Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J10: Biofluids: Single Cell and Bacteria I |
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Chair: Henry Fu, University of Utah Room: 140B |
Sunday, November 19, 2023 4:35PM - 4:48PM |
J10.00001: Red blood cell dynamics in fluid flow using a mesoscopic membrane model and immersed boundary method Pooja Vilas Bhagawat, Danesh Tafti Blood is a suspension of different types of cells in plasma, with RBCs constituting the major portion measuring around 45% of the total volume of the blood. When floating freely in plasma, RBCs have a biconcave shape, however they are flexible and easily deform under stress, which gives them ability to squeeze through narrow capillaries where oxygen and carbon dioxide are exchanged with the surrounding tissues. These factors indicate that RBCs have a significant influence on the dynamics of blood flow in the vasculature. Thus, the need of understanding the RBC dynamics, coupled with the challenges associated in-vivo studies, has driven us to develop an in-silico model to accurately simulate the dynamics of the RBCs in the capillary blood flow. A computational technique is developed where the viscoelastic RBC membranes are modelled using a mesoscopic coarse-grained model whereas the blood plasma is modelled with a finite volume Navier-Stokes solver. Immersed Body Method (IBM) is used to model the fluid-RBC interactions. The model is validated by analyzing its ability to describe RBC deformation in optical tweezers stretching tests, shape development in Poiseuille flow, and dynamics in simple shear flow. |
Sunday, November 19, 2023 4:48PM - 5:01PM |
J10.00002: Instability of wall-bound filaments induced by molecular motors Rosie A Cates, Debasish Das, Raymond E Goldstein, Eric Lauga Microtubule filaments found in biological cells may be anchored to the cell membrane at one end. Motor-driven transport along these filaments creates flows of the cytoplasmic fluid inside the cell, which in turn produces motion and deformations of the filaments. By investigating the behaviour of the resulting fluid-structure problem, we reveal a novel instability of the filaments resulting in their alignment with the cell walls. This instability mechanism may play a role in the generation of cell-spanning rotational fluid flows observed in Drosophila ooctyes. |
Sunday, November 19, 2023 5:01PM - 5:14PM |
J10.00003: A novel chemotactic response can reduce viral infection in Micromonas populations Henry C Fu, Richard J Henshaw, Marco Polin Micromonas commoda is a common motile uniflagellate pico-eukaryote found in marine environments. Previously, we have observed that the death and lysis of a single cell of Micromonas releases chemicals that triggers a novel motility response of other nearby Micromonas, in which they swim rapidly in a random direction. For the population of Micromonas surrounding a dying cell, this leads to a "burst event" in which Micromonas are locally depleted around the dying cell. It is known that viral infections are an important factor in Micromonas populations, causing up to 10% of deaths. Here, we hypothesize that burst events reduce the exposure and spread of viral infection in a Micromonas population, since dying cells release infectious viral particles. We develop a model for how a cell's motility response changes the amount of viral particles it will encounter after the lysis of a nearby cell. We find that the observed motility response can significantly reduce the exposure to viral particles. |
Sunday, November 19, 2023 5:14PM - 5:27PM |
J10.00004: Bacteria Accumulation in Confined Environments Andy S Garcia-Gordillo, Ameya Gajanan Prabhune, Anier Hernandez-Garcia, Nuris Figueroa-Morales Advancements in medicine and environmental remediation require investigation into bacterial transport and accumulation in confined geometries with the presence of flow. By looking at the dynamics of Escherichia coli bacteria in microfluidic channels of irregular cross-section, we identify a phenomenon of accumulation of bacteria in specific regions of the channel depending on the flow. We believe this accumulation results from the downstream and upstream distances covered by bacteria as they swim along the solid boundaries of the microchannel. To prove our hypothesis, we developed unique experiments for long-distance tracking of individual bacteria over macroscopic distances of a few millimeters. Our experimental findings can be rationalized through stochastic simulations incorporating the individual bacterial behavior as a function of their local environment. Our research provides insight into macroscopic transport processes in biological or soil networks. |
Sunday, November 19, 2023 5:27PM - 5:40PM |
J10.00005: Optimizing deep learning model for measuring 3D dynamics of single RBCs with AI-based digital holographic microscopy Kyler J Howard, Jihwan Kim, Sang Joon Lee Red blood cells (RBCs) can be important biomarkers for hematologic diseases as their morphology and hemodynamics may change. Current methods to measure the 3D translational and rotational motions of RBCs require complicated optical setups and post-processing, while being limited to straight microchannels. Thus, there is a strong need for a simple and effective method to measure RBCs’ 3D dynamics precisely. This study utilized novel digital in-line holographic microscopy and deep learning techniques to record holograms of RBCs flowing in a viscous fluid. The 3D position of RBCs was found by mathematically reconstructing holograms at various heights to find each cell’s focal plane and determining its in-plane centroid. Holograms of moving RBCs and their respective out-of-plane angle labels were used to train deep learning models. Supervised, residual, and self-supervised models were trained to find the best network for predicting the out-of-plane angle. The in-plane angle of each RBC was measured from the inclined angle of its major axis. The full 3D translational and rotational information of RBCs can be analyzed from sequential holographic images. These methods can be applied to various microfluidic channels to comparatively examine the 3D dynamics of RBCs with a high throughput. |
