Suspension Of Capsules Research Articles

Interplay of liquid particles and interphases on the macroscopic elastic response of Liquid-filled composites

This paper deals with providing the effective elastic response of three-phase composites consist of a matrix filled with a random suspension of liquid-filled capsules firmly bonded to the matrix in the realm of small deformation theory. The capsules shell (interphases) and the matrix are considered to be elastic solids and the liquid is considered ideal. For this purpose, the solution for dilute concentrations of the interphases and the liquid particles are derived analytically. Then, the dilute solution is passed to an iterative technique to generate the non-dilute version of the solution. The non-dilute response is available in terms of a system of two nonlinear-coupled-ODE-initial-value problems. The results are confronted with the results of a 3D full-field FE analysis and experimental data and a good agreement is observed. The solution, provided here for polydisperse microstructures, allows for considering different thicknesses for the interphases and in turn can possibly account for different physical phenomena like the size and the surface tension effects. A comprehensive study on the effects of interphases (capsules shell) thickness and mechanical properties as well as the volume concentration of the capsules and the liquid particles on the overall elastic properties of three-phase liquid-filled composites are carried out. We show that although the addition of liquid particles to the matrix has deteriorating effects on the overall elastic properties of the composites, proper selection of the interphases can compensate for these negative effects.

Hydrodynamic interactions and membrane damage for a pair of microcapsules in shear flow: Effect of membrane mechanical properties

We model the hydrodynamic interaction of two equal size capsules in simple shear flow. The capsules may have different mechanical membrane properties. The results are analyzed in terms of a macro scale model of capsule membrane damage. We show how the interaction between two capsules with a membrane rigidity mismatch may lead to damage of the more deformable capsule even when the base flow strength is below the damage threshold of both capsules. We provide charts of the peak deformation energy density in the two membranes as a function of the flow strength and the ratio of the elastic rigidity of the two capsules. Given a damage criterion, those charts can be used to determine when flow-induced damage will occur in a suspension of capsules with a distribution of mechanical properties.

Suspensions of viscoelastic capsules: effect of membrane viscosity on transient dynamics

Membrane viscosity is known to play a central role in the transient dynamics of isolated viscoelastic capsules by decreasing their deformation, inducing shape oscillations and reducing the loading time, that is, the time required to reach the steady-state deformation. However, for dense suspensions of capsules, our understanding of the influence of the membrane viscosity is minimal. In this work, we perform a systematic numerical investigation based on coupled immersed boundary–lattice Boltzmann (IB-LB) simulations of viscoelastic spherical capsule suspensions in the non-inertial regime. We show the effect of the membrane viscosity on the transient dynamics as a function of volume fraction and capillary number. Our results indicate that the influence of membrane viscosity on both deformation and loading time strongly depends on the volume fraction in a non-trivial manner: dense suspensions with large surface viscosity are more resistant to deformation but attain loading times that are characteristic of capsules with no surface viscosity, thus opening the possibility to obtain richer combinations of mechanical features.

Numerical study of suspensions of nucleated capsules at finite inertia

We perform simulations of suspension of capsules with nucleus in shear flow. Every capsule is modeled as a neo-Hookean hyperelastic membrane enclosing a rigid particle with radius equal to the half capsule radius. The rheology of the suspensions is related to the capsule deformation and orientation when varying the membrane stiffness and capsule volume fraction and compared to the dynamics of capsules without nucleus.

Structure and rheology of suspensions of spherical strain-hardening capsules

Abstract

Flow-induced segregation and dynamics of red blood cells in sickle cell disease.

