scholarly journals Filamentous active matter: Band formation, bending, buckling, and defects

2020 ◽  
Vol 6 (30) ◽  
pp. eaaw9975 ◽  
Author(s):  
Gerard A. Vliegenthart ◽  
Arvind Ravichandran ◽  
Marisol Ripoll ◽  
Thorsten Auth ◽  
Gerhard Gompper
Keyword(s):  
Molecular Motors ◽  
Persistence Length ◽  
Topological Defects ◽  
Domain Size ◽  
Self Organization ◽  
Design Strategies ◽  
Band Formation ◽  
Microscopic Interactions ◽  
Large Length ◽  
Microscopy Techniques

Motor proteins drive persistent motion and self-organization of cytoskeletal filaments. However, state-of-the-art microscopy techniques and continuum modeling approaches focus on large length and time scales. Here, we perform component-based computer simulations of polar filaments and molecular motors linking microscopic interactions and activity to self-organization and dynamics from the filament level up to the mesoscopic domain level. Dynamic filament cross-linking and sliding and excluded-volume interactions promote formation of bundles at small densities and of active polar nematics at high densities. A buckling-type instability sets the size of polar domains and the density of topological defects. We predict a universal scaling of the active diffusion coefficient and the domain size with activity, and its dependence on parameters like motor concentration and filament persistence length. Our results provide a microscopic understanding of cytoplasmic streaming in cells and help to develop design strategies for novel engineered active materials.

scholarly journals Tunable two-dimensional polarization grating using a self-organized micropixelated liquid crystal structure

RSC Advances ◽  
2018 ◽  
Vol 8 (72) ◽  
pp. 41472-41479 ◽  
Author(s):  
Reo Amano ◽  
Péter Salamon ◽  
Shunsuke Yokokawa ◽  
Fumiaki Kobayashi ◽  
Yuji Sasaki ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Liquid Crystal ◽  
Nematic Liquid Crystal ◽  
Topological Defects ◽  
Self Organization ◽  
Two Dimensional ◽  
Self Organized ◽  
Optical Grating ◽  
Liquid Crystal Structure ◽  
Polarization Grating

A micro-pixelated pattern of a nematic liquid crystal formed by self-organization of topological defects is shown to work as a tunable two-dimensional optical grating.

scholarly journals Axial-Compressive Behavior, Including Kink-Band Formation and Propagation, of Singlep-Phenylene Terephthalamide (PPTA) Fibers

2013 ◽  
Vol 2013 ◽  
pp. 1-15 ◽  
Author(s):  
M. Grujicic ◽  
S. Ramaswami ◽  
J. S. Snipes ◽  
R. Yavari ◽  
C.-F. Yen ◽  
...  
Keyword(s):  
Detrimental Effect ◽  
Mechanical Response ◽  
Topological Defects ◽  
Kink Band ◽  
Coarse Grained ◽  
Computational Investigation ◽  
Band Formation ◽  
Longitudinal Tensile Strength ◽  
Kink Bands

The mechanical response ofp-phenylene terephthalamide (PPTA) single fibers when subjected to uniaxial compression is investigated computationally using coarse-grained molecular statics/dynamics methods. In order to construct the coarse-grained PPTA model (specifically, in order to define the nature of the coarse-grained particles/beads and to parameterize various components of the bead/bead force-field functions), the results of an all-atom molecular-level computational investigation are used. In addition, the microstructure/topology of the fiber core, consisting of a number of coaxial crystalline fibrils, is taken into account. Also, following our prior work, various PPTA crystallographic/topological defects are introduced into the model (at concentrations consistent with the prototypical PPTA synthesis/processing conditions). The analysis carried out clearly revealed (a) formation of the kink bands during axial compression; (b) the role of defects in promoting the formation of kink bands; (c) the stimulating effects of some defects on the fiber-fibrillation process; and (d) the detrimental effect of the prior compression, associated with fiber fibrillation, on the residual longitudinal-tensile strength of the PPTA fibers.

scholarly journals Integer topological defects organize stresses driving tissue morphogenesis

2020 ◽  
Author(s):  
Pau Guillamat ◽  
Carles Blanch-Mercader ◽  
Karsten Kruse ◽  
Aurélien Roux
Keyword(s):  
Topological Defects ◽  
Self Organization ◽  
Tissue Architecture ◽  
Tissue Morphogenesis ◽  
Compressive Stresses ◽  
Cellular Forces ◽  
Stress Patterns

