349 research outputs found
Micro-scale cavities in the slip - and transition - flow regimes
No full textDifferences between Navier-Stokes-Fourier (NSF) slip/jump solutions and direct simulation Monte-Carlo (DSMC) computations are highlighted for a micro lid-driven cavity problem. The results indicate a need for better modelling techniques which at the same time retain low computational cost of NSF models. We also highlight the fact thatmany micro-flows that have been considered are simple planar flows and typical classification systems are defined on such flows. We show that for complex flows, such as thedriven cavity, non-equilibrium effects are more appreciable and their onset occurs at lower Knudsen numbers than expected
Effects of bile salt Sodium glycodeoxycholate on the self-assembly of PEO-PPO-PEO triblock copolymer P123 in aqueous solution
No full textA comprehensive experimental study on the interaction between the PEO-PPO-PEO block copolymer P123 (EO20PO68EO20) and the anionic bile salt sodium glycodeoxycholate (NaGDC) in water has been performed. The work was aimed at investigating the suitability of using P123 as bile salt sequestrant beside the fundamental aspects of PEO-PPO-PEO block copolymer-bile salt interactions. Various experimental techniques including dynamic and static light scattering, small-angle X-ray scattering, and differential scanning calorimetry (DSC) were employed in combination with electrophoretic mobility measurements. The system was investigated at a constant P123 concentration of 1.74 mM and with varying bile salt concentrations up to approximately 250 mM NaGDC (or a molar ratio n(NaGDC)/n(P123) = 144). In the mixed P123-NaGDC solutions, the endothermic process related to the self-assembly of P123 was observed to gradually decrease in enthalpy and shift to higher temperatures upon progressive addition of NaGDC. To explain this effect, the formation of NaGDC micelles carrying partly dehydrated P123 unimers was proposed and translated into a stoichiometric model, which was able to fit the experimental DSC data. In the mixtures at low molar ratios, NaGDC monomers associated with the P123 micelle forming a charged "P123 micelle-NaGDC" complex with a dehydrated PPO core. These complexes disintegrated upon increasing NaGDC concentration to form small "NaGDC-P123" complexes visualized as bile salt micelles including one or a few P123 copolymer chains
Truncated recombinant human SP-D attenuates emphysema and type II cell changes in SP-D deficient mice
No full textBACKGROUND: Surfactant protein D (SP-D) deficient mice develop emphysema-like pathology associated with focal accumulations of foamy alveolar macrophages, an excess of surfactant phospholipids in the alveolar space and both hypertrophy and hyperplasia of alveolar type II cells. These findings are associated with a chronic inflammatory state. Treatment of SP-D deficient mice with a truncated recombinant fragment of human SP-D (rfhSP-D) has been shown to decrease the lipidosis and alveolar macrophage accumulation as well as production of proinflammatory chemokines. The aim of this study was to investigate if rfhSP-D treatment reduces the structural abnormalities in parenchymal architecture and type II cells characteristic of SP-D deficiency. METHODS: SP-D knock-out mice, aged 3 weeks, 6 weeks and 9 weeks were treated with rfhSP-D for 9, 6 and 3 weeks, respectively. All mice were sacrificed at age 12 weeks and compared to both PBS treated SP-D deficient and wild-type groups. Lung structure was quantified by design-based stereology at the light and electron microscopic level. Emphasis was put on quantification of emphysema, type II cell changes and intracellular surfactant. Data were analysed with two sided non-parametric Mann-Whitney U-test. MAIN RESULTS: After 3 weeks of treatment, alveolar number was higher and mean alveolar size was smaller compared to saline-treated SP-D knock-out controls. There was no significant difference concerning these indices of pulmonary emphysema within rfhSP-D treated groups. Type II cell number and size were smaller as a consequence of treatment. The total volume of lamellar bodies per type II cell and per lung was smaller after 6 weeks of treatment. CONCLUSION: Treatment of SP-D deficient mice with rfhSP-D leads to a reduction in the degree of emphysema and a correction of type II cell hyperplasia and hypertrophy. This supports the concept that rfhSP-D might become a therapeutic option in diseases that are characterized by decreased SP-D levels in the lung
Complexes of PEO-PPO-PEO triblock copolymer P123 and bile salt sodium glycodeoxycholate in aqueous solution: A small angle X-ray and neutron scattering investigation
No full textSmall angle X-ray (SAXS) and neutron scattering techniques were combined to study mixed complexesformed between micelles of the nonionic amphiphilic PEO-PPO-PEO copolymer (P123) and the anionicbile salt (NaGDC) in aqueous solution. The purpose was to investigate the structural parameters of thecharged complexes, such as size and internal structure, as well as their interparticle interactions inaqueous solution. The overall aim of this work was to gain understanding of how thermoresponsivePEO-PPO-PEO block copolymers interact with bile salts in order to make predictions as to whether theycan be put forward as a new class of bile salt sequestrants in the treatment of bile-salt related diseases.The system was investigated at a constant P123 concentration of 1.74 mM and bile salt concentrationswere varied up to a molar ratio nNaGDC/nP123(MR) = 5.7. It was found that the NaGDC molecules prefer-entially associated to the PEO corona of the P123 micelle and due to their amphiphilic nature, close tothe core/corona interface. Because of this association the micelles became charged causing their recip-rocal interparticle repulsions in solution to increase. In parallel, the association caused a decrease inthe core radius accompanied by dehydration, which in turn led