Blood flow in sickle cell disease (SCD) can substantially differ from normal blood flow due to significant alterations in the physical properties of the red blood cells (RBCs). Chronic complications, such as inflammation of the endothelial cells lining blood vessel walls, are associated with SCD, for reasons that are unclear. Here, detailed boundary integral simulations are performed to investigate an idealized model flow flow in SCD, a binary suspension of flexible biconcave discoidal fluid-filled capsules and stiff curved prolate capsules that represent healthy and sickle RBCs, respectively, subjected to pressure-driven flow in a planar slit. The stiff component is dilute. The key observation is that, unlike healthy RBCs that concentrate around the center of the channel and form an RBC-depleted layer (i.e. cell-free layer) next to the walls, sickle cells are largely drained from the bulk of the suspension and aggregate inside the cell-free layer, displaying strong margination. These cells are found to undergo a rigid-body-like rolling orbit near the walls. A binary suspension of flexible biconcave discoidal capsules and stiff straight (non-curved) prolate capsules is also considered for comparison, and the curvature of the stiff component is found to play a minor role in the behavior. Additionally, by considering a mixture of flexible and stiff biconcave discoids, we reveal that rigidity difference by itself is sufficient to induce the segregation behavior in a binary suspension. Furthermore, the additional shear stress on the walls induced by the presence of cells is computed for the various cases. Compared to the small fluctuations in wall shear stress for a suspension of healthy RBCs, large local peaks in wall shear stress are observed for the binary suspensions, due to the proximity of the marginated stiff cells to the walls. This effect is most marked for the straight prolate capsules. As endothelial cells are known to mechanotransduce physical forces such as aberrations in shear stress and convert them to physiological processes such as activation of inflammatory signals, these results may aid in understanding mechanisms for endothelial dysfunction associated with SCD.

Нетермическое воздействие ультракоротких электрических импульсов на наноструктурированные липосомальные капсулы, находящиеся в водной диэлектрической среде.

For the first time, new nanocomposite liposomes and vesicles with a modified structure containing functional inorganic electrically conductive nanoparticles associated with both the inner and the outer surface of the liposomal membrane were prepared. The effect of ultrashort electric field pulses with a duration of less than 10 ns and an intensity in a dielectric aqueous medium of the order of 10 kV/cm on the aqueous suspension of such nanocomposite liposomes containing an encapsulated model low molecular weight compound (NaCl) has been studied. It was found that as a result of exposure to such impulses, decapsulation and destruction of nanocomposite liposomes present in the suspension occurs, accompanied by a corresponding increase in the conductivity of the suspension. It is shown that the sensitivity of nanocomposite liposomal capsules to external electrical effects is due to the inclusion of electrically conductive nanoparticles in their structure. It was found that the effect of decapsulation of liposomal capsules is significantly higher in the case of the impact of electric field pulses on liposomal capsules with bound magnetite nanoparticles compared with the case of a similar effect on the same capsules that do not contain conducting nanoparticles. This fact determines the selectivity of the effect of electric pulses on nanocomposite membrane vesicles containing electrically conductive nanoparticles. A theoretical analysis of non-thermal interaction of nanostructured liposomal capsules containing conducting nanoparticles on the outer and inner surfaces of the membrane with ultrashort electrical pulses was carried out. A theoretical model of non-thermal interaction of nanostructured liposomal capsules with ultrashort electrical pulses is constructed. In the model under consideration, electrically conductive nanoparticles are associated with the outer and inner surfaces of membranes of nanocomposite liposomal capsules. Within the framework of the constructed model, the mechanisms of destruction of the liposomal capsule membrane are described, due to the interaction of conducting spherical nanoparticles located on opposite surfaces of the liposomal membrane resulting from the ultrashort electrical effect on aqueous suspensions of nanostructured liposomal capsules.

Photonic Capsule Sensors with Built-In Colloidal Crystallites.

Technologies to monitor microenvironmental conditions and its spatial distribution are in high demand, yet remain unmet need. Herein, photonic microsensors are designed in a capsule format that can be injected, suspended, and implanted in any target volume. Colorimetric sensors are loaded in the core of microcapsules by assembling core-shell colloids into crystallites through the depletion attraction. The shells of the colloids are made of a temperature-responsive hydrogel, which enables the crystallites to rapidly and widely tune the structural color in response to a change in temperature while maintaining close-packed arrays. The spherical symmetry of the microcapsules renders them optically isotropic, i.e., displaying orientation-independent color. In addition, as a solid membrane is used to protect the delicate crystallites from external stresses, their high stability is assured. More importantly, each microcapsule reports the temperature of its microenvironment so that a suspension of capsules can provide information on the spatial distribution of the temperature.

