99 research outputs found
Fluid flows shaping organism morphology
A dynamic self-organized morphology is the hallmark of network-shaped
organisms like slime moulds and fungi. Organisms continuously re-organize their
flexible, undifferentiated body plans to forage for food. Among these organisms
the slime mould Physarum polycephalum has emerged as a model to investigate how
organism can self-organize their extensive networks and act as a coordinated
whole. Cytoplasmic fluid flows flowing through the tubular networks have been
identified as key driver of morphological dynamics. Inquiring how fluid flows
can shape living matter from small to large scales opens up many new avenues
for research.Comment: 5 pages, 2 figures, perspectiv
Flow rate of transport network controls uniform metabolite supply to tissue
Life and functioning of higher organisms depends on the continuous supply of
metabolites to tissues and organs. What are the requirements on the transport
network pervading a tissue to provide a uniform supply of nutrients, minerals,
or hormones? To theoretically answer this question, we present an analytical
scaling argument and numerical simulations on how flow dynamics and network
architecture control active spread and uniform supply of metabolites by
studying the example of xylem vessels in plants. We identify the fluid inflow
rate as the key factor for uniform supply. While at low inflow rates
metabolites are already exhausted close to flow inlets, too high inflow flushes
metabolites through the network and deprives tissue close to inlets of supply.
In between these two regimes, there exists an optimal inflow rate that yields a
uniform supply of metabolites. We determine this optimal inflow analytically in
quantitative agreement with numerical results. Optimizing network architecture
by reducing the supply variance over all network tubes, we identify patterns of
tube dilation or contraction that compensate sub-optimal supply for the case of
too low or too high inflow rate.Comment: 11 pages, 4 figures, 8 pages supplemen
Shapes of Semiflexible Polymer Rings
The shape of semiflexible polymer rings is studied over their whole range of
flexibility. Investigating the joint distribution of asphericity and nature of
asphericity as well as their respective averages we find two distinct shape
regimes depending on the flexibility of the polymer. For small perimeter to
persistence length the fluctuating rings exhibit only planar, elliptical
configurations. At higher flexibilities three dimensional, crumpled structures
arise. Analytic calculations for tight polymer rings confirm an elliptical
shape in the stiff regime.Comment: 4 pages, 3 figures, Version as published in Phys. Rev. Let
Spatial mapping reveals multi-step pattern of wound healing in Physarum polycephalum
Wounding is a severe impairment of function, especially for an exposed
organism like the network-forming true slime mould Physarum polycephalum. The
tubular network making up the organism's body plan is entirely interconnected
and shares a common cytoplasm. Oscillatory contractions of the enclosing tube
walls drive the shuttle streaming of the cytoplasm. Cytoplasmic flows underlie
the reorganization of the network for example by movement toward attractive
stimuli or away from repellants. Here, we follow the reorganization of Physarum
polycephalum networks after severe wounding. Spatial mapping of the contraction
changes in response to wounding reveal a multi-step pattern. Phases of
increased activity alternate with cessation of contractions and stalling of
flows, giving rise to coordinated transport and growth at the severing site.
Overall, severing surprisingly acts like an attractive stimulus enabling
healing of severed tubes. The reproducible cessation of contractions arising
during this wound-healing response may open up new venues to investigate the
biochemical wiring underlying Physarum polycephalum's complex behaviours.Comment: Felix B\"auerle and Mirna Kramar contributed equally to this wor
Buckling of stiff polymer rings in weak spherical confinement
Confinement is a versatile and well-established tool to study the properties of polymers either to understand biological processes or to develop new nanobiomaterials. We investigate the conformations of a semiflexible polymer ring in weak spherical confinement imposed by an impenetrable shell. We develop an analytic argument for the dominating polymer trajectory depending on polymer flexibility considering elastic and entropic contributions. Monte Carlo simulations are performed to assess polymer ring conformations in probability densities and by the shape measures asphericity and nature of asphericity. Comparison of the analytic argument with the mean asphericity and the mean nature of asphericity confirm our reasoning to explain polymer ring conformations in the stiff regime, where elastic response prevails
Controlling effective dispersion within a channel with flow and active walls
Channels are fundamental building blocks from biophysics to soft robotics,
often used to transport or separate solutes. As solute particles inevitably
transverse between streamlines along the channel by molecular diffusion, the
effective diffusion of the solute along the channel is enhanced - an effect
known as Taylor dispersion. Here, we investigate how the Taylor dispersion
effect can be suppressed or enhanced in different settings. Specifically, we
study the impact of flow profile and active or pulsating channel walls on
Taylor dispersion. We derive closed analytic expressions for the effective
dispersion equation in all considered scenarios providing hands-on effective
dispersion parameters for a multitude of applications. In particular, we find
that active channel walls may lead to three regimes of dispersion: either
dispersion decrease by entropic slow down at small Peclet number, or dispersion
increase at large Peclet number dominated either by shuttle dispersion or by
Taylor dispersion. This improves our understanding of solute transport e.g. in
biological active systems such as blood flow and opens a number of
possibilities to control solute transport in artificial systems such as soft
robotics
Local pore size correlations determine flow distributions in porous media
The relationship between the microstructure of a porous medium and the
observed flow distribution is still a puzzle. We resolve it with an analytical
model, where the local correlations between adjacent pores, which determine the
distribution of flows propagated from one pore downstream, predict the flow
distribution. Numerical simulations of a two-dimensional porous medium verify
the model and clearly show the transition of flow distributions from
-function-like via Gaussians to exponential with increasing disorder.
