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PubMed2005

Low viscosity hydrogel of guar gum: preparation and physicochemical characterization.

Guar gum was cross-linked with glutaraldehyde and characterized by GPC, rheology, WADX, SEM and TGA. This guar gum is a galactomannan polysaccharide, that contains small amount of arabinose, glucose and uronic acid, besides galactose and mannose. The polymer has high molar mass, with Mw, Mn and Mv values of 2.0x10(6), 1.2x10(6) and 1.9x10(6)g/mol, respectively. The reticulation follows a slow process and lead to a viscosity increase of 40 times compared with the original gum solution. The final viscosity was similar to that of Hylan G-F 20, a hyaluronate derivative, commercially used in viscosupplementation treatment. The gel contains 95.6% of water and the amount of residual glutaraldehyde is much lower than the LD-50. Porous structure was detected by SEM and thermal stability was improved by the cross-linking. The low viscosity, the small amount of remained glutaraldehyde, and the thermal stability indicates that the guar hydrogel has potential to be applied as biomaterial with specific rheological requirements.

Biocompatible Materials↗

PubMed2005

The diffusion of latex nanospheres and the effective (microscopic) viscosity of HPMC gels.

Dynamic light scattering (DLS) has been used to measure the diffusion coefficients of 108+/-7 (+/-S.D.) and 495+/-23 nm positively charged amino latex nanospheres (ALNs) and negatively charged carboxyl latex nanospheres (CLNs) (48+/-7, 91+/-9.8 and 483+/-10 nm) in three different media, water, glycerol aqueous solutions and hydroxypropyl methylcellulose (HPMC) gels. The translational diffusion coefficients (D) of these latex spheres in water were found to be 13.00 (+/-0.12), 5.11 (+/-0.06), 0.89 (+/-0.01) microm2/s for 48, 91 and 483 nm CLN, and 3.26 (+/-0.01) and 0.88 (+/-0.03) microm2/s for 108 and 495 nm ALN, respectively. In Newtonian glycerol aqueous solutions as anticipated the diffusion could be predicted by the Stokes-Einstein relationship over a range of system viscosities. In HPMC gels the results show the deviation of the diffusion coefficient from the Stokes-Einstein equation when the viscosity of the medium is increased. In addition, there was an increase in the polydispersity index (PI) from 0.217 to 0.928 with 108 nm ALN on increasing HPMC concentrations from 0.2% to 0.8% (w/v), which implied an interaction between the positively charged nanospheres and the gel. From the D values, the "effective" or "microscopic" viscosities of the HPMC medium were calculated, and ranged from 0.899 to 0.925 mPa s.

Diffusion↗

PubMed2005

Influence of magnetic interactions between clusters on particle orientational characteristics and viscosity of a colloidal dispersion composed of ferromagnetic spherocylinder particles: analysis by means of mean field approximation for a simple shear flow.

We have theoretically investigated the particle orientational distribution and viscosity of a dense colloidal dispersion composed of ferromagnetic spherocylinder particles under an applied magnetic field. The mean field approximation has been applied to take into account the magnetic interactions of the particle of interest with the other ones that belong to the neighboring clusters, besides those that belong to its own cluster. The basic equation of the orientational distribution function, which is an integrodifferential equation, has approximately been solved by Galerkin's method and the method of successive approximation. Some of the main results obtained here are summarized as follows. Even when the magnetic interaction between particles is of the order of the thermal energy, the effect of particle-particle interactions on the orientational distribution comes to appear more significant with increasing volumetric fraction of particles; the orientational distribution function exhibits a sharper peak in the direction nearer to the magnetic field one as the volumetric fraction increases. Such a significant inclination of the particle in the field direction induces the large increase in viscosity in the range of larger values of the volumetric fraction. The above-mentioned characteristics of the orientational distribution and viscosity come to appear more significantly when the influence of the applied magnetic field is not so strong compared with that of magnetic particle-particle interactions.

