SEARCH · Search PubMed

Results for “VISCOSITY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58Linked to original sources

PubMed2001

The impact of urea on viscosity of hydroxethyl cellulose and observed mobility of deoxyribonucleic acids.

The influence of urea on the viscosity of hydroxyethyl cellulose (HEC), and the state and separation of double-stranded DNA, was studied by viscometry, fluorometry, and capillary electrophoresis. The results show that double logarithm plots of specific viscosity against the volume fraction of HEC in very dilute polymer solutions are linear, the slopes of which decrease from 0.96 in 0M to 0.29 in 7M urea. The linear regression plots converge at 0.0029 g/mL, the entanglement threshold of HEC. The inclusion of urea in HEC solution thus provides an accurate method of determining its entanglement threshold from such plots. Above the entanglement threshold of HEC, urea has no effect on the specific viscosity of HEC. Results also show that urea has no effect on double-stranded DNA. No change in fluorescence was observed when increasing amounts of urea were added to a fixed concentration of DNA. To examine the influence of urea on the migration of DNA in HEC, the separation of DNA was carried out by polymer-solution capillary electrophoresis in HEC solutions containing 0 or 7M urea using unmodified capillary. Observed mobilities were used in data reduction. It was found that a parallel relationship exists between the observed mobilities and the true mobilities. In buffers containing no urea, the pseudo-free solution mobility appears to be independent of the DNA size. It was also observed to be independent of the electric field below 300 V/cm, but relates exponentially to it in 7M urea. The pseudo-retardation constants obtained by Ferguson-like plots were observed to be positive for smaller DNA molecules below 300 V/cm and increasing linearly with electric field in 0M urea, but nearly constant in 7M urea.

Cellulose↗

PubMed2002

DNA separation by microchip electrophoresis using low-viscosity hydroxypropylmethylcellulose-50 solutions enhanced by polyhydroxy compounds.

Low-viscosity polymer solutions have potential for double-stranded (ds) DNA separations in micrototal analysis systems (micro-TAS). In this paper, we report dilute, low-viscosity hydroxypropylmethylcellulose-50 (HPMC-50, 11.5 kDa) solutions containing polyhydroxy additives as separation media. Predominant operational variables, such as applied electric field strength, fluorescent intercalator (YOPro-1) concentration, polymer concentration, and additive concentration, are thoroughly investigated. Fast (within 170 s) and excellent separation of DNA restriction fragments ranging in size from 72 to 1353 base pairs (bp) is achieved in a 30 mm length channel of polymethylmethacrylate (PMMA) microchips at an electric field strength of 300 V/cm, by introducing 8% mannitol, 8% glucose or 10% glycerol additives into a 2% HPMC-50/1 x Tris-borate-EDTA (TBE) solution. The low-viscosity (40 cP) matrix formulation provides both coating of the microchannels and separation of DNA in one step. The performance in the solution surpasses that in highly concentrated HPMC-50 solution. In addition, separation using 1xTris-EDTA buffer in the 2% HPMC-50 matrix containing polyhydroxy additives also exhibits a notably increased performance. This is presumably due to formation of hydrogen-bonding interactions of polyhydroxy additives with HPMC-50 matrix and DNA so as to increase the coupling interactions between matrix and DNA molecules during electrophoresis. The result reflects that boric acid is not a prerequisite in polyhydroxy-enhanced HPMC-50 solution for separation.

Bacteriophage phi X 174↗

PubMedDate not supplied

Measuring synovial fluid viscosity with a white blood cell diluting pipette. A simple, rapid,and reproducible method.

A convenient and accurate way to measure the relative viscosity of synovial fluid is to use a white blood cell diluting pipette as a simple viscometer. The technique is reproducible with 2% accuracy and adds little to the time required for routine synovial fluid analysis. The magnitude of the variation of synovial fluid viscosity with temperature is demonstrated, and it is suggested that routine clinical measurements be made at room temperature. Clinical data confirm that a single viscosity measurement has little or no diagnostic value.

Hematology↗

PubMed2003

Pulsed feeding during fed-batch fungal fermentation leads to reduced viscosity without detrimentally affecting protein expression.

The goal in this study was to determine if pulsed addition of substrate could be used to alter filamentous fungal morphology during fermentation, to result in reduced broth viscosity. In all experiments, an industrially relevant strain of Aspergillus oryzae was grown in 20-liter fermentors. As a control, cultures were fed limiting substrate (glucose) continuously. Tests were performed by altering the feeding strategy so that the same total amount of glucose was fed in repeated 300-s cycles, with the feed pump on for either 30 or 150 s during each cycle. Variables indicative of cellular metabolic activity (biomass concentration, oxygen uptake rate, base consumed for pH control) showed no significant difference between continuous and pulse-fed fermentations. In addition, there was no significant difference between total extracellular protein expression or the apparent distribution of these proteins. In contrast, fungal mycelia during the second half of pulse-fed fermentations were approximately half the size (average projected area) of fungi during fermentations with continuous addition of glucose. As a result, broth viscosity during the second half of pulse-fed fermentations was approximately half that during the second half of continuous fermentations. If these results prove to be applicable for other fungal strains and processes, then this method will represent a simple and inexpensive means to reduce viscosity during filamentous fungal fermentation.

