scholarly journals 3D Computational Modeling of Bleb Initiation Dynamics

2021 ◽  
Vol 9 ◽  
Author(s):  
Wanda Strychalski
Keyword(s):  
Viscous Fluid ◽  
Leading Edge ◽  
Collagen Matrix ◽  
Theoretical Models ◽  
Initiation Mechanism ◽  
Scaling Properties ◽  
Cortical Tension ◽  
Actin Cortex ◽  
Expansion Time ◽  
Poroelastic Model

Blebbing occurs in cells under high cortical tension when the membrane locally detaches from the actin cortex, resulting in pressure-driven flow of the cytosol and membrane expansion. Some cells use blebs as leading edge protrusions during cell migration, particularly in 3D environments such as a collagen matrix. Blebs can be initiated through either a localized loss of membrane-cortex adhesion or ablation of the cortex in a region. Bleb morphologies resulting from different initiation mechanisms have not been studied in detail, either experimentally or with theoretical models. Additionally, material properties of the cytoplasm, such as elasticity, have been shown to be important for limiting bleb size. A 3D dynamic computational model of the cell is presented that includes mechanics and the interactions of the cytoplasm, the actin cortex, the cell membrane, and the cytoskeleton. The model is used to quantify bleb expansion dynamics and shapes that result from simulations using different initiation mechanisms. The cytoplasm is modeled as a both viscous fluid and as a poroelastic material. Results from model simulations with a viscous fluid cytoplasm model show much broader blebs that expand faster when they are initiated via cortical ablation than when they are initiated by removing only membrane-cortex adhesion. Simulation results using the poroelastic model of the cytoplasm provide qualitatively similar bleb morphologies regardless of the initiation mechanism. Parameter studies on bleb expansion time, cytoplasmic stiffness, and permeability reveal different scaling properties, namely a smaller power-law exponent, in 3D simulations compared to 2D ones.

scholarly journals Analysis of barotactic and chemotactic guidance cues on directional decision-making ofDictyostelium discoideumcells in confined environments

2020 ◽  
Vol 117 (41) ◽  
pp. 25553-25559 ◽  
Author(s):  
Yuri Belotti ◽  
David McGloin ◽  
Cornelis J. Weijer
Keyword(s):  
Decision Making ◽  
Single Cells ◽  
Model Organism ◽  
Leading Edge ◽  
Decision Making Process ◽  
Chip Design ◽  
Cortical Tension ◽  
Channel Analysis ◽  
Chemical Stimuli ◽  
Total Velocity

Neutrophils and dendritic cells when migrating in confined environments have been shown to actuate a directional choice toward paths of least hydraulic resistance (barotaxis), in some cases overriding chemotactic responses. Here, we investigate whether this barotactic response is conserved in the more primitive model organismDictyostelium discoideumusing a microfluidic chip design. This design allowed us to monitor the behavior of single cells via live imaging when confronted with bifurcating microchannels, presenting different combinations of hydraulic and chemical stimuli. Under the conditions employed we find no evidence in support of a barotactic response; the cells base their directional choices on the chemotactic cues. When the cells are confronted by a microchannel bifurcation, they often split their leading edge and start moving into both channels, before a decision is made to move into one and retract from the other channel. Analysis of this decision-making process has shown that cells in steeper nonhydrolyzable adenosine- 3', 5'- cyclic monophosphorothioate, Sp- isomer (cAMPS) gradients move faster and split more readily. Furthermore, there exists a highly significant strong correlation between the velocity of the pseudopod moving up the cAMPS gradient to the total velocity of the pseudopods moving up and down the gradient over a large range of velocities. This suggests a role for a critical cortical tension gradient in the directional decision-making process.

