Biorheology - Volume 31, issue 3

Authors: Vorob’ev, V.I. | Karpova, E.V. | Osipova, T.N.

Article Type: Research Article

Abstract: We studied the comparative hydrodynamic properties of chromatins differing in transcriptional activity and in linker DNA length. Chromatins were prepared from the nuclei of pigeon brain cortical neurones, rat thymus and sea urchin sperm. The sizes of linker DNA are 20, 50 and 100 base pairs (b.p.), respectively. Oligonucleosomes of different chain length were isolated from micrococcal nuclease-digested nuclei and studied by the method of sedimentation velocity. Rheological behavior of nucleosome oligomers depends on the number of nucleosomes in the chain and on the ionic strength in the range between 5 and 85 mM was analyzed on the basis of …a cylinder model using different hydrodynamic theories. It is shown that hydrodynamic properties of oligonucleosomes from all types of investigated chromatins at low ionic strength can be well described by the model of a three-dimensional zig-zag chain with a diameter of about 20 nm, the DNA packing ratio growing with the increase of linker DNA length. Increasing ionic strength induces condensation of the zig-zag-shaped chain of nucleosomes into a two-start double superhelix with densely packed nucleosomes. Linkers are arranged inside the superhelix, which is bent or folded into a loop, depending on its size. Show more

Keywords: Chromatin structure, sedimentation coefficient, nucleosome repeat length, histones, linker DNA

DOI: 10.3233/BIR-1994-31301

Citation: Biorheology, vol. 31, no. 3, pp. 221-234, 1994

Authors: Kobayashi, Y. | Okamoto, A. | Nishinari, K.

Article Type: Research Article

Abstract: Storage and loss moduli of hyaluronic acid solutions with different molecular weights were observed as a function of frequency in the presence of sugars and salts. The hyaluronic acid solutions of higher molecular weight (Mw > 17 × 106 ) fractions showed entanglement, whereas lower molecular weight fractions did not. For inducing the entanglement of molecular chains of hyaluronic acid, increasing the molecular weight of hyaluronic acid was more effective than increasing the concentration of the lower molecular weight fractions (Mw = 7.8 × 105 ). Glucose, fructose, galactose, and sucrose increased both storage and loss moduli, while NaCl, KCl …and CaCl2 decreased both moduli. It is suggested that sugars create hydrogen bonds and strengthen the transient network. Cations shield the electrostatic repulsion of hyaluronic acid molecules, and the polymer chains are shrunk into compact coils from expanded stiffened coils. Show more

Keywords: Hyaluronic acid, solution, molecular weight, viscoelasticity, entanglement, sugars, salts

DOI: 10.3233/BIR-1994-31302

Citation: Biorheology, vol. 31, no. 3, pp. 235-244, 1994

Authors: Deligianni, D.D. | Missirlis, Y.F. | Kafka, V.

Article Type: Research Article

Abstract: A statistical mathematical model is used to describe the viscoelastic behavior of trabecular bone from the description of its microstructure. Trabecular bone is regarded as an orthotropic composite material consisting of two phases: The trabeculae, modelled as a non-linear elastic material, and the marrow, modelled as a Maxwell element. The macroscopic constitutive equation contains, as parameters, the constants of the material phases’ constitutive equations, the respective volume fractions and parameters descriptive of the geometry of trabecular bone. With this model, the contribution of the marrow to the mechanical behavior of trabecular bone is determined and it is calculated that, under …a step load and at strain rate, 10 min−1 , the marrow can bear about 25% of the applied load. The constants of the material phases are also calculated from a series of stress-relaxation curves on trabecular bone specimens. It is concluded that the trabeculae display non-linear elastic behavior. Show more

Keywords: Trabecular bone, elastic constants, stress relaxation, viscoelasticity, structure

DOI: 10.3233/BIR-1994-31303

Citation: Biorheology, vol. 31, no. 3, pp. 245-257, 1994

Authors: van Gelder, J.M. | Nair, C.H. | Dhall, D.P.

Article Type: Research Article

Abstract: Thrombus formed under low shear conditions in the intravascular compartment consists of red cells enmeshed within a fibrin network framework. The permeability of the network determines the rate of molecular transport by convection. The effect of red cells on the permeability of the fibrin network was examined in networks developed from red cell suspensions in platelet-rich (PRP) and platelet-poor plasma (PPP). Red cell-rich networks developed in PRP were significantly more permeable than those developed in PPP. Network permeability decreased linearly with increase in hematocrit due to volume exclusion and cell surface hydraulic drag. The hydraulic resistance of the red cells …was similar in order of magnitude to that of the fibrin fibers. The hydraulic resistance was calculated to be dependent on the surface area of the red cells, as well as on red cell concentration. Calculation of red cell surface area from permeability (45–90 μ m2 ) was found to be lower than the known surface area (145 μ m2 ). From these studies, it is suggested that red cells entrapped within the network are aggregated. Aggregation is promoted by low shear plasma conditions during fibrin polymerization and by fibrin polymerization intermediaries. The degree of red cell aggregation regulates the hydraulic resistivity of the red cells, and the fibrin fiber structure regulates the hydraulic resistivity of the fibrin network. Both are significant determinants of the network permeability and, therefore, of molecular transport in thrombi. Show more

Keywords: Erythrocyte aggregation, fibrin, permeability, thrombosis

DOI: 10.3233/BIR-1994-31304

Citation: Biorheology, vol. 31, no. 3, pp. 259-275, 1994

Authors: Muralidharan, E. | Tateishi, N. | Maeda, N.

