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 A24: Biofluids: General Physiology |
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Chair: Brian Storey, Olin College Room: 302 |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A24.00001: Transcapillary Trafficking of Clustered Circulating Tumor Cells Brian Storey, Sam Au, Yeng-Long Chen, Fatih Sarioglu, Sarah Javaid, Daniel Haber, Shyamala Maheswaran, Shannon Stott, Mehmet Toner Aggregates of circulating tumor cells (CTC-clusters) are known to be more metastatic than equal numbers of singlet circulating tumor cells. Yet the mechanisms responsible for CTC-cluster dissemination and tumor seeding are still largely unknown. Without direct experimental evidence, it was assumed that because of their size, CTC-clusters would occlude and rupture capillaries. In this work, we have challenged this assumption by investigating the transit of CTC-clusters through microfluidic capillary constrictions under physiological pressures. Remarkably, cancer cell aggregates containing 2-20 cells were observed to successfully traverse constrictions 5-10 microns with over 90\% efficiency. Clusters rapidly and reversibly reorganized into chain-like geometries to pass through constrictions in single file. This observation was verified by computational simulation of clusters modeled with physiological cell-cell interaction energies. Hydrodynamic analysis suggested that CTC-clusters were able to pass narrow constrictions by acting as individual cells in series, not as cohesive units. Upon exiting constrictions, clusters remained viable, proliferative and rapidly returned to ‘typical’ cluster morphologies. [Preview Abstract] |
Sunday, November 22, 2015 8:13AM - 8:26AM |
A24.00002: Transversal mixing in the gastrointestinal tract Dmitri Vainchtein, Perry Orthey, Henry Parkman We discuss results of numerical simulations and analytical modeling of transversal intraluminal mixing in the GI tract produced by segmentation and peristaltic contractions. Particles that start in different parts of the small intestine are traced over several contractions and mixing is described using the particles' probability distribution function. We show that there is optimal set of parameters of contractions, such as the depth and frequency, that produces the most efficient mixing. We show that contractions create well-defined advection patterns in transversal direction. The research is inspired by several applications. First, there is the study of bacteria populating the walls of the intestine, which rely on fluid mixing for nutrients. Second, there are gastrointestinal diseases, such as Crohn’s disease, which can be treated effectively using a drug delivery capsule through GI tract, for which it is needed to know how long it takes for a released drug to reach the intestinal wall. And finally, certain neurological and muscular deceases change the parameters of contractions, thus reducing the efficiency of mixing. Understanding an admissible range of the parameters (when mixing is still sufficient for biological purposes) may indicate when the medical action is required. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A24.00003: Fluid dynamic modelling of renal pelvic pressure during endoscopic stone removal Alexandros Oratis, John Subasic, James Bird, Brian Eisner Endoscopic kidney stone removal procedures are known to increase internal pressure in the renal pelvis, the kidney’s urinary collecting system. High renal pelvic pressure incites systemic absorption of irrigation fluid, which can increase the risk of postoperative fever and sepsis or the unwanted absorption of electrolytes. Urologists choose the appropriate surgical procedure based on patient history and kidney stone size. However, no study has been conducted to compare the pressure profiles of each procedure, nor is there a precise sense of how the renal pelvic pressure scales with various operational parameters. Here we develop physical models for the flow rates and renal pelvic pressure for various procedures. We show that the results of our models are consistent with existing urological data on each procedure and that the models can predict pressure profiles where data is unavailable. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A24.00004: The intestine is a blender Patricia Yang, Morgan LaMarca, David Hu According to the U.S. Department of Health and Human Services, digestive disease affects 60 to 70 million people and costs over 140 billion annually. Despite the significance of the gastrointestinal tract to human health, the physics of digestion remains poorly understood. In this study, we ask a simple question: what sets the frequency of intestinal contractions? We measure the frequency of intestinal contractions in rats, as a function of distance down the intestine. We find that intestines contract radially ten times faster than longitudinally. This motion promotes mixing and, in turn, absorption of food products by the intestinal wall. We calculate viscous dissipation in the intestinal fluid to rationalize the relationship between frequency of intestinal contraction and the viscosity of the intestinal contents. Our findings may help to understand the evolution of the intestine as an ideal mixer. