Bulk Suspension Research Articles

Total glossectomy: Technique review

Advanced cancers of oral tongue and recurrent/residual tumors arising from base of tongue may require total glossectomy for curative intent treatment. This procedure is considered morbid due to possibility of life threatening aspiration. This review discusses the technical nuances to reduce functional morbidity. The pull through resection technique allows a compartmental resection of these tumors with adequate margin control without a need for mandibulotomy. Selection of appropriate flap to replace bulk and laryngeal suspension are essential components of reconstruction. With application of these technical advances and adequate post-operative swallow therapy, patients undergoing total glossectomy have acceptable functional outcome.

A Method for High-Throughput Measurements of Viscosity in Sub-micrometer-Sized Membrane Systems.

To unravel the underlying principles of membrane adaptation in small systems like bacterial cells, robust approaches to characterize membrane fluidity are needed. Currently available relevant methods require advanced instrumentation and are not suitable for high‐throughput settings needed to elucidate the biochemical pathways involved in adaptation. We developed a fast, robust, and financially accessible quantitative method to measure the microviscosity of lipid membranes in bulk suspension using a commercially available plate reader. Our approach, which is suitable for high‐throughput screening, is based on the simultaneous measurements of absorbance and fluorescence emission of a viscosity‐sensitive fluorescent dye, 9‐(2,2‐dicyanovinyl)julolidine (DCVJ), incorporated into a lipid membrane. We validated our method using artificial membranes with various lipid compositions over a range of temperatures and observed values that were in good agreement with previously published results. Using our approach, we were able to detect a lipid phase transition in the ruminant pathogen Mycoplasma mycoides.

Fast equilibration dynamics of viscous particle-laden flow in an inclined channel

A viscous suspension of negatively buoyant particles released into a wide, open channel on an incline will stratify in the normal direction as it flows. We model the early dynamics of this stratification under the effects of sedimentation and shear-induced migration. Prior work focuses on the behaviour after equilibration where the bulk suspension either separates into two distinct fronts (settled) or forms a single, particle-laden front (ridged), depending on whether the initial concentration of particles exceeds a critical threshold. From past experiments, it is also clear that this equilibration time scale grows considerably near the critical concentration. This paper models the approach to equilibrium. We present a theory of the dramatic growth in this equilibration time when the mixture concentration is near the critical value, where the balance between settling and shear-induced resuspension reverses.

Numerical study on rheological properties for dispersed and aggregated particle systems

Shear thinning behavior of colloidal suspensions is a direct consequence of shear-induced structural variation of aggregates. This study numerically simulates the shear-induced deformation of spherical aggregates of particles with close-packed and hollowed-out structures to evaluate its rheological effects on the bulk suspension. Simulations are performed by the discrete element method (DEM) coupled with direct numerical simulation (DNS), herein referred to as the “DEM–DNS method.” This method can be used to simultaneously evaluate adhesive force and contact force acting on particles, which play an essential role in aggregate breakup, combined with the two-way particle–fluid interaction. The simulations show that the weakly sheared suspensions for both aggregates, subjected to no structural rearrangement, yield the same shear viscosity. In contrast, under strong shear where both aggregates undergo an irreversible breakup, the suspension of the hollow aggregate shows greater shear thinning than that of the close-packed aggregate. This bifurcation in shear thinning suggests the mechanism underlying the oft-encountered large shear thinning: the shear-induced breakup of aggregates enables a release of the fluid caged inside the aggregates and thus a substantial decrease in the apparent volume fraction of the solid phase. We thereby demonstrate the sophisticated capacity of the DEM–DNS method for experimentally unachievable correlation of shear-induced deformation of aggregates with a macroscopic viscosity evaluation.