Article Type: Research Article

Abstract: The aggregation kinetics of erythrocytes is studied by using laser light scattering. Laser light is passed through a well mixed sample of blood and the forward-scattered light intensity is recorded continuously. During the process of aggregation and sedimentation under a gravitational field, erythrocytes are subjected to different orientations. The events of a single cell’s movement, formation of aggregates and their sedimentation produce a variation in scattered-light intensity. The mean intensity variation that bears this information is effectively employed to arrive at the kinetics of single cells, one-dimensional aggregates and three-dimensional aggregates during sedimentation. In addition to this, the time intervals …of different phases of aggregation and sedimentation are also measured. All these parameters are obtained for erythrocytes suspended in native plasma. Then, the results are compared with erythrocytes suspended in dextran (Dx) 70 and Dx 500. Show more

Keywords: Erythrocyte aggregation, sedimentation, aggregation kinetics, light scattering, dextran

DOI: 10.3233/BIR-1994-31305

Citation: Biorheology, vol. 31, no. 3, pp. 277-285, 1994

Authors: Long, M. | Wang, H.B. | Wu, Z.Z. | Wu, Y.P. | Sakanishi, A.

Article Type: Research Article

Abstract: We measured the volume fraction dependence of erythrocyte sedimentation for human red cells in autologous plasma while the volume fraction, Hct , ranges from 0.220 to 0.650. A modified electrophoretic instrument was employed to investigate the electric effect of an upward DC field on erythrocyte sedimentation at a constant source supply of V s = 60.0 ± 0.5 V . The sedimentation curves all coincided well with the sigmoidal type equation, l = l max / { 1 + ( t …50 / t ) n } , at V S = 0 , or 60.0 V. Here, lmax is the length of plasma level, l, when the time, t, tends to infinity; t50 is the elapsed time when the plasma level falls to lmax /2, and n is a constant (n > 0). A non-linear least-squares method was employed to fit experimental data. It was found that lmax decreased and t50 increased with the increase of Hct while n ranged from 1.53 to 3.95. The volume fraction dependence of sedimentation velocity, vmax , defined as the maximum slope of the sedimentation curve, fits well with an exponential-type curve, both at V S = 60.0 V and at V S = 0 V : v max = v S ( 1 − H ct ) exp ( − BH ct ) , where vs is the velocity at infinite dilution and B is a phenomenological parameter. In the range of H ct = 0.220 – 0.650 , vS and B are 326.1 mm/hr and 4.30, respectively, at V S = 60.0 V , while they are 130.4 mm/hr and 2.46, respectively, at V S = 0 V . Show more

Keywords: Erythrocyte sedimentation rate, volume fraction dependence, human red cell, plasma, DC electric field

DOI: 10.3233/BIR-1994-31306

Citation: Biorheology, vol. 31, no. 3, pp. 287-295, 1994

Authors: Kameneva, M.V. | Antaki, J.F. | Watach, M.J. | Borovetz, H.S. | Kormos, R.L.

Article Type: Research Article

Abstract: We studied the effect of relatively high dosages of heparin (25–150 U/ml) on some rheological parameters of donor blood. It was found that heparin increased the erythrocyte sedimentation rate (ESR) and low shear blood viscosity at all concentrations studied. The increase of these parameters indicates an elevation in RBC aggregation. In all samples with a heparin concentration of 100 U/ml, the average ESR was increased by approximately 75% (p < 0.001); whole blood viscosity increased under shear rate, γ ˙ = 0.277 sec − 1 , by approximately 30% (p < 0.001). …Since bolus injection of heparin may result in transient high local concentration, these results suggest a possible additional adverse effect to the well known heparin effect on platelet aggregation. Show more

Keywords: Heparin, erythrocyte aggregation, blood viscosity

DOI: 10.3233/BIR-1994-31307

Citation: Biorheology, vol. 31, no. 3, pp. 297-304, 1994

Article Type: Announcement

DOI: 10.3233/BIR-1994-31308

Citation: Biorheology, vol. 31, no. 3, pp. 305-305, 1994

Article Type: Other

DOI: 10.3233/BIR-1994-31309

Citation: Biorheology, vol. 31, no. 3, pp. 307-308, 1994