Biorheology - Volume 34, issue 4-5

Authors: Suglhara-Seki, Masako | Skalakt, Richard

Article Type: Research Article

Abstract: To evaluate the force and torque acting on leukocytes attached to the vessel wall, we numerically study the flow field around the leukocytes by using rigid spherical particles adhered to the wall of a circular cylindrical tube as a model of adherent leukocytes. The adherent particles are assumed to be placed regularly in the flow direction with equal spacings, in one row or two rows. The flow field of the suspending fluid is analyzed by a finite element method applied to the Stokes equations, and the drag force and torque acting on each particle, as well as the apparent viscosity, …are evaluated as a function of the particle to tube diameter ratio and the particle arrangements. For two-row arrangements of adhered particles where neighboring particles are placed alternately on opposite sides of the vessel, the drag and the torque exerted on each particle are higher than those for single-row arrangements, for constant particle to tube diameter ratio and axial spacing between neighboring particles. This is enhanced for larger particles and smaller axial spacings. The apparent viscosity of the flow through vessels with adhered particles is found to be significantly higher than that without adhered particles or when the particles are freely floating through the vessels. Show more

Keywords: Leukocyte, Stokes flow, apparent viscosity, force, torque

DOI: 10.3233/BIR-1997-344-501

Citation: Biorheology, vol. 34, no. 4-5, pp. 249-260, 1997

Authors: Hofer, Michael | Perktold, Karl

Article Type: Research Article

Abstract: To investigate the particle migration effects and fluid-particle interaction occurring in the flow of highly concentrated fluid-particle suspensions, a numerical method has been developed for effective computer simulation in arbitrary axisymmetric geometries. In the mathematical flow model the suspension is treated as a generalized Newtonian fluid where the effective flow properties of the suspension (density and viscosity) are determined by the local volume fraction of the particles. The description of the particle motion is governed by a modified transport equation with diffusion coefficients accounting for the effects of shear-induced particle migrations. The strongly coupled system of flow and transport equations …is solved by applying the Galerkin finite element method and a velocity-pressure projection scheme. The numerical results in tube flow demonstrate strong particle migration towards the center of the tube and an increasing blunting of the velocity profiles which is in good agreement with an available analytical solution. In the case of flow through a stenosed tube model, particle concentration is lowest at the site of maximum constriction whereas a strong accumulation of particles can be seen in the recirculation zone downstream of the stenosis. Show more

Keywords: Fluid-particle suspension, computer simulation, lateral particle migration, concentrated systems

DOI: 10.3233/BIR-1997-344-502

Citation: Biorheology, vol. 34, no. 4-5, pp. 261-279, 1997

Authors: Fu, Guangyu | Zeng, Yanjun | Xia, Zhaoji | Lee, Jingping

Article Type: Research Article

Abstract: The aim of this study was to investigate the effects of a surgical tissue expansion procedure on the biomechanical features of the expanded soft tissues. In this procedure a silicone balloon “expander” is surgically inserted into a tissue and inflated. The tissue mass increases under the stretch of the expander. The increased tissue can then be used as an autologous source for the surgical reconstruction of organs. In this article, dog saphenous neurovascular bundle was used. Expanded saphenous nerves, arteries and veins were harvested and their biomechanical features and ultrastructural, histological changes were studied. The stress relaxation features, the continuous …spectrum of relaxation time, and the stress-strain relationship of expanded and control specimens were measured. Results show that within two or three weeks after placement of the expanders, the biomechanical properties of expanded saphenous nerves, arteries and veins began to deviate from those of their controls, and the differences between them were proportional to the volume of inflation; but when the expanding period was 15 weeks or longer, the properties of expanded specimens and their controls became close again. Histological study showed that the content of collagenous fibers in blood vessel walls decreased after expansion. The content of elastic fibers in blood vessel walls FITst increased, then returned to normal, and finally decreased. Ultrastructural studies showed that when elongated by 25–40%, the expanded nerves had well preserved axons and showed fewer smooth myelin sheaths only in the middle and distal part of the expansion. Show more

Keywords: Tissue expansion, biomechanical, histological, ultrastructural features, saphenous nerves, arteries, veins, stress relaxation

DOI: 10.3233/BIR-1997-344-503

Citation: Biorheology, vol. 34, no. 4-5, pp. 281-293, 1997

Authors: Rogunova, Marina A. | Blackwell, John | Jamieson, Alexander M. | Pasumar-Thy, Murali | Gerken, Thomas A.

Article Type: Research Article

Abstract: Rheological experiments have shown that canine submaxillary mucin (CSM) forms gels in aqueous solution at low ionic strength and in 6M GdnHCl. Examination of specimens of intact CSM and also its subunits prepared by reduction and carboxymethylation showed that the presence of lipid increases the gel-forming capability, probably as a result of enhancement of the intermolecular hydrophobic interactions. The rheological evidence for gelation is that substantially larger values of the oscillatory storage modulus, G’(ω ), and the dynamic complex viscosity, η ∗ ( ω ) , are observed for lipid-containing CSM. This is backed up …by electron micrographs of freeze fractured specimens, where we observe a network morphology in which the cross-links are formed as a result of non-bonded interactions between a number of CSM chains. The intermolecular interactions responsible for gelation probably involve hydrophobic association between the interdigitated oligosaccharides, and/or between the non-glycosylated regions of the protein core, and can occur even in a highly chao tropic medium (6M GdnHCl). In contrast to previous experiments with porcine submaxillary mucin and human tracheobronchial mucin, which form microphase-separated gels in aqueous solution, CSM solutions undergo macroscopic phase separation into polymer-rich (gel) and polymer-poor (sol) phases. These data point to stronger hydrophobic interactions in lipid-containing CSM. Show more