Simple and rapid method for homogeneous dimer formation of gold nanoparticles in a bulk suspension based on van der Waals interactions between alkyl chains

We developed a simple and rapid method for dimer and higher multimer formation of gold nanoparticles (AuNPs) in bulk suspension. A coupling of AuNPs modified with COOH-terminated alkanethiol by van-der-Waals interaction between alkyl chains was employed. We demonstrated the tunability of the interparticle gap by changing the alkyl chain length from C5 to C15. Efficient dimer formation that avoids unwanted aggregation was demonstrated for AuNPs with a diameter ranging from 20 nm to 80 nm. For all cases, we found that the interparticle gap is well-defined and uniform. For the shortest alkyl chain (C5), we achieved an interparticle gap as small as 1.0 nm.

Human Serum Albumin Adsorption Kinetics on Silica: Influence of Protein Solution Stability.

Adsorption kinetics of human serum albumin (HSA) on silica substrates was studied using optical waveguide lightmode spectroscopy (OWLS) and quartz microbalance (QCM) techniques. Measurements were performed at pH 3.5, 5.6, and 7.4 for various bulk suspension concentrations and ionic strengths. The diffusion coefficient measurements showed that for pH 3.5 the HSA molecules are stable for NaCl concentrations from 10-3 to 0.15 M. This allowed us to precisely determine the mass transfer rate coefficients for the OWLS and QCM cells. The experimental data were adequately interpreted in terms of a hybrid random sequential adsorption model. The OWLS maximum coverage of HSA at pH 3.5, which is equal to 1.3 mg m-2, agrees with the QCM result and with previous results derived from streaming potential measurements. Thus, the results obtained at pH 3.5 served as reference data for the analysis of adsorption kinetics at higher pHs. In this way, it was confirmed that the adsorption kinetics of HSA molecules at pH 5.6 and 7.4 was considerably slower than at pH 3.5. This effect was attributed to aggregation of HSA solutions and interpreted in terms of a theoretical model combining the Smoluchowski aggregation theory with the convective diffusion mass transfer theory. New analytical equations were derived that can be used for the interpretation of other protein adsorption from unstable solutions.

Progress of stimuli-responsive molecular imprinted materials for capture/release of proteins

To date, molecular imprinting (MIP) materials towards proteins have been utilized in a wide range of applications encompassing the fields of samples purification, proteomics, life science, biosensor, pharmaceutical research and drug delivery. Although tremendous progress has been made in MIP technique field, the large size of macromolecules would lead to low transmission and diffusion efficiency during MIP processes, and further cause difficult in adsorption and desorption of target proteins. Therefore, great challenges still remain to be addressed, especially in the design of unique and advanced MIP materials towards macromolecules. More recently, stimuli-responsive MIP materials have attracted considerable interest because they can respond to external stimuli while modulating their affinities for the target proteins and endowing switchable capacities of the binding/releasing processes. In this review, an overview of different stimuli-responsive MIP materials towards proteins developed from 1998 to now, especially the synthetic methods, monomer species, intelligent modulating principle and application has been provided. Moreover, the future of intelligent stimuli-responsive MIP materials for target proteins is expounded. In the first section, the classical MIP fabrication process and mechanism of MIP materials have been described: template incubating with the function monomers, polymerization and template removing. Then the fundamental properties of classical MIP materials including high selectivity, stability and excellent reusability without loss of activity have been discussed. However, the MIP materials are mainly utilized as adsorbents for extraction of the small molecules. When it comes to template with large molecules, such as proteins, the MIP materials suffered from the lower diffusion efficiency and needed harsh elution conditions. Therefore, to approach challenges, new materials-the stimuli-responsive MIP materials should be explored. In the second section, several methods for synthesis of stimuli-responsive MIP materials have been introduced in detail, including bulk polymerization, emulsion polymerization, precipitation polymerization, suspension polymerization and surface imprinting method. Moreover, the advantages and shortcomings of each method and its application have been summarized. Combination of MIP materials with stimuli-responsive properties has attracted significant research interest. In the third section, a general summary of stimuli-responsive MIP technology has been made, including the design of thermo/pH sensitive MIP materials and its application in proteins analysis. Finally, this review performs prospect for the future development of stimuli-responsive MIP technology including the limitation in theoretical study, synthesis method and commercial products. The stimuli-responsive MIP materials have displayed great potential anyhow in several applications including drug delivery and environmental protection owing to their versatility properties.

