@article{li_kleinstreuer_2006, title={Analysis of biomechanical factors affecting stent-graft migration in an abdominal aortic aneurysm model}, volume={39}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2005.07.010}, abstractNote={Focusing on a representative abdominal aortic aneurysm (AAA) with a bifurcating stent-graft (SG), a fluid–structure interaction (FSI) solver with user-supplied programs has been employed to solve for blood flow, AAA/SG deformation, sac pressure and wall stresses, as well as the downward forces acting on the SG. Simulation results indicate that implanting a SG can significantly reduce sac pressure, mechanical stress, pulsatile wall motion, and maximum diameter change in AAAs; hence, it may restore normal blood flow and prevent AAA rupture effectively. The transient SG drag force is similar in trend as the cardiac pressure. Its magnitude depends on multi-factors including blood flow conditions, as well as SG and aneurysm geometries. Specifically, AAA neck angle, iliac bifurcation angle, neck aorta-to-iliac diameter ratio, SG size, and blood waveform play important roles in generating a fluid flow force potentially leading to SG migration. It was found that the drag force can exceed 5 N for an AAA with a large neck or iliac angle, wide aortic neck and narrow iliac arteries, large SG size, and/or abnormal blood waveform. Thus, the fixation of self-expandable or balloon-expandable SG contact may be inadequate to withstand the forces of blood flowing through the implant and hence means of extra fixation should be considered. A comprehensive FSI analysis of the coupled SG–AAA dynamics provides physical insight for evaluating the luminal hemodynamics, and maximum AAA-stresses as well as biomechanical factors leading potentially to SG migration.}, number={12}, journal={JOURNAL OF BIOMECHANICS}, author={Li, Z. and Kleinstreuer, C.}, year={2006}, pages={2264–2273} }
 @article{li_kleinstreuer_2005, title={A new wall stress equation for aneurysm-rupture prediction}, volume={33}, ISSN={["1573-9686"]}, DOI={10.1007/s10439-005-8979-2}, abstractNote={Aneurysms, especially in the abdominal aorta (AAA), are prone to rupture, and hence a reliable and easy-to-use predictor is most desirable. Based on clinical observations and numerical analyses, a semi-empirical equation for the peak AAA-wall stress has been developed. It can be readily used for AAA-rupture predictions or can be integrated into more elaborate AAA-assessment models.}, number={2}, journal={ANNALS OF BIOMEDICAL ENGINEERING}, author={Li, Z and Kleinstreuer, C}, year={2005}, month={Feb}, pages={209–213} }
 @article{li_kleinstreuer_2005, title={Blood flow and structure interactions in a stented abdominal aortic aneurysm model}, volume={27}, ISSN={["1873-4030"]}, DOI={10.1016/j.medengphy.2004.12.003}, abstractNote={Since the introduction of endovascular techniques in the early 1990s for the treatment of abdominal aortic aneurysms (AAAs), the insertion of an endovascular graft (EVG) into the affected artery segment has been greatly successful for a certain group of AAA patients and is continuously evolving. However, although minimally invasive endovascular aneurysm repair (EVAR) is very attractive, post-operative complications may occur. Typically, they are the result of excessive fluid-structure interaction dynamics, possibly leading to EVG migration. Considering a 3D stented AAA, a coupled fluid flow and solid mechanics solver was employed to simulate and analyze the interactive dynamics, i.e., pulsatile blood flow in the EVG lumen, pressure levels in the stagnant blood filling the AAA cavity, as well as stresses and displacements in the EVG and AAA walls. The validated numerical results show that a securely placed EVG shields the diseased AAA wall from the pulsatile blood pressure and hence keeps the maximum wall stress 20 times below the wall stress value in the non-stented AAA. The sac pressure is reduced significantly but remains non-zero and transient, caused by the complex fluid-structure interactions between luminal blood flow, EVG wall, stagnant sac blood, and aneurysm wall. The time-varying drag force on the EVG exerted by physiological blood flow is unavoidable, where for patients with severe hypertension the risk of EVG migration is very high.}, number={5}, journal={MEDICAL ENGINEERING & PHYSICS}, author={Li, ZH and Kleinstreuer, C}, year={2005}, month={Jun}, pages={369–382} }
