Biorheology - Volume 33, issue 4-5

Authors: Suh, J.-K.

Article Type: Research Article

Abstract: To study the effect of dynamic mechanical force on cartilage metabolism, many investigators have applied a cyclic compressive load to cartilage disc explants in vitro. The most frequently used in vitro testing protocol has been the cyclic unconfined compression of articular cartilage in a bath of culture medium. Cyclic compression has been achieved by applying either a prescribed cyclic displacement or a prescribed cyclic force on a loading platen placed on the top surface of a cylindrical cartilage disc. It was found that the separation of the loading platen from the tissue surface was likely when a prescribed cyclic displacement …was applied at a high frequency. The purpose of the present study was to simulate mathematically the dynamic behavior of a cylindrical cartilage disc subjected to cyclic unconfined compression under a dynamic force boundary condition protocol, and to provide a parametric analysis of mechanical deformations within the extracellular matrix. The frequency-dependent dynamic characteristics of dilatation, hydrostatic pressure and interstitial fluid velocity were analyzed over a wide range of loading frequencies without the separation of the loading platen. The result predicted that a cyclic compressive force created an oscillating positive-negative hydrostatic pressure together with a forced circulation of interstitial fluid within the tissue matrix. It was also found that the load partitioning mechanism between the solid and fluid phases was a function of loading frequency. At a relatively high loading frequency, a localized dynamic zone was developed near the peripheral free surface of the cartilage disc, where a large dynamic pressure gradient exists, causing vigorous interstitial fluid flow. Show more

Keywords: Articular cartilage, cyclic loading, unconfined compression

DOI: 10.3233/BIR-1996-334-501

Citation: Biorheology, vol. 33, no. 4-5, pp. 289-304, 1996

Authors: Hughes, P.E. | Shortland, A.P. | How, T.V.

Article Type: Research Article

Abstract: The motion of guanine particles was recorded by video to visualize transitional flow phenomena in models of a proximal side-to-end anastomosis. Close examination of successive video fields revealed that above a critical Reynolds number, particles were periodically shed into the graft from a vortex situated near the anastomosis heel, and this disturbed the flow patterns in the graft causing vortex shedding to occur near to the toe of the anastomosis. The images clearly demonstrated that periodic flow structures propagated distally along the graft for over 15 tube diameters from the proximal anastomosis. The frequency of the vortex shedding was found …to increase with Reynolds number. Under pulsatile conditions, the primary vortex at the heel of the anastomosis became unstable during the deceleration phase of the flow cycle and particles were shed downstream into the graft. Although it was possible briefly to observe the characteristic banded structure in the bypass graft, the flow patterns were highly three-dimensional and were quickly broken up by the accelerating flow. Dynamic flow visualization using guanine particles was found to be a complementary technique to particle tracer flow visualization and was highly effective in identifying transitional flow phenomena and the mass transport mechanisms associated with them. Show more

Keywords: Flow visualization, vascular graft, anastomosis angle, haemodynamics

DOI: 10.3233/BIR-1996-334-502

Citation: Biorheology, vol. 33, no. 4-5, pp. 305-317, 1996

Authors: Al-Assaf, S. | Meadows, J. | Phillips, G.O. | Williams, P.A.

Article Type: Research Article

Abstract: The shear and extensional viscosity characteristics have been compared for hyaluronan and two samples of a cross-linked derivative, hylan, of different molecular weights. While shear thinning behavior was observed for all systems in shear flow, strain thickening was observed in extensional flow for the relatively dilute systems. However, there was a progressive transition to shear thinning behavior as the polymer concentration was increased. It is evident from the results that the shear flow techniques alone provide an incomplete picture of the rheological properties of these materials and that extensional flow characteristics are potentially dominant. For example, at relatively high deformation …rates of 500 s-1 and above, our results show that the extensional viscosities of aqueous solutions of the various polymers are at least two orders of magnitude greater than their corresponding shear flow viscosities. The incremental differences in viscosity with concentration increased with increasing molecular mass of the polymers and were greater in exensional flow than shear flow. These results demonstrate that the dynamic network structure formed by the higher molecular mass hylans offer potentially better physical and mechanical properties for viscosupplementation of diseased osteoarthritis joints compared with the parent hyaluronan. Show more