Colloids↗

PubMed2006

Comparison between effectiveness of a low-viscosity glass ionomer and a resin-based glutaraldehyde containing primer in treating dentine hypersensitivity--a 25.2-month evaluation.

OBJECTIVES: The null-hypothesis tested was; there is no difference in effectiveness between a new low-viscosity glass ionomer and a resin-based glutaraldehyde containing primer in treating hypersensitive teeth after 2 years. METHODS: Using a split-mouth design, hypersensitive teeth in 14 adult patients were randomly assigned to 2 treatment groups. Hypersensitive tooth surfaces were covered with a low-viscosity glass ionomer (Fuji VII) and a resin-based glutaraldehyde containing primer (Gluma Desensitizer). The discomfort interval scale (DIS) ranging from 0 to 4 was used to test the level of hypersensitivity before and after treatment, and at 3 months using compressed air blown for 2 s, and at 1 and 25.2 months using a telephone interview. Differences between and within the treatment groups were tested using the sign rank test. RESULTS: Evaluations in the gluma group were discontinued after 3 months. The mean DIS score for hypersensitive teeth in the glass ionomer group was statistically significantly lower than that in the gluma group, immediately after application (p=0.0005), after 1 month (p=0.02) and after 3 months (p=0.003). After 3 months, 11/14 of the hypersensitive teeth in the glass ionomer group and 2/14 in the gluma group were free of sensitivity. The mean DIS score for hypersensitive teeth in the glass ionomer group remained low after 19.2 months (0.25: S.E.=0.13) and 25.2 months (0.22: S.E.=0.15). CONCLUSIONS: The null-hypothesis was rejected. The low-viscosity glass ionomer (Fuji VII) is more effective in treating hypersensitive teeth than Gluma Desensitizer after 3 months. The positive treatment effect of the glass ionomer continued until 25.2 months.

Adult↗

PubMed2004

A PFG NMR experiment for translational diffusion measurements in low-viscosity solvents containing multiple resonances.

Pulsed gradient simulated-echo (PGSE) NMR diffusion measurements provide a facile and accurate means for determining the self-diffusion coefficients for molecules over a wide range of sizes and conditions. The measurement of diffusion in solvents of low intrinsic viscosity is particularly challenging, due to the persistent presence of convection. Although convection can occur in most solvent systems at elevated temperatures, in lower viscosity solvents (e.g., short chain alkanes), convection may manifest itself even at ambient laboratory temperatures. In most circumstances, solvent suppression will also be required, and for solvents that have multiple resonances, effective suppression can likewise represent a substantial challenge. In this article, we report an NMR experiment that combines a double-stimulated echo PFG approach with a WET-based solvent suppression scheme that effectively and simultaneously address the issues of dynamic range and the deleterious effects of convection. The experiment described will be of general benefit to studies aimed at the characterization of diffusion of single molecules directly dissolved in low-viscosity solvents, and should also be of substantial utility in studies of supramolecular assemblies such as reverse-micelles dissolved in apolar solvents.

Alkanes↗

PubMed2005

Alpha-tocopherol supplementation favorable effects on blood pressure, blood viscosity and cardiac remodeling of spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) were separated into two groups (n = 6 per group) and, since 5 months old, received alpha-tocopherol (alpha-tocopherol acetate120 IU) or vehicle by daily gavage for 2 weeks. Blood viscosity, blood pressure (BP) and myocardial remodeling were analyzed. The SHRs treated with alpha-tocopherol showed a significant reduction of BP and a major reduction of blood viscosity in comparison with the control SHRs. The cardiac hypertrophy indices showed some differences when the two SHR groups were compared, the LV mass index was not different between the groups; however, the cardiomyocyte size was more than 20% smaller in SHRs treated with alpha-tocopherol than in control SHRs (P < .05). The intramyocardial vessels distribution was more than 45% greater in alpha-tocopherol-treated SHRs than in control rats, significantly improving the vessels-to-myocytes ratio in treated SHRs than in control SHRs (P < .05). In conclusion, present findings strongly suggest a beneficial effect of alpha-tocopherol supplementation to genetically hypertensive rats. This was observed by a reduction of both blood viscosity and BP, and a consequent cardiomyocyte hypertrophy in treated SHRs; an improvement of vessels-to-myocytes ratio in these rats was also observed.

