Numerical Simulation Of The Effect Of Boundary Condition On The Virtual Release Of Stent

Cardiovascular and cerebrovascular diseases have become one of the highest mortality diseases all over the world.The main reason is due to the fact that the arterial circulatory system is insufficient to provide enough oxygenated blood to the heart.Stent intervention surgery has become an effective treatment for coronary heart disease.Vascular stents,as one of the medical devices implanted into the human body,must have a good biomechanical properties.It also requires the investigaters of the stent to innovate constantly.With the development of computer science and technology,the finite element method is more and more widely used in the simulation of virtual release of stents.This method not only can obtain more accurate numerical simulation results,but also can save and reduce research costs,and has very important theoretical research significance and practical application value.However,the accuracy of the finite element calculation results depends on the accuracy of the data input.Therefore,the accurate setting of boundary conditions is particularly important.This thesis aims to start from the clinical problems,and use the finite element simulation method to investigate the influence of different boundary conditions on the numerical simulation results,such as the type of load and the value of load,the posture of the stent release(different angles,different eccentricities),the constraints of the stent freedom,and whether stent crimping is considered and whether the blood vessel is curved.It provides a basis for reasonable selection of finite element analysis strategy,and puts forward some suggestions for applying the rule setting to boundary conditions,so that the simulation results obtained by the researchers are more credible.For different boundary conditions,a grouping experiment method was used in this study.Through compare and analyze the mechanical parameters calculated from each group of examples,recommendations were made for the application of various boundary conditions.Both the type of load and the size of the load have an effect on the virtual release of the stent.The method of pressure expansion is more in line with the actual situation,but this way will increase the difficulty of simulation.Moreover,with the increasing of the pressure,the residual stenosis rate does not change significantly.Therefore,the influence of pressure size on the calculation results can be ignored.In the case of pursuing calculation accuracy,the method of balloon expansion can be used.In the case of pursuing calculation efficiency,the method of displacement expansion can be used.Within the range of small angle changes,the residual stenosis rate increasing at begin and then decreasing,and the angle factor had little effect on the residual stenosis rate of stent virtual expansion results.Both the axial eccentricity and the radial eccentricity of the stent have a certain influence on the residual stenosis rate.The axial eccentricity has greater influence on the result than the radial eccentricity.Therefore,in the virtual release of the stent,the pose has an effect on the numerical simulation results.However,this effect can be ignored when the accuracy of the results is not high,and the basic model of 0 degree without eccentricity model is feasible for numerical simulation.In terms of degrees of freedom,although the constraints adopted by different researchers are different,the purpose is the same,and the degree of freedom constraints have less influence on the calculation results.In the finite element simulation,it is necessary to ensure that the degree of freedom constraint is consistent in a set of experiments.It is important to consider the crimping process when calculating the exact mechanical values,such as the residual stenosis rate,axial shortening rate,radial recoil rate,dog boning rate,etc.,but if only to obtain the deformation and stress distribution of the models during stent expansion,you can ignore the crimping process.The virtual release of the stent in the curved vessel can cause obvious straighten effect,especially in the greater curved vessels.Therefore,it is necessary to pre-bend the stent and balloon when the finite element simulation is in the curved blood vessel.The analysis conclusions obtained in this study can provide basis for the reasonable choice of finite element analysis strategy and have important research significance.