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A24.00005: Fluid-solid modeling of lymphatic valves Alexander Caulk, Matthew Ballard, Zhanna Nepiyushchikh, Brandon Dixon, Alexander Alexeev The lymphatic system performs important physiological functions such as the return of interstitial fluid to the bloodstream to maintain tissue fluid balance, as well as the transport of immune cells in the body. It utilizes contractile lymphatic vessels, which contain valves that open and close to allow flow in only one direction, to directionally pump lymph against a pressure gradient. We develop a fluid-solid model of geometrically representative lymphatic valves. Our model uses a hybrid lattice-Boltzmann lattice spring method to capture fluid-solid interactions with two-way coupling between a viscous fluid and lymphatic valves in a lymphatic vessel. We use this model to investigate the opening and closing of lymphatic valves, and its effect on lymphatic pumping. This helps to broaden our understanding of the fluid dynamics of the lymphatic system. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A24.00006: A model for gas and nutrient exchange in the chorionic vasculature system of the mouse placenta Parisa Mirbod, John Sled The aim of this study is to develop an analytical model for the oxygen and nutrient transport from the umbilical cord to the small villous capillaries. The nutrient and carbon dioxide removal from the fetal cotyledons in the mouse placental system has also been considered. This model describes the mass transfer between the fetal and the maternal red blood cells in the chorionic arterial vasculature system. The model reveals the detail fetal vasculature system and its geometry and the precise mechanisms of mass transfer through the placenta. The dimensions of the villous capillaries, the total length of the villous trees, the total villi surface area, and the total resistance to mass transport in the fetal villous trees has also been defined. This is the first effort to explain the reason why there are at least 7 lobules in the mouse placenta from the fluid dynamics point of view. [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A24.00007: A reduced order model for fluid-structure interaction of thin shell structures conveying fluid for physiological applications Gary Han Chang, Yahya Modarres-Sadeghi In this work, a reduced-order model (ROM) is constructed to study fluid-structure interaction of thin shell structures conveying fluid. The method of snapshot Proper Orthogonal Decomposition (POD) is used to construct the reduced-order bases based on a series of CFD results, which then are improved using a QR-factorization technique to satisfy the various boundary conditions in physiological flow problems. In the process, two sets of POD modes are extracted: those due to the shell wall's motion and those due to the pulsatile flow. The Modal Assurance Criterion (MAC) technique is used for selecting the final POD modes used in the reduced-order model. The structure model is solved by Galerkin's method and the FSI coupling is done by adapting a coupled momentum method.~The results show that the dynamic behavior of thin shells conveying fluid is closely related to the distribution of the shell's Gaussian curvature, the existence of imperfections and the physiological flow conditions. This method can effectively construct a computationally efficient FSI model, which allows us to examine a wide range of parameters which exist in real-life physiological problems. [Preview Abstract] |
Sunday, November 22, 2015 9:31AM - 9:44AM |
A24.00008: Tear Film Dynamics Around a Rigid Model Blob Christiaan Ketelaar, Lan Zhong, RJ Braun, TA Driscoll, PE King-Smith, CG Begley Tear film break up (TBU) can occur after imperfections in the lipid layer arise. The imperfections may cause elevated evaporation, which causes TBU for large enough spots and grooves and for fast enough evaporation. TBU also occurs near smaller features in the lipid layer. These are apparently blobs of lipids that do not spread and which are too small for the evaporative mechanism to account for the dynamics. We investigate the tear film dynamics near a model rigid blob with a fixed constant surfactant concentration. We develop the lubrication-type equations that govern the tear film thickness, surfactant concentration, and osmolarity in the tear film beneath and near the blob. We perform numerical simulations for the evolution of the tear film thickness and analyze how the size of the blob, as well as the surfactant properties and transport, affect tear film dynamics. The thinning induced by the blob is of the correct time scale to compare with in vivo observations, and close comparison with the experiments will be made. [Preview Abstract] |
Sunday, November 22, 2015 9:44AM - 9:57AM |
A24.00009: Microfluidic model of the platelet-generating organ: beyond bone marrow biomimetics Mathilde Reyssat, Antoine Blin, Anne Le Goff, Aurelie Magniez, Sonia Poirault-Chassac, Bruno Teste, Geraldine Sicot, Kim Anh Nguyen, Feriel S. Hamdi, Dominique Baruch We present a new, rapid method for producing blood platelets in vitro from cultured megakaryocytes based on a microfluidic device. This device consists in a wide array of VWF coated micropillars. Such pillars act as anchors on megakaryocytes, allowing them to remain trapped in the device and subjected to hydrodynamic shear. The combined effect of anchoring and shear induces the elongation of megakaryocytes and finally their rupture into platelets and proplatelets. This process was observed with megakaryocytes from different origins and found to be robust. This original bioreactor design allows to process megakaryocytes at high throughput (millions per hour), with a platelet yield increasing four times in comparison with control experiments. Since platelets are produced in such a large amount, their extensive biological characterization is possible. Fluorescent microscopy observations, flow cytometry, aggregometry results indicate that platelets produced in this bioreactor are functional. [Preview Abstract] |
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