Simulation For The Degradation Process Of Mg-Zn-Y-Nd Alloy Coronary Stent

Biomedical magnesium alloy is a promising material used for coronary stents.However,its degradation rate is too fast to meet the requirement life,which limits its clinical applications.Nowadays,lots of studies mimic the degradation process in vitro conditions by immersing samples into simulated body fluid(SBF)while only few of them simulate the degradation process in vivo.The experiments of static degradation ignore the effects of blood flow and the structure of stent and has a certain deviation from the fact.To reappear the corrosion process,it is necessary to consider the effects of blood flow and stent structure.In this paper,the degradation mechanism of a novel magnesium alloy was studied and the degradation model was established.Also,different structures of stents with different links and thickness were built and the degradation process of them were simulated to optimize the structure and enhance the degradation performance.The results indicated: by simulation,the qualitative and quantitative information about the degradation of the stents can be gotten,so as to avoid the risk of collapse of the structure,which plays the guiding role for stents design;meanwhile,the degradation rate were faster in the arc transition area and the joint between two U-model structures;the degradation rate with S-links structure are faster than other structure;the structure with S-links and L-links changes the distribution of high degradation rate zone;as the thickness increases,the stents degradation rate becomes faster;chloride ions concentration and the velocity change caused by turbulence also affects the degradation rate;the distribution of chloride ions concentration agrees with the distribution of degradation rate;the lower the velocity gradient is,the more homogeneous the distribution of chloride ions concentration is.Dynamic corrosion experiments were conducted to verify the simulation.The results showed that the dynamic corrosion results are consistent with the simulationresults;the corrosion form is pitting;in the joint between two U-model structures and in the area between the arc transition and the link,degradation rate is faster;compared with S-link,L-link structure of stents has a better corrosion resistance;however,due to the S-link and L-link ordered arrangement,the results reverses,which means S-links have a better corrosion resistance than L-links in stents with alternative structure;in the purpose of avoiding collapse and improving the life of the stent,3S3 L stent is better than 6L stent,and 6L stent is better than 6S stent.