Laboratory Investigations
Comparison of the Endothelialization of Small Intestinal Submucosa, Dacron, and Expanded Polytetrafluoroethylene Suspended in the Thoracoabdominal Aorta in Sheep

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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 μm) 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

Section snippets

Animals

The study involved 12 adult female sheep weighing 49.7–70.6 kg (mean, 58.2 kg). All together, 36 devices were implanted in their thoracic aortas. The study was approved by the institutional animal care and use committee of the Oregon Health and Science University.

Devices

The devices used in the study were handmade in our research laboratory. They consisted of two parts, a small carrier for the membrane and a large square stent frame for its suspension (Fig 1) as previously described by Brountzos et al (

RESULTS

Thoracoabdominal aorta diameters ranged from 17.5 mm to 20.0 mm (mean, 19.01 mm). Thirty-five devices were successfully placed, and they self-centered in the longitudinal axis of the thoracoabdominal aorta. In one animal, the ePTFE device placed as the most proximal of the three devices tilted 90° and was positioned perpendicularly with no adverse sequelae. In all cases, including the tilted device, the suspended membranes were not in contact with the wall of the thoracoabdominal aorta.

SIS

Thickness of the SIS leaflets (Table 2) measured in their midportions ranged from 240 μmto520 μm (mean ± SD, 367.5 ± 120.8 μm) at 8 weeks and from 210 μmto490 μm (mean, 320 ± 121.9 μm) at 18 weeks. The SIS membrane material was still visible in the centers of the leaflets. At 8 weeks, it showed early remodeling, with host fibroblasts, neutrophils, plasma cells, and few macrophages interspersed among collagen fibers. At 18 weeks, SIS membranes exhibited advanced remodeling, with collagen fibers

ePTFE

Thickness of the ePTFE leaflets (Table 4) at their midportions ranged from 200 μmto360 μm (mean, 272 ± 67.6 μm) at 8 weeks and from 190 μm to 430 μm (mean, 268.3 ± 85.2 μm) at 18 weeks. Two leaflets were bare without any neointimal coating, and two were bare on their external surface. Neointima consisting of spindleshaped host cells and white blood cells covered the other membranes. On the internal surface, thickness of the neointima ranged from 10 μm to 130 μm (mean, 78.3 ± 66.4 μm) at 8 weeks

DISCUSSION

Recurring problems with endografts for endovascular aneurysm repair indicate that endograft design and coverings are both important (1, 2, 3, 4, 5, 6). Endografts should be flexible but strong enough to avoid kinking, perforation, or rupture. They also should become incorporated into the aortic wall to prevent migration and endoleaks. Endograft endothelialization could be beneficial and might decrease thrombus formation and occasional endograft occlusion that occurs mainly at its branch

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    This study was supported by a grant from Cook, Inc., Bloomington, IN. J.H. is an employee of Cook Biotech. None of the authors have identified a conflict of interest

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