Keywords: Extensional viscosity, molecular weight, hylan, hyaluronan, viscosupplementation, viscoelasticity

DOI: 10.3233/BIR-1996-334-503

Citation: Biorheology, vol. 33, no. 4-5, pp. 319-332, 1996

Authors: Bäumler, H. | Donath, E. | Krabi, A. | Knippel, W. | Budde, A. | Kiesewetter, H.

Article Type: Research Article

Abstract: A theoretical description of polymer depletion layers near smooth and hairy surfaces is developed and used for interpretation of experiments. Electrophoretic mobility measurements of human red blood cells and platelets in aqueous electrolyte solutions were performed in the presence of dextran (MW = 70 kD) to study the interaction of dextran with the cell surface. The electrophoretic mobility in the presence of dextran was considerably larger than expected from the viscosity. This behavior was interpreted as evidence for the existence of a polymer depletion layer. Depending on ionic strength, depletion layer thicknesses ranging from 2.9 to 4.4 nm were …found. The dextran concentration at the outer border of the glycocalyx was only 10% of the bulk value. One cannot exclude the possibility that this small amount reflected adsorption. In the case of platelets, the degree of the mobility reduction depended on ionic strength. Depletion of dextran from the platelet surface apparently became smaller with decreasing ionic strength. This indicated a more complex pattern of interaction of dextran with the platelet surface than with the RBC surface. Both adsorption and polymer penetration into the glycocalyx were discussed quantitatively. It was concluded that ionic strength-dependent penetration of dextran into the hairy layer is more likely than ionic strength dependent adsorption changes. As in the case of red cells, some adsorption of dextran might be present. Show more

Keywords: Dextran adsorption, depletion layer, electrophoretic mobility, platelets, RBC

DOI: 10.3233/BIR-1996-334-504

Citation: Biorheology, vol. 33, no. 4-5, pp. 333-351, 1996

Authors: Petrov, V.C. | Edissonov, I.

Article Type: Research Article

Abstract: The well-known S-shaped settling curves are obtained as solutions of an autonomic dynamical system deduced mathematically from the generalized Stokes formula, the blood volume conservation law, and the Smoluchowski theory of particle coagulation. Numerical computations and parametric analysis of the deduced two nonlinear differential equations for the plasma zone thickness and aggregate size are given. It is shown that the model presented makes it possible, on the basis of experimentally recorded sedimentation curves and aggregate size growth, to identify quantitatively the values of the essential physical parameters of the coupled processes of erythrocyte aggregation and sedimentation. This method of identification …could be used as a diagnostic test in hematological laboratories. Show more

Keywords: Aggregation kinetics, erythrocyte sedimentation, dynamical system, system identification, root-mean-square criterion

DOI: 10.3233/BIR-1996-334-505

Citation: Biorheology, vol. 33, no. 4-5, pp. 353-364, 1996

Authors: Weng, X. | Cloutier, C. | Pibarot, P. | Durand, L.-G.

Article Type: Research Article

Abstract: Erythrocyte aggregation levels in pig, horse, sheep, and calf blood samples were investigated and compared to that of normal human blood. The aggregation kinetics and adhesive forces between red cells, and an index of structure of the aggregates were determined with an erythroaggregameter (Regulest, France) at constant hematocrit (0.40 l/l) and temperature (37° C). The adhesive forces and the index of structure in pig blood were close to those of normal human blood. The results for horse blood showed a very high level of aggregation kinetics and adhesive forces between red cells. For sheep and calf blood, little erythrocyte aggregation was …found. To simulate different levels of red cell hyperaggregation in humans, a volume of horse plasma was replaced by isotonic NaCl in different proportions (5 to 40% V/V). The kinetics of rouleaux formation and especially the adhesive forces between erythrocytes were systematically decreased, while the index of structure was raised with increasing concentrations of isotonic NaCl. By replacing the porcine plasma with isotonic NaCl, normal and hypoaggregating levels of human red cells were simulated. The aggregation kinetics and the adhesive forces were reduced and the index of structure was raised when the concentration of isotonic NaCl was increased. In summary, large differences in the aggregation parameters were found between mammals. This study also showed that different human erythrocyte aggregation levels can be simulated by diluting the concentration of plasma proteins in equine and porcine bloods. Show more

