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At least 1,459 records · Page 81Linked to original sources
PubMed1993

Acanthosis nigricans--decreased extracellular matrix viscosity: cancer, obesity, diabetes, corticosteroids, somatotrophin.

Acanthosis nigricans is a reaction pattern to over a dozen different causes. The skin, most classic in the axilla, is dark, soft, velvet-like with fine folding and papillae. The mechanism of this skin change is decreased viscosity of extracellular matrix (ECM) combined with mechanical extrusion of ECM into papillae extending out from the upper dermis. It occurs in obesity (increased mechanical pressure on ECM), diabetes (decreased quality of glycosaminoglycans) (GAG), excess corticosteroids (decreased quality of GAG), pineal tumors (increased ECM and edema), other endocrine disorders (alterations in the quality of GAG), multiple genetic variants (structural and chemical change), from drugs such as nicotinic acid, estrogens, corticosteroids (weakened or altered GAG) and adenocarcinoma (fractions of depolymerized or altered GAG released from the tumor area are incorporated into and weaken the skin GAG). Acanthosis nigricans was first reported in 1890 as a cutaneous sign of internal malignancy. Acanthosis nigricans presents an opportunity to better understand what is occurring in the ECM in many disorders. The understanding of the association of AN and internal malignancy will expand our understanding of how a neoplasm decreases generalized ECM viscosity.

Acanthosis Nigricans↗
PubMed1996

Evaluation of viscosities of polymer-water solutions used in aqueous two-phase systems.

The dynamic viscosities of dilute aqueous poly(ethylene glycol) and dextran, and poly(ethylene glycol)-dextran-water solutions have been measured. The poly(ethylene glycol) and dextran samples had average molecular masses of 8000 Da and 580,000 Da, respectively. To estimate the values of viscosity of poly(ethylene glycol)-dextran-water solutions, a Grunberg like equation has been proposed which takes into account the influence of poly(ethylene glycol) and dextran concentrations. The relative errors vary between 0.76 and 11.64 in absolute value.

Dextrans↗
PubMed2004

Effect of low-density lipoprotein cholesterol apheresis on blood viscosity.

Few studies have been designed to study the hemodynamic effects of low-density lipoprotein apheresis, especially on whole blood viscosity. Six patients with cardiovascular disease and hypercholesterolemia underwent a single low-density lipoprotein apheresis, resulting in significant reductions in whole blood viscosity at all shear rates.

Blood Component Removal↗
PubMed2005

Development of high-viscosity, two-paste bioactive bone cements.

Self-curing two-paste bone cements have been developed using methacrylate monomers with a view to formulate cements with low polymerization exotherm, low shrinkage, better mechanical properties, and improved adhesion to bone and implant surfaces. The monomers include bis-phenol A glycidyl dimethacrylate (bis-GMA), urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) as a viscosity modifier. Two-paste systems were formulated containing 60% by weight of a bioactive ceramic, hydroxyapatite. A methacroyloxy silane (A174) was used as a coupling agent due to its higher water stability in comparison to other aminosilanes to silanate the hydroxyapatite particles prior to composite formulation. A comparison of the FT-infrared spectrum of hydroxyapatite and silanated hydroxyapatite showed the presence of the carbonyl groups ( approximately 1720 cm(-1)), -C=C-( approximately 1630 cm(-1)) and Si-O- (1300-1250 cm(-1)) which indicated the availability of silane groups on the filler surface. Two methods of mixing were effected to form the bone cement: firstly by mixing in an open bowl and secondly by extruding the two pastes by an auto-mixing tip using a gun to dispense the pastes. Both types of cements yielded low polymerization exotherms with good mechanical properties; however, the lower viscosity of UDMA allowed better extrusion and handling properties. A biologically active apatite layer formed on the bone cement surface within a short period after its immersion in simulated body fluid, demonstrating in vitro bioactivity of the composite. This preliminary data thus suggests that UDMA is a viable alternative to bis-GMA as a polymerizable matrix in the formation of bone cements.

Biomimetic Materials↗
PubMed2003

Viscosity B-coefficients and activation parameters for viscous flow of a solution of heptanedioic acid in aqueous sucrose solution.

