Numerical Simulation Of Degradation Process In Vitro And Supportability Analysis Of Magnesium Alloy Vascular Stent

As an important medical device for the treatment of cardiovascular diseases,magnesium alloy vascular stents have good biodegradability and excellent biocompatibility,and therefore have broad development prospects.The current research on magnesium alloy vascular stents does not consider the effect of the degradation process on mechanical properties,and it also lacks a scientific degradable numerical model.In this paper,considering the corrosion form of magnesium alloy in blood,a more complete numerical model of magnesium alloy degradation and parameter correction were proposed.Then,the self-designed simulated degradation algorithm was used to explore the change of the supportability of magnesium alloy vascular stent during the degradation process.The specific research contents are as follows:First,in view of the problem of incomplete influencing factors in the existing magnesium alloy degradation numerical model,a more perfect numerical model was proposed and some parameters were corrected.Based on the uniform corrosion numerical model,considering the effects of pitting corrosion and multi-dimensional corrosion,new parameters were introduced to form a scientific degradation model of magnesium alloy.For the unknown parameters _Uk,?and?,pitting corrosion parameter correction experiments and corresponding finite element simulations were completed.Through the comparison between the experimental results and the simulation results,the correction values were finally determined to be 0.000000014625,0.2,0.6.At the same time,?_d determined by the multi-dimensional corrosion parameter correction experiment was equal to the number of surfaces in the vascular stent surface element exposed to a corroded environment.Then,a new simulated degradation algorithm was proposed,and the algorithm was called to complete the degradation simulation of the N-type vascular stent.The simulated degradation algorithm called the vumatXtrArg subroutine,the VUMAT user subroutine and the Damage subroutine.It mainly realized three major functions:establishing a finite element element connection network,defining the magnesium alloy mechanical constitutive relationship,and updating the damage variables of surface element.The simulation results obtained showed that although the mass loss rate fluctuated,it is approximately linear as a whole.It can be seen from the analysis that the reason why the mass loss rate was approximately constant may be due to the mutual checks and balances between the pitting corrosion factor and the multidimensional corrosion influence factor.Finally,the sine wave support unit was used as a simple vascular stent to complete the finite element simulation of the vascular stent first implanted in the human body and then gradually degraded,and the radial compression method was used to analyze the change of the support of the vascular stent during the degradation process.The analysis results showed that the greater the radial displacement of the compression cylinder,the greater the reaction force generated for the vascular stent after the same corrosion time.Excluding the influence of the prestress loading analysis step,as the corrosion time increased,the reaction force showed a downward trend overall,the support of the vascular stent was getting weaker.