Suspensions of deformable particles in a Couette flow

We consider suspensions of deformable particles in a Newtonian fluid by means of fully Eulerian numerical simulations with a one-continuum formulation. We study the rheology of the visco-elastic suspension in plane Couette flow in the limit of vanishing inertia and examine the dependency of the effective viscosity μ on the solid volume-fraction Φ, the capillary number Ca, and the solid to fluid viscosity ratio K. The suspension viscosity decreases with deformation and applied shear (shear-thinning) while still increasing with volume fraction. We show that μ collapses to an universal function, μ(Φe), with an effective volume fraction Φe, lower than the nominal one owing to the particle deformation. This universal function is well described by the Eilers fit, which well approximate the rheology of suspension of rigid spheres at all Φ. We provide a closure for the effective volume fraction Φe as function of volume fraction Φ and capillary number Ca and demonstrate it also applies to data in literature for suspensions of capsules and red-blood cells. In addition, we show that the normal stress differences exhibit a non-linear behavior, with a similar trend as in polymer and filament suspensions. The total stress budgets reveals that the particle-induced stress contribution increases with the volume fraction Φ and decreases with deformability.

Ultra-high pressure modified cellulosic fibres with antimicrobial properties

In this work bleached E. globulus kraft pulp was doped with polyhexamethylene biguanide (PHMB) from an aqueous solution or from a suspension of silica capsules (PHMB@silica) by impregnation under atmospheric or ultra-high pressure (UHP) conditions (500MPa). The antimicrobial properties of pulps were evaluated towards gram-negative E. coli and gram-positive L. innocua bacteria. PHMB loads below 500mg per kg of pulp revealed negligible bacteriostatic properties, whereas PHMB loads of ca 3000–4000mg per kg demonstrated bactericidal properties of pulp without significant deterioration of its mechanical strength. The UHP impregnation allowed significant improvement of PHMB uptake. Thus, under equal conditions, PHMB uptake was ca 25% greater under UHP than under atmospheric pressure impregnation, whereas the leachable amounts of PHMB in both pulps were comparable. The sorption of PHMB@silica on pulp in suspension under UHP conditions was ca 17% greater than under atmospheric pressure with almost 70% increase of leachable PHMB.

PHARMACOLOGICAL STUDIES OF STAY-ON POWER CAPSULES IN RABBITS

The main objective of this study was to perform pharmacological evaluation of Stay-On Power Capsules in Rabbits (Non-Rodents) namely the aphrodisiac activity. The present investigation deals with Pharmacological Studies (Mating behaviour study, mating performance test, Hormonal analysis, Reproductive organ and spermal analysis) of Stay-On Power Capsules in Non-Rodents administered orally by gavage to Rabbits in accordance with the schedule Y of drugs and Cosmetic Act (2005). The acute toxicity study of Stay-On Power Capsules was done by up and down method. After the completion of acute toxicity studies, three different doses were selected for aphrodisiac activity such as 150, 300, and 600 mg/kg. Volume of oral administration was 1 ml/100 g of animals. Animals were randomly divided into five groups with six animals per group. Group I represented the control animals treated with normal water only; Groups II, III, and IV were treated with oral suspension of Stay-On Power Capsules at 18:00 h, at doses of 150, 300, and 600 mg/kg, respectively; and Group V served as a positive control treated with Sildenafil citrate of 5 mg/kg body weight. All the treatments were continued for 3 weeks only. A mating behaviour study revealed that continuous administration for 3 weeks, all the doses of Stay-On Power Capsules were able to significantly decrease mount and intromission latencies, and decrease ejaculatory latency and post ejaculatory interval when compared to vehicle control and standard drug treated Rabbits. It also resulted in a dose dependent increase in the mating performance and showed increasing ratio of testes body weight along with increase in sperm count as compared to the control group. Key Words: Stay-On Power Capsules, Pharmacological Studies, aphrodisiac activity, mating behaviour, mating performance

Buckling and its effect on the confined flow of a model capsule suspension

The rheology of confined flowing suspensions, such as blood, depends upon the dynamics of the components, which can be particularly rich when they are elastic capsules. Using boundary integral methods, we simulate a two-dimensional model channel through which flows a dense suspension of fluid-filled capsules. A parameter of principal interest is the equilibrium membrane perimeter, parameterized by ξ o, which ranges from round capsules with ξ o=1.0 to ξ o=3.0 capsules with a dog-bone-like equilibrium shape. It is shown that the minimum effective viscosity occurs for ξ o≈1.6, which forms a biconcave equilibrium shape, similar to a red blood cell. The rheological behavior changes significantly over this range; transitions are linked to specific changes in the capsule dynamics. Most noteworthy is an abrupt change in behavior for ξ o≈2.0, which correlates with the onset of capsule buckling. The buckled capsules have a more varied orientation and make significant rotational (rotlet) contributions to the capsule–capsule interactions.

