| Backgrounds:Bone defects caused by injuries or diseases usually need replacements of metal implants or prosthesis. Due to a low elastic modulus similar to human bone, appropriate mechanical properties and good biocompatibility, porous titanium alloy has become the main issue in studies related to medical metallic implants. However, titanium alloy is biologically inert and has no biological activity, which usually leads to prosthesis loosening, dislocation and so on. Thus, to achieve the goal of becoming ideal orthopaedic implants, improving the surface biological inertness of porous titanium may be an effective way.Owing to its biodegradability and multiple biological activities, magnesium alloy has always been regarded as a revolutionary metal material. However, magnesium alloy will have a rapid process of degradation, which would have a magnificent influence on its mechanical properties. This will lead to the restriction on its applications in orthopaedic fields. In recent years, there are many reports on improving corrosion resistance of the magnesium alloy and surface biological modification of the titanium alloy, respectively. But there is fewer report on preparing magnesium alloy on porous titanium alloy surface as a biodegradable coating. The preparation methods of magnesium co ating, and its bioactivity, osteogenic effects and osseo- integration still need further investigation and research.Objectives:1. To investigate the methods of preparing magnesium coating on the surface of porous titanium alloy and the biologic characteristics of magnesium alloy coating. 2. To study the effects of magnesium coating porous titanium alloy on the process of proliferation and differentiation of the bone marrow stromal cells(BMSCs), and the osteogenic effects and osseo- integration properties of magnesium coating porous titanium alloy.Methods:1. Porous titanium alloy was fabricated using electron beam melting(EBM) equipment, which was then coated with magnesium using pulsed bias arc ion plating(PBAIP) on its inner and outer surface s. The surface morphology of magnesium coating on inner and outer surfaces of porous titanium was observed using scanning electron microscopy(SEM), and the elemental composition and components of aforementioned materials was observed using energy disperse spectroscopy(EDS) and x-ray diffraction(XRD) respectively. 2. The degradation characteristics of magnesium coating, the p H value of soaking solution and the concentration of magnesium ion were detected using hank’s solution immersion test. And the curves of p H value and ion dissolution were drawn. 3. The leaching liquors and substances of materials of control groups(porous titanium alloy) and experimental groups(magnesium coat ing titanium alloy) were used to culture BMSCs of sprague dawley rats. The proliferating rate and differentiation of cells were estimated using cell counting kit-8(CCK-8) and alkaline phosphatase staining for 1, 4, 7 days, respectively. 4. 24 rabbits were divided into two groups randomly. A cylinder(Diameter: 6mm, Height: 8mm) defect was made on lateral condyle of each femur, which was then implanted with porous titanium alloy(control group)and magnesium coating porous titanium alloy(experimental group). Each animal was injected with tetracycline and calcein before the femur was harvested. Animals of each group were enthanized 2, 4, 8 weeks after the operation and the femoral condyle were harvested. Micro-CT scan were performed to test bone formation of two groups. The thickness and rate of calcium deposition were observed and measured under fluorescence microscope after hard tissue slicing. Then, the bone formation nearby the two types of materials and the integration of bone and materials were observed after van gieson(VG) staining.Results:1. The morphology of magnesium coating was de nse and regular, which combined well with porous titanium alloy surface. EDS test showed that the element of surface coating was magnesium and XRD test showed that the coating was comprised of pure magnesium. 2. The p H value of the solution was about 10 and the amount of dissolved magnesium ions was about 50 ppm 1 day after hank’s solution soaking. The former indicator dropped to 8 and the later dropped to 10 ppm 4 days after Hank’s solution soaking. Both the two indicators began to decline slowly at the fourth day of soaking. The p H value reached a steady state about 7.5 and the magnesium ions about 5 ppm. 3. Cell experiment showed that both the cell proliferation activity and differentiation of experimental group were better than those of control group at the fourth and seventh day. Cell differentiation of two group had a statistical difference(P<0.05). Alkaline phosphatase staining showed that the cell differentiation of experimental group was better than control group at the fourth and seventh day. 4. The micro-CT scan showed that the bone volume to total volume(BV/TV) of experimental group in region of interest(ROI) was significantly higher than control group 4 and 8 weeks after operation(P<0.05). Fluorescent labeling revealed that the growth rate of new bone formation of experimental group was significantly higher than control group(P<0.05). The VG staining showed that the percentage of regeneration bone of experimental group was significantly higher than control group at 4 and 8 weeks after the operation(P<0.05).Conclusion:Compared to porous titanium alloy, the magnesium coated porous titanium alloy has a better biological activity on proliferation and differentiation of BMSCs. The magnesium coated porous titanium alloy can promote the new bone formation and has positive effects of osteo-conductivity and osteogenesis. |
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