35 research outputs found
Point-like inclusion interactions in tubular membranes
We analytically study membrane mediated interactions between inclusions
embedded in a tubular membrane. We model inclusions as constraints coupled to
the curvature tensor of the membrane tube. First, as special test cases, we
analyze the interaction between ring and rod shaped inclusions. Using Monte
Carlo simulations, we further show how point-like inclusions interact to form
linear aggregates. Our results reveal that depending on the hard-core radius of
the inclusions, they arrange into either lines or rings to globally minimize
the curvature energy of the membrane.Comment: 5 + 4 pages, 4 + 3 figure
Active particle dynamics beyond the jamming density
Many biological systems form colonies at high density. Passive granular
systems will be jammed at such densities, yet for the survival of biological
systems it is crucial that they are dynamic. We construct a phase diagram for a
system of active particles interacting via Vicsek alignment, and vary the
density, self-propulsion force, and orientational noise. We find that the
system exhibits four different phases, characterized by transitions in the
effective diffusion constant and in the orientational order parameter. Our
simulations show that there exists an optimal noise such that particles require
a minimal force to unjam, allowing for rearrangements.Comment: 7 pages, 8 figure
Defect dynamics in growing bacterial colonies
Colonies of rod-shaped bacteria constitute a system of colloidal active
matter with nematic properties. As a single initial bacterium multiplies
through repeated divisions, the resulting colony quickly loses long-range
orientational order, but retains locally ordered domains. At the boundaries of
these domains, topological defects emerge, that themselves move around randomly
as the colony grows. In both experiments and simulations, we find that these
defects are created at a rate that corresponds to the exponential growth of the
colony, resulting in a stable defect density. We also characterize the
geometric and topological properties of bacterial colonies, from which we find
that the aspect ratio of the rod-shaped particles is the main regulator of both
the correlation length and the defect density. Moreover, we find that the
defect dynamics are well described by a Gamma distribution, which is due to
repeated divisions and subsequent re-orientations of the bacteria
Accurate determination of elastic parameters for multi-component membranes
Heterogeneities in the cell membrane due to coexisting lipid phases have been
conjectured to play a major functional role in cell signaling and membrane
trafficking. Thereby the material properties of multiphase systems, such as the
line tension and the bending moduli, are crucially involved in the kinetics and
the asymptotic behavior of phase separation. In this Letter we present a
combined analytical and experimental approach to determine the properties of
phase-separated vesicle systems. First we develop an analytical model for the
vesicle shape of weakly budded biphasic vesicles. Subsequently experimental
data on vesicle shape and membrane fluctuations are taken and compared to the
model. The combined approach allows for a reproducible and reliable
determination of the physical parameters of complex vesicle systems. The
parameters obtained set limits for the size and stability of nanodomains in the
plasma membrane of living cells.Comment: (*) authors contributed equally, 6 pages, 3 figures, 1 table; added
insets to figure