Comparison to experimental data further verifies our numerical approach.Comment: 5 pages, 3 figures, supplemental materia
Pruning to Increase Taylor Dispersion in Physarum polycephalum Networks
How do the topology and geometry of a tubular network affect the spread of
particles within fluid flows? We investigate patterns of effective dispersion
in the hierarchical, biological transport network formed by Physarum
polycephalum. We demonstrate that a change in topology - pruning in the
foraging state - causes a large increase in effective dispersion throughout the
network. By comparison, changes in the hierarchy of tube radii result in
smaller and more localized differences. Pruned networks capitalize on Taylor
dispersion to increase the dispersion capability.Comment: 5 pages, 4 figures, 11 pages supplemental materia
Oscillatory fluid flow drives scaling of contraction wave with system size
Flows over remarkably long distances are crucial to the functioning of many
organisms, across all kingdoms of life. Coordinated flows are fundamental to
power deformations, required for migration or development, or to spread
resources and signals. A ubiquitous mechanism to generate flows, particularly
prominent in animals and amoeba, is acto-myosin cortex driven mechanical
deformations that pump the fluid enclosed by the cortex. Yet, it is unclear how
cortex dynamics can self-organize to give rise to coordinated flows across the
largely varying scales of biological systems. Here, we develop a
mechanochemical model of acto-myosin cortex mechanics coupled to a
contraction-triggering, soluble chemical. The chemical itself is advected with
the flows generated by the cortex driven deformations of the tubular-shaped
cell. The theoretical model predicts a dynamic instability giving rise to
stable patterns of cortex contraction waves and oscillatory flows.
Surprisingly, simulated patterns extend beyond the intrinsic length scale of
the dynamic instability - scaling with system size instead. Patterns appear
randomly but can be robustly generated in a growing system or by
flow-generating boundary conditions. We identify oscillatory flows as the key
for the scaling of contraction waves with system size. Our work shows the
importance of active flows in biophysical models of patterning, not only as a
regulating input or an emergent output, but rather as a full part of a
self-organized machinery. Contractions and fluid flows are observed in all
kinds of organisms, so this concept is likely to be relevant for a broad class
of systems.Comment: 7 pages, 5 figure
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Regulatory Role of Cell Division Rules on Tissue Growth Heterogeneity
The coordination of cell division and cell expansion are critical to normal development of tissues. In plants, cell wall mechanics and the there from arising cell shapes and mechanical stresses can regulate cell division and cell expansion and thereby tissue growth and morphology. Limited by experimental accessibility it remains unknown how cell division and expansion cooperatively affect tissue growth dynamics. Employing a cell-based two dimensional tissue simulation we investigate the regulatory role of a range of cell division rules on tissue growth dynamics and in particular on the spatial heterogeneity of growth. We find that random cell divisions only add noise to the growth and therefore increase growth heterogeneity, while cell divisions following the shortest new wall or along the direction of maximal mechanical stress reduce growth heterogeneity by actively enhancing the regulation of growth by mechanical stresses. Thus, we find that, beyond tissue geometry and topology, cell divisions affect the dynamics of growth, and that their signature is embedded in the statistics of tissue growth.Engineering and Applied Science
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