Animals↗

PubMed2004

Effects of replacement fluids used for therapeutic plasma exchange on plasma viscosity and plasma oncotic pressure.

INTRODUCTION: Apheresis is a procedure in which one of the components of blood is removed. The aim of therapeutic plasma exchange (TPE) is to remove a large fraction of the patient's plasma from the body, and to exchange this with replacement solutions using automatic devices. With this procedure circulating pathogens and toxins are reduced. Before each TPE results of a baseline basal complete blood count, serum protein electrophoresis, coagulation tests and serum electrolytes must be known. The efficacy of this therapy is assessed only by these values. The proteins responsible for disease may be monoclonal proteins, cryoglobulins, lipoproteins, auto or allo antibodies or toxins. In this study, we aimed to compare the effects of several replacement fluids on plasma viscosity and oncotic pressure. At the same time, we evaluated the correlation between plasma viscosity and oncotic pressure. MATERIAL AND METHODS: 111 TPE were performed on 42 patients. Before TPE, the patients whose veins were not suitable were catheterised either by using a subclavian or jugular 11F dialysis catheter. At each session, approximately 1-1.5L of plasma was exchanged. The procedure was performed with albumin in patients whose albumin was under 3gr/dl. Over this value, the exchange fluids were randomised. RESULTS: When the overall results were analysed, there was no statistically significant difference between groups 1 (HES+albumin) and group 3 (albumin). The statistical difference between group 2 and 3 was significant, but no difference was observed between group 1 and 2. According to the decreasing plasma viscosity, there was a significant difference between group 2 and group 3, but there was no difference between group 1 and group 2. CONCLUSIONS: The replacement solutions used for plasmapheresis are similar when compared for hemorheologic effects, but we have chosen fresh frozen plasma because of fewer side effects.

Adolescent↗

PubMed2006

Effects of polyethylene glycol and hydroxyethyl starch in University of Wisconsin preservation solution on human red blood cell aggregation and viscosity.

University of Wisconsin (UW) preservation solution is considered an effective flush and cold storage liquid. However, recent studies have provided evidence of the hyperaggregating effect on human red blood cells (RBC) of hydroxyethyl starch (HES), one of the components of the UW solution. In contrast, preservation solutions containing polyethylene glycol (PEG) have been found to be effective for organ preservation. The aim of this study was to compare the effects of HES (50 g/L); PEG 20 kDa (50 and 30 g/L), and PEG35 kDa (1.05 g/L) added to UW on the rheologic parameters of human RBC at 4 degrees C. Sedimentation rate was measured by the Westergren procedure and blood viscosity evaluated at high shear rates using a cone/plate viscometer. Alterations in RBC morphology and aggregation were evaluated by light microscopy. RBC sedimentation and viscosity were not affected by the inversion of Na+ and K+ concentrations in UW, but were increased by HES. PEGs appeared to reduce RBC deformability with concomitant inhibition of RBC aggregation. These results were consistent with reduced viscosity for PEG-containing solutions. In conclusion, the use of PEG did not change the physiologic function of human RBCs and thus may be an alternative to HES in UW liquids.

Adenosine↗

PubMed2006

The estimation of elasticity and viscosity of soft tissues in vitro using the data of remote acoustic palpation.