Viscosity and density data for the system of heptanedioic acid dissolved in aqueous sucrose solution at temperature range from 288.15 to 313.15 K have been measured. The viscosity B-coefficients for heptanedioic acid in aqueous sucrose solution has been calculated. The effect of temperature and sucrose concentration on the B-coefficients is discussed. On the basis of the Feakins equation, the activation parameters (Deltamu3++, DeltaH3++, DeltaS3++, DeltaG12(0)++, DeltaH12(0)++ and DeltaS12(0)++) for viscous flow of the solution have been evaluated, together with the Gibbs energy of transfer for the solute from the ground state solvent to the hypothetical viscous transition state solvent (DeltaG3++(1-1')). The effect of sucrose concentration and temperature on the activation parameters has been discussed.

Algorithms↗
PubMed2005

Effect of viscosity and concentration of wall former, emulsifier and pore-inducer on the properties of amoxicillin microcapsules prepared by emulsion solvent evaporation.

This study reports the laboratory optimization for the preparation of sustained release amoxicillin (AMX) ethylcellulose microcapsules by an emulsion solvent evaporation process by adjusting the viscosity and concentration of ethylcellulose, ratio of amoxicillin to ethylcellulose, and concentration of emulsifier and pore inducer. When ethylcellulose with a viscosity of 45 mPa.s was used, almost no material stuck to the inside wall of the beaker and uniform microcapsules were prepared. The average diameter of microcapsules increased and yield and release rate decreased as the concentration of ethylcellulose increased from 1% to 8%. The release of amoxicillin from microcapsules was influenced by the ratio of the weight of drug to that of ethylcellulose and ratios of 2:1 and 4:1 were most suited for optimum amoxicillin release. The average diameter of microcapsules decreased and the release rate increased as the concentration of the emulsifier increased from 1.5% to 6.0%, however, the size distribution became significantly wider with the increase in the concentration of sorbitan monooleate. Addition of small amounts of a water-soluble agent sucrose improved the release of active ingredient from the microcapsule matrix without influencing the morphology and particulate properties of the microcapsules.

Absorption↗
PubMed2006

Survismeter--type I and II for surface tension, viscosity measurements of liquids for academic, and research and development studies.

For centuries surface tension (gamma) and viscosity (eta) data have been measured with individual instruments consuming much time and materials. Thus the two different types of survismeters have been designed and made of borosil glass material for surface tension and viscosity data to rationalize frictional and cohesive forces, respectively. Friccohesity (sigma (sm(-1), second per meter)) is derived from Fric of frictional and cohesity of cohesive forces of the liquid respectively, and denoted by rational coefficient a eta/gamma (sigma). The values of the friccohesity are correlated to the dipole moment of liquids and their plot gives a standard calibration curve along with an equation of the curve with definite values of the coefficients, the friccohesity values are put on the calibration curve to retrieve the dipole moment values. Here, the sigma values for each of dimethylformamide, dimethylsulfoxide and acetronitrile solvents along with their 0.05, 0.10 and 0.20 mol kg(-1) aqueous solutions, respectively, were determined at 293.15K and plotted against their dipole moment values for standard calibration curve. The range of the dipole moment values for calibration curve is pre-decided and the sigma values for homogenous solutions of compositions below their saturation point can be measured with +/-1 x 10(-5)sm(-1).

Body Fluids↗
PubMed2004

Evaluation of viscosities of aqueous two-phase systems containing protein.

The dynamic viscosities of aqueous polyethylene glycol, aqueous bovine serum albumin, and polyethylene glycol-bovine serum albumin-water solutions were measured at temperatures of 15, 20, 25, 30 and 35 degree C. To estimate the viscosity values of polyethylene glycol-bovine serum albumin-water solutions, a one parameter Grunberg-like model which was satisfactorily used earlier by the present author for polyethylene glycol-dextran-water solutions was employed. The disposable parameter a for our temperature range was estimated as 3.71. The relative errors varying from 0.29 to 18.98 in absolute value indicates that the Grunberg-like model works perfectly for polymer-protein solutions as well.

Polyethylene Glycols↗
PubMed2006

Viscosity as an inseparable partner of muscle contraction.

A simple model is presented where, by an iterative procedure, the forces delivered by the power strokes are summed up to overcome the load. The system is moderated by the viscous hindrance. The model reproduces the features of muscle contraction as defined by the data of He et al. [1997. ATPase kinetics on activation of permeabilized isometric fibres from rabbit and frog muscle: a real time phosphate assay. J. Physiol. 501, 125-148] on rabbit psoas muscle fibres. According to the model power strokes are random. Energy summation take place if the subsequent power stroke occurs before the energy delivered by the previous power stroke is completely used. In order the sarcomere to be competent to contract initial driving force must reach a threshold whose value increases with the load. The step size of the power stroke decreases with the increase of the load. The viscous regime is simulated by the equation, where 1/k measures the viscous hindrance of the system. The relationship between water activity, viscosity and stiffness is discussed. It is concluded that the three parameters vary cyclically and that when water activity decreases (sarcomere shortening, cross-bridge attachment) viscosity and stiffness increase.

