Degradation Simulation And Experimental Confirmation Of ZE21B Alloy Stents Based On Finite Element Method

Magnesium(Mg)alloys are of great potential to be used as vascular stents due to their biodegradability,good biocompatibility,and satisfactory mechanical properties.As one class of the degradable materials for coronary artery stents,they have a broad application prospect in the field of vascular stents.However,the rapid degradation rate of them results in the insufficient supporting performance.In recent years,computer simulation technology has been widely used in the design and performance analysis of biomedical materials and apparatus,and the finite element analysis(FEA)has been successfully applied in the optimization design and performance analysis of stents.Therefore,it is of great significance to study and improve the degradation properties of Mg alloy coronary stents by FEA.In this paper,the mechanical properties and degradation damage of the common sinusoidal stent and the OPT stent for ZE21 B alloy was studied by combining simulated and experimental methods.Further,the accuracy of the established degradation model was verified by a new structural stent.In view of the corrosion characteristics of ZE21 B alloy vascular stents,a degradation model of the combined mechanism of uniform corrosion and stress corrosion was established,which includes setting the corresponding main program,calling the subroutine in the ABAQUS/Explicit analysis,and calling this subroutine to complete the simulation process.At the same time,by utilizing the data of the mass loss rate and structural integrity for different vascular stents obtained from the static immersion test in Hanks' solution,the model parameters were calibrated.The corrosion resistance of the stent structure of different support units was compared by FEA simulation.The reasons for the improvement of material degradation performance were clarified.The test results showed that when immersed in Hanks' simulated body fluid for 36 hours,the SIN stent collapsed completely with a weight loss rate of about 59.21%.For the OPT stent,the weight loss rate of was only 33.54%,which can maintain a better structural integrity.The simulation results also showed that the comprehensive mechanical performance of the OPT stent is better than that of the SIN stent.After implantation into the stenosis vessel,compared with the SIN stent,the rebound rate,maximum Von Mises equivalent stress of the OPT stent are reduced by about 5.7%,91.5MPa,respectively.The stress concentration at the bottom of the inner side of the support unit is relatively low,which indicates that OPT stent has a better support performance.The analysis of stent degradation by using a modified degradation model showed that the location with a higher stress is preferentially corroded.As the degradation time increases,this part is prone to breakage which would cause vascular collapse.The failure rate of the SIN configuration stent is faster than the OPT stent.When the normalized unit time t*=0.58,the SIN stent loses its supporting ability,while the OPT stent still maintains the supporting ability although the blood vessel has a certain degree of rebound..By using the degradation model established above,the reliability of a novel structural stent developed by our group was predicted and tested.The results showed that the new stent designed exhibits a better deformability and support performance during the expansion process.The degradation simulation results are in good agreement with the experimental simulation data.