| As biomaterials for orthopaedic implants,stainless steels, titanium alloys and cobalt based alloys have been used in clinic. However,these biometals could be corroded by body fluid in vivo, releasing toxic ions and leading to inflammation,which damages their biocompatibility with tissue. Moreover,the elastic modulus of the metal materials are not well matched with that of natural bone tissue,resulting in stresss hielding effects which has deleterious effects on the growth and remolding of new bone and may lead to a second fracture. Therefore, with the deep progresss in biomedical materials, the development of biomaterials with appropriate mechanical properties, good biological property and biodegradation ability in vivo is an important issue.Compared with the metallic implant materials used in clinic, magnesium (Mg) has some large advantages:(1) Mg is essential elements of human body. (2) Mg has good biocompatibility and bioactivity. (3) The mechanical property of magnesium alloy is close to bone tissue. (4) The density of magnesium alloy is close to bone tissue. (5)The raw materials have a low cost. Therefore, Mg alloy has attracted much attention as new potential biodegradable implant materials. However, as biomedical materials, Mg alloy has a fast degradation rate, which leads to the local alkalization and hydrogen aggregation and blocked their clinical application.In this thesis, AZ31B magnesium alloy was chosen as the biodegradable magensium material. A ceramic coating composed of Mg2SiO4å'ŒSiO2 was prepared on AZ31B magnesium alloys in order to control the degradation rate of the substrate alloy, and the preparation technology, surface morphology, phase composition, coating forming mechanism and corrosion resistance, were studied. The conclusions in this investigation are summarized as following:(1) Optimum processing parameters combination, 40g/L NaOH, 40g/L Na2SiO3·9H2O,100℃of treatment temperature,7hours of treatment time, was determined thouth an orthogonal experiment.(2)The prepared coating was dense and uniform and presents gold colour by eyes. It can be seen composed of ball-like crystal investigated by SEM and the thickness of the coating was about 1.9μm.The XPS analysis indicated that main composition of the coating was composed of Mg2SiO4, MgO and little SiO2.(3)Immersion test showed that the silicon coating reduced the degradation tendency of the magnesium alloy substrate,especially at the initial stage of immersion. AZ31B magnesium alloys with and without coating showed different degradation mechanisms in the different simulated blood fluids. The silicon coating was converted to Ca3(PO4)2 gradually when immersed in Hank’s, and the newly-formed coating can prevent the magnesium alloy matrix from the corrosion in a short time. (4)The electrochemical test showed that the degradation rates of the magnesium alloy were different immersed in three different simulated blood fluids. Current densities of the samples in different simulated blood fluids showed the order of the corrosion rate in turn is normal saline>PBS> Hank’s solution, which is consistent with pH changes in immersion test.(5)The hemolysis test showed that the silicon coated magnesium alloy had good antihemolysis property when immersed in simulated body fluid for selected different time. The hemolysis ratios of the coated samples are less than 5%. Hemolysis ratio of the samples in PBS solution is less than that in normal saline.(6)The cell toxicity test showed coated AZ31B magnesium alloy presented lower toxicity and matched the need of requirement. The cell growth of cultured with the dipping solution of the coated and uncoated samples showed that the number and growth state of the cells cultured with the dipping solution of coated samples were obvious better than those of without coating. |
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