Nectar feeding by the hovering hawk moth Macroglossum stellatarum: intake rate as a function of viscosity and concentration of sucrose solutions

Although nectar feeding in insects has long been studied, the knowledge of the effect of nectar energy content on the ingestion dynamics separately from the viscosity of the fluid is very limited. To determine the effects of both factors on the feeding behavior of the hovering hawk moth Macroglossum stellatarum, we developed a method to independently manipulate sucrose concentrations and viscosity. The intake rate was analyzed as a function of sucrose concentration, the concentration at constant viscosity (kept constant by adding tylose, an inert polysaccharide), and of the different viscosities of a 30% weight/weight (w/w) sucrose solution (by adding different amounts of tylose). By increasing the concentration, and thus its viscosity, the solution intake rate (in microl s (-1)) decreased beyond a 20% w/w sucrose solution. For a 30% sucrose solution, the intake rate decreased with increasing viscosity. At constant viscosity, the solution intake rate decreased beyond a 30% w/w sucrose solution. However, if we considered the quantity of sucrose ingested per unit time (sucrose intake rate), the same fitted maximum was attained for both series in which the sucrose concentration changed (33.6% w/w). Results suggest that the gustatory input affects the dynamics of fluid ingestion separately from the viscosity.     

Effect of wheat germ agglutinin on the viscoelastic properties of erythrocyte membrane

The elasticity and viscosity of the human erythrocyte membrane were measured as a function of the concentration of wheat germ agglutinin (WGA) in a suspending solution containing 1 mg/ml albumin, approximately 5 X 10(5) cells/ml and between 0.0 and 0.2 microgram/ml WGA. Membrane elasticity was characterized by the elastic shear modulus, which provided a measure of the resistance of the membrane to constant-area elastic deformations that occurred in the membrane plane. The elastic shear modulus was determined by aspirating a portion of the membrane into a micropipette and measuring the extension of the membrane into the pipette as a function of the suction pressure. The results indicated no significant change in shear modulus for concentrations of WGA between 0.0 and 0.2 microgram/ml. Membrane viscosity was characterized by the coefficient of surface viscosity, which, in effect, was a measure of the membrane's resistance to rates of deformation. This coefficient was determined from the time required for an erythrocyte to recover its undeformed shape after it had been elongated by the application of an equal and opposite force applied at diametrically opposite points on the erythrocyte rim. The value for the coefficient of surface viscosity was found to increase by a factor of almost three when the WGA concentration was increased from 0.0 to 0.2 microgram/ml. These results indicated that, in the presence of albumin, WGA can increase membrane dissipation (viscosity) without altering the structural rigidity (elasticity) of the membrane.     

Viscoelastic properties of an exopolysaccharide: Aeromonas gum, produced by Aeromonas nichidenii 5797

The viscoelastic properties of Aeromonas (A) gum in water were investigated by using the Rheometric Scientific ARES controlled strain rheometer. An intrinsic viscosity of 8336 ml/g was obtained according to the Fuoss-Straus equation. The effect of salt concentration on intrinsic viscosity revealed that the A gum exists as semiflexible chain. Typical shear-thinning (pseudoplastic) behavior was observed at concentrations higher than 0.52%. The zero shear viscosity (eta(0)) increased with increasing polysaccharide concentration (c) showing a gradient of approximately 1.0, 2.9 and 4.8 in different concentration domains. The critical concentrations c* and c**, at which the transitions from a dilute solution of independently moving chains to semidilute and then concentrated domains occurred, were determined roughly to be 1.2% and 3.5%. The results from dynamic experiments revealed that the A gum solution shows characteristics of polymer solutions without any evidence of gel-like character. All the results from steady and dynamic tests suggest that the A gum is a non-gelling polysaccharide. The temperature dependence of apparent viscosity was described by Arrhenius equation and the flow activation energy was estimated to be 45.2 kJ/mol, which is independent on polymer concentration.     

