Computational Modeling of Thrombus Formation in Aneurysms Treated with Shape Memory Polymer Foam or Bare Metal Coils
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To mitigate the risk of intracranial aneurysm rupture, which can lead to severe debilitation or death, embolic devices (e.g., bare metal coils or polymeric open-celled foams) are often delivered via catheter to the aneurysm sac. Hemodynamic perturbations imposed by the device’s geometry and biochemical interactions between blood in the aneurysm and the biomaterial surfaces can lead to a clotting response which marks the initial phase of healing. The ideal outcome of this response to treatment is complete aneurysm occlusion and isolation from the parent artery to reduce or eliminate the risk of aneurysm rupture. To compliment in vitro and in vivo device testing, which typically reveals limited information related to thrombus formation, a computational model which couples biofluid dynamics and biochemistry has been developed to simulate the transient thrombus formation within treated aneurysms. The model consists of 28 advection-diffusion-reaction partial differential equations to track blood proteins involved in clotting. Boundary flux terms are used to model the initiation of the intrinsic clotting pathway at thrombogenic device surfaces. This “medium-fidelity” approach is applied to an idealized 2D aneurysm geometry and the results are compared to predictions produced by a lower-fidelity model representative of modeling approaches common in the literature for evaluation of device-induced thrombosis. The latter method uses time-averaged flow features to estimate locations of clot formation while disregarding physiological and biochemical phenomena. In contrast, the medium-fidelity model developed in this work is able to represent the biochemical interactions between blood and biomaterial surfaces and produce transient predictions of clot growth within the treated aneurysm. The medium-fidelity model is applied to compare two different aneurysm treatment methods. First, treatment with embolic bare metal coils is simulated. While coils are the most commonly used devices for aneurysm treatment, their use can often lead to suboptimal clinical outcomes that can result in aneurysm regrowth. An alternative treatment method, which is also simulated in this work, is the use of porous shape memory foams. These foams are delivered though a catheter and can fully expand to fill the aneurysm sac, providing a scaffold for thrombus growth. The medium-fidelity model is used to predict the clotting response within aneurysms treated with either method. Overall, the results of the coil treatments are highly dependent on the random arrangement of coils within the aneurysm sac and, in many cases, incomplete filling is likely. In contrast, shape memory polymer foams produce a more uniform and predictable result, independent of the foam geometry or orientation. The computational thrombus model, as presented in this dissertation, should be viewed as an initial iteration of a more complete model. Future work is needed to address several model limitations, and model validation with experimental data is necessary to reduce model uncertainty. Nonetheless, the simulations in this work demonstrate the advantages of the medium-fidelity model approach over low-fidelity models, and they show the model’s potential as an engineering tool to aid in device design and improve clinical outcomes.
Computational Fluid Dynamics
Shape Memory Polymer Foam
Horn, John David (2018). Computational Modeling of Thrombus Formation in Aneurysms Treated with Shape Memory Polymer Foam or Bare Metal Coils. Doctoral dissertation, Texas A & M University. Available electronically from