Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D18: Medical Devices |
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Chair: Jeremy Marston, Texas Tech University Room: Georgia World Congress Center B305 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D18.00001: The fluid mechanics of ureteroscope irrigation Jessica G Williams, Sarah L Waters, Derek E Moulton, Ben W Turney Flexible ureteroscopy is a minimally invasive treatment for kidney stone removal. The ureteroscope has a central lumen (working channel) for auxiliary instruments (working tools). Successful ureteroscopy requires a good intrarenal view, achieved by irrigation, i.e., driving a saline solution through the working channel via an applied pressure drop. Working tools within the working channel reduce the irrigation flow rate, thus posing a clinical challenge. We derive a mathematical model, based on systematic reductions of the Navier Stokes equations. We represent the channel and tool as coaxial, non-concentric cylinders of uniform cross-sections. The axial and cross-sectional flow equations decouple and the cross-sectional flow is governed by the 2D Stokes equations. Geometrical changes to the annular fluid domain affect the relationship between axial flow rate and applied pressure. The position of a working tool is predicted by determining its transverse trajectory subject to an initial perpendicular motion. Results identify an optimal geometry to maximise flow rate for a given pressure drop. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D18.00002: Evaluating Hemodynamic Performance and Drug Adsorption Efficacy of a Chemofilter Device with CFD Modeling Nazanin Maani, Steven Hetts, Vitaliy Rayz Purpose: A catheter-based Chemofilter device is proposed for reducing systemic toxicity of the Intra-Arterial Chemotherapy (IAC). The Chemofilter chemically adsorbs excessive IAC drugs when temporarily deployed in the vein, downstream of the tumor. The flow and transport are modeled to evaluate the Chemofilter efficacy. Methods: Several porous and non-porous Chemofilter prototypes are modeled with ANSYS Fluent. Electrochemical binding of the drug to the Chemofilter is modeled by coupling the Navier-Stokes and Advection-Diffusion equations. The porous prototype resembles an umbrella which consists of architected microcells. A multiscale approach is applied, where Darcy’s law is used to determine the permeability of a lattice of microcells, and the entire device is modeled as a porous media. The non-porous Chemofilter consists of multiple parallel tubes, with perforated walls to enhance flow mixing and promote drug adsorption to the membrane. Results: The porous membrane provides 4 times larger surface area per length than the parallel tubes. However, the pressure drop across the porous membrane is 3 times larger, for comparable resulting drug concentration. The CFD modeling allows the Chemofilter optimization while reducing cost and minimizing animal studies. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D18.00003: Numerical modeling of platelet margination and its impact on left ventricular assist device thrombogenicity Rodrigo Osuna-Orozco, Venkat Keshav Chivukula, Alberto Aliseda We investigate platelet margination and activation, and their role in the thrombogenicity of Left Ventricular Assist Device (LVAD) therapy. Using a novel model of platelet margination that accounts for the exclusion forces exerted by the spatial gradient of red blood cell concentration, we explore the impact of margination on the thrombogenicity in LVAD outflow graft as well as in the aortic arch region. Platelet microenvironment hemodynamics (instantaneous shear exposure, shear stress history, residence time) has been shown to be a dominant factor contributing to thrombogenesis in LVAD patients. Margination has been experimentally observed to occur in vessels with millimeter-size diameters and at shear rates relevant to LVAD flows. We elucidate the impact that platelet-red blood cell interactions have in platelet transport in the ascending aorta and the great vessels towards the brain to understand the high incidence of thromboembolic stroke in LVAD patients compared to thrombosis in other distal vessels, such as the renal or hepatic arteries. This investigation provides a validated model to be used on patient-specific vasculature reconstructions, as part of a wider effort to discover minimally thrombogenic LVAD implantation configurations and flow control strategies. |
Sunday, November 18, 2018 3:09PM - 3:22PM |
D18.00004: Ex-vivo studies of intradermal jet injection Jeremy O Marston, Jonathan A Simmons, Yatish S Rane, Rohilla Pankaj Intradermal delivery of vaccines are typically sought after due to a confluence of enhanced immune response and dose-sparing potential. For a typical fractional dose (0.1 ml) of liquid vaccine injected into the intradermal region of the skin, the primary indicator of successful injection is a raised `wheal' or skin `bleb'. This is commonly characterized as a circular region raised a few millimeters above the normal skin level with a blanched appearance. However, based purely from visual inspection of the skin, there is little information available on how to estimate the actual volume that has been correctly deposited into the ID region. Herein, we present a systematic study of skin bleb growth and ultimate bleb sizes from an ex-vivo study employing needle-free jet injection. The main focus is on correlation of the delivered volume, measured by mass diference on a fine resolution balance, and the geometrical dimensions of the skin bleb such as top-view diameter, diameter viewed from below the dermis, and the cross-section. In addition, we provide some unique observations on the growth dynamics of the skin blebs from the jet injection method. |
Sunday, November 18, 2018 3:22PM - 3:35PM |