 @article{li_kleinstreuer_2006, title={Computational analysis of type II endoleaks in a stented abdominal aortic aneurysm model}, volume={39}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2005.09.002}, abstractNote={Insertion of a stent-graft into an aneurysm to form a new (synthetic) blood vessel and prevent the weakened artery wall from rupture is an attractive surgical intervention when compared to traditional open surgery. However, focusing on a stented abdominal aortic aneurysm (AAA), post-operative complications such as endoleaks may occur. An endoleak is the net influx of blood during the cardiac cycle into the cavity (or sac) formed by the stent-graft and the AAA wall. A natural endoleak source may stem from one or two secondary branches leading to and from the aneurysm, labeled types IIa and IIb endoleaks. Employing experimentally validated fluid-structure interaction solvers, the transient 3-D lumen and cavity blood flows, wall movements, pressure variations, maximum wall stresses and migration forces were computed for types IIa and IIb endoleaks. Simulation results indicate that the sac pressure caused by these endoleaks depends largely on the inlet branch pressure, where the branch inlet pressure increases, the sac pressure may reach the systemic level and AAA-rupture is possible. The maximum wall stress is typically located near the anterior-distal side in this model, while the maximum stent-graft stress occurs near the bifurcating point, in both cases, due to local stress concentrations. The time-varying leakage rate depends on the pressure difference between AAA sac and inlet branch. In contrast, the stent-graft migration force is reduced by type II endoleaks because it greatly depends on the pressure difference between the stent-graft and the aneurysm cavity.}, number={14}, journal={JOURNAL OF BIOMECHANICS}, author={Li, Z. and Kleinstreuer, C.}, year={2006}, pages={2573–2582} }
 @article{li_kleinstreuer_2006, title={Effects of major endoleaks on a stented abdominal aortic aneurysm}, volume={128}, ISSN={["1528-8951"]}, DOI={10.1115/1.2132376}, abstractNote={Insertion of a stent-graft into an aneurysm, especially abdominal aortic aneurysms (AAAs), is a very attractive surgical intervention; however, it is not without major postoperative complications, such as endoleaks. An endoleak is the transient accumulation of blood in the AAA cavity, which is formed by the stent-graft and AAA walls. Of the four blood pathways, a type I endoleak constitutes the major one. Thus, focusing on both proximal and distal type I endoleaks, i.e., the minute net influx of blood past the attachment points of a stent-graft into the AAA cavity, the transient three-dimensional interactions between luminal blood flow, stent-graft wall, leakage flow, and AAA wall are computationally simulated. For different type I endoleak scenarios and inlet pressure wave forms, the impact of type I endoleaks on cavity pressure, wall stress, and stent-graft migration force is analyzed. The results indicate that both proximal type I-a and distal type I-b endoleaks may cause cavity pressures close to a patient’s systemic pressure; however, with reduced pulsatility. As a result, the AAA-wall stress is elevated up to the level of a nonstented AAA and, hence, such endoleaks render the implant useless in protecting the AAA from possible rupture. Interestingly enough, the net downward force acting on the implant is significantly reduced; thus, in the presence of endoleaks, the risk of stent-graft migration may be mitigated.}, number={1}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Li, Z and Kleinstreuer, C}, year={2006}, month={Feb}, pages={59–68} }
 @article{li_kleinstreuer_2005, title={Fluid-structure interaction effects on sac-blood pressure and wall stress in a stented aneurysm}, volume={127}, ISSN={["1528-8951"]}, DOI={10.1115/1.1934040}, abstractNote={Abstract
               An aneurysm is a local artery ballooning greater than 50% of its nominal diameter with a risk of sudden rupture. Minimally invasive repair can be achieved by inserting surgically a stent-graft, called an endovascular graft (EVG), which is either straight tubular, curved tubular, or bifurcating. However, post-procedural complications may arise because of elevated stagnant blood pressure in the cavity, i.e., the sac formed by the EVG and the weakened aneurysm wall. In order to investigate the underlying mechanisms leading to elevated sac-pressures and hence to potentially dangerous wall stress levels and aneurysm rupture, a transient 3-D stented abdominal aortic aneurysm model and a coupled fluid-structure interaction solver were employed. Simulation results indicate that, even without the presence of endoleaks (blood flowing into the cavity), elevated sac pressure can occur due to complex fluid-structure interactions between the luminal blood flow, EVG wall, intra-sac stagnant blood, including an intra-luminal thrombus, and the aneurysm wall. Nevertheless, the impact of sac-blood volume changes due to leakage on the sac pressure and aneurysm wall stress was analyzed as well. While blood flow conditions, EVG and aneurysm geometries as well as wall mechanical properties play important roles in both sac pressure and wall stress generation, it is always the maximum wall stress that is one of the most critical parameters in aneurysm rupture prediction. All simulation results are in agreement with experimental data and clinical observations.}, number={4}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Li, Z and Kleinstreuer, C}, year={2005}, month={Aug}, pages={662–671} }
 @article{kleinstreuer_li, title={Analysis and computer program for rupture-risk prediction of abdominal aortic aneurysms}, volume={5}, journal={Biomedical Engineering Online}, author={Kleinstreuer, C. and Li, Z. H.} }