tissue engineering,a large number of artificial bone substitute materials have been developed,but a single material usually involves technical limitations.In this thesis,a new scaffold designs comprising assembly of porous hydroxyapatite spheres and magnesium particles encased in a titanium shell were investigated.A sol gel method was used to create hydroxyapatite spheres with 3 different porosity levels.Their surface morphology and surface structure were analyzed.Anti-corrosion performance of magnesium particles was evaluated by monitoring the pH value and the concentration of magnesium ions released from the scaffolds during in vitro immersion.In vitro cell proliferation activity and osteogenic differentiation were investigated by culture of MC3T3-E1 cells.Ectopic osteogenesis was evaluated by implantation in a dorsal muscle model for 8 and 16 weeks.Stereo microscope found that,hydroxyapatite spheres had a spherical morphology and SEM found that the spheres prepared using a slurry with solid content of 20% had more pores and their grain size was smaller compared with other two groups.In vitro soaking showed that the acid pickling and passivation treatment of pure magnesium particles stabilized the pH value at about 8.50,and the resulting from material corrosion ion concentration significantly lower than other groups,suggesting this treatment can improve the corrosion resistance of magnesium particles.MC3T3-E1 cell culture indicated that the scaffolds had good cell compatibility.Micro-CT results showed that the thickness and the number of bone trabecula in Mg-scaffold group were higher than other groups at 8 weeks and 16 weeks after surgery.Moreover,tetracycline/calceinl double labeling suggested accelerated new-bone formation in the Mg-scaffold group from week 6 to 8,as compared to the bare scaffold group.toluidine blue histological observation results showed that the scaffold has good histocompatibility.At 8 weeks,the granular materials in the scaffolds were encapsulated by soft tissue,in the control group(pure hydroxyapatite spheres),there are mainly fibrous tissues between hydroxyapatite spheres,without evidence of angiogenesis or osteogenesis.In the other groups,there were mineralized bone between hydroxyapatite spheres;and the magnesium particles degradation gaps were partially filled by new bone,confirming that modification of magnesium particles improved the performance of composite scaffold osteogenesis in this animal model.In summary,the introduction of magnesium particles within a reasonable range improved the osteogenic properties of scaffolds,and the new-type assembling scaffold may be a possible candidate device for bone repair.