In vitro hemorheological effects of parenteral agents used in peripheral arterial disease

Biro, Katalin,Sandor, Barbara,Toth, Andras,Koltai, Katalin,Papp, Judit,Rabai, Miklos,Toth, Kalman,Kesmarky, Gabor 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.2

Peripheral arterial disease (PAD) is a frequent manifestation of systemic atherosclerosis. In PAD hemorheological parameters were defined as risk factors in a number of studies and several therapeutic agents were tried in these conditions. Our study aims to investigate and compare the in vitro hemorheological effects of various drugs generally used in the parenteral treatment of intermittent claudication and critical limb ischemia. Blood samples of healthy male volunteers were incubated with iloprost, alprostadil, pentoxifylline, sulodexide or pentosan polysulfate at calculated therapeutic serum concentration. Hematocrit (Hct) was determined by microhematocrit centrifuge. Plasma and apparent whole blood viscosities (WBV) were evaluated by capillary viscometer. Red blood cell aggregation was measured by LORCA (laserassisted optical rotational cell analyzer) aggregometer, and LORCA ektacytometer was used for measuring erythrocyte deformability at $37^{\circ}C$. Iloprost, alprostadil, and pentoxifylline incubation did not have any significant effect on plasma and apparent WBV. Elongation index increased in samples incubated with alprostadil at low shear stresses 0.95 and 0.53 Pa (p < 0.05). Sulodexide significantly improved WBV and Hct/WBV ratio (p < 0.05). Incubation with pentosan polysulfate resulted in higher WBV, lower Hct/WBV ratio and deterioration in the aggregation parameters (p < 0.05). Sulodexide may have beneficial effect on a macrorheological parameter; alprostadil may improve a microrheological parameter. Hemorheological alterations could be important in PAD patients with hampered vasodilator capacity.

On the yield stress of complex materials

F. Calderas,E. E. Herrera-Valencia,A. Sanchez-Solis,O. Manero,L. Medina-Torres,A. Renteria,G. Sanchez-Olivares 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.4

In the present work, the yield stress of complex materials is analyzed and modeled using the Bautista-Manero-Puig (BMP) constitutive equation, consisting of the upper-convected Maxwell equation coupled to a kinetic equation to account for the breakdown and reformation of the fluid structure. BMP model predictions for a complex fluid in different flow situations are analyzed and compared with yield stress predictions of other rheological models, and with experiments on fluids that exhibit yield stresses. It is shown that one of the main features of the BMP model is that it predicts a real yield stress (elastic solid or Hookean behavior) as one of the material parameters, the zero shear-rate fluidity, is zero. In addition, the transition to fluid-like behavior is continuous, as opposed to predictions of more empirical models.

Flow of Newtonian and non-Newtonian fluids in a concentric annulus with a rotating inner cylinder

김영주,한상목,우남섭 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.2

We examine the characteristics of helical flow in a concentric annulus with radii ratios of 0.52 and 0.9, whose outer cylinder is stationary and inner cylinder is rotating. Pressure losses and skin friction coefficients are measured for fully developed flows of water and a 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), when the inner cylinder rotates at the speed of 0~62.82 rad/s. The transitional flow has been examined by the measurement of pressure losses to reveal the relation between the Reynolds and Rossby numbers and the skin friction coefficients. The effect of rotation on the skin friction coefficient is largely changed in accordance with the axial fluid flow, from laminar to turbulent flow. In all flow regimes, the skin friction coefficient increases due to inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, becomes smaller as the Reynolds number increases for the transitional flow regime, and gradually approaches zero for the turbulent flow regime. The value of skin friction coefficient for a radii ratio of 0.52 is about two times larger than for a radii ratio of 0.9. For 0.4% CMC solution, the value of skin friction coefficient for a radii ratio of 0.52 is about four times larger than for a radii ratio of 0.9.

Viscoelasticity of coagulated alumina suspensions

Ashish Kumar,Anthony D. Stickland,Peter J. Scales 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.2

The solid-to-liquid transition of a model coagulated alumina suspension at concentrations above the gel point was investigated to explore the critical parameter for describing network failure under shear forces. Static (creep and creep-recovery) and dynamic (small and large amplitude oscillatory) shear experiments were combined to examine shear softening in these systems and time-based dependence in the yielding dynamics. The particulate network structure exhibits failure and viscous dissipation under creep and oscillatory shear tests at stress values well below the conventionally defined yield stress. Results from strain recovery tests highlight a time-dependence for failure, where only partial recovery of strain energy was possible once a specific duration of creep was surpassed. The system was observed to fail at a common strain value across all methods of rheology testing. These results are self-consistent, showing a clear transition from the linear to non-linear viscoelastic region for a coagulated material under shear stress. It provides the starting point to incorporate mechanical viscoelastic models to extract time constants for yielding behaviour. This work also presents one of the first reported LAOS and creep results for particulate suspensions using a vane geometry.