Aspergillus oryzae↗

PubMed2004

Potato flour viscosity improvement is associated with the expression of a wheat LMW-glutenin gene.

It has been previously shown that expression of a high-molecular-weight glutenin (HMW-GS) in transgenic wheat seeds resulted in the improvement of flour functional properties. In this study, potato flour viscosity was improved through a specific expression of a low-molecular-weight glutenin (LMW-GS-MB1) gene in tuber. The resulting construct was introduced into potato leaf explants (Solanum tuberosum cv Kennebec) through Agrobacterium tumefaciens-mediated gene transfer. Southern and Northern analysis of transgenic potato confirmed that the integration of LMW-GS-MB1 in genomic DNA was stable and its mRNA was abundant in transgenic line 16 tubers. Western blot analysis of line 16 extract shows a LMW-GS subunit accumulation in tuber. To demonstrate the capacity of transgenic lines to produce tubers with improved flour functional properties, transgenic lines 9 and 16 exhibiting, respectively, moderate and high expression of LMW-GS-MB1 mRNA and nontransgenic plants were transferred to field plots. The mean viscosity value of flour obtained from the field-grown tubers of transgenic line 16 exhibited a 3-fold increase in viscosity at 23 degrees C when compared to flour from nontransgenic tubers.

Cloning, Molecular↗

PubMed1996

Effect of temperature and viscosity of sieving medium on electrophoretic behavior of sodium dodecyl sulfate-proteins on capillary electrophoresis in presence of pullulan.

Pullulan was used as a sieving medium in high-performance capillary gel electrophoresis to study the effect of temperature and viscosity on electrophoretic behavior of sodium dodecyl sulfate (SDS)-proteins with molecular masses in the range of 14,400-116,000 Da. The migration time decreased with increasing capillary temperature. Equations were derived relating mobility of SDS-proteins to capillary temperature and viscosity of pullulan solution. Linear relationships were obtained from experiments between logarithm of mobility and reciprocal temperature and between double logarithmic values of mobility and viscosity of pullulan solution. The experimental results agree well with the equations.

Electrophoresis, Capillary↗

PubMed1982

The viscosity of acrylic bone cements.

The viscosity of the acrylic bone cement used in total joint arthroplasty is an important material property for determination of the proper handling characteristics and interlock with bone. In this article the rheological properties of the three leading bone cements were determined over a three-decade range of shear rates. In addition, four other cements were tested at a single shear rate. The results indicate that all the acrylic bone cements are non-Newtonian, pseudoplastic materials with significant differences between them. It is shown that the viscosity increases at different rates with respect to increases in time. For the majority of cements there is a steady or increasing rate of viscosity change with time.

Biomechanical Phenomena↗

PubMed2006

Influence of powder particle size distribution on complex viscosity and other properties of acrylic bone cement for vertebroplasty and kyphoplasty.

For use in vertebroplasty and kyphoplasty, an acrylic bone cement should possess many characteristics, such as high radiopacity, low and constant viscosity during its application, low value of the maximum temperature reached during the polymerization process (T(max)), a setting time (t(set)) that is neither too low nor too high, and high compressive strength. The objective of this study was to investigate the influence of the powder particle distribution on various properties of one acrylic bone cement; namely, residual monomer content, T(max), t(set), complex viscosity, storage and loss moduli, injectability, and quasi-static compressive strength and modulus. It was found that the formulations that possessed the most suitable complex viscosity-versus-mixing time characteristics are those in which the ratio of the large poly(methyl methacrylate) beads (of mean diameter 118.4 microm) to the small ones (of mean diameter 69.7 microm) was at least 90% w/w. For these formulations, the values of the other properties determined were acceptable.

Biocompatible Materials↗

PubMed1977

Viscosity and surface tension of dilute salicylic acid-cetrimide systems.

The viscosity and surface tension of systems containing small amounts of salicylic acid in aqueous solutions of cetrimide were determined. An abrupt increase in viscosity was observed, and the molar ratio of salicylic acid to certrimide at which this viscosity increase occurred was 1:2. The surface tension of these systems also increased sharply after an initial lowering. The salicylic acid concentration at which this behavior was demonstrated was almost the same as that at maximum solubility in the surfactant solution.

Cetrimonium Compounds↗

PubMed1982

Viscosity change after dilution with solutions of water--oil--water emulsions and solute permeability through the oil layer.

