18 research outputs found
Shear thinning behavior of cerebrospinal fluid with elevated protein or cellular concentration
Introduction: Cerebrospinal fluid (CSF) plays a crucial role in the maintenance of the central nervous system (CNS) by cushioning the brain, providing nutrients, removing interstitial waste, and maintaining homeostasis. Flow characteristics of CSF may significantly contribute to brain dynamics, injury mechanics, disease pathogenesis, and the functionality of the glymphatic system. Conventionally, CSF is considered to have very similar rheological properties to water and Newtonian behavior of CSF has been assumed, despite its complex composition, which can include proteins like albumin and tau, as well as cellular content such as blood.Methods: Recent advances in rheological techniques allow for more accurate quantification of CSF characteristics and behavior. Here, we present an updated rheological characterization of CSF, including the impact of its cellular and proteinaceous constituents. CSF samples were tested for protein and cellular concentration. Using precision torsional rheometry and recently developed extensional rheology techniques, we show that CSF with elevated cellular or protein concentration exhibits significant non-Newtonian behavior, especially at low shear rates.Results: Like other biological fluids, CSF with elevated cellular or protein concentration exhibits shear thinning behavior until reaching a steady state viscosity of approximately 1 mPa·s at shear rates greater than 10 s-1. This shear thinning behavior becomes more pronounced with increasing concentration of its constituents. In extensional flow, CSF exhibited weakly non-Newtonian behavior, with an average extensional relaxation time of 0.14 ms. The extensional relaxation time is positively correlated to cellular concentration and significantly increased with elevated protein.Discussion: Our results enhance the understanding of CSF rheology with significant implications for the analysis, modeling, and treatment of CSF-related processes
Capillary filling with wall corrugations] Capillary filling in microchannels with wall corrugations: A comparative study of the Concus-Finn criterion by continuum, kinetic and atomistic approaches
We study the impact of wall corrugations in microchannels on the process of
capillary filling by means of three broadly used methods - Computational Fluid
Dynamics (CFD), Lattice-Boltzmann Equations (LBE) and Molecular Dynamics (MD).
The numerical results of these approaches are compared and tested against the
Concus-Finn (CF) criterion, which predicts pinning of the contact line at
rectangular ridges perpendicular to flow for contact angles theta > 45. While
for theta = 30, theta = 40 (no flow) and theta = 60 (flow) all methods are
found to produce data consistent with the CF criterion, at theta = 50 the
numerical experiments provide different results. Whilst pinning of the liquid
front is observed both in the LB and CFD simulations, MD simulations show that
molecular fluctuations allow front propagation even above the critical value
predicted by the deterministic CF criterion, thereby introducing a sensitivity
to the obstacle heigth.Comment: 25 pages, 8 figures, Langmuir in pres
Capillary filling with pseudo-potential binary Lattice-Boltzmann model
We present a systematic study of capillary filling for a binary fluid by
using a mesoscopic lattice Boltzmann model for immiscible fluids describing a
diffusive interface moving at a given contact angle with respect to the walls.
The phenomenological way to impose a given contact angle is analysed.
Particular attention is given to the case of complete wetting, that is contact
angle equal to zero. Numerical results yield quantitative agreement with the
theoretical Washburn law, provided that the correct ratio of the dynamic
viscosities between the two fluids is used. Finally, the presence of precursor
films is experienced and it is shown that these films advance in time with a
square-root law but with a different prefactor with respect to the bulk
interface.Comment: 13 pages, 8 figures, accepted for publication on The European journal
of physics
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Contact line dynamics of gravity driven spreading of liquids
Abstract
The spreading dynamics of the gravity-driven liquid motion on an inclined solid surface was studied by considering two fundamental physical models: the molecular kinetic theory and the hydrodynamic theory (HDT). The molecular kinetic theory is the most appropriate model to describe the gravity driven spreading mechanism investigated in this study. The gravity driven spreading which is one form of the forced spreading mechanism was compared with the spontaneous spreading for the same liquid/solid system from previous study by Mohammad Karim et al (2016 Langmuir
32 10153). Unlike the gravity driven spreading, the HDT was appropriate model to define the spontaneous spreading. This finding reveals the importance of the mechanism of spreading which are the forced and the spontaneous on the suitability of the physical model such as the molecular kinetic theory and the HDT to describe the spreading dynamics.</jats:p
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Time dependent degradation of vitreous gel under enzymatic reaction: Polymeric network role in fluid properties.
The viscoelastic behavior of vitreous gel is due to the presence of biopolymers in its structure. Fluid properties of the vitreous is mainly the result of interactions between the characteristics of collagen type II and Hyaluronic Acid networks. Having a better understanding of the structure of each component and their changes during aging and various diseases such as diabetes can lead to better monitoring and treatment options. We study the effects of collagenase type II on 44 samples of porcine vitreous using an in situ rheological experiment in comparison with 18 eyes in a control group injected with Phosphate Buffered Saline Solution. We analyze the behavior of each component over time in both groups. We focus on the changes of viscosity and elasticity of the collagen network within the vitreous. The results of the analysis in this study show that the changes in the fluid properties of the vitreous after collagenase injection is driven by the structural alterations of the collagen network. Creep compliance values of the collagen network are significantly higher in the first group compared to the control group one hour and twenty-four hours after the injection. In contrast, creep compliance of the HA network shows no statistically significant change one hour after the injection in both groups. The results of the reported analysis of individual components in this study support the previous findings on the alterations within the vitreous structure in its entirety
Cold-Induced Spreading of Water Drops on Hydrophobic Surfaces
Superhydrophobic
surfaces are characterized by their peculiarities,
such as water-repellent, anti-icing, and freezing-delay properties.
Wetting dynamics of deposited water drops on cooling hydrophobic surfaces,
which directly affects the aforementioned properties, has not been
studied thoroughly. Here, water drops are cooled on different hydrophobic
surfaces in a controlled environment. During the cooling process,
a significant increase in the drop footprint and decrease in the apparent
contact angle are observed because of premature and capillary condensation,
followed by thin water film formation adjacent to the solid–liquid–gas
line. The water thin film propagates on the hydrophobic substrates
radially away from the trijunction, followed by spreading of the drop
on the film, which was experimentally validated through high-speed
visualization. In addition, the roles of physical variables, such
as the substrate temperature, humidity of surrounding air, types of
hydrophobic surfaces, surface roughness, and drop volume, on post-spreading
shape are investigated experimentally
Evaporation of a sessile droplet: Inside the coffee stain
International audienceWe have investigated experimentally, for the first time at microscopic level, the growth of the deposit left around a drop of colloids drying on a solid surface ("coffee stain effect"). Direct observations show that there are several distinct phases of growth, the later ones exhibiting surprising pattern formations with spatial modulation of the deposit. In addition, fluorescence reveals that the initial growth phase is governed by a single length scale, increasing with time as t 2 3. We show that this exponent is a direct consequence of the divergence of evaporation near contact line evidenced by Deegan et al. We propose a simple ballistic model that allows us to calculate both this exponent and the prefactor, in agreement with yet available more complex descriptions. This model also opens the possibility to include effects neglected up to now