Shape-mediated margination and demargination in flowing multicomponent suspensions of deformable capsules.

We present detailed simulations and theory for flow-induced segregation in suspensions of deformable fluid-filled capsules with different shapes during simple shear flow in a planar slit. This system is an idealized model for transport for blood cells and/or drug carriers in the microcirculation or in microfluidic devices. For the simulations, an accelerated implementation of the boundary integral method was employed. We studied the binary mixtures of spherical and ellipsoidal capsules, varying the aspect ratio κ of the ellipsoid while keeping constant either (a) equatorial radius or (b) volume. Effects of a variety of parameters was studied, including κ, volume fraction and number fraction of the spherical capsules in the mixture. In suspensions where the ellipsoids have the same equatorial radius as the spheres, capsules with lower κ marginate. In suspension where the ellipsoids have the same volume as the spheres, ellipsoidal (both oblate and prolate) capsules are seen to demarginate in a mixture of primarily spherical capsules. To understand these results, a mechanistic framework based on the competition between wall-induced migration and shear-induced collisions is presented. A simplified drift-diffusion theory based on this framework shows excellent qualitative agreement with simulation results.

Rheology of a dense suspension of spherical capsules under simple shear flow

We present a numerical analysis of the rheology of a dense suspension of spherical capsules in simple shear flow in the Stokes flow regime. The behaviour of neo-Hookean capsules is simulated for a volume fraction up to${\it\phi}=0.4$by graphics processing unit computing based on the boundary element method with a multipole expansion. To describe the specific viscosity using a polynomial equation of the volume fraction, the coefficients of the equation are calculated by least-squares fitting. The results suggest that the effect of higher-order terms is much smaller for capsule suspensions than rigid sphere suspensions; for example,$O({\it\phi}^{3})$terms account for only 8 % of the specific viscosity even at${\it\phi}=0.4$for capillary numbers$Ca\geqslant 0.1$. We also investigate the relationship between the deformation and orientation of the capsules and the suspension rheology. When the volume fraction increases, the deformation of the capsules increases while the orientation angle of the capsules with respect to the flow direction decreases. Therefore, both the specific viscosity and the normal stress difference increase with volume fraction due to the increased deformation, whereas the decreased orientation angle suppresses the specific viscosity, but amplifies the normal stress difference.

Fluctuations and diffusion in sheared athermal suspensions of deformable particles

We analyze fluctuations of particle displacements and stresses in a sheared athermal suspension of elastic capsules (red blood cells). Upon variation of the volume fraction from the dilute up to the highly concentrated regime, our numerical simulations reveal different characteristic power-law regimes of the fluctuation variances and relaxation times. In the jammed phase and at high shear rates, anomalous scaling exponents are found that deviate from pure dimensional predictions. The observed behavior is rationalized via kinetic arguments and a dissipation balance model that takes into account the local fluid flows between the particles. Our findings support the view that the rheology of dense suspensions is essentially governed by the non-affine displacements.

Hydrodynamic Interaction of Elastic Capsules in Bounded Shear Flow

AbstractThis paper presents a modified Loop’s subdivision algorithm for studying the deformation of a single capsule, the hydrodynamic interaction between two capsules and the hydrodynamic diffusion of a suspension of capsules in bounded shear flow. A subdivision thin-shell model is employed to compute the forces generated on the surface of the elastic capsule during deformation. The capsule surface is approximated using the modified Loop’s subdivision scheme which guarantees bounded curvature and C1 continuity everywhere on the limit surface. The present numerical technique has been validated by studying the deformation of a spherical capsule in shear flow. Computations are also performed for a biconcave capsule over a wide range of shear rates and viscosity ratios to investigate its dynamics. In addition, the hydrodynamic interaction between two elastic capsules in bounded shear flow is studied. Depending on the wall separation distance, the trajectory-bifurcation points that separate reversing and crossing motions for both spherical and biconcave capsules can be found. Compared to the spherical capsules, the biconcave capsules exhibit additional types of interaction such as rotation and head-on collision. The head-on collision results in a large trajectory shift which contribute to the hydrodynamic diffusion of a suspension. A suspension of a large number of biconcave capsules in shear flow is also simulated to show the ability of the modified scheme in running a large-scale simulation over a long period of time.