Effect of carrier fluid rheology on shear-induced particle migration in asymmetric T-shaped bifurcation channel

Separation of particles from the carrier fluid of suspension is important in many engineering applications. In this work numerical simulations of particle migration during the flow of concentrated suspension through 3D asymmetric T-shaped bifurcating channels were carried out. The carrier fluids were considered to be non-Newtonian and inelastic. Diffusive flux model of shear-induced migration in conjugation with the power-law and Bird-Carreau constitutive models for the carrier fluid was used in the simulations. The velocity and particle concentration profiles in a non-Newtonian suspending fluid showed marked differences compared to that in the Newtonian carrier. Enhanced migration was observed in the case of shear thinning fluid while low for shear thickening. The symmetric velocity and concentration profiles in the inlet branch become asymmetric in the daughter branches and the degree of asymmetry strongly depends on the carrier fluid rheology. The results showed that the particle partitioning between daughter branches do not follow the fluid partitioning and the degree of separation depends on the relative volumetric flow rate of bulk suspension in the daughter branches. Higher separation efficiency was achieved for suspension in shear thinning fluid and relatively lower in Newtonian and shear thickening fluids.

Mechanism of shear thickening in suspensions of rigid spheres in Boger fluids. Part I: Dilute suspensions

The mechanism for shear thickening of the viscometric functions of rigid non-Brownian sphere suspensions in highly elastic fluids is studied numerically. Particular focus is placed on the particle-induced fluid stress, which is the dominant contribution to the shear thickening behavior, especially at moderate to high Weissenberg numbers. We determine the Weissenberg number scaling for both the magnitude of the particle-induced fluid stress and the volume containing most of the particle-induced fluid stress to understand the overall suspension behavior at moderate Weissenberg numbers. Furthermore, we analyze the flow type in the regions of significant polymer-induced fluid stress and find that the stretch of polymers in strain-dominated flow within closed streamlines around the particles generates the large stresses that contribute to the thickening behavior. Thus, understanding the response of the suspending fluid to extensional deformation is important for predicting the shear rheology of the bulk suspension. Lastly, we explore the effect of polymer viscosity and polymer extensibility on the behavior of the particle-induced fluid stress.

Understanding the behavior of H+-protected silica nanoparticles at the oil-water interface for enhanced oil recovery (EOR) applications

A large number of core-flooding and micromodel experiments have examined the potential of nanoparticles to increase oil recovery. The mechanism of enhanced oil recovery using nanoparticles (nanoparticles-EOR) is still unclear. Nanoparticles may aid enhanced oil recovery because they may alter rock wettability and possibly reduce oil-water interfacial tension (IFT). The effect of nanoparticles on the oil-water IFT is controversial, as some have found that nanoparticles reduce IFT and others have illustrated that they have no significant effect. Nanoparticles' attachment at the oil-water interface, which causes IFT reduction is complex and bulk fluids properties (water and oil) directly affect their self-assembly. Fully understanding the driving forces causing self-assembly of nanoparticles at the oil-water interface and its controlling parameters are crucial for determining the effect of nanoparticles on IFT.In this research, by investigating the controlling parameters of nanoparticle attachment at the interface (bulk suspension properties including the concentration of nanoparticles, concentration of HCl, salinity, size and charge of nanoparticles, and operating conditions i.e. temperature and pressure), and coupling them with nanoparticles' stability in solution, the conditions under which silica nanoparticles can reduce oil-water interfacial tension are experimentally investigated. The results reveal that by appropriately designing the operating conditions, H+-protected silica nanoparticles can reduce the oil-water IFT. The maximum reduction of the oil-water IFT was obtained for 0.20 wt% silica nanoparticles in a solution containing 0.025 wt% HCl and 0.15 wt% nanoparticles in 0.0076 wt% HCl, where the IFT was reduced from 23.56 ± 0.36 mN/m to 12.81 ± 0.77 mN/m and from 22.61 ± 0.41 mN/m to 14.01 ± 0.87 mN/m, respectively. However, the minimum IFT reduction occurs when the surface energy reduction due to the adsorption of nanoparticles is minimal, i.e. the chance of nanoparticles to desorb from the interface due to thermal fluctuations is high, and nanoparticles' aggregation on the bulk surface is initiating.

