Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M26: Biofluids: Medical Devices |
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Chair: Jeremy Marston, Texas Tech University Room: 306 |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M26.00001: Hydrodynamics of jets in needle-free injections Jeremy Marston, Momene Moradi We present results from an experimental study of jets used in needle-free injections. Ultra-high-speed imaging at frame rates over 300 kfps was used to study the jet formation time, initial contact stage and penetration depth evolution when fired into gel substrates. Both commercial devices using gas and spring mechanisms and custom-made devices were tested, exhibiting some key differences. We also explored a range of liquid physical properties, in particular viscosity, in order to quantitatively explore the parameter space for this intriguing process. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M26.00002: A Computational and Mathematical Model for Device Induced Thrombosis Wei-Tao Wu, Nadine Aubry, Mehrdad Massoudi, James Antaki Based on the Sorenson's model of thrombus formation[1, 2], a new mathematical model describing the process of thrombus growth is developed. In this model the blood is treated as a Newtonian fluid, and the transport and reactions of the chemical and biological species are modeled using CRD (convection-reaction-diffusion) equations. A computational fluid dynamic (CFD) solver for the mathematical model is developed using the libraries of OpenFOAM. Applying the CFD solver, several representative benchmark problems are studied: rapid thrombus growth in vivo by injecting Adenosine diphosphate (ADP) using iontophoretic method and thrombus growth in rectangular microchannel with a crevice which usually appears as a joint between components of devices and often becomes nidus of thrombosis. Very good agreements between the numerical and the experimental results validate the model and indicate its potential to study a host of complex and practical problems in the future, such as thrombosis in blood pumps and artificial lungs. 1. Sorensen, E.N., et al., Computational simulation of platelet deposition and activation: I. Model development and properties. Ann Biomed Eng, 1999. 27(4): p. 436-48. 2. Sorensen, E.N., et al., Computational simulation of platelet deposition and activation: II. Results for Poiseuille flow over collagen. Ann Biomed Eng, 1999. 27(4): p. 449-58. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M26.00003: Selective control for helical microswimmers Panayiota Katsamba, Eric Lauga One of the greatest aspirations for artificial microswimmers is their application in non-invasive medicine. For any practical use, adequate mechanisms enabling control of multiple artificial swimmers is of paramount importance. Here we propose a multi-helical, freely-jointed motor as a novel selective control mechanism. We show that the nonlinear step-out behavior of a magnetized helix driven by a rotating magnetic field can be exploited, when used in conjunction with other helices, to obtain a velocity profile that is non-negligible only within a chosen interval of operating frequencies. Specifically, the force balance between the competing opposite-handed helices is tuned to give no net motion at low frequencies while in the middle frequency range, the swimming velocity increases monotonically with the driving frequency if two opposite helices are used, thereby allowing speed adjustment by varying the driving frequency. We illustrate this idea in detail on a two-helix system, and demonstrate how to generalize to N helices, both numerically and theoretically. We finish by explaining how to solve the inverse problem and design an artificial swimmer with an arbitrarily-complex velocity vs. frequency relationship. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M26.00004: Effects of bileaflet mechanical heart valve orientation on coronary flow Laura Haya, Stavros Tavoularis The aortic sinus is approximately tri-radially symmetric, but bileaflet mechanical heart valves (BMHVs), which are commonly used to replace diseased aortic valves, are bilaterally symmetric. This mismatch in symmetry suggests that the orientation in which a BMHV is implanted within the aortic sinus affects the flow characteristics downstream of it. This study examines the effect of BMHV orientation on the flow in the coronary arteries, which originate in the aortic sinus and supply the heart tissue with blood. Planar particle image velocimetry measurements were made past a BMHV mounted at the inlet of an anatomical aorta model under physiological flow conditions. The complex interactions between the valve jets, the sinus vortex and the flow in the right coronary artery were elucidated for three valve orientations. The coronary flow rate was directly affected by the size, orientation, and time evolution of the vortex in the sinus, all of which were sensitive to the valve's orientation. The total flow through the artery was highest when the valve was oriented with its axis of symmetry intersecting the artery's opening. The findings of this research may assist surgeons in choosing the best orientation for BMHV implantation. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M26.00005: Numerical Simulations of the Mechanics of Vitrectomy Ethan Young, Jeff Eldredge, Jean-Pierre Hubschman Vitreous is the clear, gel-like substance that fills the cavity between the lens and retina in the eye. Treating certain eye abnormalities requires removing this substance using a minimally-invasive device called a vitreous cutter. Understanding the behavior of this viscoelastic biofluid during surgeries is essential to improving the effectiveness of the procedure. In this study, three-dimensional computational models of vitreous cutters are investigated using an immersed boundary method paired with a viscoelastic constitutive model. The solver uses a fractional-step method to satisfy continuity and traction boundary conditions to simulate the applied suction. The current work extends previous efforts to accurately model the rheological parameters measured by Sharif-Kashani et al. using the Giesekus constitutive equation [Retina, 2013]. The simulations were used to quantify both the average and time-varying flow rate through the device. Values for flow rate are compared with experimental results from Hubschman et al. [Retina, 2009]. Flow features associated with the cutting dynamics are of particular interest, as is the geometry of the cutter itself. These operational and design changes are a target for improving cutter efficacy while minimizing potential tissue damage. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M26.00006: Correlation between Hemodynamics and Treatment Outcome of Intracranial Aneurysms after Intervention with Flow Diverters Nikhil Paliwal, Robert Damiano, Jason Davies, Adnan Siddiqui, Hui Meng Endovascular intervention by Flow Diverter (FD) - a densely woven stent - occludes an aneurysm by inducing thrombosis in the aneurysm sac and reconstructing the vessel. Hemodynamics plays a vital role in the thrombotic occlusion of aneurysms and eventual treatment outcome. CFD analysis of pre- and post-treatment aneurysms not only provides insight of flow modifications by FD, but also allows investigation of interventional strategies and prediction of their outcome. In this study 80 patient-specific aneurysms treated with FDs were retrospectively studied to evaluate the effect of intervention. Out of these cases, 16 required retreatment and thus are considered as having unfavorable outcome. Clinical FD deployment in these cases was simulated using an efficient virtual stenting workflow. CFD analysis was carried out on both pre- and post-treatment cases, and changes in hemodynamic parameters were calculated. Support vector machine algorithm was used to correlate the hemodynamic changes with outcome. Results show that cases having higher flow reduction into the aneurysmal sac have a better likelihood of occlusion. This suggests that changes in hemodynamics can be potentially used to predict the outcome of different clinical intervention strategies in aneurysms. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M26.00007: Computational modeling of Endovascular Chemofiltration device for removing toxins from blood Vitaliy Rayz, Ben Tompkins, Albert Chin, Anand Patel, Steven Hetts Purpose: Chemotherapy drugs injected intra-arterially in order to destroy tumor cells can cause systemic toxic effects. A catheter-based filtering device temporarily inserted into the veins downstream of the tumor can remove chemotherapy drugs out of the blood stream right after these drugs have had their effect on the tumor. CFD modeling can help optimize hemodynamic performance of the chemofilter membrane, which chemically binds the toxins. Methods: Two alternative designs of the chemofilter were evaluated in order to increase the contact area of the membrane, while minimizing its obstruction to the flow. The Navier-Stokes equations were solved with a finite-volume solver Fluent. Virtual contrast injections were computed by solving the advection-diffusion equation in order to determine the effect of the chemofilter configuration on the flow residence time. Results: The results demonstrated that one of the chemofilter configurations, while having a 10-fold larger contact area, is substantially less obstructive to the flow. Additional considerations, such as feasibility of deployment and re-sheathing of the device, will affect its final design. The optimization of the chemofilter hemodynamic performance will help minimize drug toxicity, thus allowing to use high-dose therapy [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M26.00008: Flow diversion and coil embolization may perform best in conjunction for treatment of intracranial aneurysms: a hemodynamic investigation Robert Damiano, Ding Ma, Adnan Siddiqui, Hui Meng Coiling and flow diversion is the current standard for treatment of intracranial aneurysms (IAs). Coils deployed into the IA sac trigger its thrombotic occlusion, while flow diverters (FDs) deployed across the IA ostium redirect blood flow and reconstruct the parent vessel. Despite the wide adoption of these interventions, poor treatment outcomes have been reported. Recent clinical reports indicate that IA patients treated with both coils and FDs had better outcomes, compared to individual strategies alone. To better understand the hemodynamic mechanisms underlying coiling and flow diversion, we applied our advanced FEM-based device modeling toolset in conjunction with CFD to investigate 3 clinical strategies: coiling, FD, and FD with adjunctive coiling. Using 3 patient-specific IAs as test beds, we assessed the hemodynamic modifications induced by each strategy. Hemodynamic modifications in inflow rate, velocity, and wall shear stress revealed that coils were most effective at reducing intra-aneurysmal flow, while FD worked best at reducing flow into the IA sac. When coils were combined with FD, these effects appeared to be synergistically enhanced. Our modeling results support clinical observations that flow diversion and coiling may work best in conjunction for treating IAs. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M26.00009: Computational fluid dynamics evaluation of incomplete stent apposition in a tapered artery Eric Poon, Vikas Thondapu, Andrew Ooi, Umair Hayat, Peter Barlis, Stephen Moore Coronary stents are deployed to prop open blocked arteries and restore normal blood flow, however in-stent restenosis (ISR) and stent thrombosis (ST) remain possibly catastrophic complications. Computational fluid dynamics (CFD) analyses can elucidate the pathological impact of alterations in coronary hemodynamics and correlate wall shear stress (WSS) with atherosclerotic processes. The natural tapering of a coronary artery often leads to proximal incomplete stent apposition (ISA) where stent struts are not in contact with the vessel wall. By employing state-of-the-art computer-aided design (CAD) software, generic open-cell and closed-cell coronary stent designs were virtually deployed in an idealised tapered coronary artery. Pulsatile blood flow (80 mL/min at 75 beats/min) was carried out numerically on these CAD models using a finite volume solver. CFD results reveal significant fluctuations in proximal WSS and large recirculation regions in the setting of proximal ISA, resulting in regions of high wall shear stress gradient (WSSG) that have been previously linked to poor endothelial cell coverage and vascular injury. The clinical significance of these proximal high WSSG regions will be correlated with findings from high-resolution in-vivo imaging. [Preview Abstract] |
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