| The disease of artery dilatation caused by arteriosclerosis,atheroma,fat, hypertension,congenital defect,inheritance,hemodynamics,and biomechanical factors has a strong impact on humans' health.Artery dilatation would threaten people's life since the artery may break with the gradual dilatation of the tumor, although it is not malignant.There are two ways to cure this kind of disease: traditional open surgery and endovascology.However,late complications as fatigue failures are always reported after the implantation of endovascular prostheses(also known as stent-graft(SG)),which failed the whole therapy. Therefore,evaluation and prediction of fatigue resistance of endovascular prostheses is very importantIn vitro fatigue resistance of endovascular prostheses was studied by this dissertation.Fatigue resistance,also known as durability,is an ability of the devices to maintain the original physical structure after they were implanted into human's body.There are many vacancies in fatigue research of endovascular prostheses,for example,the existed fatigue testers can't simulate real human conditions completely;there are no systematic report of fatigue properties of endovascular prostheses;people haven't understood the fatigue mechanism yet.;in vitro characterization and studying methods of fatigue failures haven't established yet,etc.According to the current situation of this field,an in vitro fatigue resistance testing system for vascular prostheses(FretsVP) has been designed and established by ourselves.This system contains 6 main parts as temperature control unit, peristaltic pump,specimen frame,silicone tube for guiding fluid,valve and pressure measuring device,which was designed according to the mechanism of humans' arterial system.Among which,the rotor of the peristaltic pump is equivalent to humans' ventricle,the roller is equivalent to aortic valve or mitral valve of humans' arterial system,temperature control unit is equivalent to vein and atrium,silicone tube and the specimen are equivalent to the arteries,the resisting force of the system plays the role of capillary vessels.FretsVP relatively simulates the real human conditions comparing to the existed testing equipments,which has applied China patent of invention,the publication No.is CN101105435. Changes of tubular diameter,fabric warp and weft count,thickness,mass per unit area,porosity and water permeability were used to characterize the macroscopic fatigue performances.Testing methods has been established through the preliminary test on FretsVP,meanwhile,testing efficiency of it has been verified.Through the analysis of systematic error and random error,testing methods and its steps have been optimized.Notandum during testing has also been obtained.Specimen size and testing time has been determined according to the characterization parameters and fatigue conditions.Influence of device frequency, pulsatile pressure and testing time was also obtained.According to statistical analysis,the optimized testing parameters were selected as 10Hz frequency, 450mmHg pressure,three testing time points as 0,24,38 hours.Twelve tubular fabrics of endovascular prostheses with different textile parameters(fabric construction,yarn size and yarn type) were tested on FretsVP.Changes of tubular diameter,fabric warp and weft count,porosity and water permeability etc before and after fatigue test indicated that those specimens did undergo fatigue process.It is discussed that fatigue is caused by the changes of energy inside the fabric under the condition of continuous pulsatile pressure.In order to approach new energy balance,yarn shifting will be occurred and fabric structure will be reorganized, thus the fatigue performances will be shown.It is also found that,besides testing frequency,pressure and testing time,textile parameters of the specimens also had impact on the fatigue performances.Quantification theory I was used to analyze the relationship of textile parameters and fatigue performances,different textile parameters has different contribution ratio to the fatigue failures.Fabric construction,yarn size and yarn type had interactive influences on the fatigue performance of tubular fabrics of endovascular prostheses,therefore,preferable textile parameter need to be considered according to different characterization parameters when the fabric tubes are designed and manufactured.The same twelve samples were also tested on EnduraTec fatigue tester in North Carolina State University.Testing conditions were selected as 100Hz frequency,140mmHg～200mmHg pressure range,three time points as 0,10 and 38.5 months.Quantification theory I was also used to analyze the results.Testing results of the two equipments,FretsVP and EnduraTec fatigue tester,were compared.Tubular diameter,fabric warp and weft count etc were all changed to different extent,the overall trend of the two results was the same,that is to say,the two equipments can simulate or predict the fatigue process of endovascular prostheses.It is to be noted that the difference of mechanism and testing condition of the two equipments also influence fatigue performance of the samples.EnduraTec fatigue tester provided pulsatile pressure to the samples,the fluid was not circulated as human's blood system.However,FretsVP provided pulsatile flow to samples,which is similar to human's real condition,and its frequency is much lower,therefore the recovery time of the sample is relatively longer after each pulse.Besides,testing time is also an important factor to impact the fatigue performance,the longer the testing time,the more significant it fatigued.Stent-graft sample,which is combined by tubular fabric and metallic stent, were also tested by FretsVP.Textile parameters of the tubular fabric were selected as 30 denier monofilament warp yarn,20 denier multifilament weft yarn,and 3/1 twill weave construction,its tubular diameter was 8 mm.Metallic stent was made of Nitinol wire.Suture specification was 3-0 and 5-0.Testing frequency was 10Hz, pressure range was 100-120 kPa(849-1019mmHg).After fatigue testing,raveling, breakage of fabric and suture were occurred.The coarser the suture,the earlier and easier the sample fatigued.It is discussed that there may be two reasons for the breakage of the samples:the pressure difference between the entering position and the outlet position and stress concentration of the sutures.In vitro fatigue evaluation system of textile vascular prostheses was established primarily.The in vitro fatigue evaluation system contains three aspects as macroscopic,mesoscopic,and microscopic,characterization parameters of each aspect were also established.Macroscopic characterization parameters include fabric tensile strength,bursting strength,tubular diameter,thickness,fabric warp and weft count,mass per unit area,porosity,and water permeability etc. Mesoscopic and microscopic characterization parameters include tensile strength and work of fracture of fibers,glass transition temperature,rate of dissolution etc. This in vitro fatigue evaluation system has laid a certain foundation for the further research on fatigue performances of endovascular prostheses.In summary,in vitro fatigue resistance testing system(FretsVP) and its testing method has been established;fatigue characterization parameters has been determined primarily;in vitro fatigue evaluation system of endovascular prostheses was established;the relationship between textile parameters and fatigue performance was also obtained.Above all,this dissertation is meaningful for the future design and optimization of textile structure of endovascular prostheses.It also did fatigue research of textile vascular prostheses systematically,which could lay a certain foundation for further relevant studies.
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