A water-in-oil-water (W/O/W) multiple phase emulsion was prepared by a two-step emulsification procedure. The oil phase consisted of paraffin oil and sorbitan monooleate. The inner aqueous phase and the outer aqueous phase were 0.5% glucose solution and 3% polysorbate 80 solution, respectively. Viscosity measurements were carried out on the W/O/W emulsion after diluting it with a number of solutions. A given sequence for the solutes that would increase the emulsion viscosity after dilution was determined. This sequence was identical with that obtained with the solutes in an independent permeability experiment using a planar membrane composed of sorbitan monooleate alone. As a result, it was suggested that solutes as well as water can permeate the oil layer of vesicles of the emulsion to change the vesicle volume, thereby causing a change in the emulsion viscosity.

Emulsions↗

PubMed1987

Mass transport in dissolution kinetics. I: Convective diffusion to assess the role of fluid viscosity under forced flow conditions.

The quantitative influence of viscosity on dissolution kinetics is assessed under laminar flow conditions by utilizing a convective diffusion model for drug dissolution. Functional dependency of three types of viscosity inducing agents is established with respect to the parameters of fluid flow rate, diffusivity, and solubility. Studies of aqueous solutions of sucrose and of glycerol demonstrate that the decrease in dissolution rate of ethyl p-aminobenzoate is related to the decrease in solute diffusivity in these solutions, whereas the solubility change in the glycerol solutions has an additional independent simultaneous effect. Dissolution in hydroxypropyl cellulose solutions remains constant under fixed fluid flow conditions because of the negligible effect of the polymer upon the drug diffusivity. A change in fluid flow rate, however, alters the dissolution rate and correlates quantitatively with the rate of shear in the convective diffusion model. The interpretation of the effect of viscosity on dissolution kinetics with the convective diffusion model explains these phenomena quantitatively in terms of the fundamental mass transport processes.

Cellulose↗

PubMed2003

Correction of the high blood viscosity syndrome by a mixture of Diquertin and Ascorbic Acid in vitro and in vivo.

Diquertin was shown to diminish blood viscosity, to decrease the aggregation of erythrocytes, and to increase their deformability using a model of the high blood viscosity syndrome in vitro. A mixture of Diquertin with Ascorbic Acid was more effective in improving rheological indicators of blood, then either Diquertin or Tanakan. On a model of chronic brain ischemia, which is accompanied by significant deterioration of the rheological properties of blood, it was shown that a therapy with a mixture of Diquertin and Ascorbic Acid decreases the expression of the high blood viscosity syndrome.

Animals↗

PubMed1999

Molecular crowding and viscosity as determinants of translational diffusion of metabolites in subcellular organelles.

The role of molecular crowding and viscosity on the apparent translational diffusion coefficient (ADC) of small metabolites was investigated in different subcellular organelles using the pulse-field gradient spin-echo 1H NMR technique. ADCs of metabolites with increasing radius of gyration (0.7 A < RG < 4.5 A) were measured in the cytoplasm of rat or chicken erythrocytes, in the nucleus of chicken erythrocytes, and in isolated rat liver mitochondria. Metabolite ADCs in these systems were compared with the corresponding ADCs determined in model solutions of increasing bulk viscosity but different molecular crowding. For solutions having the same viscosity, metabolite ADCs decreased with increasing concentration of cosolutes. This effect is adequately described by the modified Stokes-Einstein relationship, ADC = k/RG (1 + 2.5Phi), where k is a constant for a given temperature and Phi is an obstruction factor reporting the fractional volume of solution occupied by cosolutes, a measure of the molecular crowding in the solution. Cytoplasmic values of Phi for metabolites of different sizes did not depend exclusively on metabolite RG but on additional factors including the chemical nature of the metabolite, the presence of diffusional barriers, and metabolite-specific binding sites. In the case of water, nuclear Phi values approached those of the extracellular space while mitochondrial Phi values were significantly higher than those of the cytoplasm. Taken together, these results reveal important differences in molecular crowding within the different subcellular compartments, suggesting considerable diffusional heterogeneity for small metabolites within the different intracellular organelles.

Animals↗

PubMed1994

Role of sialic acid on the viscosity of canine tracheal mucin glycoprotein.

The role of sialic acid on the viscosity of canine tracheal mucin (CTM) was investigated. The mucin glycoprotein, purified from canine tracheal mucus, was subjected to mild acid hydrolysis with aqueous acetic acid and autohydrolysis in water, in which approximately 50% drop in the relative viscosity (nr) occurred. Carbohydrate compositional analysis before and after mild acid hydrolysis and autohydrolysis showed the complete removal of glycosidically bound sialic acid residues while all other sugar residues (i.e. galactose, N-acetyl galactosamine and N-acetyl glucosamine) remained unaltered, indicating that sialic acid residues are contributing towards the viscosity of CTM to a greater extent.