Induced Strain Actuation for Solid-State Ornithopters: Pitch and Heave Coupling

2017 ◽  
Author(s):  
Francis Hauris ◽  
Onur Bilgen
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Fiber Composite ◽  
Leading Edge ◽  
Theoretical Models ◽  
Element Model ◽  
Harmonic Excitation ◽  
Edge Stiffener ◽  
Modes Of Vibration ◽  
Composite Wing

This paper investigates the heaving and pitching of a wing-like parameterized cantilevered plate with a leading edge stiffener and clamp variation when actuated with a surface-bonded piezoelectric actuator. The response is analyzed using a finite element model that is validated by comparison with known analytical solutions. The validated finite-element model is subjected to a harmonic excitation parametric analysis. The parameters varied in the model are the root clamped percentage, leading edge stiffener thickness, and the aspect ratio of the plate. The model is examined at the first two Eigen frequencies. Metrics of heaving and pitching are developed using surface fitting methods and their amplitudes and phases are reported throughout the parameter space. Emphasis is placed on the interaction and coupling of the first two modes of vibration with respect to the parameters. A piezo-composite wing prototype is fabricated and actuated harmonically with a Macro-Fiber Composite actuator while leading edge stiffener thickness and root clamped percentage is varied. The resulting experimental data is used to further validate the theoretical models.

scholarly journals Lymphocyte egress signal sphingosine-1-phosphate promotes ERM-guided, bleb-based migration

2021 ◽  
Vol 220 (6) ◽  
Author(s):  
Tanner F. Robertson ◽  
Pragati Chengappa ◽  
Daniela Gomez Atria ◽  
Christine F. Wu ◽  
Lyndsay Avery ◽  
...  
Keyword(s):  
T Cells ◽  
Severe Combined Immunodeficiency ◽  
Leading Edge ◽  
Erm Proteins ◽  
T Cell Migration ◽  
Actin Cortex ◽  
Sphingosine 1 Phosphate ◽  
Cytoskeletal Responses ◽  
Lymphocyte Egress

Ezrin, radixin, and moesin (ERM) family proteins regulate cytoskeletal responses by tethering the plasma membrane to the underlying actin cortex. Mutations in ERM proteins lead to severe combined immunodeficiency, but the function of these proteins in T cells remains poorly defined. Using mice in which T cells lack all ERM proteins, we demonstrate a selective role for these proteins in facilitating S1P-dependent egress from lymphoid organs. ERM-deficient T cells display defective S1P-induced migration in vitro, despite normal responses to standard protein chemokines. Analysis of these defects revealed that S1P promotes a fundamentally different mode of migration than chemokines, characterized by intracellular pressurization and bleb-based motility. ERM proteins facilitate this process, controlling directional migration by limiting blebbing to the leading edge. We propose that the distinct modes of motility induced by S1P and chemokines are specialized to allow T cell migration across lymphatic barriers and through tissue stroma, respectively.

scholarly journals The interplay of stiffness and force anisotropies drives embryo elongation

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Thanh Thi Kim Vuong-Brender ◽  
Martine Ben Amar ◽  
Julien Pontabry ◽  
Michel Labouesse
Keyword(s):  
Experimental Data ◽  
Material Properties ◽  
Myosin Ii ◽  
Mechanical Forces ◽  
Cell Behaviour ◽  
Cortical Tension ◽  
Actin Cortex ◽  
Stiffness Anisotropy ◽  
Spatiotemporal Changes ◽  
Tissue Material

The morphogenesis of tissues, like the deformation of an object, results from the interplay between their material properties and the mechanical forces exerted on them. The importance of mechanical forces in influencing cell behaviour is widely recognized, whereas the importance of tissue material properties, in particular stiffness, has received much less attention. Using Caenorhabditis elegans as a model, we examine how both aspects contribute to embryonic elongation. Measuring the opening shape of the epidermal actin cortex after laser nano-ablation, we assess the spatiotemporal changes of actomyosin-dependent force and stiffness along the antero-posterior and dorso-ventral axis. Experimental data and analytical modelling show that myosin-II-dependent force anisotropy within the lateral epidermis, and stiffness anisotropy within the fiber-reinforced dorso-ventral epidermis are critical in driving embryonic elongation. Together, our results establish a quantitative link between cortical tension, material properties and morphogenesis of an entire embryo.

