Tangent simple systems method applied to a precise study of viscoelastic behaviour of human blood

The tangent simple systems (TSS) method, proposed in (1), is applied in order to study the viscoelastic behaviour of human blood in transient flow for a rectangular low shear rate step. The tangent simple systems which were used are Maxwell liquids. These systems allow one to obtain plots of variations of instantaneous values of viscosity coefficient mu, elasticity modulus G and retardation time tau = mu/G of the studied blood samples, as a function of flow duration. Variations of both parameters mu and G versus time are represented by two exponential functions which involve three couples of parameters (mu o, mu infinity), (Go, G infinity) and (tau mu, tau G). These parameters can be considered as the characteristics of each blood sample. Another representation of the results, called the dual rheogram, is also indicated. The dual rheogram enables one to follow the evolution of the blood structure. Several examples of application of the TSS method to normal blood sample and to suspensions of artificially modified red blood cells (RBC) are given.     

Rheological evidence of the gelation behavior of hyaluronan-gellan mixtures

It was found that solutions of calcium hyaluronate (CaHA) (0.1 to approximately 0.5 wt%) could form a gel by mixing with solutions of sodium type gellan (0.1 to approximately 0.5 wt%), although neither polymer by itself forms a gel at low concentrations (0.1 to approximately 0.5 wt% in this experiment). The rheological properties of CaHA-gellan mixtures were investigated by dynamic and steady shear measurements. Both storage shear modulus G' and loss shear modulus G' for CaHA-gellan mixtures increased with increasing time, and tended to an equilibrium value after 1 h. After reaching steady values of G' and G", the frequency dependence of G' and G' was observed. G' was always larger than G' in the accessible frequency range from 10(-2) to 10(2) rad/s. The effects of pH and calcium ions were examined. Gel formation of the mixtures was promoted by decreasing pH and adding from 0.01 to 0.1 M calcium ions, but excessive calcium ions weakened the gel.     

Rheology of passive and adhesion-activated neutrophils probed by atomic force microscopy

The rheology of neutrophils in their passive and activated states plays a key role in determining their function in response to inflammatory stimuli. Atomic force microscopy was used to study neutrophil rheology by measuring the complex shear modulus G*(omega) of passive nonadhered rat neutrophils on poly(HEMA) and neutrophils activated through adhesion to glass. G*(omega) was measured over three frequency decades (0.1-102.4 Hz) by indenting the cells 500 nm with a spherical tip and then applying a 50-nm amplitude multi-frequency signal. G*(omega) of both passive and adhered neutrophils increased as a power law with frequency, with a coupling between elastic (G') and loss (G') moduli. For passive neutrophils at 1.6 Hz, G' = 380 +/- 121 Pa, whereas G' was fourfold smaller and the power law coefficient was of x = 1.184. Adhered neutrophils were over twofold stiffer with a lower slope (x = 1.148). This behavior was adequately described by the power law structural damping model but not by liquid droplet and Kelvin models. The increase in stiffness with frequency may modulate neutrophil transit, arrest, and transmigration in vascular microcirculation.     

Membrane viscoplastic flow.

In this paper, a theory of viscoplasticity formulated by Prager and Hohenemser is developed for a two-dimensional membrane surface and applied to the analysis of the flow of "microtethers" pulled from red blood cells attached to glass substrates. The viscoplastic flow involves two intrinsic material constants: yield shear and surface viscosity. The intrinsic viscosity for plastic flow of membrane is calculated to be 1 X 10(-2) dyn-s/cm from microtether flow experiments, three orders of magnitude greater than surface viscosities of lipid membrane components. The fluid dissipation is dominated by the flow of a structural matrix which has exceeded its yield shear. The yield shear is the maximum shear resultant that the membrane can sustain before it begins to deform irreversibly. The yield shear is found to be in the range 2-8 X 10(-2) dyn/cm, two or three orders of magnitude smaller than the isotropic tension required to lyse red cells.     