The presented study revealed the significant dependence of displacement magnitude and strain relaxation on phantom elasticity and viscosity. It has been shown that simultaneous analysis of temporal behavior and magnitude of shear strain induced by the radiation force of focused ultrasonic beam gives the necessary data for quantitative estimation of tissue shear modulus because of the known functional dependencies of displacement on local viscosity and elasticity. As a result, the simplest calibration procedure of acoustic radiation force-based methods is performed and algorithm for separate reconstruction of tissue elasticity and viscosity is proposed. These findings were tested, in particular, using the data obtained for specially prepared phantoms containing calf liver and muscle tissue in vitro. The observed complex character of shear strain relaxation and noise in some tissue phantoms and tissues in vitro reduces the preciseness of viscoelastic properties estimation.

Algorithms↗

PubMed1996

Development of an objective method for assessing viscosity of formulated foods and beverages for the dysphagic diet.

OBJECTIVE: To develop and validate a practical, economical, and objective viscosity assessment tool, the line-spread test, for foods and beverages formulated for the dysphagic diet. The line-spread test is based on the measure of product dispersion over a flat surface. DESIGN: Viscosity-altering formulations for a selection of soups and beverages commonly served to patients with dysphagia at a local hospital were developed under controlled conditions. The samples were presented to a trained sensory panel for evaluation by quantitative descriptive analysis and were measured by the line-spread test. Numeric results of the two tests were compared. SETTING: The Food Research Laboratory with private sensory booths at Mount Saint Vincent University. MAIN OUTCOME MEASURES: Results of the sensory evaluation and the line-spread test would strongly correlate, indicating predictive validity, but the line-spread test would be more reliable and show variability in measurement. STATISTICAL ANALYSES PERFORMED: Correlation, analysis of variance (ANOVA), and standard deviations (calculated from the within-group mean square error of the ANOVAs). RESULTS: ANOVA showed that both the sensory panel results and the line-spread test values indicated significant differences among the samples. Standard deviations indicated less variability in line-spread values. There was a strong positive correlation (r = .90 to .97) between the two types of results, which indicated strong predictive validity for the line-spread test. APPLICATIONS: The line-spread test is a reliable and valid tool to assess viscosity of formulated foods and beverages for the dysphagic diet and can be readily and economically adapted to any dietary department for product development and quality control.

Analysis of Variance↗

PubMed1982

Surface viscosity measurements from large bilayer vesicle tether formation. I. Analysis.

Recent observations indicate that it is possible to form tethers from large phospholipid vesicles. The process of tether formation is analyzed using a continuum mechanical approach to obtain the surface viscosity of the bilayer in terms of experimentally measurable parameters. The membrane is treated as a two-dimensional isotropic material which deforms a constant area. The constitutive equation relates the maximum surface shear resultant to the rate of deformation via the surface viscosity coefficient. The force which acts to increase the tether length is generated by fluid moving past the vesicle. The magnitude of the force is estimated from Stoke's drag equation. The analysis predicts that there is a critical force necessary to produce an increase in the tether length. A dimensionless tether growth parameter is defined, and its value is obtained as a function of the ratio of the applied force on the vesicle to the critical force. This relationship is independent of both the size of the vesicle and the radius of the tether. Knowing the force on the vesicle, the critical force, and the rate of tether growth, the surface viscosity can be calculated.

Lipid Bilayers↗

PubMed1982

Surface viscosity measurements from large bilayer vesicle tether formation. II. Experiments.

A mechanical experiment has been developed that measures an upper bound for the viscosity of a lipid bilayer membrane. In this experiment, strands of membrane (tethers) are formed from phospholipid vesicles attached to micropipettes by subjecting the vesicles to fluid drag. The rate of tether formation is measured as a function of the velocity of the suspending fluid. The surface viscosity can be calculated from this data using a theoretical relationship derived in a companion paper. Because of the multilamellar character of the vesicles, these values provide an upper bound for the viscosity of a single bilayer. The smallest values obtained in these measurements fell in the range 5.0-13.0 x 10(-6) dyn s/cm. These values are in relatively good agreement with the values calculated from lateral and rotational mobility measurements.