Animals↗

PubMed1993

Alterations in viscosity and filterability of whole blood and blood cell subpopulations in diabetic cats.

Capillary closure and venous dilatation occur early in diabetic retinopathy, and altered blood rheology may play a role. For example previous studies have shown leukocytes are less deformable, are more activated, and occlude retinal capillaries more often in diabetic subjects. The purpose of this study was to determine if rheologic changes developed in diabetic cats, a model in which we have documented retinal capillary basement membrane thickening, microaneurysms, and intraretinal hemorrhage characteristics of early diabetic retinopathy. Viscosity of blood, plasma and purified erythrocyte suspensions was measured by rotational viscometry and plasma fibrinogen content was determined by heat precipitation. Filterability of blood and purified erythrocyte, mononuclear leukocyte, and granulocyte suspensions was determined at constant flow, measuring the increase in pressure over 2 min relative to the pressure generated by buffer alone. Viscosity of whole blood and plasma, but not erythrocytes, was significantly elevated (P < 0.005) in the diabetic cats over normals at all shear rates studied (450, 225 and 90 sec-1). Furthermore, fibrinogen levels were significantly elevated in diabetic cats compared to normals (P < 0.004), and were positively correlated with the viscosity of whole blood and plasma. The filterability of mononuclear leukocytes and whole blood in diabetic cats was decreased 56% and 74% when compared to normals, P < 0.0006 and P < 0.025, respectively. In contrast, the filterability of granulocytes and erythrocytes was not significantly different between the two groups. These results suggest that the rheologic alterations in diabetes are numerous, and involve both cellular and plasma protein changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

The effect of denbufylline on the viscosity of rat whole blood and on the deformability (filterability) of rat blood cell suspensions.

The novel alkylxanthine, denbufylline [1,3-di-n-butyl-7-(2-oxopropyl)-xanthine] has been examined, in vitro, for effects on the viscosity of rat whole blood and on the filterability of rat blood cell suspensions. For comparison, pentoxifylline was also examined for rheological activity. Denbufylline reduced the viscosity of whole blood at all shear rates utilised, up to 128.5 s-1. The effect was, however, more pronounced at a low (0.7 s-1) than at a high (94.5 s-1) shear rate indicating that the compound reduces blood cell aggregation and increases blood cell deformability. Denbufylline also increased the filterability of blood cell suspensions. This is further evidence that the compound increases the deformability of blood cells. Denbufylline elevated the filterability of both pure erythrocyte and mixed erythrocyte/leucocyte suspensions, the effect being greatest with the latter. This suggests that denbufylline may influence the deformability of both red and white blood cells. However, the effect on white blood cells, under the experimental conditions employed, is apparently more marked. Pentoxifylline also reduced the viscosity of rat whole blood and increased the filterability of rat blood cell suspensions. However, denbufylline was 10-100-fold more potent in these tests than pentoxifylline.

Animals↗

PubMed1991

Influence of the strength, drop size and viscosity of metipranolol eye drops on the concentration of the substance in human aqueous humour.

Concentrations of metipranolol were determined in the aqueous humour of patients undergoing cataract surgery. At 30 min before the operation, patients were given 20- or 30 microliters drops of 0.1% or 0.3% metipranolol solutions with a viscosity of 7.5 cP or drops (20 or 30 microliters) of a 0.3% solution with a viscosity of 1.5 cP. Samples of the aqueous humour were obtained at the beginning of the cataract operation, and desacetyl-metipranolol content was determined by means of gas chromatography and mass spectroscope. The Wilcoxon signed-rank test and Jonckheere's method were used for evaluation of the results. A 3-fold increase in the strength of metipranolol was associated with an approx. 8-fold increase in the concentration of metabolite found in the aqueous humour. Drop size had no apparent effect on the concentration of this substance in the aqueous humour, but viscosity had a significant influence when large drops were applied. An increase in the amount of metipranolol applied as eye-drops was associated with an increase in the intraocular concentration of the metabolite.

Administration, Topical↗

PubMed1988

Minor effects of bulk viscosity on lipid translational diffusion measured by the excimer formation technique.

We have investigated the effect of bulk viscosity on lipid translational diffusion using the excimer formation technique. In contrast to a study by Vaz et al. (1987), performed with the fluorescence recovery after photobleaching technique, we observed only a minor decrease of less than a factor of two for pyrene labelled phosphatidylcholine in glycerinated phosphatidylcholine bilayer membranes compared to an aqueous dispersion. Even the diffusion of pyrene labelled gangliosides with an oligosaccharide head-group that protrudes from the membrane surface is not strongly restricted by the increased bulk viscosity. We conclude that the viscosity of the fluid bounding the lipid bilayers is of minor importance for the diffusion of membrane lipids.

Gangliosides↗