Alpha and beta mechanical dispersions in high sugar/acyl gellan mixtures

The real (G') and imaginary (G") components of the complex modulus have been measured between 0.1 and 100 rad/s in the temperature range of 70--55 degrees C for a mixture of 1% high acyl gellan with 79% glucose syrup, and 79% glucose syrup. The method of reduced variables gave superposed curves of G' and G" as a function of timescale of measurement, which matched the thermal profiles of shear modulus obtained by scanning at the constant rate of 1 degrees C/min. Data of the gellan/co-solute mixture could be analysed in terms of two distinct mechanisms. For the alpha dispersion, G' and G" superposed with the horizontal reduction factor a(T) whose temperature dependence followed an equation of the Williams-Landel-Ferry form. Mechanical spectra of the beta dispersion also superposed with the factor a(T) whose temperature dependence, however, corresponded to a constant energy of activation. Relaxation spectra have been calculated for both dispersions. Those for the alpha mechanism were attributed to the chain backbone motions and the friction coefficient per tetrasaccharide repeat unit in backbone motion was calculated from the extended Rouse theory. When the contribution of the solvent alone was studied, no spectra for the beta dispersion were observed supporting the hypothesis of the dispersion being attributed to the side-chain motions of the acyl groups. The spectra of the beta mechanism were relatively broader than for the alpha dispersion. The relative location of the beta dispersion on the time scale or temperature range was found to be between the alpha dispersion (glass transition region) and the glassy state.     

Magnetic resonance microscopy determined velocity and hematocrit distributions in a Couette viscometer

Magnetic resonance microscopy is used to non-invasively measure the radial velocity distribution in Couette flow of erythrocyte suspensions of varying aggregation behavior at a nominal shear rate of 2.20 s(-1) in a 1 mm gap. Suspensions of red blood cells in albumin-saline, plasma and 1.48% Dextran added plasma at average hematocrits near 0.40 are studied, providing a range of aggregation ability. The spatial distribution of the red blood cell volume fraction, hematocrit, is calculated from the velocity distribution. The hematocrit profiles provide direct measure of the thickness of the aggregation and shear rate dependent red blood cell depletion at the Couette surfaces. At the nominal shear rate studied hematocrit distributions for the red blood cells in plasma show a depletion zone near the inner Couette wall but not the outer wall. The red blood cells in plasma with Dextran show cell depletion regions of approximately 100 mum at both the inner and outer Couette surfaces, with greater depletion at the inner wall, but approach the normal blood hematocrit distribution with a doubling of shear rate due to decreased aggregation. The material response of the blood is spatially dependent with the shear rate and the hematocrit distribution non-uniform across the gap.     

Analysis of thromboelastogram on coagulation and fibrinolysis

Hartert's thromboelastography has been used in the diagnosis of abnormal blood clotting for more than 20 years. From a thromboelastogram three parameters are obtained, viz, the reaction time 'r', the rate of formation of fibrin clot 'k', the maximum elasticity of thrombus 'amax'. It is desirable, however, to know the equation that describes the thromboelastogram both in the period in which the complex modulus increases with time because of coagulation, and in the period in which the complex modulus decreases with time because of fibrinolysis. The parameters of the equation could then be used as a diagnostic criterion; yielding information on the mechanism of coagulation and fibrinolysis. Based on our experimental results on human blood in normal and abnormal subjects, we found that the complex modulus of thromboelastograms can be expressed by the sum of two terms, one describing the increase of the complex modulus during coagulation, G1 = G'1 Exp (-tau 1/t), the other describing the decrease of the complex modulus during fibrinolysis, G2 = G'2 Exp (-tau 2/(t-D) when t greater than D. G2 = 0 when t less than D. The compound complex modulus from coagulation to fibrinolysis is G = G1 - G2. Here t is the clotting time, and G'1, G'2, tau 1, tau 2, and D are five constants to be identified. These five constants can be used for diagnostic and prognostic purposes.     