Animals↗
PubMed2005

The primate amygdala: Neuronal representations of the viscosity, fat texture, temperature, grittiness and taste of foods.

The primate amygdala is implicated in the control of behavioral responses to foods and in stimulus-reinforcement learning, but only its taste representation of oral stimuli has been investigated previously. Of 1416 macaque amygdala neurons recorded, 44 (3.1%) responded to oral stimuli. Of the 44 orally responsive neurons, 17 (39%) represent the viscosity of oral stimuli, tested using carboxymethyl-cellulose in the range 1-10,000 cP. Two neurons (5%) responded to fat in the mouth by encoding its texture (shown by the responses of these neurons to a range of fats, and also to non-fat oils such as silicone oil ((Si(CH(3))(2)O)(n)) and mineral oil (pure hydrocarbon), but no or small responses to the cellulose viscosity series or to the fatty acids linoleic acid and lauric acid). Of the 44 neurons, three (7%) responded to gritty texture (produced by microspheres suspended in cellulose). Eighteen neurons (41%) responded to the temperature of liquid in the mouth. Some amygdala neurons responded to capsaicin, and some to fatty acids (but not to fats in the mouth). Some amygdala neurons respond to taste, texture and temperature unimodally, but others combine these inputs. These results provide fundamental evidence about the information channels used to represent the texture and flavor of food in a part of the brain important in appetitive responses to food and in learning associations to reinforcing oral stimuli, and are relevant to understanding the physiological and pathophysiological processes related to food intake, food selection, and the effects of variety of food texture in combination with taste and other inputs on food intake.

Action Potentials↗
PubMed2005

The viscosity and temperature dependence of X-band ESR lineshapes of Gd(III) aqueous complex.

X-band ESR spectra of Gd-aqua complex in various weight concentration of glycerol have been recorded at four temperatures. The interpretation of the ESR linewidth is preformed using both the stochastic Liouville approach (SLA) and a perturbation theory. The SLA uses a one dynamic model of the zero-field splitting whereas the perturbation approach uses a two dynamic model. Both models can reproduce the variation of the linewidth with respect to viscosity. In the SLA model, both the zero-field splitting (ZFS) interaction and the correlation time vary with the glycerol content. In the two dynamic perturbation model, only the correlation times are viscosity dependent. The two models give different NMRD profiles.

Electron Spin Resonance Spectroscopy↗
PubMed2004

[Blood viscosity modifications in patients with presbycusis].

OBJECTIVE: [corrected] To evaluate the existence of blood viscosity alterations in presbyacusis as an eventual pathophysiological mechanism. MATERIAL AND METHODS: Nine 75 year-old subjects bearing of bilateral slowly progressive sensorineural deafness were considered to be studied on a yearly basis in a ten year folow-up period, evaluating the binaural hearing loss in speech tones (500, 1000, 2000 and 3000 Hz). Hemorheological profile on peripheral blood included total blood viscosity (BV) at different shear rates (SR), blood filterability (BF), erythrocyte deformability and aggregability (EA). RESULTS: There was a trend of all parameters towards hyperviscosity, with an increase at ten years of BV at high SR and EA at total stasis which were statistically significant. The level of deafness correlated significativelly to low values of BF and increases on BV at high SR. CONCLUSIONS: Presbyacustic patients do show hemorheological evidences that suggest a tendency towards hyperviscosity as a predisposing factor for hearing loss.

Aged↗
PubMed2006

[Blood viscosity profile in rapidly progressive sensorineural hearing loss with positive Western-blot].

OBJECTIVE: To value a possible association between disorders in blood viscosity of patients with rapidly progressive sensorineural hearing loss (RPSHL) of autoimmune origin. PATIENTS AND METHODS: We studied the viscoelastic properties of blood in 43 subjects bearing of RPSHL and a positive Western-blot for anticochlear antibodies: whole blood viscosity (WBV) at different shear rates and erythrocyte filterability (EF). These results were related to hearing loss initially detected and recovery average one year later from steroid therapy. RESULTS: Just WBV at 230 sec(-1) shear rate was significatively higher in cases than in controls (p < 0.01). Hearing recovery degree correlated in an statistically way to increased values of EF (p < 0.01). There was no relation between initial hearing loss level and any rheology parameter. CONCLUSIONS: Autoimmune RPSHL does not show a pathophysiology mechanism associated to blood hyperviscosity. So, rheoactive therapies as plasmapheresis warrant no clinical improvement.

