Comparison of the endothelialization of small intestinal submucosa, dacron, and expanded polytetrafluoroethylene suspended in the thoracoabdominal aorta in sheep

PURPOSE: This study was undertaken to evaluate and compare endothelialization of small intestinal submucosa (SIS), Dacron, and expanded polytetrafluoroethylene (ePTFE) in high-pressure flow without aortic wall contact and to evaluate the suitability of SIS as a vascular graft material. MATERIALS AND METHODS: In 12 adult sheep, three types of membrane leaflets of similar thickness (approximately 200 mu m) were suspended within large square stents without contact with the thoracoabdominal aortic wall: SIS (n = 12), Dacron (n = 12), and ePTFE (n = 12). Each animal received one leaflet of each material. Aortograms were obtained before and after percutaneous implantation and when the animal was killed at 8 weeks (n = 6) or 18 weeks (n = 6). Cell coverage and remodeling of SIS, Dacron, and ePTFE membranes were assessed by gross and histologic microscopic examinations. RESULTS: Thirty-five successfully implanted leaflets were evaluated. SIS showed progressive remodeling. Thirty-three leaflets exhibited thickening as a result of neointimal formation and endothelialization, most likely from circulating endothelial cells. Dacron exhibited the greatest and most progressing degree of neointimal formation and endothelialization, followed by SIS and then ePTFE. With SIS and ePTFE, neointimal formation decreased with time, but endothelialization was stable. Uneven neointimal formation and endothelialization on the outer surfaces and distal leaflet positions were seen. CONCLUSIONS: SIS showed progressive remodeling with moderate and regressive neointimal formation and moderate stable endothelialization. Further study of its durability and incorporation into the aortic wall needs to be performed to evaluate its suitability as a cover for aortic endografts.