| Magnesium,as one of the biometals,becomes the hot point these years,owing to its excellent biodegradable ability,biocompatibility and good mechanical properties.However,the fast and uncontrollable corrison rate of magnesium when located in fluid enviromments,limits its applied in varies vivo environment.In the present study,different surface modification methods were conducted for various application of magnesium when located in different vivo microenvironment,such as temporary load-bearing implant,bone defect activity-induced repair,and antibacterial activity-induced repair,etc.Microarc oxidation(MAO)and MAO with post treatment were employed to enhance the corrosion resistance;fatigue test under corrosion environment was used to stimulate the practical application environment and to investigate the failure mode and selection priciples of MAO coated magnesium;hydrothermal method was employed to fabricated MAO composite coatings for bone defect repair;antibacterial MAO coatings were developed to solve the infection problems;and an animal implant experiment was conducted to verify the corrosion degradation behavior of the coated implant and the repair effect of the bone defect.The 10?m and 20?m thick MAO coatings were mainly composed of Mg O,Mg2Si O4,Ca Si O3,and Mg3(PO4)2.For the 20?m thick MAO samples,the corrosion potential was increased to-1.62V,and the corrosion current decreased by one order of magnitude to1.60×10-5A/cm2,compared with 6.30×10-4A/cm2 that of magnesium.Fatigue experiment in stimulate body fliud(SBF)solution was carried out to investigate the compound action of the corrosion and stress effect when used for load-bearing implant.The results show that when the stress was greater than 60MPa,the antifatigue properties of the MAO coated samples were both lower than bare Mg,owing to the key limit fator of the residual internal stress and defect of the coating-substrate interface.When the the cycle life was more than105N,because of the better corrosion resistance,the antifatigue properties of the 10?m MAO coating was better than the bare Mg.The mean relative fatigue life of the 10?m and 20?m MAO samples were 0.4 and 0.28 compared with 0.06 of bare Mg.The results reveal that the corrosion fatigue sensitivity of Mg was decreased significantly by the coatings.A novel multilayered Mg(OH)2/MAO/Mg(OH)2coating was produced on Mg successfully utilized MAO and alkaline hydrothermal method for better anticorrosion properties.When the hydrothermal time was 8h,the coating thickness increased from6?m to 24?m.The composite coatings decreased the corrosion current of the MAO coatings with one order of magnitude and increased the corrosion potential from-1.49V of the MAO samples to-1.30V.Long term immersion results reveal that the weight loss of the composite coatings was 6.5mg/cm2after 2 weeks,lower than 17.9mg/cm2of MAO samples.Meanwhile,the composite coatings avoid the appearance that the micro defects appear in the first immersion period of MAO samples,which avoid the accelerate corrosion.Hydrothermal method was employed to modified the MAO coatings for better bonding strength,compactness,and corrosion resistance.The immersion test reveals that the weight loss of the composite coatings were below 20mg/cm2compared with84.9mg/cm2of bare Mg after 6 weeks.Meanwhile,the composite coatings maintain the structural intergrity for 6 weeks.Cu,Zn,and Ag contained MAO coatings were successfully produced for antibacterial and anticorrosion properties.The element content of Cu,Zn,and Ag were3.31w.t%,5.39w.t%,and 5.45w.t%on the coatings respectively.Cell proliferation test reveals that the anibacterial samples exhibit good compatibility.The Zn contained MAO samples show good antibacterial ability to S.carnosus,with the antibacterial rate of 91.42%compared with MAO smaples,while the Ag contained MAO samples show good antibacterial ability to E.coli,with the antibacterial rate of 99.99%.A 15mm wide bone defect model was employed to investigate the in vivo degradation of MAO coated Mg implant and new bone formation response.Bare Mg,10?m(MAO10)and 20?m(MAO20)thick MAO samples were implanted into the defect area.After 4weeks,the volume loss of the MAO20 was 53.39mm3lower than 101.57mm3 of bare Mg.After 8 weeks,the bare Mg corroded completely,while the MAO20 samples still remain the volume and provided the growth position and mechanical stimulation to bone tissue.8 weeks after surgery,amount of bone callus was detected around the implants,and the15mm bone gap was bridged initially.The MAO coatings avoid the direct contact between the corrosive ions and the magnesium substrate and the corrosion rate of magnesium can be adjusted by different thickness of the MAO coatings. |
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