Preparation And Degradation Properties Of Mesoporous Bioglass Coatings On Magnesium Alloy

Magnesium and its alloys have attracted much attention as potentialbiodegradable implant materials due to their excellent biocompatibility, mechanicalcompatibility and degradability and osteoinduction. However, the corrosion resistanceof magnesium and its alloys is poor. In the high chloride containing physiologicalenvironment, they have high corrosion rate, which could lead to the local alkalization,hydrogen release and high magnesium ion concentration, limiting their applications.Therefore, it is important to develop magnesium and its alloys with controllabledegradation rate matching that of bone healing. Surface modification of magnesiumand its alloys with appropriate coating materials is an efficient way to improve theircorrosion resistances.In this work, mesoporous45S5bioactive glass–ceramic coatings andmesoporous58S bioactive glass coatings have been successfully fabricated on AZ31magnesium alloys by surfactant-assisted sol–gel method and dip–coating technology,in which block copolymer F127(F127) was added as the template. The influence ofprocess conditions on surface morphology of the coating was studied. The corrosionresistance and bioactivity, as well as the corrosion mechanism of the materials werealso investigated by electrochemical testing and in vitro simulated body fluidimmersion test.The results showed that homogeneous, integrated and crack-free mesoporous45S5bioactive glass–ceramic coatings with the thickness of approximately1.1μmwere successfully fabricated on AZ31magnesium alloys under the condition ofpreparing the sol at TEOS/F127/C2H5OH ratio of1/0.018/80and subsequentlyheat-treated at400℃. The coatings were comprised of amorphous phase andNa2Ca2Si3O9phase, showing high adhesion with the substrate. The pitting corrosionpotential of mesoporous45S5bioactive glass–ceramic coated magnesium alloy is320mV higher than magnesium alloy, the corrosion current density reduced about2orders of magnitude and the charge transfer resistance increased1850Ω·cm2,therefore, the coating improve the corrosion resistance of magnesium alloy. In theprocess of immersion, the coatings delayed the degradation of magnesium alloy substrate and showed excellent protection effect. At the initial stage of the immersion,a great number of hydroxyapatite (HA) was deposited on the coating surface, thusimproving the bioactivity of the substrate.Mesoporous58S bioglass coatings with the thickness of1.2μm, uniform andintact, free of microcracks, with high specific surface area and desirable adhesion tothe substrate were successfully fabricated on AZ31magnesium alloys afterheat-treated at450°C. The coatings improved the corrosion potential and chargetransfer resistance of magnesium alloy substrate, and also reduced their corrosioncurrent density. The results of in vitro SBF immersion tests demonstrated that thecoatings could reduce the degradation rate of magnesium alloy substrate and inducethe rapid deposition of hydroxyapatite, thus improving the corrosion resistance andbioactivity of magnesium alloy. Meanwhile, mesoporous58S bioglass coatingsameliorated the surface wettability of magnesium alloy substrate, thus enhancing theirbiocompatibility and bioactivity.