Preparation of Gallic Acid Modified Micro Arc Oxidation Coating on Magnesium Alloy: Corrosion and Biocompatibility Assessment

  • 李 泓邦

Student thesis: Master's Thesis

Abstract

Magnesium alloys are biodegradable materials with good biocompatibility Its mechanical properties are close to human’s natural bone and thus magnesium alloys are good candidates of biodegradable bone implants However the unmodified magnesium alloys may suffer from the rapid corrosion in the physiological environment Moreover the byproducts of the corrosion such as hydrogen high concentration of metallic and alkaline ions will cause the inflammatory of the osseous tissue Thus this research utilized surface modification to decrease the corrosion rate and improve the biocompatibility First micro arc oxidation (MAO) process created a porous and passivated coating on the magnesium alloy The coating mainly composed of MgO and Mg2SiO4 could inhibit the corrosive solution contacting with the substrates to increase the corrosion resistance In this study by modulating the components of the electrolytes and the final voltages the highest corrosion resistance of MAO coating could be obtained Second the scattering pores of MAO coating could increase surface roughness and area In addition Mg(OH)2 covered the outmost part of the coating which provide great sites for combining Polyethyleneimine (PEI) through hydrogen bond The amine group of PEI could further react with the carboxyl group of gallic acid (GA) a natural and multifunctional phenolic molecule by forming amide bond Although there was a protective layer on the magnesium alloy under the aqueous condition GA still would break the structure of the MAO coating Therefore the grafting reaction must process in the non-aqueous solution to ensure the sufficient corrosion resistance In this study PEI and GA were successfully immobilized onto the MAO coating confirmed by FT-IR XPS and contact angle The corrosion resistance was assessed by the surface morphology the variation of the pH value the releasement of the hydrogen and the electrochemical tests indicating that the immobilization wouldn’t decline the quality of the MAO coating In vitro tests the cell cytotoxicity and adhesion tests found that PEI and GA modified group had the best biocompatibility and can stimulate osteoblastic-like cells adhesion Moreover GA can further combine with some biofuctional molecules such as vascular endothelial growth factor (VEGF) In conclusion this study successfully developed a method for immobilizing GA onto MAO coating of biodegradable magnesium alloy for the first time
Date of Award2018 Mar 28
Original languageEnglish
SupervisorMing-Long Yeh (Supervisor)

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