Mechanical Model And Experimental Study Of Polymer Self-expanding Braided Stents

Nowadays,self-expanding braided stents have been widely used in the treatment of peripheral vascular disease for its good flexibility.Poly(L-lactic acid)(PLLA)shows great potential in the application of stents for its superior mechanical properties and good biocompatibility.Compared with metallic self-expanding braided stents,polymer braided stents are still insufficient especially in mechanical properties,which needs further research.This works focuses on the mechanical properties of polymer braided stents,including radial supporting performance and flexibility.By summarizing and analyzing the research status at home and abroad,the radial force analytical model of polymer braided stents is the focus in terms of theoretical research.At the same time,with theoretical guidance,the preparation method of polymer braided stents with good mechanical properties is also the key in experimental research.The main research contents and achievements of this work are concluded as follows:(1)In view of the main factors affecting the mechanical properties of polymer selfexpanding braided stents,the research methods of the effects of polymer monofilament and stent preparation process on the its mechanical properties were put forward.The forming process from initial polymer powder to monofilament is introduced.In order to obtain PLLA monofilaments that meet the needs of braided stents,the mechanical properties of the original PLLA monofilaments were improved by solid-state stretching and thermal annealing after extrusion.Then,the preparation process of PLLA braided stents is proposed,including stents braiding,thermal annealing and demolding,which lays a foundation for subsequent research.(2)According to the theoretical basis of the metallic self-expanding braided stents and the characteristics of polymer braided stents,an analytical model of radial force for polymer braided stents is deduced and proposed.In view of the traditional Jedwab theoretical model is not suitable for polymer braided stents,then the reasons for the failure are found out through a series of experiments.Finally,the modified analytical model for PLLA braided stents is deduced based on the original model.Besides it,the testing method and principle of evaluating the radial supporting performance and flexibility of the braided stents are also introduced.(3)Based on the theoretical model,the related PLLA stents were designed and prepared.Through a series of experiments,the effects of design parameters on the mechanical properties of polymer braided stents were summarized,and the important factors such as cyclic load and temperature were deeply studied.The effects of geometric parameters on the mechanical properties of braided stents were evaluated by changing the initial inner diameter,initial pitch angle and the diameter of the monofilament.In order to accurately simulate the cyclic load and obtain the radial performance curve of the braided stents,the loading rate and range of the radial force testing lumen are configured according to the actual conditions.In addition,the effects of temperature on the mechanical properties of the braided stents were studied by changing the preheating conditions of the radial force testing lumen.(4)The theoretical model is further verified by studying the effect of stiffener constraint on the mechanical properties of PLLA braided stents.Firstly,the preparation methods of axial,radial and helical stiffener stents and mixed braided stents are proposed.Then,the mechanical properties of stiffener stents in different directions were comprehensively evaluated.Finally,it is proposed that the rational use of stiffener restraint can be a method to improve the mechanical properties of the PLLA braided stents.In conclusion,the mechanical properties of polymer braided stents were studied in the theoretical and experimental aspects,which can provide guidance and suggestions for the customized design and manufacture of self-expanding braided stents with suitable mechanical properties to meet clinical needs.