Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K11: Fluid Dynamics in Biological SystemsRecordings Available
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Sponsoring Units: DFD Chair: Gerardo Pradillo, Georgetown University Room: McCormick Place W-181B |
Tuesday, March 15, 2022 3:00PM - 3:12PM |
K11.00001: A multiscale biophysical model gives quantized metachronal waves in a lattice of cilia Brato Chakrabarti, Sebastian Fürthauer, Michael J. Shelley Motile cilia are slender, hair-like cellular appendages that spontaneously oscillate under the action of internal molecular motors and are typically found in dense arrays. These active filaments coordinate their beating to generate metachronal waves that drive long-range fluid transport and locomotion. Until now, our understanding of their collective behavior largely comes from the study of minimal models that coarse-grain the relevant biophysics and the hydrodynamics of slender structures. Here we build on a detailed biophysical model to elucidate the emergence of metachronal waves on millimeter scales from nanometer-scale motor activity inside individual cilia. Our study of a 1D lattice of cilia in the presence of hydrodynamic and steric interactions reveals how metachronal waves are formed and maintained. We find that in homogeneous beds of cilia these interactions lead to multiple attracting states, all of which are characterized by an integer charge that is conserved. This even allows us to design initial conditions that lead to predictable emergent states. These ideas from a 1D lattice of cilia generalize to 2D carpets and we show that in nonuniform ciliary tissues, boundaries and inhomogeneities provide a robust route to metachronal waves. |
Tuesday, March 15, 2022 3:12PM - 3:24PM |
K11.00002: Frequency Response Characteristics of Fluid-Immersed Hair Beds Jonas Smucker Fluid immersed hair beds are a common occurrence in the body. Bronchial cilia, the capillary glycocalyx layer, and intestinal microvilli (among others) serve critical regulatory functions. To better understand these functions, and the role of passive hairs on fluid dynamics in biological settings, we investigate the frequency response characteristics of hair beds immersed in sinusoidally driven fluid. While the governing equations for the fluid are linear in this regime, we show that the presence of the hair bed induces a nonlinear relationship between the forcing parameters and the system’s mechanical impedance, contrasting the rigid limit. The response of the system is characterized via rheology experiments and compared to a bead-rod model. The nonlinearity of the system, and the ability of the hairs to respond with many degrees of freedom to shear makes them an interesting candidate for stirring fluids at low Reynolds number. |
Tuesday, March 15, 2022 3:24PM - 3:36PM |
K11.00003: Flow-induced fast and slow waltz of red blood cells, with rheological consequences. Yeng-Long Chen, Chih-Tang Liao, An-Jun Liu Flow induced self-organization into crysalline-like structures have been reported in tank-treading dilute red blood cell suspensions in recent studies [Shen et al, PRL 2018]. Here, we report "waltz"-like synchronized tumbling / rotation of red blood cell (RBC) pairs, under moderate volume fraction (3 to 10 %) and confined simple shear flow, observed using a computational model with lattice Boltzmann fluid coupled with biconcave discs matching RBC elasticity. Without accounting for RBC-RBC attraction, hydrodynamic interactions (HI) between RBCs is the main contribution to the spontaneous formation of waltzing pairs. Furthermore, HI between RBC and the wall boundary result in cross-stream migration to the flow centerline with zero velocity, leading to localized waltzing RBC pairs exhibing crystalline-like order. We further examined how RBC doublet formation increases the tumbling rotation period and reduces the suspension intrinsic viscosity. |
Tuesday, March 15, 2022 3:36PM - 3:48PM |
K11.00004: Correlating rheological time scales of human blood and physiology using transient flow protocols Elahe Javadi, Matthew Armstrong, Safa Jamali Blood is considered a complex fluid with a rate and time-dependent response to an applied deformation rate. At low shear rates, the bridging of fibrinogen proteins results in the formation of rouleaux structures manifesting in a large increase of overall viscosity and measurable yield stress. These internal flocculated mesostructures are however broken down under sufficient shear forces in a dynamical fashion giving rise to thermokinematic memory formation and thixotropic behavior of the blood. Thus, the rheological behavior of blood and more specifically timescales associated with thixotropic behavior in the blood can be used as a proxy to hematocrit and protein concentration in blood. We combine a series of experimental measurements with in silico flow measurements and show that using well-characterized flow protocols we can measure characteristic thixotropic timescale of blood under flowing conditions. We also present a continuum-level description of the rheological behavior based on a population balance model and correlate its model parameters to blood characteristics. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K11.00005: Fluid-Structure-Fracture Simulation of Endograft Stability in a Stent-Graft Abdominal Aortic Aneurysm Model Nguyen T Nguyen, Luka Pocivavsek Implementation of a stent-graft into an aneurysm is the most effective means to prevent rupture and aneurysm-related sudden death. Computer modeling is commonly used in abdominal aortic aneurysms to quantify the hemodynamic factors for endovascular aortic repair (EVAR). One such factor is the intrasac pressure, which is important for investigating endoleak. Endoleak is the blood flow into the aneurysmal cavity after EVAR. Stents that are optimally placed and sized can limit endoleak and reduce the risk of aneurysm rupture. We perform a novel simulation that couples fluid structure and fracture to model endoleak. The deformability of the stent and aorta is modeled through finite element analysis with appropriate constitutive models while the complex blood flow is simulated with computational fluid dynamics. We vary the system pressure to mimic the conditions of aortic blood flow to predict endoleak after EVAR. In this study, when endoleaks occur, it is due to the loss of elastic energy at the interface between the endograft and the aortic wall. We therefore propose a series of equations for the elasto-adhesive stability of an ideal seal zone. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K11.00006: Insect-inspired two-vein flapping wings with anisotropic rigidity Romeo Antier, Carlos García-Baena, Benjamin Thiria, Ramiro Godoy-Diana A network of veins confers insect wings their anisotropic rigidity. We study the aerodynamics of a flapping flexible wing with a two-vein pattern that mimics the elastic response of insect wings in a simplified manner. The experiments reveal an optimal configuration for aerodynamic force production by the flapping wings when the two veins are spaced at an angle of about 20 degrees. The 3D deformation of the wings is monitored during the experiment while, simultaneously, the instantaneous aerodynamic forces are recorded with a force balance. The optimal distribution of the vein network in terms of propulsive force is well explained by a model based on the average wing deformation during a flapping cycle. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K11.00007: Skydiving acrobatics and controllable leaping redefines springtails Victor M Ortega-Jimenez, Hungtang Ko, Saad Bhamla Springtails (Arthopoda: Collembola) have been erroneously portraited as impulsive jumpers with poor locomotion control and maneuvering abilities. Paradoxically, for these Collembolans that live on the surface of water, these locomotion skills are crucial for survival by evading a host of aquatic, semiaquatic and terrestrial predators. In this talk, we will describe our discovery of how semi-aquatic springtails (Isotomurus retardatus) execute controlled leaping and landing from the surface of water by changing their body posture and exploiting the tightly-coupled physics of two anatomical structures – their tail-like appendage (furcula) and a hydrophilic tube-like structure (collophore). For take-off, we discover that springtails control their trajectory angle, speed, and rotation rate by modulating the propulsive force generated by the furcula through the collophore interfacial adhesion. Through biological experiments and mathematical modeling, we demonstrate that simple body angle enables this directed control. In mid-air, the body posture change, from a linear to a U-shape, which influences aerodynamic forces and thus self-righting. We confirm self-righting using vertical wind tunnel experiments and 3d-printed physical models. And finally, for landing, we reveal how the collophore provides stability for perfectly landing on their feet (>85% of the time). Together, our work sees springtails in a new light as actively-controlled and directional jumpers as well as perfect landers, reinforcing why collembolans are one of the most diverse and abundant animal taxon on the planet. Our results can be applied to improving controlled jumping and landing in small robots. |
Tuesday, March 15, 2022 4:24PM - 4:36PM |
K11.00008: How sharpshooter insects exploit biological superpropulsion to catapult their droplet pee Elio J Challita, Prateek Sehgal, Shuvam Samadder, Rodrigo Krugner, Saad Bhamla Sharpshooter insects feed on plants' xylem fluid using their pierce-sucking mouthparts. Due to the low-nutrient content of this ingested fluid, these insects suck up to 300 times their natural body weight per day in order to obtain adequate nutrients. Interestingly, these insects resort to an exquisite mechanism to discharge their fluidic waste: they catapult their droplet pee one at a time using a resilin-actuated anal stylus at high speeds and accelerations. In this talk, we show that by tuning the kinematics of their stylus to the physical properties of the droplet, these insects fling the droplets at higher speeds than their stylus in a phenomenon dubbed as superpropulsion. Using a mathematical framework, we showcase the limits of superpropulsion in biological settings and we seek to disrupt this finely tuned mechanism by snipping their hydrophobic hairs. We also demonstrate how this mode of propulsion is energetically favorable compared to other mechanisms of waste disposal such as jetting at the length scale of these insects. |
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