Lipid Bilayers↗

PubMed1984

Determination of red blood cell membrane viscosity from rheoscopic observations of tank-treading motion.

Measurements of the dimensions and membrane rotational frequency of individual erythrocytes steadily tank-treading in a rheoscope are used to deduce the surface shear viscosity of the membrane. The method is based on an integral energy principle which says that the power supplied to the tank-treading cell by the suspending fluid is equal to the rate at which energy is dissipated by viscous action in the membrane and cytoplasm. The integrals involved are formulated with the aid of an idealized mathematical model of the tank-treading red blood cell (RBC) (Keller and Skalak, 1982, J. Fluid Mech., 120:24-27) and evaluated numerically. The outcome is a surface-averaged value of membrane viscosity which is representative of a finite interval of membrane shear rate. The numerical values computed show a clear shear-thinning characteristic as well as a significant augmentation of viscosity with cell age and tend toward agreement with those determined for the rapid phase of shape recovery in micropipettes (Chien, S., K.-L. P. Sung, R. Skalak, S. Usami, and A. Tozeren, 1978, Biophys. J., 24:463-487). The computations also indicate that the rate of energy dissipation in the membrane is always substantially greater than that in the cytoplasm.

Blood Viscosity↗

PubMed1987

Magnetic particle motions within living cells. Measurement of cytoplasmic viscosity and motile activity.

Submicrometer magnetic particles, ingested by cells and monitored via the magnetic fields they generate, provide an alternative to optical microscopy for probing movement and viscosity of living cytoplasm, and can be used for cells both in vitro and in vivo. We present methods for preparing lung macrophages tagged with magnetic particles for magnetometric study. Interpretation of the data involves fitting experimental remanent-field decay curves to nonlinear mechanistic models of intracellular particle motion. The model parameters are sensitive to mobility and apparent cytoplasmic viscosity experienced by particle-containing organelles. We present results of parameter estimation for intracellular particle behavior both within control cells and after (a) variable magnetization duration, (b) incubation with cytochalasin D, and (c) particle twisting by external fields. Magnetometric analysis showed cytoplasmic elasticity, dose-dependent motion inhibition by cytochalasin D, and a shear-thinning apparent viscosity.

Animals↗

PubMed1989

Apparent viscosity and cortical tension of blood granulocytes determined by micropipet aspiration.

Continuous deformation and entry flow of single blood granulocytes into small caliber micropipets at various suction pressures have been studied to determine an apparent viscosity for the cell contents and to estimate the extent that dissipation in a cortical layer adjacent to the cell surface contributes to the total viscous flow resistance. Experiments were carried out with a wide range of pipet sizes (2.0-7.5 microns) and suction pressures (10(2)-10(4) dyn/cm2) to examine the details of the entry flow. The results show that the outer cortex of the cell maintains a small persistent tension of approximately 0.035 dyn/cm. The tension creates a threshold pressure below which the cell will not enter the pipet. The superficial plasma membrane of these cells appears to establish an upper limit to surface dilation which is reached after microscopic "ruffles" and "folds" have been pulled smooth. With aspiration of cells by small pipets (less than 2.7 microns), the limit to surface expansion was derived from the maximal extension of the cell into the pipet; final areas were measured to be 2.1 to 2.2 times the area of the initial spherical shape. For suctions in excess of a threshold, the response to constant pressure was continuous flow in proportion to excess pressure above the threshold with only a small nonlinearity over time until the cell completely entered the pipet (for pipet calibers greater than 2.7 microns). With a theoretical model introduced in a companion paper, (Yeung, A., and E. Evans., 1989, Biophys. J. 56:139-149) the entry flow response versus pipet size and suction pressure was analyzed to estimate the apparent viscosity of the cell interior and the ratio of cortical flow resistance to flow resistance from the cell interior. The apparent viscosity was found to depend strongly on temperature with values on the order of 2 x 10(3) poise at 23 degrees C, lower values of 1 x 10(3) poise at 37 degrees C, but extremely large values in excess of 10(4) poise below 10 degrees C. Because of scatter in cell response, it was not possible to accurately establish the characteristic ratio for flow resistance in the cortex to that inside the cell; however, the data showed that the cortex does not contribute significantly to the total flow resistance.

