Preparation Technology Of Braided Biodegradable Ureteral Stentand Its Strcturesand Properties

Ureteral stents are widely used in urologic practice to keep ureteral patency, assure urinaryflow, protect renal function, and prevent ureteral stricture and obstruction. At present, the stentsused in the clinical practice are nondegradable which caused many complications and need thesecondary removal operation. With the enormous progress of biodegradable materials,biodegradable ureteral stents are being extensively studied. Because of their degradable properties,they could relieve or avoid some complications, and also eliminate the secondary removal surgery.On the basis of previous works, poly (glycolic acid)(PGA) and poly (lactic-co-glycolic acid)(PLGA) multi-filaments were selected in this study. PGA and PLGA multi-filaments were pliedinto a yarn, and then some of them were braided onto a Teflon cord by a conventional2-D tubularbraiding machine. After the heat treatment, the braided ureteral stent had a composite structureincluding the fiber and film components which had a good tensile strength and compressionresistance. Before the braiding process of the ureteral stents, the experimental work and theoreticalanalysis of tubular braids’ braiding process was studied. The change law of braiding angle andthread tension during braiding process and the effect of braiding technology on pore size andsurface coverage were investigatedThis study investigated the relationship between the process of braiding and post-processtreatment and mechanical properties and morphology. The results showed that as the gear ratiodecreased, the tensile strength of stent increased slightly, while its compressive load decreasedsignificantly with some pores on the stents. As the number of braiding yarns decreased, bothtensile and compression stresses were decreased. The compression resistance of iron heat-treatedstents are better than that of copper heat-treated stents, and its surfaces are smoother. The mechanical properties dramatically dropped after the chemical treatment, and there were somemicro-pores on the surface of chemical treated stents.The changes of tensile property, compression property, morphology and mass loss wereobserved during the in vitro degradation. The effect of braiding angles, number of braiding yarnsand chemical modification on the properties of the stents were also analyzed. The results indicatedthat the degradation rate of the membrane structure is faster than the fiber structure of the stent.The smaller the braiding angle was, the less the number of braiding yarns was, and the longer thechemical treated time was, the faster the degradation rate was.The study had investigated and analyzed the change law of some important braidingparameters, which laid the foundation of braiding technology study. Furthermore, this studyinvestigated the relationship between the preparation technology and mechanical and degradationproperties, which laid the foundation of biodegradable gradient stent study.