Keywords: Hydrophobic interactions, phase separation, gel formation

DOI: 10.3233/BIR-1997-344-504

Citation: Biorheology, vol. 34, no. 4-5, pp. 295-308, 1997

Authors: Thoumine, Olivier | Ott, Albrecht

Article Type: Research Article

Abstract: In order to achieve coordinated migration through extracellular matrix and endothelial barriers during metastasis, cancer cells must be endowed with specific structural and adhesive properties. In this context, comparison of the mechanical properties of transformed versus normal cells, on which little quantitative information is available, was the focus of this study. Normal human dermal fibroblasts and their SV40-transformed counterparts were analyzed using various manipulations. First, micropipet aspiration of suspended cells allowed calculation of a cortical tension (similar for normal and transformed cells), and an apparent viscosity (30% lower for transformed than for normal fibroblasts); in addition, transformed fibroblasts exhibited a …more fragile surface than their normal counterparts. Second, tangential ultracentrifugation of adherent cells demonstrated cellular elongation in the direction of the centrifu al field and the existence of critical forces for cell detachment, around 10−7 N: these were 1.6-fold greater for normal than for transformed cells. Finally, examination of the wrinkle patterns formed by cells plated on a deformable polydimethylsiloxane substrate, plus analysis of cell retraction caused by ATP treatment following detergent permeabilization showed that normal fibroblasts exhibited much more contractility than their transformed counterparts, which we characterized by a cell contraction rate. Such quantitative parameters which reveal differences in the mechanical behavior of normal and transformed cells may be used in the future as new markers of oncogenic transformation. Show more

Keywords: Micropipet, centrifugation, cell contraction, cytoskeleton, adhesion

DOI: 10.3233/BIR-1997-344-505

Citation: Biorheology, vol. 34, no. 4-5, pp. 309-326, 1997

Authors: Hansen, J.C. | Skalak, R. | Chien, S. | Hoger, A.

Article Type: Research Article

Abstract: Two models of spectrin elasticity are developed and compared to experimental measurements of the red blood cell (RBC) membrane shear modulus through the use of an elastic rmite element model of the RBC membrane skeleton. The two molecular models of spectrin are: (i) An entropic spring model of spectrin as a flexible chain. This is a model proposed by several previous authors. (ii) An elastic model of a helical coiled-coil which expands by increasing helical pitch. In previous papers, we have computed the relationship between the stiffness of a single spectrin molecule (K) and the shear modulus of a network …(µ), and have shown that this behavior is strongly dependent upon network topology. For realistic network models of the RBC membrane skeleton, we equate µ to micropipette measurements of RBCs and predict K for spectrin that is consistent with the coiled-coil molecular model. The value of spectrin stiffness derived from the entropic molecular model would need to be at least 30 times greater to match the experimental results. Thus, the conclusion of this study is that a helical coiled-coil model for spectrin is more realistic than a purely entropic model. Show more

Keywords: Molecular mechanics, cytoskeleton, erythrocytes, entropic spring, triple coiled-coil

DOI: 10.3233/BIR-1997-344-506

Citation: Biorheology, vol. 34, no. 4-5, pp. 327-348, 1997

Authors: Razavian, S.M. | Wenby, R.B. | Fisher, T.C. | Meiselman, H.J.

Article Type: Research Article

Abstract: The sedimentation rate (SR) of non-aggregated spherical particles in suspension was determined using an ultrasonic interferometry technique (Echo-Cell); this method is based on A-mode echography and measures the rate of formation of a sediment on a solid plate during settling. The particle accumulation rate, which is related to SR, is obtained from the interference of two waves reflected by two interfaces: one between the plate and the sediment and the other between the sediment and the suspension. Studies were carried out at 25°C using latex spheres of different diameters (7 to 20 µm) and densities (1.062 to 1.190 g/cm3 ) …suspended in distilled water at various volume fractions (1% to 5%). As anticipated by the Stokes model, linear relations were found between SR and both particle density and the square of particle radius. Experimental SR values decreased with increasing suspension particle concentration; these concentration effects were in good agreement with those predicted by the Steinour model. Our results thus serve to validate the theoretical aspects of the Echo-Cell method and suggest its usefulness as a tool for studies of RBC interaction and RBC aggregation. Show more

Keywords: Interferometry, sedimentation, spheres, Stokes, ultrasound

DOI: 10.3233/BIR-1997-344-507

Citation: Biorheology, vol. 34, no. 4-5, pp. 349-362, 1997

Authors: Cokelet, C.R.

Article Type: Article Commentary

DOI: 10.3233/BIR-1997-344-508

Citation: Biorheology, vol. 34, no. 4-5, pp. 363-367, 1997

Authors: Pries, Axel R. | Secomb, Timothy W.

Article Type: Reply

DOI: 10.3233/BIR-1997-344-509

Citation: Biorheology, vol. 34, no. 4-5, pp. 369-373, 1997

Authors: Baskurt, Oguz K. | Meiselman, Herbert J.

Article Type: Letter

DOI: 10.3233/BIR-1997-344-510

Citation: Biorheology, vol. 34, no. 4-5, pp. 375-376, 1997