Finite element modeling of a novel self-expanding endovascular stent method in treatment of aortic aneurysms

Abstract

A novel large self-expanding endovascular stent was designed with strut thickness of 70 μm × 70 μm width. The method was developed and investigated to identify a novel simpler technique in aortic aneurysm therapy. Stage 1 analysis was performed after deploying it in a virtual aneurysm model of 6 cm wide × 6 cm long fusiform hyper-elastic anisotropic design. At cell width of 9 mm, there was no buckling or migration of the stent at 180 Hg. Radial force of the stents was estimated after parametric variations. In stage 2 analysis, a prototype 300 μm × 150 μm stent with a cell width of 9 mm was chosen, and it was evaluated similarly after embedding in the aortic wall, and also with a tissue overgrowth of 1 mm over the stent. The 300/150 μm stent reduced the peak wall stress by 70% in the aneurysm and 50% reduction in compliance after embedding. Stage 3 analysis was performed to study the efficacy of stents with struts (thickness/width) 70/70, 180/100 and 300/150 μm after embedding and tissue overgrowth. The adjacent wall stresses were very minimal in stents with 180/100 and 70/70 μm struts after embedding. There is potential for a novel stent method in aortic aneurysm therapy.

Figure 1. The upper panel shows an overlay of the stent over the aneurysm model.

The stent is larger than the aneurysm and is deployed internally. The figure shows a cross sectional analysis of the stent deployed in 7.5 and 9 mm cell sizes. The cell width of 9 mm had no buckling as shown in the figure.

Figure 2. The upper panels show the aortic shape before and after stenting at 100 and 160 mmHg pressures.

Stress and strain distribution, and the contact pressures in the aortic wall after deployment of 70/70 μm at 0 mmHg and 100 mmHg.

Figure 3. Stress distribution and strain of the aorta before and after stenting with the 70/70 μm Nitinol stent at 160 mmHg.

Figure 4. Results of the radial force testing of the stents at various (70/70, 180/100 and 300/150 μm) strut dimensions.

Figure 5. The maximal stress distribution pattern in the aortic wall after deployment of 300/150 μm in the wall at 100 mmHg and 180 mmHg is depicted.

There are 4 panels. The first panel has no stent, the second panel has stent deployed, the third panel has the stent embedded, and the fourth panel shows the stent embedded with tissue growth.

Figure 6. The maximal stress distribution pattern in the aortic wall after deployment of stents with strut thickness of 70/70, 180/100 and 300/150 μm's in the aortic wall, at 100 mmHg and 180 mmHg is depicted.

Figure 7. The aneurysm model used in the study is shown in Panel A. Panel B shows the helical and straight pattern of the stents developed in the study for testing.

Panel C shows the enlarged view of the helical pattern of the stent used.

Figure 8. The aneurysm model before and after deployment of 300/150 μm stent is shown.

The stent was embedded and thereafter a model was created with a tissue overgrowth of 1 mm.