scholarly journals Dictyostelium myosin IK is involved in the maintenance of cortical tension and affects motility and phagocytosis

2000 ◽  
Vol 113 (4) ◽  
pp. 621-633 ◽  
Author(s):  
E.C. Schwarz ◽  
E.M. Neuhaus ◽  
C. Kistler ◽  
A.W. Henkel ◽  
T. Soldati
Keyword(s):  
Class I ◽  
Actin Binding ◽  
Cell Cortex ◽  
Tail Domain ◽  
Cortical Actin ◽  
Cortical Tension ◽  
Actin Cortex ◽  
Significant Enrichment ◽  
Motor Velocity ◽  
Distinctive Role

Dictyostelium discoideum myosin Ik (MyoK) is a novel type of myosin distinguished by a remarkable architecture. MyoK is related to class I myosins but lacks a cargo-binding tail domain and carries an insertion in a surface loop suggested to modulate motor velocity. This insertion shows similarity to a secondary actin-binding site present in the tail of some class I myosins, and indeed a GST-loop construct binds actin. Probably as a consequence, binding of MyoK to actin was not only ATP- but also salt-dependent. Moreover, as both binding sites reside within its motor domain and carry potential sites of regulation, MyoK might represent a new form of actin crosslinker. MyoK was distributed in the cytoplasm with a significant enrichment in dynamic regions of the cortex. Absence of MyoK resulted in a drop of cortical tension whereas overexpression led to significantly increased tension. Absence and overexpression of MyoK dramatically affected the cortical actin cytoskeleton and resulted in reduced initial rates of phagocytosis. Cells lacking MyoK showed excessive ruffling, mostly in the form of large lamellipodia, accompanied by a thicker basal actin cortex. At early stages of development, aggregation of myoK null cells was slowed due to reduced motility. Altogether, the data indicate a distinctive role for MyoK in the maintenance and dynamics of the cell cortex.

scholarly journals The evolution of city life

2018 ◽  
Vol 285 (1884) ◽  
pp. 20181529 ◽  
Author(s):  
James S. Santangelo ◽  
L. Ruth Rivkin ◽  
Marc T. J. Johnson
Keyword(s):  
Urban Areas ◽  
Evolutionary Biology ◽  
Natural Populations ◽  
Leading Edge ◽  
Theoretical Models ◽  
Global Scale ◽  
Urban Environments ◽  
Ecological Communities ◽  
Natural Ecosystems ◽  
Evolutionary Mechanisms

Urbanization represents a dominant and growing form of disturbance to Earth's natural ecosystems, affecting biodiversity and ecosystem services on a global scale. While decades of research have illuminated the effects of urban environmental change on the structure and function of ecological communities in cities, only recently have researchers begun exploring the effects of urbanization on the evolution of urban populations. The 15 articles in this special feature represent the leading edge of urban evolutionary biology and address existing gaps in our knowledge. These gaps include: (i) the absence of theoretical models examining how multiple evolutionary mechanisms interact to affect evolution in urban environments; (ii) a lack of data on how urbanization affects natural selection and local adaptation; (iii) poor understanding of whether urban areas consistently affect non-adaptive and adaptive evolution in similar ways across multiple cities; (iv) insufficient data on the genetic and especially genomic signatures of urban evolutionary change; and (v) limited understanding of the evolutionary processes underlying the origin of new human commensals. Using theory, observations from natural populations, common gardens, genomic data and cutting-edge population genomic and landscape genetic tools, the papers in this special feature address these gaps and highlight the power of urban evolutionary biology as a globally replicated ‘experiment’ that provides a powerful approach for understanding how human altered environments affect evolution.

