Fabrication And Evaluation Of Layered Double Hydroxide Coatings On Magnesium Alloy

Magnesium(Mg)and its alloy are honored as the next generation biomedical metal for its suitable mechanical properties and biodegradable ability.It can be totally degraded through corrode and the corrosion product can be adsorbed by the body and/or excreted out via metabolism.However,its high chemical activity would lead to a fast degradation rate,and then damage the mechanical integrity of the implant.In addition,the alkaline microenvironment and hydrogen chamber produced during the degradation would cause tissue inflammation around the implant.Therefore,enhance the corrosion resistance of Mg alloy is a vital step for its clinical application.In this dissertation,Mg-Al layered double hydroxide(Mg-Al LDH)and Mg(OH)2 mixed film was constructed on Mg alloy via hydrothermal treatment.Furthermore,combining hydrothermal treatment with plasma electrolytic oxidation(PEO)and dopamine self-polymerization methods,the author fabricated a series of composite coatings on Mg alloy.The main results are described as follows:1.Coating containg Mg(OH)2 and Mg-Al LDH phases was fabricated on the surface of Mg alloy via hydrothermal treatment.Compared with Mg(OH)2 coating,the as prepared coating shows better corrosion resistance.The extract of the as prepared sample exhibites no cytoxicity,and is favorable for human umbilical vein endothelial cells(HUCECs)migration.MC3T3-E1 cells can adhere,spread and proliferate on its surface.Meanwhile,its hemolysis rate is about 6%,almost fulfil the requirement of clinic application.In vivo experiment reveals that the as prepared smaple shows lower corrosion rate and milder inflammation,comparing to Mg(OH)2 samples.2.Firstly,porous MgO ceramic coating was fabricated on Mg alloy via PEO.Then,Mg-Al LDH was constructed on the PEO layer by hydrothermal treatment.The porous PEO layer was successfully filled by mico-nano Mg-Al LDH sheets,leading to a better corrosion resistance.The cell viability of rat bone marrow mesenchymal stem cells(rBMSCs)is higher than 80%after culturing on the extract of the as prepared samples for 4 days.rBMSCs can adhere,spread and proliferate on the surface of the prepared sample,and even after culturing for 14 days,show well cell viability.The hemolysis rate of the sample is about 1.1%,fulfil the requriment of the clinic application.Moreover,the prepared coating exhibites drug loading property,owing to the exsistance of Mg-Al LDH structure.3.Mg-Zn-Al LDH with different Zn contents are prepared on PEO treated Mg alloy.rBMSCs show cytocompatibility and enhanced osteogenic differentiation when cultured on the coating with the Zn content of 1.17 at%.When Zn content increased to 1.56 at%,rBMSCs exhibit higher proliferate rate.Further increased to 2.13 at%,the proliferation of rBMSCs is inhibited.All the Zn incorporated samples show favorable antibacterial property against staphylococcus aureus.4.Hydrothermal coating is first fabricated on Mg alloy,and then heparin modified composite coating is prepared via self-polymerization of dopamine and its covalent bonding.The composite coating shows enhanced corrosion resistance and HUVECs display better adhesion,spreding and proliferation on its surface.Moreover,the migration ratio of HUVECs on the composite coating is even faster than that on biomedical Ti.Meanwhile,the hemolysis ratio of the composite coating is about 0.7%,and no platelets can adhered on its surface.The in vivo experiment suggests that the composite coating possessed good tissue compatibility.5.Superhydrophobic coating is fabricated on Mg via hydrothermal treatment.The coating shows superhydrophobic property when the pH value of tested water droplet bertween 4-12.Its contact angle is higher than 140 degrees after advancing 500 mm on 1000#SiC paper under the pressure of 2.45 kPa.The superhydrophobic coating shows favorable corrosion resistance.HUVECs exhibit favorable cell viability and migradtion rate when culturing in the extract of the prepared coating sample.Morever,the coating possessed desirable hemolysis ratio and anti-platelet adhesion ability.