Protein adsorption mechanisms at rough surfaces: Serum albumin at a gold substrate

Adsorption kinetics of human serum albumin (HSA) at a gold substrate was studied using the quartz microbalance (QCM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Measurements were performed at pH 3.5 for various bulk suspension concentrations and ionic strengths. The QCM experimental data were compared with the dry coverage of HSA derived from AFM and from the solution of the mass transfer equation acquired using a hybrid random sequential adsorption model. In this way, the water factor and the dynamic hydration function for HSA monolayers were quantitatively evaluated as a function of dry coverage for various ionic strengths. A comparison of these results with previously known for a silica sensor confirmed that the QCM kinetic measurements are sensitive to the roughness of the sensor characterized in terms of the rms parameter. For the more rough gold sensor (rms = 2.5 nm, average surface feature size 6 nm) the QCM mass transfer rate constant was 2.6 times lower than for the silica sensor characterized by rms = 0.86 nm. This gives for the gold sensor the apparent water factor equal to one and zero hydration function. Moreover, the hydration function increased for larger HSA coverage and was dependent on ionic strength in contrast to the silica substrate. This unexpected behavior was interpreted in terms of the buoyancy effect where the HSA molecules adsorbing in cavities existing at rough surfaces replace the stagnant (hydrodynamically bound) water. Hence, these results confirm that the sensor roughness of the size comparable with protein molecule dimensions exerts a decisive influence on their adsorption kinetic derived from QCM measurements.

Improved electrocatalytic metabolite production and drug biosensing by human liver microsomes immobilized on amine-functionalized magnetic nanoparticles

A biocatalytic system constructed by electrostatically immobilizing drug metabolizing human liver microsomes (HLM, negatively charged due to phospholipids) onto positively charged amine-functionalized magnetic nanoparticles (MNPamine, 100 nm hydrodynamic diameter) for biosensing of cytochrome P450 (CYP)-specific drug candidates and electrocatalyzing drug conversion into metabolites is reported. The MNP-adsorbed HLM biomaterial (denoted as MNPamine/HLM) was magnetically separated from the bulk suspension of HLM, washed twice in phosphate buffer (pH 7.0), and adsorbed onto polished edge-plane pyrolytic graphite (EPG) electrodes. Direct electrochemical properties and oxygen reduction currents were obtained by cyclic voltammetry (CV). Direct electron transfer kinetics from the microsomal redox proteins present in the adsorbed film of MNPamine/HLM on EPG surface was accomplished using square wave voltammetry due to its smaller background charging currents and improved faradaic peak intensity than CV. The MNPamine/HLM bioelectrodes exhibited a formal potential of −0.46 V vs Ag/AgCl reference (1 M KCl), which was in agreement with the FAD/FMN cofactor containing CYP-reductase (CPR) as the electron receiver from the electrode. This conclusion was drawn based on the formal potentials of only CPR (∼-0.47 V vs Ag/AgCl) containing bactosomal films adsorbed on EPG electrodes (bactosomes are bacterial membrane expressed enzymes). Whereas, bactosomal CYP 2C9 film showed a much more positive formal potential (−0.34 V vs Ag/AgCl). A heterogeneous electron transfer rate constant of 19 ± 5 s−1 was exhibited by the MNPamine/HLM film. Oxygen reduction currents and electrocatalytic diclofenac hydroxylation characteristics of the CYP enzymes present in the HLM film indicated the electron mediation by the CYP-reductase from the electrode to CYP-heme centers to initiate the catalytic cycle. Amperometric i-t curves with diclofenac drug concentration yielded the apparent Michaelis-Menten affinity constants (KMapp) of MNPamine/HLM and only HLM films as 302 ± 33 and 365 ± 36 μM, respectively. This is the first electrocatalysis report of bioelectrodes featuring HLM-bound MNPamine for applications in drug activity assays, enhanced metabolite production, and sensitive biosensing of CYP-specific drugs and environmental pollutants. Eliminations of tedious isolation and purification of membrane-containing CYPs, and the need for expensive NADPH cofactor (as electrode donates the reducing equivalents in an inexpensive and sustainable manner) are added advantages. Our future work aims to gain quantitative metabolite estimations upon scalability of such bioelectrode designs useful for pharmacological and toxicological evaluations of new drugs in development.