Sunday, November 19, 2023 5:40PM - 5:53PM |
J10.00006: Cortex-driven cytoplasmic flows in elongated cells Pyae Hein Htet, Eric Lauga The Drosophila melanogaster embryo, an elongated multinucleated cell, is a classical model system for eukaryotic development and morphogenesis. Recent work has shown that bulk cytoplasmic flows, driven by cortical contractions along the walls of the embryo, enable the uniform spreading of nuclei along the anterior-posterior (AP) axis necessary for proper embryonic development. Here we first use mathematical modelling to develop analytical solutions for the cytoplasmic flows driven by tangential cortical contractions in elongated cells. We then apply our results to recent experiments on nuclear transport in cell cycles 4-6 of Drosophila embryo development. By fitting the cortical contractions in our model to measurements, we reveal numerically and theoretically that experimental cortical flows enable near-optimal axial spreading of nuclei. |
Sunday, November 19, 2023 5:53PM - 6:06PM |
J10.00007: The Role of Strain Energy Stored in the bent Harpoon of Sea Anemone Elijah G James, Leslie Babonis, Chris Roh Cnidarians (Jellyfish, Coral, and Sea Anemone) are known for their explosive cnidocyte cells, used mainly for predation; Indeed, they use these explosive cells in aqueous environments to capture prey and defend themselves in seemingly unfavorable conditions given the dense medium that imposes a high drag force. Previous studies have identified that the pressurized cell chamber as the main driver of the harpoon. However, cnidocytes vary in size, shape and therefore diversity in firing mechanisms is entirely possible. Recently, we have successfully measured the firing mechanism of a cnidocyte of Nematostella Vectensis (starlet sea anemone) using micro-high-speed videography. The video suggested that the firing mechanism utilizes the release of bent harpoon, which is a strain energy release, much like spring, different from the pressure driven mechanism. To further study the role of the bent harpoon, we created a mechanical counterpart using a thin NiTiNol wire. To preserve the associated physics, dimensionless ratio between strain energy inside the harpoon and the hydrodynamic energy loss due to the drag was kept at a comparable ratio. The resulting kinematics of the mechanical model showed that the potential energy stored in the bending of the harpoon drives the forward acceleration of the harpoon. This mechanism contrasts with the previous notion that the pressurized chamber is solely responsible for their extreme harpoon speed and thus demonstrate the diverse evolution cnidocyte firing mechanism. |
Sunday, November 19, 2023 6:06PM - 6:19PM |
J10.00008: Spindle flow stability Weida Liao, Eric Lauga Intracellular transport plays a key role in fundamental cellular processes such as cell division. Advection by cytoplasmic streaming, the persistent flow of fluid inside a cell, is an example of active transport in eukaryotic cells. Experimental studies on mouse oocytes (immature egg cells) have investigated the influence of intracellular flow in meiosis II (cell division resulting in reproductive cells). In meiosis II, the spindle (the protein structure responsible for dividing the genetic material in a cell) maintains its position near the cortex (thin actin network bound to the cell membrane) for hours to days. The stable positioning of the spindle in the oocyte beneath the cortical cap, which is rich in filamentous actin and myosin-II motor proteins, is accompanied by cytoplasmic streaming, driven by the flow of actin filaments away from the cortical cap. In this talk, we use a combination of numerical and analytical modelling to reveal the physical origin of the stability of the spindle. |
Sunday, November 19, 2023 6:19PM - 6:32PM |
J10.00009: Cargo Transport by Schooling Microswimmers: from artificial to biological swimmers. Ivy Liu, Maggie Liu, Albane Théry, Ran Tao, Arnold J Mathijssen Through their motion, microswimmers entrain the fluid around them, allowing small surrounding objects like particles to get pushed or pulled along. We have developed a Brinkman squirmer model to match the experimental entrainment of self-propelling droplets to simulate schooling microswimmers and predicted that collective entrainment greatly enhances the cargo transport capabilities of microswimmers compared to a single microswimmer. To investigate the biological consequences of collective transport further, we turn to Chlamydomonas Reinhardtii, a unicellular algae that perform phototaxis. We present our experimental setup to explore the transport of tracer particles by biased biological swimmers in microfluidic chambers. We expect our study on collective entrainment to have applications for particle transport, oxygen redistribution, and food intake. |
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