AbstractTissues acquire their function and shape via differentiation and morphogenesis. Both processes are driven by coordinating cellular forces and shapes at the tissue scale, but general principles governing this interplay remain to be discovered. Here, we report that self-organization of myoblasts around integer topological defects, namely spirals and asters, triggers localized differentiation and, when differentiation is inhibited, drives the growth of cylindrical multicellular protrusions. Both localized differentiation and growth require specific stress patterns. By analyzing the experimental velocity and orientation profiles through active gel theory, we show that integer topological defects can concentrate compressive stresses, which we measure by using deformable pillars. Altogether, we envision topological defects as mechanical organizational centers that control differentiation and morphogenesis to establish tissue architecture.

scholarly journals Emergence of self-organized multivortex states in flocks of active rollers

2020 ◽  
Vol 117 (18) ◽  
pp. 9706-9711 ◽  
Author(s):  
Koohee Han ◽  
Gašper Kokot ◽  
Oleh Tovkach ◽  
Andreas Glatz ◽  
Igor S. Aranson ◽  
...  
Keyword(s):  
Computational Modeling ◽  
Collective Behavior ◽  
Rotational Motion ◽  
Collective Motion ◽  
Self Organization ◽  
Design Strategies ◽  
Vortex Phase ◽  
Active Elements ◽  
Self Organized ◽  
Dynamic Materials

Active matter, both synthetic and biological, demonstrates complex spatiotemporal self-organization and the emergence of collective behavior. A coherent rotational motion, the vortex phase, is of great interest because of its ability to orchestrate well-organized motion of self-propelled particles over large distances. However, its generation without geometrical confinement has been a challenge. Here, we show by experiments and computational modeling that concentrated magnetic rollers self-organize into multivortex states in an unconfined environment. We find that the neighboring vortices more likely occur with the opposite sense of rotation. Our studies provide insights into the mechanism for the emergence of coherent collective motion on the macroscale from the coupling between microscale rotation and translation of individual active elements. These results may stimulate design strategies for self-assembled dynamic materials and microrobotics.

Structural characterization of α,ω-DH6T monolayer films grown at the liquid–liquid interface

Soft Matter ◽  
2021 ◽  
Author(s):  
Manuel Johnson ◽  
Tim Hawly ◽  
Mingjian Wu ◽  
Erdmann Spiecker ◽  
Rainer H. Fink
Keyword(s):  
Structural Characterization ◽  
Liquid Interface ◽  
Self Organization ◽  
Water Interface ◽  
Monolayer Films ◽  
Solvent Water ◽  
Microscopy Techniques

The molecular self-organization of alkyl-functionalized hexathiophene monolayers prepared at the solvent–water interface is investigated by complementary microscopy techniques.

Domain Size Driven Instability: Self-Organization in Systems with Advection

2018 ◽  
Vol 78 (5) ◽  
pp. 2298-2322 ◽  
Author(s):  
Václav Klika ◽  
Michal Kozák ◽  
Eamonn A. Gaffney
Keyword(s):  
Domain Size ◽  
Self Organization

A Three-Dimensional Autowave Turbulence

1998 ◽  
Vol 08 (04) ◽  
pp. 677-684 ◽  
Author(s):  
V. N. Biktashev
Keyword(s):  
Three Dimensional ◽  
Topological Defects ◽  
Self Organization ◽  
Time Behavior ◽  
Long Time Behavior ◽  
Vortex Filaments ◽  
Principal Role ◽  
Cardiac Fibrillation ◽  
Internal Instability ◽  
Long Time

Autowave vortices are topological defects in autowave fields in nonlinear active media of various natures and serve as centers of self-organization in the medium. In three-dimensional media, the topological defects are lines, called vortex filaments. Evolution of three-dimensional vortices, in certain conditions, can be described in terms of evolution of their filaments, analogously to that of hydrodynamical vortices in LIA approximation. In the motion equation for the filament, a coefficient called filament tension, plays a principal role, and determines qualitative long-time behavior. While vortices with positive tension tend to shrink and so either collapse or stabilize to a straight shape, depending on boundary conditions, vortices with negative tension show internal instability of shape. This is an essentially three-dimensional effect, as two-dimensional media with the same parameters do not possess any peculiar properties. In large volumes, the instability of filaments can lead to propagating, nondecremental activity composed of curved vortex filaments that multiply and annihilate in an apparently chaotic manner. This may be related to a mechanism of cardiac fibrillation.

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