Flow properties of N-(carboxymethyl) chitosan aqueous systems in the sol and gel domains

The flow behaviour and the viscoelastic properties of N-(carboxymethyl) chitosan aqueous systems in the sol and gel domains have been investigated by means of dynamic, steady and transient shear techniques. For polymer concentrations Cp up to 1%, a typical response of moderately concentrated polymer solutions was observed under continuous and oscillatory shear conditions. No time-dependent properties were detected during transient shear experiments. On the other hand, for all the samples with Cp greater than 1%, the rheological properties were more similar to those of a weak gel system. The continuous shear flow behaviour was of the plastic type and the viscoelastic quantities G' and G" were parallel to each other and slightly dependent on the frequency of oscillation omega. Stress overshoots were observed during transient shear experiments, and the kinetics of the structural breakdown and build-up processes were found to be dependent both on the polymer concentration and the applied shear rate.     

Microrheology of human lung epithelial cells measured by atomic force microscopy

Lung epithelial cells are subjected to large cyclic forces from breathing. However, their response to dynamic stresses is poorly defined. We measured the complex shear modulus (G(*)(omega)) of human alveolar (A549) and bronchial (BEAS-2B) epithelial cells over three frequency decades (0.1-100 Hz) and at different loading forces (0.1-0.9 nN) with atomic force microscopy. G(*)(omega) was computed by correcting force-indentation oscillatory data for the tip-cell contact geometry and for the hydrodynamic viscous drag. Both cell types displayed similar viscoelastic properties. The storage modulus G'(omega) increased with frequency following a power law with exponent approximately 0.2. The loss modulus G"(omega) was approximately 2/3 lower and increased similarly to G'(omega) up to approximately 10 Hz, but exhibited a steeper rise at higher frequencies. The cells showed a weak force dependence of G'(omega) and G"(omega). G(*)(omega) conformed to the power-law model with a structural damping coefficient of approximately 0.3, indicating a coupling of elastic and dissipative processes within the cell. Power-law behavior implies a continuum distribution of stress relaxation time constants. This complex dynamics is consistent with the rheology of soft glassy materials close to a glass transition, thereby suggesting that structural disorder and metastability may be fundamental features of cell architecture.     

Gelation behaviour of konjac glucomannan with different molecular weights

The deacetylation and gelation of konjac glucomannan (KGM) following alkali addition was investigated by Fourier transform infrared, while the rheological properties of KGM with different molecular weights were studied by dynamic viscoelastic measurements in shear mode and penetration force tests. It was found that gelation occurred after significant deacetylation had taken place. Rheometrical studies revealed that KGM with different molecular weights exhibited different gelation characteristics in small amplitude oscillatory shear flow. For the samples of fractionated KGM with lower molecular weights, a decrease in both the storage shear modulus (G') and loss shear modulus (G") was observed during gelation at temperatures above 75 degrees C. It is suggested that the decrease results from the wall slip between sample and measuring geometry owing to a rapid gelation process with syneresis and/or disentanglement of molecular chains adsorbed on the surface of parallel plates from those located in the bulk. Penetration force tests were employed to confirm the occurrence of slippage and thereby no decreases in rigidity of samples were observed during gelation. For the native KGM samples decreases in G' and G" during gelation were not observed, and it is suggested that this is due to the effect of the higher molecular weight and increased solution viscosity of these samples on the gelation kinetics.     

Shear‐induced diffusion of red blood cells measured with dynamic light scattering‐optical coherence tomography

Quantitative measurements of intravascular microscopic dynamics, such as absolute blood flow velocity, shear stress and the diffusion coefficient of red blood cells (RBCs), are fundamental in understanding the blood flow behavior within the microcirculation, and for understanding why diffuse correlation spectroscopy (DCS) measurements of blood flow are dominantly sensitive to the diffusive motion of RBCs. Dynamic light scattering‐optical coherence tomography (DLS‐OCT) takes the advantages of using DLS to measure particle flow and diffusion within an OCT resolution‐constrained three‐dimensional volume, enabling the simultaneous measurements of absolute RBC velocity and diffusion coefficient with high spatial resolution. In this work, we applied DLS‐OCT to measure both RBC velocity and the shear‐induced diffusion coefficient within penetrating venules of the somatosensory cortex of anesthetized mice. Blood flow laminar profile measurements indicate a blunted laminar flow profile and the degree of blunting decreases with increasing vessel diameter. The measured shear‐induced diffusion coefficient was proportional to the flow shear rate with a magnitude of ~0.1 to 0.5 × 10^?6 mm². These results provide important experimental support for the recent theoretical explanation for why DCS is dominantly sensitive to RBC diffusive motion.      

