Preparation,degradation,and Blood Compatibility Of Biomedical High-purity Magnesium Modified By Composite Coatings

The research and development of new biodegradable stent materials with good biological and mechanical compatibility are vitally significant to safeguard human health and improve the standard of living.Compared with the traditional biomedical metal materials such as titanium alloys,stainless steels,and cobalt-base alloys,magnesium（Mg）-based materials have good biocompatibility and biodegradability,known as the new generation of advanced biomaterials.However,the degradation rate of Mg and Mg alloys in the human body is too fast and the premature mechanical instability and metabolic absorption of excessive degradation products in the human body limit their extensive promotion and application in the fields of surgical implants and intervention.In this paper,Mg hydroxide/silane/sodium alginate and micro-arc oxidation/poly（trimethylene carbonate）composite coatings are prepared on the surface of biomedical high-purity Mg to mitigate the degradation rate to mitigate degradation of Mg in the physiological environment.A sodium alginate coating is firstly fabricated on alkalinized high-purity Mg with a silane transition layer by spin coating.The surface morphology and composition are investigated by scanning electron microscopy,energy-dispersive X-ray spectrometry,X-ray diffraction,Fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy.Electrochemical and immersion tests are performed in the simulated body fluids（SBF）at 37℃.The thickness of Mg hydroxide/silane/sodium alginate composite coating is 10.3±0.3μm and that of sodium alginate coating is 5.6±0.1μm.The composite coating is uniform and compact and adheres well to the Mg substrate.Compared to the bare substrate,the corrosion current density of the sample with the composite coating in SBF decreases from 130.9±6.2 to 1.3±0.3μA cm^-2,the charge transfer resistance of that increases by 190 times and the average degradation rate drops to 0.80±0.26 mm y^-1 from 3.47±0.25 mm y^-1.The Mg hydroxide/silane/sodium alginate composite coating remains in good integrity after 7-days soaking in SBF.The composite coating with uniform,compact,and excellent adhesion properties and formation of chelated[Mg-SA]by corrosion offer synergistic protection to the substrate under physiological conditions.In addition,the composite coating also improve the blood compatibility of high-purity Mg.The micro-arc oxidation/poly（trimethylene carbonate）composite coating is further prepared on the surface of medical high-purity Mg by micro-arc oxidation and solvent evaporation methods.The thickness of the micro-arc oxide layer is about 19.6±0.6μm,while the thickness of poly（trimethylene carbonate）coating is around 11.4±1.1μm.The surface morphology of the micro-arc oxide layer is porous and rough and the surface can be densified by further preparation of poly（trimethylene carbonate）coating.For the samples modified by the micro-arc oxidation/poly（trimethylene carbonate）composite coating,the corrosion current density in SBF decreases by nearly 3 orders of magnitude,the charge transfer resistance increases by nearly 4 orders of magnitude,the pore resistance increases by about 3 orders of magnitude,and the average degradation rate in SBF decreases to 0.78±0.16 mm y^-1 from 3.47±0.25 mm y^-1.By fabricating a polytrimethylene carbonate coating on the surface of high-purity Mg treated by micro-arc oxidation for sealing,the degradation rate of the substrate can be further delayed,indicating that the poly（trimethylene carbonate）coating can provide good barrier protection for the matrix and effectively prevent the rapid degradation of the Mg matrix after implantation in the human body.The hemolysis rate of the modified sample decreases to 1.23±0.35%from 14.31±1.32%and the number of activated platelets adhering on the surface are significantly reduced.