Effect Of Membrane Viscosity Research Articles

Lattice Boltzmann simulations on the tumbling to tank-treading transition: effects of membrane viscosity

The tumbling to tank-treading (TB-TT) transition for red blood cells (RBCs) has been widely investigated, with a main focus on the effects of the viscosity ratio [Formula: see text] (i.e., the ratio between the viscosities of the fluids inside and outside the membrane) and the shear rate [Formula: see text] applied to the RBC. However, the membrane viscosity [Formula: see text] plays a major role in a realistic description of RBC dynamics, and only a few works have systematically focused on its effects on the TB-TT transition. In this work, we provide a parametric investigation on the effect of membrane viscosity [Formula: see text] on the TB-TT transition for a single RBC. It is found that, at fixed viscosity ratios [Formula: see text], larger values of [Formula: see text] lead to an increased range of values of capillary number at which the TB-TT transition occurs; moreover, we found that increasing [Formula: see text] or increasing [Formula: see text] results in a qualitatively but not quantitatively similar behaviour. All results are obtained by means of mesoscale numerical simulations based on the lattice Boltzmann models. This article is part of the theme issue 'Progress in mesoscale methods for fluid dynamics simulation'.

Dynamic mode of viscoelastic capsules in steady and oscillating shear flow

Because capsules exhibit viscoelasticity and shear resistance, the study of their dynamic motion under external flow is vital for biomedical and industrial applications. Toward this end, the present study uses the finite-element method to delve into the motion and deformation of viscoelastic capsules under steady and oscillating shear flow. In the steady shear, the effect of membrane viscosity is not obvious enough, which only slows the phase angle of capsules, which is consistent with previous work. However, the effect of membrane viscosity is more significant in the oscillatory shear, and we find that the deformation of capsules is affected by both viscosity and elasticity and exhibits two modes: For shear amplitudes γ0 < 0.06 or frequencies f > 0.3 Hz, the capsules essentially return to their original shape after being deformed. For amplitudes γ0 ≥ 0.06 or frequencies f ≤ 0.3 Hz, the capsules are strongly deformed and cannot return to their original state, which easily leads to membrane wrinkles and stress concentration. The results of this study systematically illustrate the dynamic behavior of viscoelastic capsules, which is critical to expound a capsule for use in drug transport, cell screening, and physiological processes.

On the effects of membrane viscosity on transient red blood cell dynamics.

Computational Fluid Dynamics (CFD) is currently used to design and improve the hydraulic properties of biomedical devices, wherein the large scale blood circulation needs to be simulated by accounting for the mechanical response of red blood cells (RBCs) at the mesoscale. In many practical instances, biomedical devices work on time-scales comparable to the intrinsic relaxation time of RBCs: thus, a systematic understanding of the time-dependent response of erythrocyte membranes is crucial for the effective design of such devices. So far, this information has been deduced from experimental data, which do not necessarily adapt to the broad variety of fluid dynamic conditions that can be encountered in practice. This work explores the novel possibility of studying the time-dependent response of an erythrocyte membrane to external mechanical loads via mesoscale numerical simulations, with a primary focus on the detailed characterisation of the RBC relaxation time tc following the arrest of the external mechanical load. The adopted mesoscale model exploits a hybrid Immersed Boundary-Lattice Boltzmann Method (IB-LBM), coupled with the Standard Linear Solid (SLS) model to account for the RBC membrane viscosity. We underscore the key importance of the 2D membrane viscosity μm to correctly reproduce the relaxation time of the RBC membrane. A detailed assessment of the dependencies on the typology and strength of the applied mechanical loads is also provided. Overall, our findings open interesting future perspectives for the study of the non-linear response of RBCs immersed in time-dependent strain fields.

Aqueous Viscosity Is the Primary Source of Friction in Lipidic Pore Dynamics

A new theory, to our knowledge, is developed that describes the dynamics of a lipidic pore in a liposome. The equations of the theory capture the experimentally observed three-stage functional form of pore radius over time—stage 1, rapid pore enlargement; stage 2, slow pore shrinkage; and stage 3, rapid pore closure. They also show that lipid flow is kinetically limited by the values of both membrane and aqueous viscosity; therefore, pore evolution is affected by both viscosities. The theory predicts that for a giant liposome, tens of microns in radius, water viscosity dominates over the effects of membrane viscosity. The edge tension of a lipidic pore is calculated by using the theory to quantitatively account for pore kinetics in stage 3, rapid pore closing. This value of edge tension agrees with the value as standardly calculated from the stage of slow pore closure, stage 2. For small, submicron liposomes, membrane viscosity affects pore kinetics, but only if the viscosity of the aqueous solution is comparable to that of distilled water. A first-principle fluid-mechanics calculation of the friction due to aqueous viscosity is in excellent agreement with the friction obtained by applying the new theory to data of previously published experimental results.

Dynamics of fluid vesicles in shear flow: Effect of membrane viscosity and thermal fluctuations

The dynamical behavior of vesicles is investigated in simple shear flow. A simulation technique is presented that combines a three-dimensional particle-based mesoscopic model (multiparticle collision dynamics) for the solvent with a dynamically triangulated surface model for the membrane. In this model, thermal fluctuations of the solvent and of the membrane are consistently taken into account. The membrane viscosity can be varied by changing the bond-flip rate of the dynamically triangulated surface. Vesicles are found to transit from steady tank-treading to unsteady tumbling motion with increasing membrane viscosity. At small reduced volumes, the shear induces a transformation from a discocyte to a prolate shape at low membrane viscosity. On the other hand, at high membrane viscosity, the shear induces a transformation from prolate to discocyte, or tumbling motion accompanied by shape oscillations between these two states. Thermal fluctuations induce intermittent tumbling and smooth out the transitions. This effect can be understood from a simplified stochastic model.

