Study Of Modification On Medical AZ91D Magnesium Alloy

Metal material is an important biological material to repair or replace the diseased bone tissue. Compared with the current clinic metal biomaterials, such as titanium alloy and stainless steel, elasticity modulus and yield strength of magnesium alloy are closer to that of nature bone, which could reduce the occurring possibility of stress shielding effect. Magnesium is a body metabolism necessary element, and magnesium and magnesium alloys have good mechanical properties and biocompatibility, therefore, magnesium is a kind of ideal potentially metallic biomaterials. In the early20th century, magnesium as the body material is used in the research and application. However, due to the active chemical property of magnesium, a lot of bubbles were released because magnesium corrodes fast in the physiological environment, leading the occurring of subcutaneous tissue bubbles, which made it as a biological material applied research has been put on hold. With the development of a variety of science and technology, the application of magnesium alloys as biomaterials research now drew wide public concern again. Therefore, the study of modification on magnesium alloy surface has important significance.In the present paper, the improvements of modification on magnesium alloy were investigated. Based on the investigation, the anodizing coating was developed on magnesium alloy surface through the anodic electrodeposition technique combination involving the widely used in medical industry sodium stearate as the raw material. The coating was composed of magnesium stearate, which was formed through Mg2+released by magnesium alloy under the action of anodic potential combination with stearic acid radical ion in the electrolyte. Electrochemical experiments were involved to study the protection for the substrate, and biomineralization immersion tests were also used to investigate the effect of the anodizing coating on the corrosion behavior and physiological behavior of the substrate. Based on electrochemical experiments, it can be concluded that corrosion rate of the coated sample was obviously lower than that of the bare substrate, showing the anodizing coating could enhance the substrate corrosion resistance. The anodizing coating could induce the formation of hydroxyapatite through the FT-IR experiments, showing the enhancing of the biocompatibility.Starting with low cost, easy to operate and effect modification, the composite coating composed of stearic acid and hydroxyapatite was firstly prepared on the magnesium alloy surface. Based the results of XRD and FT-IR, the composite coating was formed through the electrostatic adsorption between the Ca2+in hydroxyapaptie and the COOH group in stearic acid. The modification on hydroxyapatite would not change its physiological bioactivity. Based on electrochemical experiments, it can be seen that the low frequency impedance modulus|Z|of the coated sample increased by2orders of magnitude compared to that of the bare substrate, showing the composite coating could provide effective protection and enhance the corrosion resistance for the magnesium alloy substrate.Be sure that the modified coating could enhance the corrosion resistance and biocompatibility of magnesium alloy, tetracycline doped calcium phosphate coating was prepared on magnesium alloy surface through hydrothermal method on condition that mature processing technique and further reduce the cost. Electrochemical technology was involved to screen reactant concentrations and the amount of added tetracycline to optimize the best experimental conditions for developing the modification coating. The composition and morphology of the modification coating were characterized by FT-IR and SEM. Electrochemical experiments were used to study the effect of the modified coating to corrosion behavior and physiology behavior of the bare substrate. Potentiodynamic polarization test results indicated that the corrosion current density of the tetracycline doped calcium phosphate coated sample reduced2orders of magnitude compared to that of the bare substrate, showing the modified coating obviously reduce the corrosion rate of the substrate. The immersion experiments results indicated that the modification coating could not only word as the effective barrier to provide protection for magnesium alloy, it but also enhance the substrate compatibility by inducing the formation of hydroxyapatite to improve the possibility of magnesium alloy as-potentially biomaterials.