Study On Numerical Simulation Of Service Performance Of Nitinol Tracheal Stent

As a common clinical instrument for the treatment of trachea diseases,Nitinol stent can rapidly relieve the symptoms of dyspnea in patients with stenosis.However,there are inevitable complications associated with stent implantation in the human body.Stent loss is easy to occur when the stent radial strength is insufficient,which will cause secondary trauma to the endotracheal wall.On the other hand,the stent size doesn’t conform to the trachea physiological environment is prone to fatigue damage,affecting the long-term therapeutic effect.Therefore,it is great significant to analyze the phenomena of tissue hyperplasia,stent loss and fatigue damage that often occur in the clinical application.Through theoretical analysis and finite element simulation,the support performance,forced vibration and fatigue performance of the stent during service were studied in this thesis,and the main research contents were as follows:The material properties of Nitinol alloy and trachea tissue were analyzed and the corresponding hyperelastic model was selected for fitting.Due to the stent structure with symmetrical nature,the stent unit is selected for analysis.The mechanical model of the stent unit under axial tension and radial compression was established,and the structural parameters affecting the support performance were determined.The contact mechanics model of the stent and trachea was established to determine the influence of structural parameters on the contact force.To comprehensively analyze the forced vibration characteristics of the stent in service,the periodic vibration equation and nonlinear dynamic equation were established,and the influence of random excitation parameters such as respiration and cough on the stability of the support was discussed.To study the influence of the length,outer diameter and thickness of the Nitinol stent on the supporting performance,the stent compression simulation was carried out by ABAQUS software to obtain the variation curves of the stent compression stress under different parameters.Combined with the supporting performance evaluation formula,it was concluded that the smaller the length and outside diameter of the stent,the better the supporting performance,and the influence of the thickness factor was not obvious.Based on the analysis of the stent compression performance,the expansion process was simulated to study the changes in the contact force between the stent and tissue under the tracheal inner diameter,lesion length and expansion depth.And the selection criteria of stents were given based on the conditions of tissue hyperplasia.To ensure that the stent could provide sufficient support,the stent with smaller length and outer diameter could reduce the occurrence of complications.The vibration and deformation of the stent under different breathing conditions were discussed by Ansys simulation,and the risk of the stent loss was predicted by combining the radial stiffness formula.The nonlinear dynamic equation was solved by Matlab software,and the influence of equation parameters on the stability of the stent coefficients was discussed.The results showed that the stent was easy to fall off when the pressure of coughing was too great.Based on the analysis of the forced vibration of the stent,fatigue life analysis of the stent was conducted based on FE-safe software to investigate whether the stents meet the clinical standards for use in normal breathing conditions and in the ideal condition of persistent cough.This thesis comprehensively investigates the mechanical properties of nickel-titanium alloy stents in service,and the results provide a theoretical basis for guiding the selection and optimal design of stents,which have greater value in clinical practice.