Rheological characterization of nephila spidroin solution

We report the results of an investigation into the rheology of solutions of natural spider silk dope (spinning solution). We demonstrate that dilute dope solutions showed only shear thinning as the shear rate increased while more concentrated solutions showed an initial shear thinning followed by a shear thickening and a subsequent decline in viscosity. The critical shear rate for shear thickening depended on dope concentration and was very low in concentrated solutions. This helps to explain how spiders are able to spin silk at very low draw rates and why they use a very concentrated dope solution. We also show that the optimum shear rate for shear thickening in moderately concentrated solutions occurred at pH 6.3 close to the observed pH at the distal end of the spider's spinning duct. Finally, we report that the addition of K(+) ions to dilute dope solutions produced a spontaneous formation of nanofibrils that subsequently aggregated and precipitated. This change was not seen after the addition of other common cations. Taken together, these observations support the hypothesis that the secretion of H(+) and K(+) by the spider's duct together with moderate strain rates produced during spinning induce a phase separation in the silk dope in which the silk protein (spidroin) molecules are converted into insoluble nanofibrils.     

透明质酸溶液的流变性能初步研究

透明质酸是一种酸性粘多糖,其特有的粘弹性使其广泛应用于眼科手术等医药领域。使用高级流变扩展系统研究浓度对于透明质酸溶液流变性能的影响。结果表明,透明质酸溶液的粘度随剪切速率的增加而减小。在任何剪切速率作用下,粘度总是与浓度呈正相关。而随着浓度的增加,溶液粘性与弹性频率交叉点降低。     

Quantitative analysis of the effects of hyaluronan and aggrecan concentration and hyaluronan size on the elasticity of hyaluronan-aggrecan solutions

We determined elasticity (G') and viscosity (G') of various aggrecan-hyaluronan solutions using a controlled-stress rheometer with high (10 Hz) to low (0.1 Hz) frequencies. Aggrecan solution (50 mg/ml) alone showed little elasticity at any frequency, but the addition of 3300 kDa hyaluronan at 0.001-0.1 mg/ml markedly increased the elasticity, but not the viscosity, at all frequencies. Increasing hyaluronan concentration at >0.1 mg/ml did not further increase the elasticity of the aggrecan solution, and the elasticity of the aggrecan-hyaluronan complex solution reached a plateau at a 500:1 (w/w) ratio. In studies with increasing concentrations of aggrecan and a constant concentration (0.5 mg/ml) of 3300 kDa hyaluronan, aggrecan induced elasticity only at >20 mg/ml, indicating the presence of a critical concentration for elasticity. In the presence of 50 mg/ml aggrecan, 1000 kDa hyaluronan had far less effect on the elasticity of the aggrecan solution than did 3300 kDa hyaluronan. These findings suggest that only approximately 50% reduction in aggrecan concentration (<20 mg/ml), or reduced hyaluronan size (<1000 kDa)--compared with their physiological levels in young cartilage--can abolish the elastic network of the aggrecan-hyaluronan complex.     

Pullulan-sodium alginate based edible films: Rheological properties of film forming solutions

Rheological properties of pullulan, sodium alginate and blend solutions were studied at 20 °C, using steady shear and dynamic oscillatory measurements. The intrinsic viscosity of pure sodium alginate solution was 7.340 dl/g, which was much higher than that of pure pullulan (0.436 dl/g). Pure pullulan solution showed Newtonian behavior between 0.1 and 100 s⁻¹ shear rate range. However, increasing sodium alginate concentration in pullulan-alginate blend solution led to a shear-thinning behavior. The effect of temperature on viscosities of all solutions was well-described by Arrhenius equation. Results from dynamical frequency sweep showed that pure sodium alginate and blend solutions at 4% (w/w) polymer concentration were viscoelastic liquid, whereas the pure pullulan exhibited Newtonian behavior. The mechanical properties of pure sodium alginate and pullulan-alginate mixture were analyzed using the generalized Maxwell model and their relaxation spectra were determined. Correlation between dynamic and steady-shear viscosity was analyzed with the empirical Cox-Merz rule.     

Rheological and Performance Research on a Regenerable Polyvinyl Alcohol Fracturing Fluid

A regenerable polyvinyl alcohol/organic boron fracturing fluid system with 1.6 wt% polyvinyl alcohol (PVOH) and 1.2 wt% organic boron (OBT) was studied, and its main regeneration mechanism is the reversible cross-linking reaction between B(OH)₄ ^- and hydroxyl groups of PVOH as the change of pH. Results of rheology evaluations show that both the apparent viscosity and the thermal stability of the fracturing fluid decreased with the regeneration number of times increasing. In addition, the apparent viscosity of the fluid which was without regeneration was more sensitive to the shear action compared with that of the fluid with regeneration once or twice. When the fracturing fluid was without regeneration, the elasticity was dominating due to the three-dimensional network structure of the formed gel; the viscosity gradually occupied the advantage when the fracturing fluid was regenerated once or twice. The settling velocity of proppant was accelerated by both the regeneration process and the increasing temperature, but it was decelerated when the proppant ratio increased. Results of core damage tests indicate that less permeability damage was caused by the PVOH/OBT fracturing fluid compared with that caused by the guar gum fracturing fluid after gel breaking.     

