27,954 research outputs found
Poly(2-oxazolines) in biological and biomedical application contexts.
Polyoxazolines of various architectures and chemical functionalities can be prepared in a living and therefore controlled manner via cationic ring-opening polymerisation. They have found widespread applications, ranging from coatings to pigment dispersants. Furthermore, several polyoxazolines are water-soluble or amphiphilic and relatively non-toxic, which makes them interesting as biomaterials. This paper reviews the development of polyoxazoline-based polymers in biological and biomedical application contexts since the beginning of the millennium. This includes nanoscalar systems such as membranes and nanoparticles, drug and gene delivery applications, as well as stimuli-responsive systems
Dynamics of Cell Shape and Forces on Micropatterned Substrates Predicted by a Cellular Potts Model
Micropatterned substrates are often used to standardize cell experiments and
to quantitatively study the relation between cell shape and function. Moreover,
they are increasingly used in combination with traction force microscopy on
soft elastic substrates. To predict the dynamics and steady states of cell
shape and forces without any a priori knowledge of how the cell will spread on
a given micropattern, here we extend earlier formulations of the
two-dimensional cellular Potts model. The third dimension is treated as an area
reservoir for spreading. To account for local contour reinforcement by
peripheral bundles, we augment the cellular Potts model by elements of the
tension-elasticity model. We first parameterize our model and show that it
accounts for momentum conservation. We then demonstrate that it is in good
agreement with experimental data for shape, spreading dynamics, and traction
force patterns of cells on micropatterned substrates. We finally predict shapes
and forces for micropatterns that have not yet been experimentally studied.Comment: Revtex, 32 pages, 11 PDF figures, to appear in Biophysical Journa
Effect of adhesion geometry and rigidity on cellular force distributions
The behaviour and fate of tissue cells is controlled by the rigidity and
geometry of their adhesive environment, possibly through forces localized to
sites of adhesion. We introduce a mechanical model that predicts cellular force
distributions for cells adhering to adhesive patterns with different geometries
and rigidities. For continuous adhesion along a closed contour, forces are
predicted to be localized to the corners. For discrete sites of adhesion, the
model predicts the forces to be mainly determined by the lateral pull of the
cell contour. With increasing distance between two neighboring sites of
adhesion, the adhesion force increases because cell shape results in steeper
pulling directions. Softer substrates result in smaller forces. Our predictions
agree well with experimental force patterns measured on pillar assays.Comment: 4 pages, Revtex with 4 figure
Unifying autocatalytic and zeroth order branching models for growing actin networks
The directed polymerization of actin networks is an essential element of many
biological processes, including cell migration. Different theoretical models
considering the interplay between the underlying processes of polymerization,
capping and branching have resulted in conflicting predictions. One of the main
reasons for this discrepancy is the assumption of a branching reaction that is
either first order (autocatalytic) or zeroth order in the number of existing
filaments. Here we introduce a unifying framework from which the two
established scenarios emerge as limiting cases for low and high filament
number. A smooth transition between the two cases is found at intermediate
conditions. We also derive a threshold for the capping rate, above which
autocatalytic growth is predicted at sufficiently low filament number. Below
the threshold, zeroth order characteristics are predicted to dominate the
dynamics of the network for all accessible filament numbers. Together, this
allows cells to grow stable actin networks over a large range of different
conditions.Comment: revtex, 5 pages, 4 figure
Stability of freely falling granular streams
A freely falling stream of weakly cohesive granular particles is modeled and
analysed with help of event driven simulations and continuum hydrodynamics. The
former show a breakup of the stream into droplets, whose size is measured as a
function of cohesive energy. Extensional flow is an exact solution of the
one-dimensional Navier-Stokes equation, corresponding to a strain rate,
decaying like 1/t from its initial value, gammaDot0. Expanding around this
basic state, we show that the flow is stable for short times (gammaDot0 * t <<
1), whereas for long times (gammaDot0 * t >> 1) perturbations of all wavelength
grow. The growthrate of a given wavelength depends on the instant of time when
the fluctuation occurs, so that the observable patterns can vary considerably.Comment: 4 page, 5 figures. Submitted to PRL. Supplementary material: see
http://wwwuser.gwdg.de/~sulrich/research/#Publication
- …