Interplay of inertia and deformability on rheological properties of a suspension of capsules

AbstractThe interplay of inertia and deformability has a substantial impact on the transport of soft particles suspended in a fluid. However, to date a thorough understanding of these systems is still missing, and only a limited number of experimental and theoretical studies are available. We combine the finite-element, immersed-boundary and lattice-Boltzmann methods to simulate three-dimensional suspensions of soft particles subjected to planar Poiseuille flow at finite Reynolds numbers. Our findings confirm that the particle deformation and inclination increase when inertia is present. We observe that the Segré–Silberberg effect is suppressed with respect to the particle deformability. Depending on the deformability and strength of inertial effects, inward or outward lateral migration of the particles takes place. In particular, for increasing Reynolds numbers and strongly deformable particles, a hitherto unreported distinct flow focusing effect emerges, which is accompanied by a non-monotonic behaviour of the apparent suspension viscosity and thickness of the particle-free layer close to the channel walls. This effect can be explained by the behaviour of a single particle and the change of the particle collision mechanism when both deformability and inertia effects are relevant.

Rheology of dense suspensions of elastic capsules: normal stresses, yield stress, jamming and confinement effects.

We study the shearing rheology of dense suspensions of elastic capsules, taking aggregation-free red blood cells as a physiologically relevant example. Particles are non-Brownian and interact only via hydrodynamics and short-range repulsive forces. An analysis of the different stress mechanisms in the suspension shows that the viscosity is governed by the shear elasticity of the capsules, whereas the repulsive forces are subdominant. Evidence for a dynamic yield stress above a critical volume fraction is provided and related to the elastic properties of the capsules. The shear stress is found to follow a critical jamming scenario and is rather insensitive to the tumbling-to-tank-treading transition. The particle pressure and normal stress differences display some sensitivity to the dynamical state of the cells and exhibit a characteristic scaling, following the behavior of a single particle, in the tank-treading regime. The behavior of the viscosity in the fluid phase is rationalized in terms of effective medium models. Furthermore, the role of confinement effects, which increase the overall magnitude and enhance the shear-thinning of the viscosity, is discussed.

Flow-induced segregation in confined multicomponent suspensions: effects of particle size and rigidity

AbstractThe effects of particle size and rigidity on segregation behaviour in confined simple shear flow of binary suspensions of fluid-filled elastic capsules are investigated in a model system that resembles blood. We study this problem with direct simulations as well as with a master equation model that incorporates two key sources of wall-normal particle transport: wall-induced migration and hydrodynamic pair collisions. The simulation results indicate that, in a mixture of large and small particles with equal capillary numbers, the small particles marginate, while the large particles antimarginate in their respective dilute suspensions. Here margination refers to localization of particles near walls, while antimargination refers to the opposite. In a mixture of particles with equal size and unequal capillary number, the stiffer particles marginate while the flexible particles antimarginate. The master equation model traces the origins of the segregation behaviour to the size and rigidity dependence of the wall-induced migration velocity and of the cross-stream particle displacements in various types of collisions. In particular, segregation by rigidity, especially at low volume fractions, is driven in large part by heterogeneous collisions, in which the stiff particle undergoes larger displacement. In contrast, segregation by size is driven mostly by the larger wall-induced migration velocity of larger particles. Additionally, a non-local drift-diffusion equation is derived from the master equation model, which provides further insights into the segregation behaviour.

Characterizing the membrane properties of capsules flowing in a square-section microfluidic channel: Effects of the membrane constitutive law

A microfluidic method is presented to measure the elastic membrane properties of a population of microcapsules with diameter of order 60 μm. The technique consists of flowing a suspension of capsules enclosed by a polymerized ovalbumin membrane through a square-section microfluidic channel with cross dimension comparable with the capsule mean diameter. The deformed profile and the velocity of a given capsule are recorded. A full mechanical model of the motion and deformation of an initially spherical capsule flowing inside a square-section channel is designed for different flow strengths, confinement ratios, and membrane constitutive laws. The experimental deformed profiles are analyzed with the numerical model. This allows us to find the ratio between the viscous and elastic forces and thus the shear elastic modulus of the membrane. We show that the ovalbumin membrane tends to have a strain-softening behavior under the conditions studied here.