Fluid Vesicles with Viscous Membranes in Shear Flow

The effect of membrane viscosity on the dynamics of vesicles in shear flow is studied. We present a new simulation technique, which combines three-dimensional multiparticle collision dynamics for the solvent with a dynamically triangulated membrane model. Vesicles are found to transit from steady tank treading to unsteady tumbling motion with increasing membrane viscosity. Depending on the reduced volume and membrane viscosity, shear can induce both discocyte-to-prolate and prolate-to-discocyte transformations. This behavior can be understood from a simplified model.

Effect of membrane viscosity on the dynamic response of an axisymmetric capsule

The role of membrane surface viscosity is investigated in the transient response of an axisymmetric capsule following a sudden start of external flow. Results obtained in a recent study for capsules with a hyperelastic membrane [Phys. Fluids 12, 948 (2000)] are extended to account for membrane viscosity. The common feature between hyperelastic and viscoelastic membranes is the time evolution of capsule deformation which can be fitted to an exponential function and thus characterized with only two parameters, the deformation at steady state D∞ and the response time τs. Membrane and bulk viscosity have quasilinear and independent effects on the transient response.

Dynamic microstructure of plasma and mitochondrial membranes from bullfrog myocardium-A nanosecond time-resolved fluorometric study.

The viscosity of the phospholipid bilayer and the wobbling angle of the phospholipid molecules of mitochondrial membranes and plasma membranes from bullfrog myocardium were measured with a nanosecond time-resolved fluorometer using pulsed excitation of a hydrophobic fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH). The mean +/- S.D. in the viscosity of the mitochondrial and plasma membranes was 0.54 +/- 0.9 and 0.37 +/- 0.03 P, respectively, at 30 degrees C. The wobbling angle of phospholipid molecules was 42 +/- 1 and 47 +/- 1 degree, respectively. Cholesterol content was lower in mitochondria (6.4 micrograms/mg protein) than in plasma membranes (43.7 micrograms/mg protein) but phosphatidylethanolamine concentration was higher in mitochondria (31.8%) than in plasma membranes (27.3%). Cardiolipin was contained only in mitochondria. The results of these lipid analyses appear consistent with the measurements of membrane viscosity and phospholipid wobbling angle. When the results are compared with those from a previous study on the erythrocyte membranes from bullfrogs, viscosity is found to increase in the order mitochondrial membranes less than plasma membranes less than erythrocyte membranes. The complex requirements of biomembranes of organelles performing different functions appear to be met by the particular dynamic microstructure of the biomembrane. The effect of membrane viscosity on oxygen diffusion through membranes is discussed.

Interactions of lipids and proteins: some general principles.

Methods to describe the binding of phospholipids to membrane proteins are described. It is shown that it is difficult to obtain estimates of the number of phospholipids bound to the surface of a membrane protein from ESR experiments in which plots of free to bound spin label (y) vs. molar ratio of lipid to protein are extrapolated to y = 0. The relative advantages and disadvantages of ESR and fluorescence methods for measuring relative binding constants of phospholipids to membrane proteins are discussed. The particular problems associated with comparing binding constants of molecules of very different sizes (e.g., fatty acids and cardiolipin) are described and equations are presented to account for these problems. The possible effects of membrane viscosity and thickness on activity of membrane proteins are discussed, but it is concluded that effects of phospholipid structure on activity can only be understood in terms of a reasonably complete kinetic model for the protein.

The Modulatory Effect of Membrane Viscosity on Structural and Functional Properties of the Anion Exchange Protein of Human Erythrocytes

The sterol content of human erythrocyte membranes was modified by polyvinylpyrrolidone (PVP)-mediated enrichment or depletion of cholesterol (CHL) or incorporation of cholesteryl hemisuccinate (CHS). The effects of these modifications on osmotic fragility and anion exchange protein (AEP) disposition and function were evaluated. CHS enrichment was fast (1 hr, 37 degrees C) and led to a concentration-dependent crenation as well as a decrease in osmotic cell fragility, in parallel with increased membrane microviscosity. CHL caused similar but considerably less marked effects due to slower incorporation rates into membranes. CHS enrichment of cells induced susceptibility of AEP to trypsin, a protease which otherwise does not affect AEP in intact cells. Although transport rates of monosaccharides, nucleosides, and anions were markedly slowed down by CHS enrichment of cells in parallel with increased membrane viscosity, anion transport was the most affected. The temperature profile of anion transport in CHS-enriched cells revealed a 10-kcal/mol increase in the enthalpy of activation relative to normal cells. Anion transport measured in heteroexchange conditions (Cl in--pyruvate out) and (Cl in-sulfate out) was relatively more susceptible to CHS modification than when it was measured in homoexchange conditions (Cl in-Cl out). The results of these measurements indicate that CHS-mediated increase in membrane viscosity affects AEP translocation capacity and transmembrane disposition via changes in lipid compressibility. Specific effects of CHS on AEP function, however, could not be ruled out.