Electric-field-induced deformation of a chiral liquid-crystal elastomerin smectic A phase

Yuki Aburaya,나양호,Hiroshi Orihara,Kazuyuki Hiraoka 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.2

Mechanical response to electrical stimulus has been investigated in a chiral smectic A elastomer. During the application of electric field, the two-dimensional strain tensor was precisely measured by tracking fluorescent beads dispersed on the film. It was found that the shear strain is dominantly induced by the electric field and proportional to the applied electric field.

A numerical study on the effect of hematocrit on hemodynamic characteristics in arteriovenous graft

김지태,성건혁,유홍선 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.3

Stenosis at an arteriovenous graft is related with the critical ranges of hemodynamic characteristics. Hematocrithas a significant effect on the blood viscosity. During hemodialysis, hematocrit is changed by the dialysismachine. The effect of hematocrit on hemodynamic characteristics is investigated by numerical study. A multiphase non-Newtonian blood model was used to analyze the changes of hematocrit. The hematocritof blood flows at injection needle changed 40%, 50%, and 60%. As a result, the blood viscosity increasedby about 6% point. Also, the high wall shear stress region (over 3 Pa) increased about 6% point when thehematocrit at the vein anastomosis increased by about 2% point. When the hematocrit increased by 4% atthe vein anastomosis, an extremely high wall shear stress region (over 7.5 Pa) increased by 3 times. Thus,the variation of hematocrit should be predicted using a multiphase blood model to avoid the critical rangeof wall shear stress when hematocrit changes regionally.

Operability window of slot coating using viscocapillary model forCarreau-type coating liquids

Hyun Jung Koh,Ilyoung Kwon,정현욱,Jae Chun Hyun 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.2

Based on the simplified viscocapillary models for Newtonian and power-law coating liquids reported in Lee et al. (2011a), the one-dimensional (1-D) viscocapillary model for Carreau-type liquids containing zeroshear viscosity information has been developed for constructing the operability window in slot coating. Velocity distribution and position of upstream meniscus were numerically solved to determine onsets of leaking and bead break-up defects. The results obtained by 1-D model are quantitatively corroborated by two-dimensional (2-D) fluent calculations.

Dynamic measurement of stress optical behavior of three amorphous polymers

Inki Min,Kyunghwan Yoon 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

In the present study, rheo-optical and mechanical properties of three amorphous polymers, i.e., PS (polystyrene), PC(polycarbonate) and COC(cyclo olefin copolymer), widely used for optical products have been investigated. Accurate measurement of stress optical coefficients and elastic modulus data across the glass transition region are essential for predicting optical anisotropy in many injection molded optical products like pickup lenses and waveguide in LCD module since the final products have both flow and thermal history from the melt to glass. To obtain stress optical behavior in wide range of frequency and temperature including rubbery, glassy and glass transition regime, frequency sweep tests with extensional bar and shear sandwich tools were undertaken. As a result, glassy and melt extreme values of stress optical coefficient of PS and PC were evaluated as well as master plots in wide frequency region. The sign change of stress optical coefficient was shown clearly for PS as the frequency increased. On the other hand, the sign of stress optical coefficient over the whole frequency region is always positive for PC. For COC's of different composition, even though the glass transition temperature can vary, the stress optical coefficient of COC's with different composition stays almost constant at two extremes

Influence of viscosity modifying admixtures on the rheologicalbehavior of cement and mortar pastes

R. Bouras,A. Kaci,M. Chaouche 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

The influence of Viscosity-modifying admixtures (VMA) dosage rate on the steady state rheological properties, including the yield stress, fluid consistency index and flow behaviour index, of cementitious materials is considered experimentally. The investigation is undertaken both at cement paste and mortar scales. It is found that the rheological behaviour of the material is in general dependent upon shear-rate interval considered. At sufficiently low shear-rates the materials exhibit shear-thinning. This behaviour is attributed to flow-induced defloculation of the solid particles and VMA polymer disentanglement and alignment. At relatively high shear-rates the pastes becomes shear-thickening, due to repulsive interactions among the solid particles. There is a qualitative difference between the influence of VMA dosage at cement and mortar scales: at cement scale we obtain a monotonic increase of the yield stress, while at mortar scale there exists an optimum VMA dosage for which the yield stress is a minimum. The flow behaviour index exhibit a maximum in the case of cement pastes and monotonically decreases in the case of mortars. On the other hand, the fluid consistency index presents a minimum for both cement pastes and mortars.

Peristaltic flow of a Casson fluid in an annulus

P. Nagarani,A. Lewis 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

Peristaltic transport of a non-Newtonian fluid through the annular gap between two coaxial tubes is studied. We assumed that the inner tube is rigid whereas the outer tube has sinusoidal wave travelling down its wall. We modelled the flowing fluid as a Casson fluid to study the combined effects of yield stress (plug width) and annular gap on peristaltic transport. The flow is investigated in a wave frame of reference moving with velocity of the wave under long wavelength and low Reynolds number assumption. The expressions for velocity, stream function, pressure rise, flow rate and frictional force on inner and outer wall are obtained. Results are shown graphically and discussed in the results and discussion section. It is observed that yield stress and annular gap both have significant impact on the pressure rise, frictional resistance on the walls and on the formation and variation of trapped bolus.