Effect of Different Light Quality on Photosynthetic Characteristics of Cucumber Leaves

Cucumber (Cucumis sativus L. cultivar "Changchun Mici") seedlings were cultured in Hoagland solution under irradiation with different light spectra (8 h per day) for 20 days. The red light (λmax 658 nm, λ1/2 25 nm), blue light (λmax 450 nm, λ1/2 43 nm) and white fluorescent light possessed the same fluent rate (20 μmol· m-2·s-1 ). The experimental results showed that chlorophyll content of the leaves grown under white light was 7 % and 22.4% higher than those in red and blue light, respectively. Compared with white and blue light, red light induced a lower Chl a/b ratio and a higher level of Chl b in the cucumber leaves. Measurements of the low temperature (77 K) fluorescence emission spectra and kinetics of Chl a fluorescence induction of the leaves proved that the leaves grown under red light expressed the highest PSⅡ and the lowest PSⅠactivities while the leaves under blue light had the lowest PSⅡand the highest PSⅠ activities. The O2 evolution rate of red light-grown leaves was 44.9% higher than that of the white light-grown leaves, while blue light effect was similar to that of white in respect of O2 evolution. It is concluded that light quality is an important factor in regulating the development and activities of PSⅡ and PSⅡand the O2 evolution of photosynthesis in cucumber leaves.     

Effect of aggregation and shear rate on the dispersion of red blood cells flowing in venules

Previous in vitro studies of blood flow in small glass tubes have shown that red blood cells exhibit significant erratic deviations in the radial position in the laminar flow regime. The purpose of the present study was to assess the magnitude of this variability and that of velocity in vivo and the effect of red blood cell aggregation and shear rate upon them. With the use of a gated image intensifier and fluorescently labeled red blood cells in tracer quantities, we obtained multiple measurements of red blood cell radial and longitudinal positions at time intervals as short as 5 ms within single venous microvessels (diameter range 45-75 microm) of the rat spinotrapezius muscle. For nonaggregating red blood cells in the velocity range of 0.3-14 mm/s, the mean coefficient of variation of velocity was 16.9 +/- 10.5% and the SD of the radial position was 1.98 +/- 0.98 microm. Both quantities were inversely related to shear rate, and the former was significantly lowered on induction of red blood cell aggregation by the addition of Dextran 500 to the blood. The shear-induced random movements observed in this study may increase the radial transport of particles and solutes within the bloodstream by orders of magnitude.     

Rheological behaviors of bovine blood forming artificial rouleaux

A purpose of the present study is to make an artificial rouleau of bovine red blood cells which is not capable of rouleau formation under physiological condition. Rheological behaviors of bovine blood forming artificial rouleaux were examined. The modification of cell surface by enzyme trypsin induced rouleau formation, whereas the modification of cell surface by neuraminidase did not cause any aggregate formation. The drastic elevation of the fibrinogen content in bovine red blood cells suspension also brought about the formation of rouleau. The value of dynamic rigidity modulus G' of bovine red blood cells in saline solution containing high concentration of fibrinogen is somewhat smaller than that of trypsin treated bovine red blood cells in plasma. The value of G' of trypsin treated bovine red blood cells in plasma first increased to a maximum value and then decreased with the time. It is supposed that the removal of macro-molecules from the cell surface facilitates the mutual approach of cells and causes the formation of rouleau which seems to be the same as that of human and horse bloods.     