Keywords: Erythrocyte aggregation, animal blood models, laser light erythroaggregameter, aggregation kinetics, adhesive forces, index of structure of the aggregates

DOI: 10.3233/BIR-1996-334-506

Citation: Biorheology, vol. 33, no. 4-5, pp. 365-377, 1996

Authors: Lindmark, K. | Engström, K.G.

Article Type: Research Article

Abstract: At flow onset the blood filtration rate accelerates to a steady state, this may affect the interpretation of red blood cell (RBC) filterability. We studied the acceleration of flow while the pressure is built up across the filter to analyse effects of various hematocrits and RBC rigidity by glutaraldehyde (GA) hardening. This was analysed by a new filtration system with high time resolution and unlimited filtration volume. The system uses a digital balance that samples the accumulated weight (e.g., filtration rate through 5 µm Nuclepore membranes) with on-line computer communication. The filtration is computer controlled via a pneumatic valve. White …blood cells (WBC) were removed prior to filtration by a WBC-eliminating filter to avoid clogging artifacts. When flow is initiated a steady state is reached at 0.3–0.4 s. This timing was also tested and confirmed by a video monitoring technique of filtration flow into a horizontal pipette. The digital balance has a mathematical function to reduce the effects of vibration noise; when this function was activated the apparent acceleration was retarded to 1.2 s. With any of these techniques the steady state timing did not vary with the hematocrit, however, the volume of filtered suspension during acceleration varied with both the hematocrit and the GA hardening (p < 0.001). Extrapolation to yield the initial filtration rate from the relative flow curve (RBC suspension divided by buffer flow) varied depending on if the acceleration phase was included or not. In the most unfavourable situation, with GA-hardened RBC, this difference was 340% (p < 0.01). The slope to calculate clogging rate was affected in a similar way. Moreover, with the most GA-hardened RBC a delay in flow onset was observed with this technique. The acceleration phenomenon may cause artifacts in systems employing volume-derived filtration kinetics because of fixed volumes of filtrated medium. Show more

Keywords: Erythrocyte aggregation, animal blood models, laser light erythroaggregameter, aggregation kinetics, adhesive forces, index of structure of the aggregates

DOI: 10.3233/BIR-1996-334-507

Citation: Biorheology, vol. 33, no. 4-5, pp. 379-395, 1996

Authors: Häusler, K. | Reinhart, W.H. | Schaller, P. | Dual, J. | Goodbread, J. | Sayir, M.

Article Type: Research Article

Abstract: A newly designed type of oscillating viscometer is described. The viscometer consists of either a tube or a rod oscillating at a resonance frequency with amplitudes in the micro- and nanometer range. A fluid flowing through the tube or surrounding the rod damps the torsional oscillations. The increase in the damping depends on the viscosity of the fluid and is used to determine viscosity. It was found that viscosity measurements are feasible during blood flow. This new type of viscometer may be useful to the study of biophysical properties of blood at the wall surface during flow and give new …insights into blood flow. The device allows direct viscosity measurement on blood directly as it is drawn from the vein through the tube without any anticoagulant. Show more

Keywords: Blood, viscosity

DOI: 10.3233/BIR-1996-334-508

Citation: Biorheology, vol. 33, no. 4-5, pp. 397-404, 1996

Article Type: Abstract

DOI: 10.3233/BIR-1996-334-509

Citation: Biorheology, vol. 33, no. 4-5, pp. 405-435, 1996

Article Type: Other

DOI: 10.3233/BIR-1996-334-510

Citation: Biorheology, vol. 33, no. 4-5, pp. 437-438, 1996