The Development Of A Functional Stent-Graft And The Animal Experiment Of Its Effect Of Preventing Type-Ⅰ Endoleak After Endovascular Aortic Aneurysm Repair

Objectives:1. To develop a functional stent-graft which can prevent some type-I endoleaks after endovascular aortic aneurysms repair (EVAR).2. To establish animal models of aortic aneurysm and type-I endoleak, then perform EVAR on them with the functional stent-grafts and general ones, and evaluate both the feasibility of the method for creating type-I endoleak model and the effect of preventing type-I endoleak with the functional stent-graft.3. To evaluate the biocompatibility between the functional stent-graft and the host aorta.Methods:1. The functional stent-graft was developed based on two kinds of commercialized products. Some kind of polymer which has the property of slowly swelling after contacting water was packaged with expanding-polytetra-fluroethylene(e-PTFE) graft, then the package was attached to the cephalic end of the stent-graft by sewing or sintering. Simultaneously theoretical calculation and a simulating experiment were performed to verify the hypothesis that there is some "cause and effect" relationship between the structural characteristics of the currently used stent-grafts and typr I endoleaks, and to evaluate the effect of preventing simulated type I leaks with the functional device.2. Aortic aneurysm models were established on 22 dogs weighing above 20 kg by sewing e-PTFE patches onto the abdominal or thoracic aortas, the aneurysm neck was also patched and surrounded by a sheared plastic pipe so that a local protrusion appeared and the post-EVAR type I endoleak can be expected. The survival animals were divided into 2 groups, then functional device and common device was implanted to each group dog, so the feasibility of type I endoleak model making method and the preventing type I endoleak efficacy of the functional device can be evaluated through DSA in operation and post-procedureCT follow-up. The specimens were retrieved at 4, 8 weeks after EVAR, the general status of biocompatibility and thrombolization of the aneurysm lumen can be observed.3. Specimens taken from the proximal, distal ends and the middle part of the endoprosthesis were cut into 5 urn sections, and stained with HE, Weigert's and Masson for histological analysis. Immunohistochemical staining was performed using antibodies to endothelial factor VIII antigen and smooth muscle cell (SMA) a-actin antibodies. Scanning electron microscopy was also performed on samples taken from the experimental group dogs.Results:1. Both the sewing and sintering methods can effectively attach the polymer package to the mainbody of the endoprosthesis, and it showed a satisfactory expansion in vitro. In theory the sintered package is safer than the sewing one. Calculation and simulated experiment proved that the structural characteristics of the currently used devices can lead to some type I endoleaks, and the functional stent-graft can effectively reduce the theoretical endoleak flow ratio.2. 16 of the 22 dogs survived and CT angiography showed that the aneurysm models were successfully created. During the EVAR procedure the instant type I endoleak appeared in 13 dogs. According to CT follow-up, in experimental group only 1 leak lasted for more than 3 days, 1 for lweek. However, all leaks of the control group lasted for more than 3 days, and 4 of them lasted for more than 4 weeks, the difference was significant (p=0.0006). Polymer leakage and mesenteric artery embolization events occurred on 2 dogs. On the 4 weeks' specimen of the control group, there was a thin, white, glistening neointima covering the luminal surface of the devices, the aneurysm lumen was not totally thrombolized compared with the experimental group. At 8 weeks the observations of the two groups were comparatively similar, and the "biologic fixation"of the device was not apparently influenced by the polymer expansion.3. In microscopic observation, no obvious inflammatory cells infiltration in both 2 kinds of stent-grafts. However, there is an abundance of granulation tissues around the grafts. The neointima at both ends showed formation of 2 layers-an inner cellular layer composed of fibrablasts, smooth muscle cells (SMC) and a few endothelial cells (EC), and an outer collagen-rich layer, and the neointima at the...