Clinical assessment of rheumatic diseases using viscoelastic parameters for synovial fluid

For the first time it is clearly exhibited that synovial fluid (SF) is thixotropic. Although no hysteresis loops were observed for SF, not even at high shear rates, thixotropy may be exhibited by measuring the rate of recovery after extensive shearing. The rebuilding of the structure in a small-amplitude oscillatory state following the high-shear-rate state reveals the thixotropic behaviour. Five different viscoelastic parameters for various synovial fluids (SF) were obtained using oscillatory rheometry. It was also shown that for SF in the low frequency range, corresponding to a knee joint almost at rest, the shear loss modulus G" is greater than the shear storage modulus G', since the system is allowed to dissipate energy at rest. However, with movement, G' increases and eventually becomes greater than G" at a characteristic frequency above which the system has insufficient time to dissipate energy and hence responds as an elastic body. This functional behaviour, characteristic for normal SF, broke down in the SF of rheumatoid arthritis. It was also absent in the SF of knee joints with meniscus lesions and ligament defects.     

Red blood cell orientation in orbit C = 0.

Two modes of behavior of single human red cells in a shear field have been described. It is known that in low viscosity media and at shear rates less than 20 s-1, the cells rotate with a periodically varying angular velocity, in accord with the theory of Jeffery (1922) for oblate spheroids. In media of viscosity greater than approximately 5 mPa s and sufficiently high shear rates, the cells align themselves at a constant angle to the direction of flow with the membrane undergoing tank-tread motion. Also, in low viscosity media, as the shear rate is increased, more and more cells lie in the plane of shear, undergoing spin with their axes of symmetry aligned with the vorticity axis of the shear field in an orbit "C = 0" (Goldsmith and Marlow, 1972). We have explored this latter phenomenon using two experimental methods. First, the erythrocytes were observed in the rheoscope and their diameters measured. Forward light scattering patterns were correlated with the red cell orientation mode. Light flux variations after flow onset or stop were measured, and the characteristic times of erythrocyte orientation and disorientation were assessed. The characteristic time of erythrocyte orientation in Orbit C = 0 is proportional to the inverse of the shear rate. The corresponding coefficient of proportionality depends on the suspending medium viscosity eta o. The disorientation time tau D, after flow has been stopped, is such that the ratio tau D/eta o is independent of the initial applied shear stress. However, tau D is much shorter than one would expect if pure Brownian motion were involved. The proportion of erythrocytes in orbit C = 0 was also measured. It was found that this proportion is a function of both the shear rate and eta o. At low values of eta o, the proportion increases with increasing shear rate and then reaches a plateau. For higher values of eta o (5 to 10 mPa s), the proportion of RBC in orbit C = 0 is a decreasing function of the shear stress. A critical transition between orbit C = 0 and parallel alignment was observed at high values of eta o, when the shear stress is on the order of 1 N/m2. Finally, the effect of altering membrane viscoelastic properties (by heat or diamide treatment) was tested. The proportion of oriented cells is a steep decreasing function of red cell rigidity.     

Lateral mobility of integral proteins in red blood cell tethers.

The red blood cell membrane is a complex material that exhibits both solid- and liquidlike behavior. It is distinguished from a simple lipid bilayer capsule by its mechanical properties, particularly its shear viscoelastic behavior and by the long-range mobility of integral proteins on the membrane surface. Subject to sufficiently large extension, the membrane loses its shear rigidity and flows as a two-dimensional fluid. These experiments examine the change in integral protein mobility that accompanies the mechanical phenomenon of extensional failure and liquidlike flow. A flow channel apparatus is used to create red cell tethers, hollow cylinders of greatly deformed membrane, up to 36-microns long. The diffusion of proteins within the surface of the membrane is measured by the technique of fluorescence redistribution after photobleaching (FRAP). Integral membrane proteins are labeled directly with a fluorescein dye (DTAF). Mobility in normal membrane is measured by photobleaching half of the cell and measuring the rate of fluorescence recovery. Protein mobility in tether membrane is calculated from the fluorescence recovery rate after the entire tether has been bleached. Fluorescence recovery rates for normal membrane indicate that more than half the labeled proteins are mobile with a diffusion coefficient of approximately 4 x 10(-11) cm2/s, in agreement with results from other studies. The diffusion coefficient for proteins in tether membrane is greater than 1.5 x 10(-9) cm2/s. This dramatic increase in diffusion coefficient indicates that extensional failure involves the uncoupling of the lipid bilayer from the membrane skeleton.     

