101 research outputs found
Effect of fluid-colloid interactions on the mobility of a thermophoretic microswimmer in non-ideal fluids
Janus colloids propelled by light, e.g., thermophoretic particles, offer
promising prospects as artificial microswimmers. However, their swimming
behavior and its dependence on fluid properties and fluid-colloid interactions
remain poorly understood. Here, we investigate the behavior of a thermophoretic
Janus colloid in its own temperature gradient using numerical simulations. The
dissipative particle dynamics method with energy conservation is used to
investigate the behavior in non-ideal and ideal-gas like fluids for different
fluid-colloid interactions, boundary conditions, and temperature-controlling
strategies. The fluid-colloid interactions appear to have a strong effect on
the colloid behavior, since they directly affect heat exchange between the
colloid surface and the fluid. The simulation results show that a reduction of
the heat exchange at the fluid-colloid interface leads to an enhancement of
colloid's thermophoretic mobility. The colloid behavior is found to be
different in non-ideal and ideal fluids, suggesting that fluid compressibility
plays a significant role. The flow field around the colloid surface is found to
be dominated by a source-dipole, in agreement with the recent theoretical and
simulation predictions. Finally, different temperature-control strategies do
not appear to have a strong effect on the colloid's swimming velocity
Stability of heterogeneous parallel-bond adhesion clusters under static load
Adhesion interactions mediated by multiple bond types are relevant for many
biological and soft matter systems, including the adhesion of biological cells
and functionalized colloidal particles to various substrates. To elucidate
advantages and disadvantages of multiple bond populations for the stability of
heterogeneous adhesion clusters of receptor-ligand pairs, a theoretical model
for a homogeneous parallel adhesion bond cluster under constant loading is
extended to several bond types. The stability of the entire cluster can be
tuned by changing densities of different bond populations as well as their
extensional rigidity and binding properties. In particular, bond extensional
rigidities determine the distribution of total load to be shared between
different sub-populations. Under a gradual increase of the total load, the
rupture of a heterogeneous adhesion cluster can be thought of as a multistep
discrete process, in which one of the bond sub-populations ruptures first,
followed by similar rupture steps of other sub-populations or by immediate
detachment of the remaining cluster. This rupture behavior is qualitatively
independent of involved bond types, such as slip and catch bonds.
Interestingly, an optimal stability is generally achieved when the total
cluster load is shared such that loads on distinct bond populations are equal
to their individual critical rupture forces. We also show that cluster
heterogeneity can drastically affect cluster lifetime.Comment: 11 pages, 8 figure
Sharp-edged geometric obstacles in microfluidics promote deformability-based sorting of cells
Sorting cells based on their intrinsic properties is a highly desirable
objective, since changes in cell deformability are often associated with
various stress conditions and diseases. Deterministic lateral displacement
(DLD) devices offer high precision for rigid spherical particles, while their
success in sorting deformable particles remains limited due to the complexity
of cell traversal in DLDs. We employ mesoscopic hydrodynamics simulations and
demonstrate prominent advantages of sharp-edged DLD obstacles for probing
deformability properties of red blood cells (RBCs). By consecutive sharpening
of the pillar shape from circular to diamond to triangular geometry, a
pronounced cell bending around an edge is achieved, serving as a deformability
sensor. Bending around the edge is the primary mechanism, which governs the
traversal of RBCs through such DLD device. This strategy requires an
appropriate degree of cell bending by fluid stresses, which can be controlled
by the flow rate, and exhibits good sensitivity to moderate changes in cell
deformability. We expect that similar mechanisms should be applicable for the
development of novel DLD devices that target intrinsic properties of many other
cells.Comment: 16 pages, 9 figure
Margination of micro- and nano-particles in blood flow and its effect on drug delivery
Drug delivery by micro- and nano-carriers enables controlled transport of pharmaceuticals to targeted sites. Even though carrier fabrication has made much progress recently, the delivery including controlled particle distribution and adhesion within the body remains a great challenge. The adhesion of carriers is strongly affected by their margination properties (migration toward walls) in the microvasculature. To investigate margination characteristics of carriers of different shapes and sizes and to elucidate the relevant physical mechanisms, we employ mesoscopic hydrodynamic simulations of blood flow. Particle margination is studied for a wide range of hematocrit values, vessel sizes, and flow rates, using two- and three-dimensional models. The simulations show that the margination properties of particles improve with increasing carrier size. Spherical particles yield slightly better margination than ellipsoidal carriers; however, ellipsoidal particles exhibit a slower rotational dynamics near a wall favoring their adhesion. In conclusion, micron-sized ellipsoidal particles are favorable for drug delivery in comparison with sub-micron spherical particle
Effect of cytosol viscosity on the flow behavior of red blood cell suspensions in microvessels
The flow behavior of blood in microvessels is directly associated with tissue
perfusion and oxygen delivery. Current efforts on modeling blood flow have
primarily focused on the flow properties of blood with red blood cells (RBCs)
having a viscosity ratio of unity between the cytosol and suspending
medium, while under physiological conditions the cytosol viscosity is about
five times larger than the plasma viscosity (i.e., ). The
importance of for the behavior of single RBCs in fluid flow has already
been demonstrated, while the effect of on blood flow has only been sparsely