Kinetics of human serum albumin adsorption at silica sensor: Unveiling dynamic hydration function.

Adsorption kinetics of human serum albumin (HSA) at a silica substrate was studied using the QCM-D and AFM methods. Measurements were performed at pH 3.5 for various bulk suspension concentrations and ionic strengths. The QCM experimental data were compared with the dry coverage of HSA derived from AFM and from the solution of the mass transfer equation. In this way, the dynamic hydration functions and water factors of HSA monolayers were quantitatively evaluated as a function of dry coverage for various ionic strengths. Using the hydration functions, the HSA adsorption runs derived from QCM-D measurements were converted to the dry coverage vs. the time relationships. In this way, the maximum coverage of irreversibly bound HSA molecules was determined. It was equal to 0.35 and 1.4 mg m-2 for NaCl concentration of 0.001 and 0.15 M, respectively. These results agree with previous experimental data derived by streaming potential measurements for mica and with theoretical modeling. Therefore, the side-on mechanism of HSA adsorption at silica sensor at pH 3.5 was confirmed. Also, a quantitative analysis of the desorption runs allowed one to calculate the binding energy of the reversibly bound HSA fraction. Beside significance to basic science, these results enable to develop a robust technique of preparing HSA monolayers at silica sensor of well-controlled coverage and molecule orientation.

Suspension flow through an asymmetric T-junction

The flow of a suspension through a bifurcating channel is studied experimentally and by computational methods. The geometry considered is an ‘asymmetric T’, as flow in the entering branch divides to either continue straight or to make a right angle turn. All branches are of the same square cross-section of side length $D$, with inlet and outlet section lengths $L$ yielding $L/D=58$ in the experiments. The suspensions are composed of neutrally buoyant spherical particles in a Newtonian liquid, with mean particle diameters of $d=250~\unicode[STIX]{x03BC}\text{m}$ and $480~\unicode[STIX]{x03BC}\text{m}$ resulting in $d/D\approx 0.1$ to $d/D\approx 0.2$ for $D=2.4~\text{mm}$. The flow rate ratio $\unicode[STIX]{x1D6FD}=Q_{\Vert }/Q_{0}$, defined for the bulk, fluid and particles, is used to characterize the flow behaviour; here $Q_{\Vert }$ and $Q_{0}$ are volumetric flow rates in the straight outlet branch and inlet branch, respectively. The channel Reynolds number $Re=(\unicode[STIX]{x1D70C}DU)/\unicode[STIX]{x1D702}$ was varied over $0<Re<900$, with $\unicode[STIX]{x1D70C}$ and $\unicode[STIX]{x1D702}$ the fluid density and viscosity, respectively, and $U$ the mean velocity in the inlet channel; the inlet particle volume fraction was $0.05\leqslant \unicode[STIX]{x1D719}_{0}\leqslant 0.30$. Experimental and numerical results for single-phase Newtonian fluid both show $\unicode[STIX]{x1D6FD}$ increasing with $Re$, implying more material tending toward the straight branch as the inertia of the flow increases. In suspension flow at small $\unicode[STIX]{x1D719}_{0}$, inertial migration of particles in the inlet branch affects the flow rate ratio for particles ($\unicode[STIX]{x1D6FD}_{\mathit{particle}}$) and suspension ($\unicode[STIX]{x1D6FD}_{\mathit{suspension}}$). The flow split for the bulk suspension satisfies $\unicode[STIX]{x1D6FD}>0.5$ for $\unicode[STIX]{x1D719}_{0}<0.16$ while $\unicode[STIX]{x1D719}_{0}=0.16$ crosses from $\unicode[STIX]{x1D6FD}\approx 0.5$ to $\unicode[STIX]{x1D6FD}>0.5$ at $Re\approx 100$. For $\unicode[STIX]{x1D719}_{0}\geqslant 0.2$, $\unicode[STIX]{x1D6FD}<0.5$ at all $Re$ studied. A complex dependence of the mean solid fraction in the downstream branches upon inlet fraction $\unicode[STIX]{x1D719}_{0}$ and $Re$ is observed: for $\unicode[STIX]{x1D719}_{0}<0.1$, the solid fraction in the straight downstream branch initially decreases with $Re$, before increasing to surpass the inlet fraction at large $Re$ ($Re\approx 500$ for $\unicode[STIX]{x1D719}_{0}=0.05$). At $\unicode[STIX]{x1D719}_{0}>0.1$, the solid fraction in the straight branch satisfies $\unicode[STIX]{x1D719}_{\Vert }/\unicode[STIX]{x1D719}_{0}>1$, and this ratio grows with $Re$. Discrete-particle simulations employing immersed boundary and lattice-Boltzmann techniques are used to analyse these phenomena, allowing rationalization of aspects of this complex behaviour as being due to particle migration in the inlet branch.