to a decrease in total radius of the“P123 micelle-NaGDC” complexes. To elucidate the effect of the interactions on their diffusive motion, aninteraction model based on a spherical particle with a hard-core interaction shell was employed using the fitted SAXS data. At higher molar ratios, the interparticle interaction was increasingly screened becauseof nonadsorbed bile salt in the surrounding solution. Meanwhile, a further decrease in total radial sizeof the P123 micelle-NaGDC complexes occurred due to a decrease in the aggregation number of P123as the bile salt finally disintegrated the complexes. However, the micelles were found to be more stableand less prone to disintegration in D2O. This investigation demonstrated the importance of using smallangle scattering techniques for studying intermolecular interactions in order to gain understanding ofhow natural surfactants influence the aggregation behavior of amphiphilic polymers
A recombinant fragment of human surfactant protein D lacking the short collagen-like stalk fails to correct morphological alterations in lungs of SP-D deficient mice
No full textEmphysema-like pathology is a characteristic feature of surfactant protein D (SP-D) knock-out mice. Treatment with a recombinant fragment of human SP-D consisting of a short collagen-like stalk (but not the entire collagen-like domain of native SP-D), neck, and carbohydrate recognizing domain (CRD) inhibits development of emphysema-like pathology in SP-D deficient mice. On the other hand, it has been shown that the entire collagen-like domain is necessary for preventing SP-D knock-out mice from pulmonary emphysema development. Thus, in the present study, we aimed to elucidate the role of the short collagen-like stalk for the function of the recombinant fragment of human SP-D. We treated SP-D knock-out mice with a fragment of human SP-D lacking the short collagen-like stalk and compared the effects on lung morphology with results from untreated wild-type and SP-D knock-out mice and from SP-D knock-out mice treated with a recombinant fragment of human SP-D including the short collagen-like stalk. The fragment of SP-D lacking the short collagen-like stalk failed to correct pulmonary emphysematous alterations demonstrating the importance of the short collagen-like stalk for the biological activity of the recombinant fragment of human SP-
A diffusive information preservation method for small Knudsen number flows
No full textThe direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker–Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn ~ 10^(-3)–10^(-4) have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively
Molecular simulation of small Knudsen number flows
No full textThe direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker-Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn similar to 10(-3)-10(-4) have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively
Synthesis and Characterization of a Thermoresponsive Copolymer with an LCST-UCST-like Behavior and Exhibiting Crystallization
No full textIn this work, the diblock copolymer methoxy-poly(ethylene glycol)-block-poly(ϵ-caprolactone) (MPEG-b-PCL) was synthesized with a block composition that allows this polymer in aqueous media to possess both an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST) over a limited temperature interval. The value of the UCST, associated with crystallization of the PCL-block, depended on heating (H) or cooling (C) of the sample and was found to be CPUCSTH = 32 °C and CPUCSTC = 23 °C, respectively. The LCST was not affected by the heating or cooling scans; assumed a value of 52 °C (CPLCSTH = CPLCSTC). At intermediate temperatures (e.g., 45 °C), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM) showed that the solution consisted of a large population of spherical core-shell particles and some self-assembled rodlike objects. At low temperatures (below 32 °C), differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) in combination with SAXS disclosed the formation of crystals with a cylindrical core-shell structure. Cryo-TEM supported a thread-like appearance of the self-assembled polymer chains. At temperatures above 52 °C, incipient phase separation took place and large aggregation complexes of amorphous morphology were formed. This work provides insight into the intricate interplay between UCST and LCST and the type of structures formed at these conditions in aqueous solutions of MPEG-b-PCL diblock copolymers
Interactions in Aqueous Mixtures of Cationic Hydroxyethyl Cellulose and Different Anionic Bile Salts
No full textIt is known that the reduction of blood cholesterol can
be accomplished
through foods containing a large number of dietary fibers; this process
is partially related to the binding of bile salt to fibers. To gain
new insights into the interactions between dietary fibers and bile
salts, this study investigates the interactions between cationic hydroxyethyl
cellulose (catHEC) and sodium deoxycholate (NaDC) or sodium cholate
(NaC), which have a similar structure. Turbidity measurements reveal
strong interactions between catHEC and NaDC, and under some conditions,
macroscopic phase separation occurs. In contrast, the interactions
with NaC are weak. At a catHEC concentration of 2 wt %, incipient
phase separation is approached at concentrations of NaC and NaDC of
32.5 and 19.3 mM, respectively. The rheological results show strong
interactions and a prominent viscosification effect for the catHEC/NaDC
system but only moderate interactions for the catHEC/NaC system. Both
cryogenic transmission electron microscopy and small-angle X-ray scattering
results display fundamental structural differences between the two
systems, which may explain the stronger interactions in the presence
of NaDC. The surmise is that the extended structures formed in the
presence of NaDC can easily form connections and entanglements in
the network
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