| Focusing on post-operative problems of endovascular aneurysm repair for an abdominal aortic aneurysm (AAA), transient 3D fluid-structure interaction (FSI) simulations were performed to study the hemodynamics and biomechanics of stented AAAs. The main objectives of this research include: generating physical insight of blood flow and wall stress coupling; AAA rupture analysis; impact of endoleaks, factors leading to migration, mechanism of endotension, proper stent-graft placement as well as optimal surgical recommendations; and improved stent-graft design. Simulation results indicate that: (i) the most likely AAA-rupture site is located near the anterior distal or right distal sides; (ii) the aneurysm monitoring program based on eight biomechanical risk factors can evaluate the severity of AAA-rupture risk and hence provides useful recommendations for endovascular surgeons; (iii) a secure stent-graft placement can significantly reduce sac pressure, mechanical stress, pulsatile wall motion and maximum AAA diameter, and hence may prevent AAA rupture effectively; (iv) a certain sac-pressure level may be caused by fluid-structure interactions in spite of the absence of endoleaks; (v) excessive AAA neck angle, iliac bifurcation angle, stent-graft size, aorto-uni-iliac stent-graft and hypertension are the key factors causing stent-graft migration; (vi) Type I and Type III endoleaks can elevate the sac-pressure to a patient's systemic level with a reduced pulsatility. The sac pressure caused by Type II endoleaks depends on the inlet branch pressure. The AAA-wall stress is elevated remarkably by endoleaks; but, endoleaks may mitigate the risk of stmt-graft migration; (vii) a higher von Mises stress is observed near the bending point of stems. A z-bend stent is suitable for largely angulated necks; but, hooks or barbs should be considered. The ultra-thin ePTFE graft material is not suited for z-bend stmt-grafts, whereas woven polyester (PET) graft is appropriate for both diamond and z-bend stent-grafts. Z-bend stems are appropriate for matching irregular necks or aneurysm geometries, while PET graft sheaths are better in reducing the level of endotension as well as axial shortening. Validated fluid-structure interaction simulations are realistic, predictive and powerful tools to generate physical insight of the hemodynamics and biomechanics of stented AAAs. |
