Study On The Surface Morphology And Mechanical Properties Of 3D Printed 316L Stainless Steel Vascular Stent

With the change of people’s living standards and the intensification of aging population,the prevalence rate of cardiovascular diseases is showing a rising trend.The interventional therapy of vascular stent implantation is currently widely used.However,the manufacturing methods of stent,such as laser cutting and electrostatic spinning,are complicated,and the cost of making patient-specific stent is high.3D printing technology provides a new idea for the manufacture of vascular stents and patient-specific stents.However,at present,the structural strength and surface quality of 3D printing cannot meet the requirements for the production of precision medical instruments such as vascular stents.Therefore,how to improve the mechanical properties of the printed stent,improve the printing accuracy and improve the surface quality of the stent are the key problems faced by 3D printing stent.In this thesis,the structural design and fabrication,surface morphology,in vitro mechanical properties testing and finite element analysis were studied.According to the poor mechanical properties of the 3D printing support,a support ring structure with unequal height was designed to improve the radial support force,and bending bars were designed to solve the problem of axial shortening in the expansion of the support.The connection mode was a closed-loop structure suitable for 3D printing.The final data of the bracket model are the outer diameter of the bracket 2.4mm,the inner diameter of the bracket 2.1mm and the length 19.37mm.The stent model was printed by laser selective melting technology,and the laser cut vascular stent was made to compare with the 3D printed stent.The powder attached to the surface of the 3D printed stent was removed by electrochemical polishing technology.The in vitro mechanical experiments of balloon expansion,plane compression and three-point bending were carried out on the printed stent,polished stent and laser cut stent,and the results were analyzed and compared with those of finite element software ABAQUS.The following conclusions are drawn.The stent was printed by laser selective melting technology,and no collapse and macro defects were found in the stent structure,indicating that the stent structure is suitable for 3D printing by laser selective melting.When the composition of polishing liquid is H₂SO₄:H₃PO₄:When water=45:35:20,voltage 10 V,temperature 70℃,anode and cathode distance 40 mm,polishing time 15 s,electrolytic polishing effect of 316L stainless steel vascular stent is the best.The powder particles and solidification marks on the surface of the stent are basically removed,and the surface roughness Ra of the stent decreases from 1.36μm to 0.82μm.Rz decreased from 6.59μm to 2.53μm.The polished support showed good expansibility and flexibility.The pressure required for expansion from 2.4 mm to 3.6 mm under balloon pressure was 6 bar,the radial rebound rate was1.61%,and the mid-span bending moment of three-point bending was 10.5 N·mm,but the radial support force of the polished support was 0.38 N/mm.Compared with the laser cutting bracket of 1.05N/mm is still a big gap.The finite element method was used to simulate the balloon expansion,plane compression and three-point bending of the stent.The radial rebound rate and axial shortening rate of the stent during the expansion process were basically consistent with the experimental results,and the maximum error was 22%,which verified the accuracy of the finite element model.This provides a reference for the subsequent design of stents and the application of 3D printing stents.