Study On The Factors Of Mechanical Properties Of PLLA Helical-Structural Stents

Stent implantation is an important treatment for peripheral vascular diseases,among which,helical-structural stent has a broad application prospect because of its sufficient radial force and low bending stiffness.Although the metallic stents currently used in clinical practice have a strong radial supporting performance,they are permanently present in blood vessels,which is easy to cause various complications.Biodegradable poly(L-lactic acid)(PLLA)stents are the best alternative to metallic stents because of their better biocompatibility.However,the material properties of polymers such as elastic modulus and viscoelastic properties are very different from those of metals,and the previous research results on the mechanical properties of metallic stents cannot be well applied to polymeric stents.Therefore,the factors influencing the mechanical properties of PLLA helical-sturctural stents were studied in this paper,so as to provide suggestions for the development of PLLA helical-structural stents with excellent properties.The main research contents and results of this thesis are as follows:1.Preparation method of PLLA monofilaments and helical-structural stents were studied.The mechanical properties of PLLA monofilaments under different heat treatment conditions were studied by uniaxial tensile test and the basic physical parameters of PLLA monofilaments were obtained.The preparation methods of the stents were determined,and the braiding molds were designed and a variety of PLLA helical-structural stents were prepared.2.Based on the tensile test data,the influencing factors of radial compression performance of PLLA helical stents were studied.In order to provide a theoretical basis for structural optimization of the stent,a mechanical model of radial compression of the helical stents was deduced.The effects of structure parameters(initial pitch angle,initial diameter and monofilament diameter)on the radial compression performance of the stents were studied by combining theory with experiment,and the applicability of the mechanical model was evaluated.Accoring to the experimental results,the influencing of the test environment(temperature,compression rate)on the radial compression performance of the stent was evaluated,and the dependence of viscoelastic PLLA materials on the test environment was explained from a macro point of view.3.The influencing factors of bending performance of PLLA helical stents were studied.The bending performance test equipment was designed,and the bending performance of the stents with different structural parameters(initial pitch angle,initial diameter and monofilament diameter)was experimentally studied.Combined with the radial compression performance,the selection of structure parameters in the design of the stents was discussed.4.The effects of the number of monofilaments and extremity configuration on the mechanical properties of PLLA helical braided stents were studied.In order to explore the mechanical properties of helical stents and helical braided stents with complex structure,the mechanical model of radial compression of helical braided stents was deduced,and the mechanical properties of helical braided stents with different number of monofilements and end shapes were studied.The influencing factors of mechanical properties were analyzed to provide ideas for the design and performance optimization of PLLA helical-structural stents.In conclusion,the study and evalucation of the design parameters of PLLA helical-structural stents in this thesis may provide constructive suggestions for the personalized and customized medical treatment of stents.