The motion of a viscous drop sliding down a Hele-Shaw cell

1986 ◽  
Vol 163 ◽  
pp. 59-67 ◽  
Author(s):  
Kalvis M. Jansons
Keyword(s):  
Surface Tension ◽  
Viscous Fluid ◽  
Contact Angle Hysteresis ◽  
Leading Edge ◽  
Governing Equations ◽  
Drop Shape ◽  
Viscous Drop ◽  
Special Case ◽  
Hele Shaw Cell ◽  
Effect Of Surface

The motion of a viscous drop in a vertical Hele-Shaw cell is studied in a limit where the effect of surface tension through contact-angle hysteresis is significant. It is found that a rectangular drop shape is a possible steady solution of the governing equations, although this solution is unstable to perturbations on the leading edge. Even though the unstable edge is one where a viscous fluid is moving into a less viscous fluid, in this case air, this is shown to be a special case of the well-known Saffman—Taylor instability. An experiment is performed with an initially circular drop in which it is observed that the drop shape becomes approximately rectangular except at the leading edge, where it becomes rounded and sometimes has a ragged appearance.A drop sliding down a vertical Hele-Shaw cell is an example of a system where the action of surface tension is not always one of smoothing, since in this case it leads to the formation of right-angle corners at the back of the drop (rounded only slightly on the lengthscale of the gap thickness of the cell).

Locomotion of a self-propulsive pitching plate in a quiescent viscous fluid

2020 ◽  
pp. 095440622090333
Author(s):  
Li Wang
Keyword(s):  
Viscous Fluid ◽  
Leading Edge ◽  
Immersed Boundary ◽  
Flexible Plate ◽  
Bending Rigidity ◽  
Pitching Motion ◽  
Fluid Mass ◽  
Boltzmann Method ◽  
Ib Method ◽  
Insight Into

The locomotion of a flexible plate pitching in a quiescent viscous fluid is numerically studied by using the lattice Boltzmann method (LBM) for the fluid and a finite element method (FEM) for the plate, with an immersed boundary (IB) method for the fluid–structure interaction (FSI). In the simulation, the leading edge of the plate undergoes a prescribed pitching motion, and the entire plate moves freely due to the fluid–plate interaction. The effects of the pitching amplitude, bending rigidity, plate-to-fluid mass ratio and Reynolds number on the propulsive performance of the flexible plate are examined in a range of parameters. The numerical results show that a certain flexibility can remarkably improve the propulsive speed and efficiency. The optimal parameters for the pitching plate are obtained, i.e. [Formula: see text] ([Formula: see text] is a non-dimensional frequency, with [Formula: see text] means rigid plate and larger [Formula: see text] means more flexible) and 20° ≤  α0 ≤ 25° ( α0 is the pitching amplitude). The comparisons of three plate-to-fluid mass ratios (1.0, 2.5 and 5.0) show that the mass of the plate decreases the propulsive speed, but contrarily increases the efficiency. The results obtained in the present study provide an insight into the understanding of the performance of self-propulsive plate in pitching motion and can further guide the engineering design of micro aerial vehicles.

Validation of GenEcAm Software Results in Simulation of Seismic Behavior of Buildings Equipped with Damping System

2018 ◽  
Vol 880 ◽  
pp. 359-364 ◽  
Author(s):  
Adriana Ionescu ◽  
Mihai Negru ◽  
Cristian Oliviu Burada ◽  
Raluca Malciu
Keyword(s):  
Viscous Fluid ◽  
Dynamic Analysis ◽  
Computational Model ◽  
Seismic Behavior ◽  
Theoretical Models ◽  
Validation Process ◽  
The Creation ◽  
Fluid Dampers ◽  
Viscous Fluid Dampers

This paper presents the validation process of the GenEcAm program made by the author by comparing the results obtained with this program with the results obtained with the SAP2000 program at the dynamic analysis of a P+10E building equipped with viscous fluid dampers, one on each facade on each level. The results obtained with these two programs are very close, which validates the correctness of the analytical and computational model that underpinned the creation of the GenEcAm program. The GenEcAm program allows the use of 9 theoretical models of hysteresis to simulate seismic behavior of the dampers that equippe the structure of a building.

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