The main disadvantage of conventional ureteral stents commonly used to provide urinary drainage after urological practice is that the patients have to undergo a secondary surgical procedure to remove stents. A new braided thin-walled biodegradable ureteral stent composed of PGA （ polyglycolic acid） and PLGA （ eopolymer of polylactic and polygiycolic acid） mnltifilaments was evaluated in v/tro in this study. In vitro degradation was performed in artificial urine with pH of 5.8 and the temperature of 37~C. The mass loss, mechanical properties, and morphology were observed at different degradaing time intervals of 0, 1, 2, 3, 4, and 5 weeks. The stent had a thinner wail than those of other degradable stents and provided better mechanical properties. The braided thin-walled biodegradable ureteral stents began to degrade after 2 weeks. At the week of 5, the stents were fully degraded. The degradative process of stents is smooth and well controlled.
Small diameter arterial prostheses were required to treat coronary and cerebrovascular arterial diseases. The diameters of the artificial blood vessels should match the diameters of the host arteries. Besides,the mechanical properties of the arterial prostheses should be strong enough to endure the forces in the body after implantation. In this study,silk and polyester were woven into small diameter arterial prostheses and the dimensional and mechanical properties,as well as the water permeability,were investigated. The woven samples had an inner diameter ranging from 3. 65 to 3. 94mm. The wall thickness of the samples ranged from 0. 26 to 0. 28mm. Compared with polytetrafiuoroethylene( ePTFE) commercial devices,whose probe bursting strength was measured to be 15. 64 N /mm2,the woven samples had superior strength values ranging from20. 53 to 28. 97 N /mm2. In addition,the radial compliance of the woven samples was found to lie between the ePTFE sample and the pig's carotid artery,and the water permeability of all the woven samples was less than 300 mL /( cm2·min) which indicated that these woven samples could be implanted without preclotting.
Stent-grafts were commercialized rapidly and gained a broad clinical acceptance over the past two decades. However,relatively more recent recognition of particular stent-graft design shortcomings have been identified which need to be addressed. It appears that various stent-graft designs may be more or less resistant to metal fatigue and /or fabric abrasions which can lead to type III and type IV endoleaks over the long term. Therefore,it is necessary to investigate the fatigue performance of the most common stentgraft designs: Z-stents and ringed stents,in a long-term in vitro fatigue simulation environment. This paper aimed to analyze nondestructively( gross observations) and destructively( fabric characteristics,mechanical and chemical properties) in order to put forward suggestions to improve the fabric and stent characteristics that may prevent type III and IV endoleaks. The fabric supported with ringed stent-grafts remained nearly completely intact after 168h. However, the fabric supported with Z-stents demonstrated significant damage. Fabric characteristics and tensile strength of the fibers did not present a significant difference between the control and fatigue simulated specimens. The crystallinity declined for both specimens. The fatigue performance of fabrics supported with ringed stents appears to be superior to that supported with Z-stents. The potential for a dynamic and destructive interaction between the apices of Z-stents which can lead to fraying and /or tearing of the graft fabric must be addressed in future designs.
