Spontaneous flow created by active topological defects

Risler, Thomas; Joanny, Jean‐François

doi:10.1140/epje/s10189-022-00186-2

Cited by 4 publications

(2 citation statements)

References 52 publications

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“…We also computed the flow fields' vorticity ω zv y zx − zv x zy (color code in Figures 2C,F). In line with nematic field theories [14,51] the +1/2 defect displays two regions of vorticity with opposite sign and the −1/2 defect shows a combination of six regions with alternating sign. These results for isolated defects lead us to expect that the +1/2 defect self-propulsion dynamics familiar from fixed-size active nematics will compete with the radial expansion flow in growing active nematics.…”

Section: Velocity Field For Isolated Nematic Defectssupporting

confidence: 73%

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Do Active Nematic Self-Mixing Dynamics Help Growing Bacterial Colonies to Maintain Local Genetic Diversity?

Schwarzendahl

Beller

2022

Front. Phys.

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Recent studies have shown that packings of cells, both eukaryotic cellular tissues and growing or swarming bacterial colonies, can often be understood as active nematic fluids. A key property of volume-conserving active nematic model systems is chaotic self-mixing characterized by motile topological defects. However, for active nematics driven by growth rather than motility, less is understood about mixing and defect motion. Mixing could affect evolutionary outcomes in bacterial colonies by counteracting the tendency to spatially segregate into monoclonal sectors, which reduces the local genetic diversity and confines competition between subpopulations to the boundaries between neighboring sectors. To examine whether growth-driven active nematic physics could influence this genetic demixing process, we conduct agent-based simulations of growing, dividing, and sterically repelling rod-like bacteria of various aspect ratios, and we analyze colony morphology using tools from both soft matter physics and population genetics. We find that despite measurable defect self-propulsion in growth-driven active nematics, the radial expansion flow prevents chaotic mixing. Even so, at biologically relevant cell aspect ratios, self-mixing is more effective in growing active nematics of rod-like cells compared to growing isotropic colonies of round cells. This suggests potential evolutionary consequences associated with active nematic dynamics.

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Section: Velocity Field For Isolated Nematic Defectssupporting

confidence: 73%

“…As a measure of nematic order, we compute the orientational correlation function, commonly used for characterizing nematic liquid crystals [51], which reads…”

Section: Nematic Order and Defects In A Growing Colonymentioning

confidence: 99%

Do Active Nematic Self-Mixing Dynamics Help Growing Bacterial Colonies to Maintain Local Genetic Diversity?

Schwarzendahl

Beller

2022

Front. Phys.

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Crisscross multilayering of cell sheets

et al. 2023

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Hydrostatic skeletons such as the Hydra’s consist of two stacked layers of muscle cells perpendicularly oriented. In vivo, these bilayers first assemble, and then the muscle fibers of both layers develop and organize with this crisscross orientation. In the present work, we identify an alternative mechanism of crisscross bilayering of myoblasts in vitro, which results from the prior local organization of these active cells in the initial monolayer. The myoblast sheet can be described as a contractile active nematic in which, as expected, most of the +1/2 topological defects associated with this nematic order self-propel. However, as a result of the production of extracellular matrix by the cells, a subpopulation of these comet-like defects does not show any self-propulsion. Perpendicular bilayering occurs at these stationary defects. Cells located at the head of these defects converge toward their core where they accumulate until they start migrating on top of the tail of the first layer, while the tail cells migrate in the opposite direction under the head. Since the cells keep their initial orientations, the two stacked layers end up perpendicularly oriented. This concerted process leading to a crisscross bilayering is mediated by the secretion of extracellular matrix.

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Orientational order and topological defects in a dilute solutions of rodlike polymers at low Reynolds number

Puggioni,

Musacchio

2024

Phys. Rev. E

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Spontaneous flow created by active topological defects

Cited by 4 publications

References 52 publications

Do Active Nematic Self-Mixing Dynamics Help Growing Bacterial Colonies to Maintain Local Genetic Diversity?

Do Active Nematic Self-Mixing Dynamics Help Growing Bacterial Colonies to Maintain Local Genetic Diversity?

Crisscross multilayering of cell sheets

Orientational order and topological defects in a dilute solutions of rodlike polymers at low Reynolds number

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