Acoustic Fabrication via the Assembly and Fusion of Particles.

Acoustic assembly promises a route toward rapid parallel fabrication of whole objects directly from solution. This study reports the contact-free and maskless assembly, and fixing of silicone particles into arbitrary 2D shapes using ultrasound fields. Ultrasound passes through an acoustic hologram to form a target image. The particles assemble from a suspension along lines of high pressure in the image due to acoustic radiation forces and are then fixed (crosslinked) in a UV-triggered reaction. For this, the particles are loaded with a photoinitiator by solvent-induced swelling. This localizes the reaction and allows the bulk suspension to be reused. The final fabricated parts are mechanically stable and self-supporting.

The Effect of Ultrasound on the Crystallisation of Paracetamol in the Presence of Structurally Similar Impurities

Sono-crystallisation has been used to enhance crystalline product quality particularly in terms of purity, particle size and size distribution. In this work, the effect of impurities and ultrasound on crystallisation processes (nucleation temperature, yield) and crystal properties (crystal size distribution determined by Focused Beam Reflectance Measurement (FBRM), crystal habit, filtration rate and impurity content in the crystal product by Liquid Chromatography-Mass Spectroscopy (LC-MS)) were investigated in bulk suspension crystallisation experiments with and without the use of ultrasound. The results demonstrate that ultrasonic intervention has a significant effect on both crystallisation and product crystal properties. It increases the nucleation rate resulting in smaller particles and a narrower Particle Size Distribution (PSD), the yield has been shown to be increase as has the product purity. The effect of ultrasound is to reduce the level acetanilide impurity incorporated during growth from a 2 mol% solution of the selected impurity from 0.85 mol% to 0.35 mol% and likewise ultrasound reduces the uptake of metacetamol from 1.88 mol% to 1.52 mol%.

Absorption Study of Genistein Using Solid Lipid Microparticles and Nanoparticles: Control of Oral Bioavailability by Particle Sizes.

In this study, the effect of particle size of genistein-loaded solid lipid particulate systems on drug dissolution behavior and oral bioavailability was investigated. Genistein-loaded solid lipid microparticles and nanoparticles were prepared with glyceryl palmitostearate. Except for the particle size, other properties of genistein-loaded solid lipid microparticles and nanoparticles such as particle composition and drug loading efficiency and amount were similarly controlled to mainly evaluate the effect of different particle sizes of the solid lipid particulate systems on drug dissolution behavior and oral bioavailability. The results showed that genistein-loaded solid lipid microparticles and nanoparticles exhibited a considerably increased drug dissolution rate compared to that of genistein bulk powder and suspension. The microparticles gradually released genistein as a function of time while the nanoparticles exhibited a biphasic drug release pattern, showing an initial burst drug release, followed by a sustained release. The oral bioavailability of genistein loaded in solid lipid microparticles and nanoparticles in rats was also significantly enhanced compared to that in bulk powders and the suspension. However, the bioavailability from the microparticles increased more than that from the nanoparticles mainly because the rapid drug dissolution rate and rapid absorption of genistein because of the large surface area of the genistein-solid lipid nanoparticles cleared the drug to a greater extent than the genistein-solid lipid microparticles did. Therefore, the findings of this study suggest that controlling the particle size of solid-lipid particulate systems at a micro-scale would be a promising strategy to increase the oral bioavailability of genistein.

