Abstract
Event Abstract Back to Event Accelerated fatigue study of in situ fenestrated endovascular stent grafts deployed inside the 3D phantom of a patient's aortic arch aneurysm Tong Yao1, Leonard W. Tse2, Kongteng Tan2, Steven L. Marks3, Ian Robertson3, Kyle G. Mathews3, Jon P. Rust1, Gilles Soulez4, Sean A. Crawford2 and Martin W. King1, 5 1 North Carolina State University, College of Textiles, United States 2 Toronto General Hospital, UHN, University of Toronto, Divisions of Vascular Surgery & Interventional Radiology, Canada 3 North Carolina State University, College of Veterinary Medicine, United States 4 Hôpital Notre-Dame, CHUM, Université de Montréal, Département de radiologie, Canada 5 Donghua University, College of Textiles, China Introduction: An in situ fenestration technique is used to treat complex aortic aneurysms when the aneurysm involves vital arteries such as the renal arteries or left subclavian artery, and deployment of a conventional stent-graft would block blood flow to the kidneys or left arm[1]-[4]. The objective of the present study is to investigate the long term fatigue properties of this technique, by developing a fatigue test method using Bose Electroforce pulsatile fatigue tester and an accelerated cardiac motion system to reproduce the influence of cardiac and pulsatile motion to test the long-term stability of a stent graft system which is deployed and in situ fenestrated into a 3-D aortic aneurysmal model. Materials and Methods: Four polyurethane elastomeric phantoms (Fig1) of a specific patient’s aortic arch aneurysm were fabricated by using a 3D printing technique. This patient has previously undergone stent-graft deployment and retrograde in situ fenestration via the left subclavian artery. Then four Medtronic Valiant® stent grafts were deployed inside the phantoms followed by in situ fenestration. Atrium® covered stent extensions were then deployed at the fenestration site. An accelerated fatigue test method (Fig1) was established by modifying the Bose Electroforce fatigue tester and fabricating a cardiac motion system. The cardiac motion system was fabricated by utilizing a high speed 3000 rpm motor driven cam, which was selected to achieve 50 Hz frequency. This test method combined two types of fatigue, a pulsatile test and a tensile test, to mimic the real fatigue situation for the stent grafts. The phantoms with stent-grafts deployed inside were then attached to the fatigue tester and cycled at 50 Hz for 400 million cycles which is equivalent to 10 years’ of cardiac motion. CT scanning were used to capture change in the dimension of the covered stent and endoscopy were used to capture the appearance of tears around the covered stent and evaluate the size of the fenestration outside the covered stent (outer lumen). Results and Discussions: The dimensions, shape and size of the fenestrated areas were measured by CT scanning and endoscopy at 0 fatigue cycles under 120 mmHg (Fig2). The dimensions of the fenestrated area measured by these two imaging modalities were compared and the results are shown below (Fig3). Following an ANOVA test (confidence interval 95%), the dimensions measured by CT scanning endoscopy had no significant difference. After undergoing the fatigue test for 40 million cycles (equivalent to 1-year’s time), no significant difference in fenestrated dimensions and stent graft appearance were found either by CT scanning or by endoscopy. Conclusions: A fatigue test method has been developed using a Bose pulsatile fatigue tester and an accelerated cardiac motion at 50 Hz frequency. Dimensions measured with CT scan and endoscopy have no significant difference. Endovascular stent grafts were successfully fenestrated, and after 1 year (40 million cycles) of fatigue, there was no significant change in dimensions as measured by CT scan or endoscopy. Accelerated fatigue testing is continuing for a period equivalent to 10 years in vivo. Boris Chayer
Highlights
Introduction of fatigueFatigue is defined as the failure of a material to perform as intended after repeated cyclic stresses at a level less than its ultimate failure strength as measured by a single application of stress [62]
At the same time the silicon based radio-opaque ink dots could be observed on the polyester fabric when viewed in the x-ray radiographic imaging system (Figure 6.3), which indicates that the radioopacity of the silicon based ink appeared to be similar to that of the nitinol stent material
The average bursting strength test results measured before and after coating the polyester fabrics with silicon based radio opaque ink, were calculated and are shown in Tables 6.1 and 6.2 (For the individual measurements made on the specimen, see Appendix A and B): Table 6.1: Bursting strength results of Cook Zenith® flat polyester fabric
Summary
Fatigue is defined as the failure of a material to perform as intended after repeated cyclic stresses at a level less than its ultimate failure strength as measured by a single application of stress [62]. This is a problem that causes the failure of many materials such as metals on the railway and in aircraft, concrete in buildings and textile fabrics used for clothing, medical and industrial applications. To evaluate whether these clinical CT scans or micro CT techniques are able to visualize the polyester material with and without contrast agent In this case, no radio opaque coating was applied
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