Adult↗
PubMed2002

Viscosity of concentrated suspensions: influence of cluster formation.

Dispersed particles can form clusters even at low concentrations. Colloidal and hydrodynamic forces are responsible for this phenomenon and these forces determine both structure and size of clusters. We assume that the viscosity of a concentrated suspension is completely determined by cluster size distribution, regardless if clusters form under the action of colloidal, hydrodynamic interactions or applied shear rates. Based on this assumption an equation, which describes dependency of viscosity on a concentration of dispersed particles taking into account cluster formation, is deduced. Under special restrictions the deduced dependency coincides with the well-known Dougherty-Krieger's equation except for a clear physical meaning of parameters entered. Our consideration shows that Dougherty-Krieger's equation has deeper physical background than it has been supposed earlier. Experimental verification of the suggested model shows a good agreement with the theory predictions and proves a presence of clusters even at low concentrations of dispersed particles.

Mathematics↗
PubMed1993

The effect of pentoxifylline on retinal capillary blood flow velocity and whole blood viscosity.

Ten normal, healthy, nonsmoking volunteers participated in a double-masked, placebo-controlled one-day trial of 2,000 mg of oral pentoxifylline to determine the short-term effects of orally administered pentoxifylline on retinal circulation and rheologic properties of whole blood. Retinal capillary blood velocity and leukocyte density, whole blood viscosity, and whole blood filterability were measured before and after therapy by the blue-field entoptic phenomenon computer simulation, rotational viscometry, and micropore filtration techniques, respectively. Treatment with pentoxifylline for one day resulted in a significant improvement in retinal capillary blood flow velocity (P = .02) and in viscosity (P < .01), but not filterability, of whole blood. These results suggest that pentoxifylline may be useful in the treatment of early diabetic retinopathy.

Administration, Oral↗
PubMed1997

Temperature and viscosity dependence of the electron-transfer reaction between plastocyanin and cytochrome c labeled with a ruthenium(II) bipyridine complex.

The temperature and viscosity dependence of the photo-induced electron-transfer reaction between plastocyanin and cytochrome c labeled at Lys13 with Ru(4,4'-dicarboxybipyridine)(bipyridine)(2+)2 have been investigated. In these studies, a short pulse of 450 nm light was used to excite the ruthenium complex which was oxidatively quenched by the iron center of cytochrome c. The resulting Fe(II) cytochrome c was then rapidly reoxidized by plastocyanin. The reactions were investigated over a temperature range of 3.5 to 37 degrees C under low ionic strength conditions such that protein/protein complex formation was favored. The enthalpy of activation was 7 kcal mol-1 and the entropy of activation was -20 cal mol-1 K-1. Increasing the viscosity by the addition of sucrose up to 70% resulted in a 4-fold decrease in the rate constant for electron transfer. The overall results suggest a rate-limiting step that involves either dissociation of the dominant protein/protein complex or surface diffusion of the associated proteins.

2,2'-Dipyridyl↗
PubMed1977

Inositol-less death in yeast results in a simultaneous increase in intracellular viscosity.

Inositol auxotrophs of yeast developing on isositol-deficient medium continue protein synthesis for 4-6 h, lose viability rapidly after 6 h, and show an increase in cytoplasmic viscosity as measured by spin label rotational motion. Cycloheximide prevents the rapid loss of cell viability, stops protein synthesis, and simultaneously prevents an increase in cytoplasmic viscosity. From these observations, we infer that intracellular translational diffusion is upset as a consequence of inositol starvation. Cell death may be caused by a modified intracellular diffusion environment.

Cell Survival↗
PubMed1979

Red cell extensional recovery and the determination of membrane viscosity.

A theory of membrane viscoelasticity developed by Evans and Hochmuth in 1976 is used to analyze the time-dependent recovery of an elongated cell. Before release, the elongated cell is the static equilibrium where external forces are balanced by membrane elastic force resultants. Upon release, the cell recovers its initial shape with a time-dependent exponential behavior characteristic of the viscoelastic solid model. It is shown that the model describes the time-dependent recovery process very well for a time constant in the range of 0.1-0.13 s. The time constant is the ratio membrane surface viscosity eta:membrane surface elasticity mu. Measurements for the shear modulus mu of 0.006 dyne/cm give a value for the surface viscosity of red cell membrane as a viscoelastic solid material of eta = mu tc = (6-8) X 10(-4) poise . cm.

Elasticity↗