Biorheology - Volume 44, issue 3

Authors: Stokes, Jason R. | Davies, Georgina A.

Article Type: Research Article

Abstract: The rheology of saliva is highly important due to its influence on oral health and physiochemical processes within the oral environment. While the rheology of human whole saliva (HWS) is considered important for its functionality, its measurement is often performed erroneously and/or limited to the viscosity at a single shear rate. To ensure accurate rheological measurements, it is necessary to test HWS immediately after expectoration and to apply a thin layer of surfactant solution around the rim of the rheometer plates so that protein adsorption is minimized at the air–liquid interface. It is shown for the first time that the …viscosity and viscoelasticity of HWS depends greatly upon the method of stimulation. Mechanical action stimulates slightly shear-thinning and relatively inelastic saliva, while acidic solutions (e.g. 0.25% citric acid) stimulate secretion of saliva that is highly elastic and shear-thinning. However, both acidic solutions and mechanical action stimulate similar volumes of saliva. For acid-stimulated saliva, the ratio of the primary normal stress difference to the shear stress is of order 100 and the viscosity at high shear rates is only marginally above that of water. This extremely high stress ratio for such a low viscosity fluid indicates that saliva's elastic properties dominate its flow behavior and may assist in facilitating lubrication within the oral cavity. It is anticipated that the variation in saliva rheology arises because the individual glands secrete saliva of different rheology, with the proportion of saliva secreted from each gland depending on the method of stimulation. The steady-shear rheology and linear viscoelasticity of HWS are described reasonably well using a FENE-P constitutive model and a 3-mode Maxwell model respectively. These models indicate that there are several long relaxation modes within saliva, possibly arising from the presence of large flexible macromolecules such as mucin glycoproteins. Show more

Keywords: Viscoelastic, viscosity, normal stress, mucin, glycoprotein, mucus, protein

Citation: Biorheology, vol. 44, no. 3, pp. 141-160, 2007

Authors: Zhao, Rui | Kameneva, Marina V. | Antaki, James F.

Article Type: Research Article

Abstract: Thrombosis is a common complication following the surgical implantation of blood contacting artificial organs. Platelet transport, which is an important process of thrombosis and strongly modulated by flow dynamics, has not been investigated under the shear stress level associated with these devices, which may range from tens to several hundred Pascal. The current research investigated platelet transport within blood under supra-physiological shear stress conditions through a micro flow visualization approach. Images of platelet-sized fluorescent particles in the blood flow were recorded within microchannels (2 cm × 100 μm × 100 μm). The results successfully demonstrated the occurrence of platelet-sized …particle margination under shear stresses up to 193 Pa, revealing a platelet near-wall excess up to 8.7 near the wall (within 15 μm) at the highest shear stress. The concentration of red blood cells was found to influence the stream-wise development of platelet margination which was clearly observed in the 20% Ht sample but not the 40% Ht sample. Shear stress had a less dramatic effect on the margination phenomenon than did hematocrit. The results imply that cell–cell collision is an important factor for platelet transport under supra-physiologic shear stress conditions. It is anticipated that these results will contribute to the future design and optimization of artificial organs. Show more

Keywords: Platelet margination, thrombosis, shear stress, artificial organs

Citation: Biorheology, vol. 44, no. 3, pp. 161-177, 2007

Authors: Suzuki, Yoji | Ohkubo, Nobutaka | Aoto, Mamoru | Maeda, Nobuji | Cicha, Iwona | Miki, Tetsuro | Mitsuda, Noriaki

Article Type: Research Article

Abstract: Erythrocytes are very susceptible to oxidative stress, having a high content of intracellular oxygen and hemoglobin. In the present study, exposure to oxidative stress resulted in a significant impairment of erythrocyte membrane functions, such as deformability and anion exchange. Band 3 protein, also known as anion exchanger-1, plays an important role in these two functions. We show that oxidative stress activated caspase-3 inside the erythrocytes, which resulted in band 3 protein cleavage. Interestingly, inhibition of the caspase-3 with its specific inhibitor not only suppressed the digestion of band 3 protein, but also blunted the functional damage to erythrocytes, such as …deformability and anion exchange, without changing the level of peroxidation of membrane lipids. These results provide experimental evidence that activation of caspase-3 plays an important role in the oxidative stress-induced impairment of membrane functions of erythrocytes. Show more

Keywords: Band 3, oxidative stress, erythrocyte deformation, anion exchange

Citation: Biorheology, vol. 44, no. 3, pp. 179-190, 2007

Authors: Pappu, Vijay | Bagchi, Prosenjit

Article Type: Research Article

Abstract: Hydrodynamic interaction between erythrocytes (RBC) and leukocytes (WBC) in a microvessel of size 20–40 micron, typical of a postcapillary venule, is studied using a two-dimensional computational model. The model is based on immersed boundary method, and it takes into consideration the particulate nature of blood by explicitly modeling individual blood cell, and cell deformation. Due to their highly flexible nature, RBC drift away from the wall and toward the center of a vessel creating a cell-free layer. It is shown here that the lateral motion of RBC is strongly affected in presence of a WBC, and is dependent on whether …the WBC is non-adherent or firmly adhered. When the WBC is non-adherent, some RBC, depending on their initial radial locations and vessel size, may be deflected closer toward the wall, resulting in a decrease in the cell-free layer. The apparent viscosity of the whole blood containing both RBC and WBC is computed, and shown to be much higher than that containing RBC only. The increased viscosity cannot be accounted for by the contribution due to WBC only. This observation is in agreement with a previous in vivo measurement. Here we show that the additional flow resistance is due to the decrease in the cell-free layer resulting from the WBC-RBC interaction. It can be accounted for by a two-layer model of blood when the reduced values of the cell-free layer thickness are used. When the WBC is firmly adhered, RBC easily move away from the wall, and the cell-free layer is not significantly changed. In such cases, the major contribution to whole blood viscosity comes from the WBC alone. The hydrodynamic interaction between WBC and RBC, though it exists, does not contribute significantly when WBC are adhered. Show more

Keywords: Microcirculation, hemorheology, erythrocyte deformation, leukocyte adhesion, computational fluid dynamics

Citation: Biorheology, vol. 44, no. 3, pp. 191-215, 2007

Article Type: Other

Citation: Biorheology, vol. 44, no. 3, pp. 217-220, 2007