Fabrication And Performance Evaluation Of New Degradable Magnesium Alloy Tracheal Stent

Tracheal stenosis has produced an increasing number of trachea and bronchi diseases in recent years,tracheal stent is an effective method to deal with these diseases.Clinical tracheal stents（Ni-Ti alloy）are non-biodegradable and require secondary surgery after implantation,at the same time,their low biocompatibility can easily generate granulation hyperplasia and result in airway restenosis,which create pain and economic burden to the patients.Therefore,the research and development of new degradable tracheal stent as a new technology for the treatment of tracheal stenosis has attracted much attention.This research selects Mg-Zn-Y-Nd alloy microwire developed by our own laboratory,monofilament integration integrity braiding technology and diamond structure were adopted to prepare new full-degradable magnesium alloy tracheal stent supplemented by annealing treatment of 100 °C×10min,the diameter of the stents is Φ8 mm × 20 mm and the mesh size is 5 mm2.Tensile and compression test,electrochemical test,immersion test,SEM analysis,weight loss analysis and animal experiments were applied to optimize the braiding technology of stents and evaluate the in vivo and in vitro degradation behavior and biocompatible properties.Based on Mg alloy tracheal stent for the axial tensile properties and the radial compression performance test,the results indicates that the tensile strength,elongation rate,Compression strength and resilient rate for the stents prepared by wires of Φ0.16 mm,0.20 mm,0.24 mm and 0.28 mm are 107 MPa,193MPa,252 MPa,310MPa;35%,32%,49% 43%;84cN,173 cN,330cN 552 cN and 87.3%,85.4%,84.6%,85.4% respectively.The mechanical properties of tracheal stent braided with microwire of Φ0.24 mm are approximate to that of commercial Ni-Ti alloy stent.In vitro test indicates that the average degradation rate of braided stent and annealed stent immersed in Gamble’s solution for 4 weeks is 0.3085 mm/y and 0.0736 mm/y.There were obvious cracks on the surface of braided stent after immersion test,while the annealed stent still maintained a complete structure,which exhibit well degradation performance.The degradation behavior of annealed stent are as follows: i)in the junction areas,degradation extended from local pitting corrosion to fully corrosion as time went on,and the stent break down firstly in this area;ii)In other areas of stent,the degradation started from pitting corrosion homogeneously distributed on the area,the corrosion pits were small and shallow,and developed into uniform degradation at last.Magnesium alloy tracheal stent were implanted through balloon expansion technique to explore the degradation performance and biocompatibility of braided stent in vivo.The average degradation rate of magnesium alloy stent after implantation for 4 weeks is 0.5536 mm/y,which is faster than that of in vitro.X-ray observation,CT imaging,tracheal tissue dissection and pathological results indicates that the tracheal stents expanded well after implantation and fully degraded after 4 weeks,no granulation tissue hyperplasia and inflammation appeared,the tracheal didn’t show structural lesion,and the airway epithelial cells grew well,showing that the tracheal stent has good biocompatibility.Mg²⁺ concentration detection shows that the Mg²⁺ concentration in blood and urine didn’t change significantly.Viscera pathological observation results reveal that the stents didn’t cause lesions in important organs such as heart,liver,spleen,kidney,indicating that the tracheal stent has good biological safety in vivo.