Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session HB: Bio-Fluid Dynamics: Leukocyte Transport |
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Chair: Jonathan Freund, University of Illinois, Urbana-Champaign Room: Hilton Chicago Waldorf |
Monday, November 21, 2005 1:20PM - 1:33PM |
HB.00001: Viscoelastic Compound-Drop Models for Neutrophil Deformation and Transport in Capillaries James J. Feng, Pengtao Yue, Chunfeng Zhou It is well known that neutrophils take much longer time to traverse the pulmonary capillary bed than erythrocytes. This results in their accumulation in the lungs and formation of a reservoir readily recruited when needed. In recent years, neutrophil transport in the lungs has been modeled using increasingly realistic representation of the capillary network. However, the cell deformation has mostly been accounted for empirically. Thus, the determination of the transit time is often ambiguous for lack of a direct knowledge of the cell shape during the transit. In this talk, we will describe a detailed numerical simulation of a neutrophil passing through capillaries. Motivated by the intuition that the difference in transit time is due to the white cells' higher rigidity than red cells, we explore how the cell rheology affects its deformation and passage through capillaries. Using a novel phase-field representation, we first test the well-known Newtonian and viscoelastic drop models. Then we examine whether the apparent cell viscoelasticity can be captured by accounting for the existence of a more rigid nucleus. Comparison with measurements will determine which model features are appropriate. Finally we discuss geometric effects relevant to the pulmonary capillary network as well as various microfluidic devices developed for analysis and separation of blood cells. [Preview Abstract] |
Monday, November 21, 2005 1:33PM - 1:46PM |
HB.00002: Simulation of Cell Adhesion using a Particle Transport Model Jennifer Chesnutt, Jeffrey Marshall An efficient computational method for simulation of cell adhesion through protein binding forces is discussed. In this method, the cells are represented by deformable elastic particles, and the protein binding is represented by a rate equation. The method is first developed for collision and adhesion of two similar cells impacting on each other from opposite directions. The computational method is then applied in a particle-transport model for a cloud of interacting and colliding cells, each of which are represented by particles of finite size. One application might include red blood cells adhering together to form rouleaux, which are chains of red blood cells that are found in different parts of the circulatory system. Other potential applications include adhesion of platelets to a blood vessel wall or mechanical heart valve, which is a precursor of thrombosis formation, or adhesion of cancer cells to organ walls in the lymphatic, circulatory, digestive or pulmonary systems. [Preview Abstract] |
Monday, November 21, 2005 1:46PM - 1:59PM |
HB.00003: Computational modeling of leukocyte adhesion cascade (LAC) Kausik Sarkar, Xiaoyi Li In response to an inflammation in the body, leukocytes (white blood cell) interact with the endothelium (interior wall of blood vessel) through a series of steps--capture, rolling, adhesion and transmigration--critical for proper functioning of the immune system. We are numerically simulating this process using a Front-tracking finite-difference method. The viscoelastcity of the cell membrane, cytoplasm and nucleus are incorporated and allowed to change with time in response to the cell surface molecular chemistry. The molecular level forces due to specific ligand-receptor interactions are accounted for by stochastic spring-peeling model. Even though leukocyte rolling has been investigated through various models, the transitioning through subsequent steps, specifically firm adhesion and transmigration through endothelial layer, has not been modeled. The change of viscoelastic properties due to the leukocyte activation is observed to play a critical role in mediating the transition from rolling to transmigration. We will provide details of our approach and discuss preliminary results. [Preview Abstract] |
Monday, November 21, 2005 1:59PM - 2:12PM |
HB.00004: Towards a computational model of leukocyte adhesion cascade: Leukocyte rolling Damir Khismatullin, George Truskey Recruitment of leukocytes into sites of acute and chronic inflammation is a vital component of the innate immune response in humans and plays an important role in cardiovascular diseases, such as ischemia-reperfusion injury and atherosclerosis. Leukocytes extravasate into the inflamed tissue through a multi-step process called “leukocyte adhesion cascade”, which involves initial contact of a leukocyte with activated endothelium (tethering), leukocyte rolling, firm adhesion, and transendothelial migration. Recently we developed a fully three-dimensional CFD model of receptor-mediated leukocyte adhesion to endothelium in a parallel-plate flow chamber. The model treats the leukocyte as a viscoelastic cell with the nucleus located in the intracellular space and cylindrical microvilli distributed over the cell membrane. Leukocyte-endothelial adhesion is assumed to be mediated by adhesion molecules expressed on the tips of cell microvilli and on endothelium. We show that the model can predict both shape changes and velocities of rolling leukocytes under physiological flow conditions. Results of this study also indicate that viscosity of the cytoplasm is a critical parameter of leukocyte adhesion, affecting the cell's ability to roll on endothelium. This work is supported by NIH Grant HL- 57446 and NCSA Grant BCS040006 and utilized the NCSA IBM p690. [Preview Abstract] |
Monday, November 21, 2005 2:12PM - 2:25PM |
HB.00005: Floppy capsules in a viscous channel flow with application to leukocyte transport Jonathan Freund A boundary integral method is used to simulate the Stokes flow of 100 two-dimensional capsules in a rectangular streamwise periodic channel. The capsule walls are two-dimensional shells with reference length, linear tensile elasticity modulus, and linear bending modulus selected so that the an isolated capsule has a bi-concave minimum energy shape analogous to a human red blood cell. The reference shape of the capsules is circular with diameter $d$ and the channel is 13.5$d$ wide and its period in the streamwise direction is also 13.5$d$. Viscosity of the fluids inside and outside the capsules is matched. For fixed tensile-bending moduli ratio, it is found that the distribution of cell centroids in the channel is insensitive to the floppiness of the capsules. A larger stiff circular capsule is added to model a leukocyte (white cell). It is found that hydrodynamic forces alone keep the leukocyte in near contact with the channel wall for tens to hundreds of channel flow-through periods, with floppier red-cell-like capsules significantly promoting extended contact. A leukocyte in the free stream tends to stay near the center of the channel and has not been yet been observed to return to the wall even after nearly 1000 flow through periods. [Preview Abstract] |
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