Investigations into the rheological characteristics of bovine amniotic fluid

The rheological characteristics of bovine amniotic fluid have been studied at different shear rates. The viscosity of bovine amniotic fluid at 20°C was found to increase with time at a constant low shear rate during the measurement. Additionally, the viscosity was observed to decrease with increasing shear rate, indicating that a shear thinning behaviour of the fluid was occurring. The log-log plot of shear stress versus shear rate yielded a straight line, consistent with non-Newtonian behaviour of the fluid and characteristic of pseudoplastic liquids. The data of shear stress versus shear rate could be represented by a power law model. The treatment of amniotic fluid with cetylpyridinium chloride (CPC) resulted in the precipitation of a mixture of components, including complex sulphated polysaccharides and extracellular proteoglycans, with the viscosity of the resulting liquid similar to that of water at 20°C. In addition, the viscosity of the CPC-pretreated fluid did not increase with time at constant shear rate and remained constant with the increase in shear rate. The apparent increase in viscosity with time and the shear thinning behaviour of the amniotic fluid can thus be attributed to pseudoplastic liquid behaviour associated with the presence of structurally complex polysaccharides and extracellular proteoglycans. The implications of this fluid viscosity behaviour are discussed in terms of their impact on the operation of packed or expanded (fluidized) chromatographic bed systems when amniotic fluid biofeed-stocks are used as a source of commercially important proteins.     

Enhancement of the viscosity of mucin by serum albumin.

The interaction of serum albumin with a model epithelial mucin from pig stomach was explored by rotary viscometry. During 30 min of incubation of human serum albumin(20mg/ml) and pig gastric mucin (8mg/ml) in iso-osmotic buffers at 37 degrees C, the solution became markedly viscous. Viscosity enhancement was proportional to albumin concentration (2-40mg/ml), was most pronounced under conditions of low shear rate (less than 45S-1), and was considerably greater than the additive or multiplicative viscosity values calculated from albumin or mucin solutions measured separately. The viscous mucin-albumin complex was destroyed by high shear rates (greater than 90S-1), but slowly re-formed under zero shear conditions. Elevation of pH (7 to 9), ionic strength (0.1 to 1.0), and addition of disodium EDTA (5mM) did not cause marked or specific alterations in the viscosity of the mixture, suggesting that electrostatic interactions probably do not stabilize mucin-albumin complexes. Urea (7M) and heating (35 to 55 degrees C) caused a major increase in the viscosity of mucin and mucin-albumin mixtures, suggesting that rupture of hydrogen bonds, unfolding and partial denaturation of mucin promotes greater intertangling (possibly hydrophobic interactions) between mucin and albumin molecules. The implications of mucin-albumin interaction in diseases associated with mucus obstruction are briefly discussed.     

The nonequilibrium phase and glass transition behavior of beta-lactoglobulin

Concentrated solutions of bovine beta-lactoglobulin were studied using osmotic stress and rheological techniques. At pH 6.0 and 8.0, the osmotic pressure was largely independent of NaCl concentration and could be described by a hard sphere equation of state. At pH 5.1, close to the isoelectric point, the osmotic pressure was lower at the lower NaCl concentrations (0 mM, 100 mM) and was fitted by an adhesive hard sphere model. Liquid-liquid phase separation was observed at pH 5.1 at ionic strengths of 13 mM and below. Comparison of the liquid-liquid and literature solid-liquid coexistence curves showed these solutions to be supersaturated and the phase separation to be nonequilibrium in nature. In steady shear, the zero shear viscosity of concentrated solutions at pH 5.1 was observed at shear rates above 50 s(-1). With increasing concentration, the solution viscosity showed a progressive increase, a behavior interpreted as the approach to a colloidlike glass transition at approximately 60% w/w. In oscillatory shear experiments, the storage modulus crossed the loss modulus at concentrations of 54% w/w, an indication of the approaching glass transition. Comparison of the viscous behavior with predictions from the Krieger-Dougherty equation indicates the hydrodynamic size of the protein decreases with increasing concentration, resulting in a slower approach to the glass transition than a hard sphere system.     