studied. We employ mesoscopic hydrodynamic simulations to perform a systematic
investigation of flow properties of RBC suspensions with different cytosol
viscosities for various flow conditions in cylindrical microchannels. Our main
aim is to link macroscopic flow properties such as flow resistance to single
cell deformation and dynamics as a function of . Starting from a dispersed
cell configuration, we find that the flow convergence and the development of a
RBC-free layer (RBC-FL) depend only weakly on , and require a convergence
length in the range of , where is the channel diameter. The flow
resistance for is nearly the same as that for , which is facilitated
by a slightly larger RBC-FL thickness for . This effect is due to the
suppression of membrane motion and dynamic shape deformations by a more viscous
cytosol for , resulting in a more compact cellular core of the flow in
comparison to . The weak effect of cytosol viscosity on the flow
resistance and RBC-FL explains why cells can have a high concentration of
hemoglobin for efficient oxygen delivery, without a pronounced increase in the
flow resistance.Comment: 16 pages, 13 figures, 4 table
Computational Biorheology of Human Blood Flow in Health and Disease
Hematologic disorders arising from infectious diseases, hereditary factors and environmental influences can lead to, and can be influenced by, significant changes in the shape, mechanical and physical properties of red blood cells (RBCs), and the biorheology of blood flow. Hence, modeling of hematologic disorders should take into account the multiphase nature of blood flow, especially in arterioles and capillaries. We present here an overview of a general computational framework based on dissipative particle dynamics (DPD) which has broad applicability in cell biophysics with implications for diagnostics, therapeutics and drug efficacy assessments for a wide variety of human diseases. This computational approach, validated by independent experimental results, is capable of modeling the biorheology of whole blood and its individual components during blood flow so as to investigate cell mechanistic processes in health and disease. DPD is a Lagrangian method that can be derived from systematic coarse-graining of molecular dynamics but can scale efficiently up to arterioles and can also be used to model RBCs down to the spectrin level. We start from experimental measurements of a single RBC to extract the relevant biophysical parameters, using single-cell measurements involving such methods as optical tweezers, atomic force microscopy and micropipette aspiration, and cell-population experiments involving microfluidic devices. We then use these validated RBC models to predict the biorheological behavior of whole blood in healthy or pathological states, and compare the simulations with experimental results involving apparent viscosity and other relevant parameters. While the approach discussed here is sufficiently general to address a broad spectrum of hematologic disorders including certain types of cancer, this paper specifically deals with results obtained using this computational framework for blood flow in malaria and sickle cell anemia.National Institutes of Health (U.S.)Singapore-MIT Alliance for Research and Technology (SMART)United States. Dept. of Energy. Collaboratory on Mathematics for Mesoscopic Modeling of MaterialsUnited States. Dept. of Energy (INCITE Award
A new look at blood shear-thinning
Blood viscosity decreases with shear stress, a property essential for an
efficient perfusion of the vascular tree. Shear-thinning is intimately related
to the dynamics and mutual interactions of red blood cells (RBCs), the major
constituents of blood. Our work explores RBCs dynamics under physiologically
relevant conditions of flow strength, outer fluid viscosity and volume
fraction. Our results contradict the current paradigm stating that RBCs should
align and elongate in the flow direction thanks to their membrane circulation
around their center of mass, reducing flow-lines disturbances. On the contrary,
we observe both experimentally and with simulations, rich morphological
transitions that relate to global blood rheology. For increasing shear
stresses, RBCs successively tumble, roll, deform into rolling stomatocytes and
finally adopt highly deformed and polylobed shapes even for semi-dilute volume
fractions analogous to microcirculatory values. Our study suggests that any
pathological change in plasma composition, RBCs cytosol viscosity or membrane
mechanical properties will impact the onset of shape transitions and should
play a central role in pathological blood rheology and flow behavior
War and love in prose opus of Drago Jančar
Magistrsko delo se ukvarja s tematiko vojne in ljubezni v proznem opusu Draga Jančarja. Najprej so okvirno predstavljena dela, ki se izbrane tematike le dotikajo oziroma obravnavajo le posamezno temo. Podrobneje so obravnavani romani, v katerih je omenjena tematika v ospredju. Prvi roman, v katerem sta vojna in ljubezen glavni temi, je Katarina, pav in jezuit. V ospredju romana je ljubezenska zgodba dveh posameznikov, zaradi zla se par razide. Ostali obravnavani romani – Drevo brez imena, To noč sem jo videl ter In ljubezen tudi – sledijo podobnemu vzorcu. Nasprotje med ljubeznijo in vojno je tudi nasprotje med posameznikom in množico, med zasebnostjo in javnostjo, med ljudmi, ki so hoteli samo živeti, in med ljudmi, ki pod vplivom ideologije uničujejo ostale. Jančar je vedno na strani posameznika, zato so vojna in njene posledice prikazane negativno.A master\u27s thesis represents themes of war and love in prose opus of Drago Jančar. Firstly it represents works which slightly express the themes. Then thesis discusses in details novels with those themes as mainly themes. The novel Katarina, the Peacock and the Jesuit is the first analyzed novel. It is about love between two people. Their story ends because of evilness. Other discussed novels – The Tree with no Name, I Saw Her That Night, And Love Itself – follow the example. The opposition between love and war is also the opposition between an individual and a crowd, privacy and publicity, between people who just want to live and those who in the name of ideology destroy others. Jančar stands on individual’s side, therefore are war and her consequences shown as negative
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