158 research outputs found
Swinging of red blood cells under shear flow
We reveal that under moderate shear stress (of the order of 0.1 Pa) red blood
cells present an oscillation of their inclination (swinging) superimposed to
the long-observed steady tanktreading (TT) motion. A model based on a fluid
ellipsoid surrounded by a visco-elastic membrane initially unstrained (shape
memory) predicts all observed features of the motion: an increase of both
swinging amplitude and period (1/2 the TT period) upon decreasing the shear
stress, a shear stress-triggered transition towards a narrow shear stress-range
intermittent regime of successive swinging and tumbling, and a pure tumbling
motion at lower shear stress-values.Comment: 4 pages 5 figures submitted to Physical Review Letter
Dynamics of Fluid Vesicles in Oscillatory Shear Flow
The dynamics of fluid vesicles in oscillatory shear flow was studied using
differential equations of two variables: the Taylor deformation parameter and
inclination angle . In a steady shear flow with a low viscosity
of internal fluid, the vesicles exhibit steady tank-treading
motion with a constant inclination angle . In the oscillatory flow
with a low shear frequency, oscillates between or
around for zero or finite mean shear rate ,
respectively. As shear frequency increases, the vesicle
oscillation becomes delayed with respect to the shear oscillation, and the
oscillation amplitude decreases. At high with , another limit-cycle oscillation between and
is found to appear. In the steady flow, periodically rotates
(tumbling) at high , and and the vesicle shape
oscillate (swinging) at middle and high shear rate. In the
oscillatory flow, the coexistence of two or more limit-cycle oscillations can
occur for low in these phases. For the vesicle with a fixed shape,
the angle rotates back to the original position after an oscillation
period. However, it is found that a preferred angle can be induced by small
thermal fluctuations.Comment: 11 pages, 13 figure
Flow of red blood cells suspensions through hyperbolic microcontractions
The present study uses a hyperbolic microchannel with a low aspect ratio (AR) to investigate how the red blood cells (RBCs) deform under conditions of both extensional and shear induced flows. The deformability is presented by the degree of the deformation index (DI) of the flowing RBCs throughout the microchannel at its centerline. A suitable image analysis technique is used for semi-automatic measurements of average DIs, velocity and strain rate of the RBCs travelling in the regions of interest. The results reveal a strong deformation of RBCs under both extensional and shear stress dominated flow conditions
Semiflexible polymer conformation, distribution and migration in microcapillary flows
The flow behavior of a semiflexible polymer in microchannels is studied using
Multiparticle Collision Dynamics (MPC), a particle-based hydrodynamic
simulation technique. Conformations, distributions, and radial cross-streamline
migration are investigated for various bending rigidities, with persistence
lengths Lp in the range 0.5 < Lp/Lr < 30. The flow behavior is governed by the
competition between a hydrodynamic lift force and steric wall-repulsion, which
lead to migration away from the wall, and a locally varying flow-induced
orientation, which drives polymer away from the channel center and towards the
wall. The different dependencies of these effects on the polymer bending
rigidity and the flow velocity results in a complex dynamical behavior.
However, a generic effect is the appearance of a maximum in the monomer and the
center-of-mass distributions, which occurs in the channel center for small flow
velocities, but moves off-center at higher velocities.Comment: in press at J. Phys. Condens. Matte
Effective swimming strategies in low Reynolds number flows
The optimal strategy for a microscopic swimmer to migrate across a linear
shear flow is discussed. The two cases, in which the swimmer is located at
large distance, and in the proximity of a solid wall, are taken into account.
It is shown that migration can be achieved by means of a combination of sailing
through the flow and swimming, where the swimming strokes are induced by the
external flow without need of internal energy sources or external drives. The
structural dynamics required for the swimmer to move in the desired direction
is discussed and two simple models, based respectively on the presence of an
elastic structure, and on an orientation dependent friction, to control the
deformations induced by the external flow, are analyzed. In all cases, the
deformation sequence is a generalization of the tank-treading motion regimes
observed in vesicles in shear flows. Analytic expressions for the migration
velocity as a function of the deformation pattern and amplitude are provided.
The effects of thermal fluctuations on propulsion have been discussed and the
possibility that noise be exploited to overcome the limitations imposed on the
microswimmer by the scallop theorem have been discussed.Comment: 14 pages, 5 figure
Combined Simulation and Experimental Study of Large Deformation of Red Blood Cells in Microfluidic Systems
Author manuscript; available in PMC 2012 March 1.We investigate the biophysical characteristics of healthy human red blood cells (RBCs) traversing microfluidic channels with cross-sectional areas as small as 2.7 × 3 μm. We combine single RBC optical tweezers and flow experiments with corresponding simulations based on dissipative particle dynamics (DPD), and upon validation of the DPD model, predictive simulations and companion experiments are performed in order to quantify cell deformation and pressure–velocity relationships for different channel sizes and physiologically relevant temperatures. We discuss conditions associated with the shape transitions of RBCs along with the relative effects of membrane and cytosol viscosity, plasma environments, and geometry on flow through microfluidic systems at physiological temperatures. In particular, we identify a cross-sectional area threshold below which the RBC membrane properties begin to dominate its flow behavior at room temperature; at physiological temperatures this effect is less profound.Singapore-MIT Alliance for Research and TechnologyUnited States. National Institutes of Health (National Heart, Lung, and Blood Institute Award R01HL094270
Coupling of Rotational Motion with Shape Fluctuations of Core-shell Microgels Having Tunable Softness
The influence of shape fluctuations on deformable thermosensitive microgels
in aqueous solution is investigated by dynamic light scattering (DLS) and
depolarized dynamic light scattering (DDLS). The systems under study consist of
a solid core of polystyrene and a thermosensitive shell of cross-linked
poly(N-isopropylacrylamide) (PNIPA) without and with embedded palladium
nanoparticles. PNIPA is soluble in water, but has a lower critical solution
temperature at 32 C (LCST). Below the LCST the PNIPA shell is swollen. Here we
find that besides translational and rotational diffusion, the particles exhibit
additional dynamics resulting from shape fluctuations. This leads to a
pronounced apparent increase of the rotational diffusion coefficient. Above the
transition temperature the shell collapses and provides a rather tight envelope
of the core. In this state the dynamics of the shell is frozen and the
core-shell particles behave like hard spheres. A simple physical model is
presented to capture and explain the essentials of the coupling of rotational
motion and shape fluctuations.Comment: 9 pages, 7 figure
Processing of Plasmodium falciparum Merozoite Surface Protein MSP1 activates a Spectrin-binding function enabling parasite egress from RBCs
The malaria parasite Plasmodium falciparum replicates within erythrocytes, producing progeny merozoites that are released from infected cells via a poorly understood process called egress. The most abundant merozoite surface protein, MSP1, is synthesized as a large precursor that undergoes proteolytic maturation by the parasite protease SUB1 just prior to egress. The function of MSP1 and its processing are unknown. Here we show that SUB1-mediated processing of MSP1 is important for parasite viability. Processing modifies the secondary structure of MSP1 and activates its capacity to bind spectrin, a molecular scaffold protein that is the major component of the host erythrocyte cytoskeleton. Parasites expressing an inefficiently processed MSP1 mutant show delayed egress, and merozoites lacking surface-bound MSP1 display a severe egress defect. Our results indicate that interactions between SUB1-processed merozoite surface MSP1 and the spectrin network of the erythrocyte cytoskeleton facilitate host erythrocyte rupture to enable parasite egress
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