Shear degradation of DNA.

A concentric-cylinder flow-birefringence instrument is used to generate sufficient shear fields to break T2 DNA (M = 1.2 X 10(8)) and E. coli DNA (M = 2.5 X 10(9)) in dilute solution. Breakage is monitored in situ by measuring the change in birefringence relaxation after the flow has been stopped. The breakage of T2 DNA follows first-order kinetics. Rate constants are obtained as functions of shear rate and viscosity (varied by adding glycerol). The data are fitted by a modified Arrhenius equation, assuming that stess increases the rate by lowering the activation energy. The rate increases with temperature, pH, and water concentration, and appears to be a base-catalyzed hydrolysis of the phosphate-ester linkage. La3+ ions catalyze the reaction. E. coli DNA was reduced to half molecules at a shear stress of 0.4 dynes/cm2, which is about 2500 times less than that required for T2. The difference in rates is accounted for in part by the difference in size of the two, but may also reflect the presence of many single-strand nicks in the coli DNA.     

Rheological properties of extracellular polysaccharide, Pestan, produced by Pestalotiopsis sp.

Summary The fluid behaviour of Pestan produced from Pestalotiopsis sp. KCTC 8637P was as a non-Newtonian fluid. The rheological behaviour of Pestan solution was examined by Power-law model, Herschel-Bulkley model and Arrhenius equation. As the result, Pestan solution was pseudoplastic behaviour with yield stress. According to increase of Pestan concentration, its flow index was decreased. Thus, low concentrations of Pestan solution were well exposed pseudoplastic property. Apparent viscosity of 0.2 % Pestan solution was 268.2 cP at 14.3 sec^–1 and was higher about 2.8 times than that of Xanthan gum solution. Apparent viscosity of Pestan solution was stable over a wide pH and was maximum at pH 8. Also, consistency index of Pestan solution was very stable over wide temperature than that of Xanthan gum solution.     

犬脾切除对阻断冠脉后血液流变学变化的影响

本实验旨在观察切除脾脏对犬心肌缺血时血液流变学变化的影响。结果表明,切除脾脏后,阻断冠脉血流120min内血细胞比容与高切变率下全血粘度升高程度明显减轻;心肌缺血40min和80min时低切变率下全血粘度升高程度减轻;但对心肌缺血120min时低切变率下全血粘度变化及血浆纤维蛋白原浓度、血浆粘度变化均无明显影响。     

Interaction of paratropomyosin with beta-connectin and its 400-kilodalton fragment from chicken skeletal muscle as influenced by the calcium ion concentration.

The binding of paratropomyosin to beta-connectin, which has been suggested to interact at the A-I junction of a sarcomere, was confirmed by measuring the changes in turbidity of a mixture with changing NaCl concentration, pH and free calcium ions, and by morphological observation and a coprecipitation assay of the aggregates formed in the mixture. Paratropomyosin also bound to the 400-kDa fragment which is the N-terminal portion of beta-connectin and contains the A-I junction region. Moreover, the interaction of paratropomyosin with the 400-kDa fragment was enhanced by a calcium ion concentration from 10(-7) M to 10(-5) M and markedly suppressed above 10(-4) M calcium ions. We conclude that paratropomyosin probably binds to the 400-kDa fragment of beta-connectin in the A-I junction region in living and pre-rigor skeletal muscle. In postmortem skeletal muscle paratropomyosin may be released from the 400-kDa portion of the connectin filament by increased calcium ion concentration and translocated on to thin filaments to induce meat tenderization.     

Microcontinuum model for pulsatile blood flow through a stenosed tube

The effects of polar nature of blood and pulsatility on flow through a stenosed tube have been analysed by assuming blood as a micropolar fluid. Linearized solutions of basic equations are obtained through consecutive applications of finite Hankel and Laplace transforms. The analytical expressions for axial and particle angular velocities, wall shear stress, resistance to flow and apparent viscosity have been obtained. The axial velocity profiles for Newtonian and micropolar fluids have been compared. The interesting observation of this analysis is velocity, in certain parts of cycle, for micropolar fluid is higher than Newtonain fluid. Variation of apparent viscosity eta a with tube radius shows both inverse Fahraeus-Lindqvist and Fahraeus-Lindqvist effects. Finally, the resistance to flow and wall shear stress for normal and diseased blood have been computed and compared.     

