118 research outputs found
Packing defects and the width of biopolymer bundles
The formation of bundles composed of actin filaments and cross-linking
proteins is an essential process in the maintenance of the cells' cytoskeleton.
It has also been recreated by in-vitro experiments, where actin networks are
routinely produced to mimic and study the cellular structures. It has long been
observed that these bundles seem to have a well defined width distribution,
which has not been adequately described theoretically. We propose here that
packing defects of the filaments, quenched and random, contribute an effective
repulsion that counters the cross-linking adhesion energy and leads to a well
defined bundle width. This is a two-dimensional strain-field version of the
classic Rayleigh instability of charged droplets
Signatures of motor susceptibility in the dynamics of a tracer particle in an active gel
We study a model for the motion of a tracer particle inside an active gel,
exposing the properties of the van Hove distribution of the particle
displacements. Active events of a typical force magnitude give rise to
non-Gaussian distributions, having exponential tails or side-peaks. The
side-peaks appear when the local bulk elasticity of the gel is large enough and
few active sources are dominant. We explain the regimes of the different
distributions, and study the structure of the peaks for active sources that are
susceptible to the elastic stress that they cause inside the gel. We show how
the van Hove distribution is altered by both the duty cycle of the active
sources and their susceptibility, and suggest it as a sensitive probe to
analyze microrheology data in active systems with restoring elastic forces.Comment: 4 pages, 4 figures and supplemental information (5 pages, 4 figures
Patterning of polar active filaments on a tense cylindrical membrane
We study the dynamics and patterning of polar contractile filaments on the
surface of a cylindrical cell using active hydrodynamic equations that
incorporate couplings between curvature and filament orientation. Cables and
rings spontaneously emerge as steady state configurations on the cylinder, and
can be stationary or moving, helical or segments moving along helical
trajectories. Contractility induces coalescence of proximal rings. We observe
phase transitions in the steady state patterns upon changing cell diameter and
make several testable predictions. Our results are relevant to the dynamics and
patterning of a variety of active biopolymers in cylindrical cells.Comment: 10 pages, 8 figures, (Includes Supplementary information
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