Refractive index and thickness determination in Langmuir monolayers of myelin lipids

Langmuir monolayers at the air/water interface are widely used as biomembrane models and for amphiphilic molecules studies in general. Under controlled intermolecular organization (lateral molecular area), surface pressure, surface potential, reflectivity (R) and other magnitudes can be precisely determined on these planar monomolecular films. However, some physical parameters such as the refractive index of the monolayer (n) still remain elusive. The refractive index is very relevant because (in combination with R) it allows for the determination of the thickness of the film. The uncertainties of n determine important errors that propagate non-linearly into the calculation of monolayers thickness.Here we present an analytical method for the determination of n in monolayers based on refractive index matching. By using a Brewster angle microscopy (BAM) setup and monolayers spread over subphases with variable refractive index (n2), a minimum in R is search as a function of n2. In these conditions, n equals n2. The results shown correspond to monolayers of myelin lipids. The n values remain constant at 1.46 upon compression and equals the obtained value for myelin lipid bilayers in suspension. The values for n and R allow for the determination of thickness. We establish comparisons between these thicknesses for the monolayer and those obtained from two X-ray scattering techniques: 1) GIXOS for monolayers at the air/water interface and 2) SAXS for bilayers in bulk suspension. This allows us to conclude that the thickness that we measure by BAM includes the apolar and polar headgroup regions of the monolayer.

Mapping of hemoglobin in erythrocytes and erythrocyte ghosts using two photon excitation fluorescence microscopy.

The present study describes utilization of two photon excitation fluorescence (2PE) microscopy for visualization of the hemoglobin in human and porcine erythrocytes and their empty membranes (i.e., ghosts). High-quality, label- and fixation-free visualization of hemoglobin was achieved at excitation wavelength 730 nm by detecting visible autofluorescence. Localization in the suspension and spatial distribution (i.e., mapping) of residual hemoglobin in erythrocyte ghosts has been resolved by 2PE. Prior to the 2PE mapping, the presence of residual hemoglobin in the bulk suspension of erythrocyte ghosts was confirmed by cyanmethemoglobin assay. 2PE analysis revealed that the distribution of hemoglobin in intact erythrocytes follows the cells’ shape. Two types of erythrocytes, human and porcine, characterized with discocyte and echinocyte morphology, respectively, showed significant differences in hemoglobin distribution. The 2PE images have revealed that despite an extensive washing out procedure after gradual hypotonic hemolysis, a certain amount of hemoglobin localized on the intracellular side always remains bound to the membrane and cannot be eliminated. The obtained results open the possibility to use 2PE microscopy to examine hemoglobin distribution in erythrocytes and estimate the purity level of erythrocyte ghosts in biotechnological processes.

Particle-wall tribology of slippery hydrogel particle suspensions.

Slip is an important phenomenon that occurs during the flow of yield stress fluids like soft materials and pastes. Densely packed suspensions of hydrogel microparticles are used to show that slip is governed by the tribological interactions occurring between the samples and shearing surfaces. Both attractive/repulsive interactions between the dispersed particles and surface, as well as the viscoelasticity of the suspension, are found to play key roles in slip occurring within rheometric flows. We specifically discover that for two completely different sets of microgels, the sliding stress at which slip occurs scales with both the modulus of the particles and the bulk suspension modulus. This suggests that hysteresis losses within the viscoelastic particles contribute to friction forces and thus slip at the particle-surface tribo-contact. It is also found that slip during large amplitude oscillatory shear and steady shear flows share the same generic features.