160 research outputs found
Migration of semiflexible polymers in microcapillary flow
The non-equilibrium structural and dynamical properties of a semiflexible
polymer confined in a cylindrical microchannel and exposed to a Poiseuille flow
is studied by mesoscale hydrodynamic simulations. For a polymer with a length
half of its persistence length, large variations in orientation and
conformations are found as a function of radial distance and flow strength. In
particular, the polymer exhibits U-shaped conformations near the channel
center. Hydrodynamic interactions lead to strong cross-streamline migration.
Outward migration is governed by the polymer orientation and the corresponding
anisotropy in its diffusivity. Strong tumbling motion is observed, with a
tumbling time which exhibits the same dependence on Peclet number as a polymer
in shear flow.Comment: 6 pages, 7 figures, accepted by EP
Flow-Induced Helical Coiling of Semiflexible Polymers in Structured Microchannels
The conformations of semiflexible (bio)polymers are studied in flow through
geometrically structured microchannels. Using mesoscale hydrodynamics
simulations, we show that the polymer undergoes a rod-to-helix transition as it
moves from the narrow high-velocity region into the wide low-velocity region of
the channel. The transient helix formation is the result of a non-equilibrium
and non-stationary buckling transition of the semiflexible polymer, which is
subjected to a compressive force originating from the fluid-velocity variation
in the channel. The helix properties depend on the diameter ratio of the
channel, the polymer bending rigidity, and the flow strength.Comment: Accepted in Phys. Rev. Let
Mechanisms regulating intestinal barrier integrity and its pathological implications
The gastrointestinal tract is a specialized organ in which dynamic interactions between host cells and the complex environment occur in addition to food digestion. Together with the chemical barrier of the mucosal layer and the cellular immune system, the epithelial cell layer performs a pivotal role as the first physical barrier against external factors and maintains a symbiotic relationship with commensal bacteria. The tight junction proteins, including occludin, claudins, and zonula occludens, are crucial for the maintenance of epithelial barrier integrity. To allow the transport of essential molecules and restrict harmful substances, the intracellular signaling transduction system and a number of extracellular stimuli such as cytokines, small GTPases, and post-translational modifications dynamically modulate the tight junction protein complexes. An imbalance in these regulations leads to compromised barrier integrity and is linked with pathological conditions. Despite the obscurity of the causal relationship, the loss of barrier integrity is considered to contribute to inflammatory bowel disease, obesity, and metabolic disorders. The elucidation of the role of diseases in barrier integrity and the underlying regulatory mechanisms have improved our understanding of the intestinal barrier to allow the development of novel and potent therapeutic approaches.11Ysciescopuskc
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