Granulocytes↗

PubMed1993

Viscosity of passive human neutrophils undergoing small deformations.

At issue is the type of constitutive equation that can be used to describe all possible types of deformation of the neutrophil. Here a neutrophil undergoing small deformations is studied by aspirating it into a glass pipet with a diameter that is only slightly smaller than the diameter of the spherically shaped cell. After being held in the pipet for at least seven seconds, the cell is rapidly expelled and allowed to recover its undeformed, spherical shape. The recovery takes approximately 15 s. An analysis of the recovery process that treats the cell as a simple Newtonian liquid drop with a constant cortical (surface) tension gives a value of 3.3 x 10(-5) cm/s for the ratio of the cortical tension to cytoplasmic viscosity. This value is about twice as large as a previously published value obtained with the same model from studies of large deformations of neutrophils. This discrepancy indicates that the cytoplasmic viscosity decreases as the amount of deformation decreases. An extrapolated value for the cytoplasmic viscosity at zero deformation is approximately 600 poise when a value for the cortical tension of 0.024 dyn/cm is assumed. Clearly the neutrophil does not behave like a simple Newtonian liquid drop in that small deformations are inherently different from large deformations. More complex models consisting either of two or more fluids or multiple shells must be developed. The complex structure inside the neutrophil is shown in scanning electron micrographs of osmotically burst cells and cells whose membrane has been dissolved away.

Biophysical Phenomena↗

PubMed1995

Calculation of translational friction and intrinsic viscosity. I. General formulation for arbitrarily shaped particles.

A general method for calculating translational friction and intrinsic viscosity is developed through exploiting relations between hydrodynamics and electrostatics. An approximate relation xi = 6 pi eta 0C between the translational friction coefficient xi of a particle (eta 0: solvent viscosity) and its capacitance C was derived previously. This involved orientationally preaveraging the Oseen tensor, but the result was found to be very accurate. Based on preaveraging, we find that the intrinsic viscosity [eta] of a particle can be estimated from its polarizability alpha through [eta] = 3/4 alpha + 1/4 Vp, where Vp is the volume of the particle. Both the capacitance and the polarizability can be obtained in a single calculation using the boundary-element technique. An efficient approach is thus found for estimating [eta], a quantity that is very useful in practice because of its sensitivity to particle shape but is notoriously difficult to calculate. Illustrative calculations on ellipsoids, cylinders, and dumbbells demonstrate both the accuracy of the approximate relations and the efficiency of the present method.

Computer Simulation↗

PubMed2000

c,T-dependence of the viscosity and the self-diffusion coefficients in some aqueous carbohydrate solutions.

Self-diffusion coefficients for both components are reported for the highly concentrated aqueous solutions of some disaccharides and fructose as a function of temperature and concentration. These data are complemented by viscosity measurements. The disaccharides studied are sucrose, alpha,alpha-trehalose, allosucrose, and leucrose. Up to a sugar concentration of approximately 30% w/w the viscosity and the self diffusion coefficients of the four disaccharides are identical within experimental error for a given concentration and temperature. Water diffusion shows no differences in the four systems studied under these conditions. At higher concentrations significant differences are observed that become more pronounced with increasing temperature. Analysis of the data by the VTF equation yields the result that at a given concentration the self diffusion coefficients of the sugar Dc and the viscosity eta are described by identical ideal glass transition temperatures T0, while the diffusion of the water D(W) molecule decouples from these properties. T0(W) is always lower than T0(c,eta).

Carbohydrates↗