Trehalose-mediated inhibition of the plasma membrane H+-ATPase from Kluyveromyces lactis: dependence on viscosity and temperature

The effect of increasing trehalose concentrations on the kinetics of the plasma membrane H+-ATPase from Kluyveromyces lactis was studied at different temperatures. At 20 degrees C, increasing concentrations of trehalose (0.2 to 0.8 M) decreased V(max) and increased S(0.5) (substrate concentration when initial velocity equals 0.5 V(max)), mainly at high trehalose concentrations (0.6 to 0.8 M). The quotient V(max)/S(0.5) decreased from 5.76 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the absence of trehalose to 1.63 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the presence of 0.8 M trehalose. The decrease in V(max) was linearly dependent on solution viscosity (eta), suggesting that inhibition was due to hindering of protein domain diffusional motion during catalysis and in accordance with Kramer's theory for reactions in solution. In this regard, two other viscosity-increasing agents, sucrose and glycerol, behaved similarly, exhibiting the same viscosity-enzyme inhibition correlation predicted. In the absence of trehalose, increasing the temperature up to 40 degrees C resulted in an exponential increase in V(max) and a decrease in enzyme cooperativity (n), while S(0.5) was not modified. As temperature increased, the effect of trehalose on V(max) decreased to become negligible at 40 degrees C, in good correlation with the temperature-mediated decrease in viscosity. The trehalose-mediated increase in S(0.5) was similar at all temperatures tested, and thus, trehalose effects on V(max)/S(0.5) were always observed. Trehalose increased the activation energy for ATP hydrolysis. Trehalose-mediated inhibition of enzymes may explain why yeast rapidly hydrolyzes trehalose when exiting heat shock.     

Electroviscous effect of lysozyme in aqueous solutions

Reduced viscosity of a dilute aqueous solution of hen egg white lysozyme is measured in the pH range from 1.4 to 12.7 for various NaCI concentrations. The viscosity decreases with increasing pH below the isoelectric point (pH 11) on account of diminution in the electroviscous effect, reaches a minimum at pH 11, and then increases at high pH's because of coagulation. The electroviscous effect is depressed by the increase in the small ion concentration. The dependence of reduced viscosity on small ion concentration and pH is discussed on the basis of Booth's theory and a partial agreement between theory and experiment is obtained. The discrepancy between theory and experiment is attributed to non-spherical distribution of charges in the protein. The volume of lysozyme obtained through Einstein's equation by extrapolating the reduced viscosity to a sufficiently high ion concentration compares well with the molecular volume in the crystal.     

Impact of engineering flow conditions on plasmid DNA yield and purity in chemical cell lysis operations

Chemical lysis of bacterial cells using an alkaline solution containing a detergent may provide an efficient scalable means for selectively removing covalently closed circular plasmid DNA from high-molecular-weight contaminating cellular components including chromosomal DNA. In this article we assess the chemical lysis of E. coli cells by SDS in a NaOH solution and determine the impact of pH environment and shear on the supercoiled plasmid and chromosomal DNA obtained. Experiments using a range of plasmids from 6 kb to 113 kb determined that in an unfavorable alkaline environment, where the NaOH concentration during lysis is greater than 0.15 +/- 0.03 M (pH 12.9 +/- 0.2), irreversible denaturation of the supercoiled plasmid DNA occurs. The extent of denaturation is shown to increase with time of exposure and NaOH concentration. Experiments using stirred vessels show that, depending on NaOH concentration, moderate to high mixing rates are necessary to maximize plasmid yield. While NaOH concentration does not significantly affect chromosomal DNA contamination, a high NaOH concentration is necessary to ensure complete conversion of chromosomal DNA to single-stranded form. In a mechanically agitated lysis reactor the correct mixing strategy must balance the need for sufficient mixing to eliminate potential regions of high NaOH concentrations and the need to avoid excessive breakage of the shear sensitive chromosomal DNA. The effect of shear on chromosomal DNA is examined over a wide range of shear rates (10(1)-10(5) s(-1)) demonstrating that, while increasing shear leads to fragmentation of chromosomal DNA to smaller sizes, it does not lead to significantly increased chromosomal DNA contamination except at very high shear rates (about 10(4)-10(5) s(-1)). The consequences of these effects on the choice of lysis reactor and scale-up are discussed.