D18.00005: Investigation of fluid properties and ambient pressure on jet performance for needle-free injections Yatish Rane, Jeremy O Marston Needle free jet injections have been used for more than a half century and are attractive for reductions in sharps waste and elimination of needle-stick injuries and cross-contamination. Previously, jet injectors have targeted intramuscular delivery, however recent developments in DNA-based vaccines necessitate intradermal and subcutaneous delivery. This presents a significant challenge because a successful device must consistently achieve a specific delivery depth, while simultaneously addressing the variability in mechanical properties of the skin and the physical properties of drugs. We attack this problem experimentally (with high-speed video), studying the effect of parameters such as fluid viscosity, rheology and ambient pressure on the jet characteristics such as coherence and speed. We also performed CFD simulations to examine the pressure drop and shear layer development in the orifice and how they might influence the jet characteristics. The simulations compared favourably to the experiments, thus providing us with a tool to development a broader understanding of the fluid flow in jet injection devices. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D18.00006: In-vitro studies of jet injection dynamics FNU Pankaj, Jeremy O Marston Recent advances in DNA-based vaccines require a precise drug delivery into intradermal and subcutaneous tissues, and drug manufacturers are increasingly seeking needle-free delivery methods, such as jet injection. In addition to jet speed and diameter, a key parameter that is thought to control deposition depth is the stand-off distance between the jet orifice and the skin. In this talk, we will present some recent results from an in-vitro study on the dynamics of needle-free jet injection. The principle control parameter used in our study was the stand-off distance between the jet orifice and the target and we show that there is a counter-intuitive (nonlinear) relationship between the stand-off and the depth of injection. We also study the effect of fluid viscosity and target strength. |
Sunday, November 18, 2018 3:48PM - 4:01PM |
D18.00007: The Control of temperature in Cavitation of Skin Sonoporation Sid Becker, Jeremy Robertson A Franz diffusion cell is modified in order to maintain a constant coupling fluid temperature during the sonoporation of porcine skin. The passive transport of calcein that followed sonoporation at each of these coupling fluid temperatures was then quantified with spectrofluorometry. A comparison was made between the post-sonoporation transports in order to determine the influence of the coupling fluid temperature. The transdermal transport of calcein following sonoporation increased with increasing coupling fluid temperature. After 5 hours of post-sonoporation diffusion at room temperature, the mean transport achieved with a coupling fluid temperature of 46°C was 1.5 times that achieved with a coupling fluid temperature of 33°C and 5.8 times that achieved with a coupling fluid temperature of 14°C. These increases were attributed to the well-established relationship between skin temperature and skin permeability, as well as the potential influence of temperature on the effectiveness of individual inertial cavitation collapse events. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D18.00008: Left ventricular hemodynamics with an implanted assisting device: an in-vitro PIV study Elizabeth Jermyn, Francesco Viola, James Warnock, Roberto Verzicco A left ventricular assist device (LVAD) is a mechanical pump implanted in heart failure patients to help the impaired left ventricle (LV) pump blood throughout the body. The LVAD continuously takes blood from the LV and delivers it to the aorta, thus decreasing the LV load. Getting a LVAD, however, involves several risks such as blood clot formation due to the presence of the pump and the modified fluid dynamics. In this work, the modified ventricular hemodynamics due to LVAD implantation is studied in-vitro using an elastic ventricle produced by transparent silicone. The ventricle is incorporated (with artificial mitral and aortic valves) into a pulse duplicator setup, which prescribes realistic pulsatile inflow/outflow to mimic a weak ejection fraction (EF) of about 20%. Thereafter, a continuous axial pump is connected at the LV’s apex to mimic a LVAD and its effect on the ventricular hemodynamics is investigated as a function of the pump flow suction. Using particle image velocimetry (PIV), we observe that the continuous pump flow effectively provides unloading on the LV and yields the EF to increase. However, proper recirculation at the apex and blood sweeping of the myocardium walls does not show much improvement under varying velocities of the continuous flow pump. |
Sunday, November 18, 2018 4:14PM - 4:27PM |
D18.00009: In-vitro investigation of the hemodynamics of the Left Ventricle supported by a Left Ventricular Assist Device Fanette Chassagne, Nathanael Machicoane, Venkat Keshav Chivukula, Jennifer Beckman Beckman, Claudius Mahr, Alberto Aliseda Use of Left Ventricular Assist Devices (LVAD) therapy has grown over the last decade with increased prevalence of advanced heart failure coupled with stagnant heart donor availability. Despite recent advances in LVAD design, thromboembolic and hemorrhaging events remain the primary cause of mortality and morbidity. We investigate unfavorable intraventricular hemodynamics around the LVAD inflow canula and apical region. Particle Image Velocimetry was used to analyze the flow inside a patient-specific LV phantom implanted with an LVAD. A pulsatile pump programmed to simulate the reduced native output of the failing LV was used to circulate an index of refraction matched blood-mimicking fluid through the LV. Clinically relevant parameters such as pulsatility and preload and afterload pressures were changed to understand their role in LV hemodynamics. Flow patterns conducive to intraluminal thrombus formation were identified. Specifically, stagnation and recirculation zones were observed in the apical region. These patterns are strongly influenced by the pulsatility and by the preload and afterload pressures. Such unfavorable hemodynamics may explain the incidence of thrombosis even in third generation optimized pumps, via platelet activation, aggregation and thrombus formation. |
Sunday, November 18, 2018 4:27PM - 4:40PM |
D18.00010: On the Characterization of Blood Velocity in Arteries Using a Combined Analytical and Doppler Imaging Approach Bchara Sidnawi, Zhen Chen, Chandra Sehgal, Srihdar Santhanam, Qianhong Wu In this work, we report a novel experimental and analytical approach to characterize the pulsatile blood flow field based on Doppler ultrasound imaging of the carotid and brachial arteries. The diameter-averaged (DA) velocity, obtained from the instantaneous velocity histograms extracted from the Doppler waveform, was adapted to the solution of a pulsatile flow in a pipe; from which the instantaneous velocity profiles were predicted and compared to local velocity measurements in the carotid and brachial arteries of four healthy human subjects. Excellent agreement as demonstrated by the regression slope of 0.97 and near-zero intercept was observed between the spatiotemporal flow field predictions and local velocity measurements at specific distances from the vessel wall. The DA velocity approach with a suitable mathematical interpretation, was statistically shown, based on near-real time in vivo measurements, to be more appropriate to use than the commonly used centerline-velocity (VC) approach reported in the literature by many previous studies. |
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