利用高光谱参数反演水稻叶片类胡萝卜素含量

为了探讨快速、准确预测水稻(Oryza sativa)叶片类胡萝卜素(Car)含量的敏感光谱波段和光谱指数, 通过实施涉及不同年份、不同生态点、不同施氮水平和不同品种类型的4个田间试验, 于主要生育期同步测定了水稻顶部4张叶片的光谱反射率及Car含量, 系统分析了350-2 500 nm范围内任意两波段组合而成的比值(SR (λ1, λ2))、归一化(ND (λ1, λ2))及已报道的对Car敏感的光谱指数与水稻叶片Car含量间的定量关系。结果表明, 不同Car含量水平下水稻叶片光谱反射率存在着明显变化, 以绿光及红边波段对水稻叶片Car含量变化最为敏感。723 nm附近的波段与近红外波段的比值组合以及713 nm附近的波段与近红外波段的归一化组合可以较好地预测水稻叶片Car含量, 以SR (723, 770)和ND (770, 713)表现最好, 线性拟合R²分别达到0.897和0.898。基于独立的试验资料的检验表明, 预测值和实测值的拟合R²分别为0.856和0.858, 均方根差RMSE均为0.072, 平均相对误差RE分别为11.9%和12.0%, 表明SR (723,770)和ND (770, 713)可有效地估算水稻上部叶片的Car含量。     

Dynamic shear behavior of mandibular condylar cartilage is dependent on testing direction

Little information is available on the direction-dependency of shear behavior in mandibular condylar cartilage. Therefore, we tested the hypothesis that such a dependency of the dynamic shear properties is present in mandibular condylar cartilage. From each of 17 condyles, two cartilage-bone plugs were dissected and tested in a simple shear sandwich configuration under a compressive strain of 10%. Sinusoidal shear strain (frequency range: 0.01-10 Hz) was applied in the medio-lateral or antero-posterior direction with an amplitude of 1.0%, 2.0%, and 3.0%. The magnitudes of the dynamic shear moduli, as calculated from the resulting shear stress, were found to increase with applied frequency and the shear strain amplitude. The values |G*|, G' and G' for a medio-laterally applied shear were about 20-33% of those in the antero-posterior shear, although the loss tangent (elasticity/viscosity ratio) was almost the same. In conclusion, the present results clearly show the direction-dependent characteristic of the mandibular condylar cartilage in dynamic shear.     

Mechanical perturbation elicits a phenotypic difference between Dictyostelium wild-type cells and cytoskeletal mutants.

To determine the specific contribution of cytoskeletal proteins to cellular viscoelasticity we performed rheological experiments with Dictyostelium discoideum wild-type cells (AX2) and mutant cells altered by homologous recombination to lack alpha-actinin (AHR), the ABP120 gelation factor (GHR), or both of these F-actin cross-linking proteins (AGHR). Oscillatory and steady flow measurements of Dictyostelium wild-type cells in a torsion pendulum showed that there is a large elastic component to the viscoelasticity of the cell pellet. Quantitative rheological measurements were performed with an electronic plate-and-cone rheometer, which allowed determination of G', the storage shear modulus, and G", the viscous loss modulus, as a function of time, frequency, and strain, respectively. Whole cell viscoelasticity depends strongly on all three parameters, and comparison of wild-type and mutant strains under identical conditions generally produced significant differences. Especially stress relaxation experiments consistently revealed a clear difference between cells that lacked alpha-actinin as compared with wild-type cells or transformants without ABP120 gelation factor, indicating that alpha-actinin plays an important role in cell elasticity. Direct observation of cells undergoing shear deformation was done by incorporating a small number of AX2 cells expressing the green fluorescent protein of Aequorea victoria and visualizing the strained cell pellet by fluorescence and phase contrast microscopy. These observations confirmed that the shear strain imposed by the rheometer does not injure the cells and that the viscoelastic response of the cell pellet is due to deformation of individual cells.