Design And Performance Of A New Mechanically Braided Metal Ureteral Stent

Upper urinary tract obstruction caused by calculi,tumor compression and inflammatory stenosis is one of the most common diseases of the urinary system.Indwelling ureteral stents are the preferred treatment option to relieve the obstruction and protect renal function.The commonly used ureteral stents are"double J"stents.In the narrow ureter that leads to obstruction,the hollow lumen of the stent provides intraperitoneal drainage channels,and the lateral holes distributed longitudinally along the wall of the stent can realize the exchange of urine in the stent lumen and out of the stent to promote drainage.However,ureteral stents still have some problems,such as inadequate supporting performance,difficulty in resisting ureteral compression to provide unobstructed intraperitoneal passage,few lateral holes,poor drainage effect and urine reflux,which affect the treatment and recovery of patients.In order to improve the supporting and drainage performance of commercial polymer stents,combined with the domestic requirements of metal ureteral stents,and considering the requirements of ideal ureteral stents in terms of biological compatibility,anti-displacement and low cost,a new mechanical brassisted metal ureteral stent was designed and prepared.Medical Nitinol wire with excellent mechanical properties was selected as the scaffold material,and the scaffold was fabricated by the weaving process of textile machinery which is easy to form porous structure and convenient for large-scale production.The radial support performance of mechanical braided ureteral stent was enhanced by a double-layer composite braided tube,and a limit wire was introduced into the inner layer to realize the integration of the two layers and improve the interlayer stability of the double-layer stent.In vitro anti-migration,drainage,anti-reflux and biocompatibility tests were performed to verify the structural function and safety of the fabricated braided scaffolds.To be specific:(1)With Ni Ti alloy as raw material,regular braiding structure is selected as the mechanical braiding bracket structure,and horizontal braiding equipment is selected to ensure the stability of wire braiding process.To investigate the technological feasibility of metal wire braided ureteral stents with different wire diameters,and analyze the effect of braided density on the mechanical properties of mechanical braided metal ureteral stents with the same diameter.(2)In order to enhance the radial supporting performance of mechanical braided metal ureteral stent,a double-layer stent was obtained by covering a layer ofⅢ-4 braided layer with large braided angle and small pitch on the single braided tube.The results of flat panel compression and local compression show that the flat panel compression strength of A,B and C double-layer stents is increased by 196%,204%and 36%respectively,and the local compression strength is increased by 131%,205%and 374%respectively.The C double-layer stent with the best radial support are obtained,which also has good tensile fracture and the best bending flexibility.(3)The limit wire was introduced to solve the problem of interlayer separation during C-double layer stent placement.Two kinds of limit wires,0.08 mm and 0.15 mm,were mixed into the inner layer to obtain two kinds of longitudinal limit double bracket respectively.According to the results of interlayer separation test,the interlayer binding force of C-2 stent mixed with 0.15 mm limit wire is 7.6 times higher than that of C stent,and the interlayer separation is not easy to occur.In addition,the C-2 stent also has the same local compression performance as the commercial bracket,which is better than the flat compression performance,tensile performance and bending flexibility of the commercial bracket.The compression strength of the flat compression reaches 2215.44±42.87c N,and the elastic recovery rate of the flat compression reaches 97.32±0.60%.The breaking strength is 38.44±1.83N,the elongation at break is 72.88±8.89%,and the bending stiffness is 2.360±0.122c N·cm~2.(4)Evaluate the function of C-2 braided stent compared with commercial stent.The test results show that the C-2 braided stent has the same anti-displacement effect as the commercial bracket.The results of drainage test showed that the braided stent could achieve full drainage at low flow rate of 4.26 m L/min and high flow rate of 79.6 m L/min.The results of reflux test verify the anti-reflux effect of the porous structure of the braided scaffold.At the same time,C-2 stent also have good cytocompatibility.In summary,the new mechanical braided metal ureteral stent designed and prepared in this subject has been shown by in vitro tests to have good radial support,full drainage of liquid,obvious anti-reflux advantages,good biocompatibility and anti-displacement effect,and can meet the clinical functional requirements for ureteral stents.It provides the theoretical and experimental basis for the subsequent animal test and clinical application.