Biorheology - Volume 34, issue 2

Authors: Müller, G.H.

Article Type: Research Article

Abstract: This study examines the relative contributions of the cytoplasmic and membranous compartments to the shear-induced elongation of single red blood cells (RBC). The mechanical properties of the cell membrane of normal human RBC were altered by controlled heat treatment (HT) (48°C for 1, 5 and 9 min). Using RBC transformed by conversion of intracellular hemoglobin to methemoglobin with nitrite as the oxidizing agent, a concomitant modification of cytosolic rheological properties was achieved by the same HT procedure. On exposure to heat, the viscosity of the methemoglobin solutions increased considerably. Cell elongation was measured in Dextran 60 suspensions sheared in a …cone and plate rheoscope. Normal cells after 5 min of HT, and transformed cells after 1 min of HT yielded a two phase index of elongation curve which had a zero value within the lower shear rate range. Consequently, two indices of stiffening were introduced. One characterized the shear rate of transition from the zero value to the second inclined portion of the elongation curve. This index related to those cells that were oriented in the flow field but were not elongated. The other index characterized the maximum elongation at maximal shear rate in the rheoscope. In spite of the different kinematic states of cells described by the above two indices, identical rates of stiffening, as measured by the critical shear rate at which elongation sets in, or by the elongation parameter, with time of HT, were observed for normal and transformed cells. Further, transformed cells were stiffer than normal cells throughout the time of HT. These results may be explained by assuming that methemoglobin (MetHb) was bound to the endoface of the erythromembrane. The contribution of cytosolic dissipation of energy to cell elongation appears to be small. Show more

Keywords: Human red blood cell, rheoscope, cytosol, membrane, hemoglobin, methemoglobin, heat treatment

DOI: 10.3233/BIR-1997-34201

Citation: Biorheology, vol. 34, no. 2, pp. 85-98, 1997

Authors: Mazeron, P. | Muller, S. | El Azouzi, H.

Article Type: Research Article

Abstract: In this study, sharp small-angle light scattering (SALS) images of erythrocytes under increasing shear stresses in a Couette flow were obtained, and accurate measurements of the angular positions of the two first minima and maxima have been carried out. The deformed cells were assumed to be three-axis ellipsoids of constant volume for all shear stresses. Application of the Physical Optics Approximation (POA) then permitted the determination of the cell dimensions as a function of the applied shear stress. Our results agree with determinations obtained by other methods.

Keywords: Erythrocytes, deformability, light scattering, ellipsoids, small-angle light-scattering patterns

DOI: 10.3233/BIR-1997-34202

Citation: Biorheology, vol. 34, no. 2, pp. 99-110, 1997

Authors: Lee, D. | Chiu, Y.L. | Jen, C.J.

Article Type: Research Article

Abstract: In the present study, the data of the initial adhesion of platelets onto the wall of a flow chamber with an obstacle in steady human blood flows were obtained. The flowfields and the distribution of stress-related factors were simulated numerically by a finite volume method and the fluid dynamic effect on the platelet adhesion is discussed. In addition to the wall shear effect, the normal stress effect was also taken into account. A parameter Vn/|Vt| was devised to assess the combined effect of both shear and normal forces in platelet adhesion. It was found that the peak adhesion occurred next …to, but not on, the impingement point on the obstacle where the value of Vn/|Vt| was negative. In these regions, direct impact played a major role in platelet adhesion. On the other hand, near the separation point before the obstacle where Vn/|Vt| was insignificant, the mechanism was believed to be different from that in the direct impact region. Denser adhesion there might be caused by the accumulation and frequent collision of particles due to flow retardation and/ or detour of the flow path. Interestingly, relatively low adhesion was found inside the recirculation regions. These results show that the normal stress effect (impingement) should be considered in platelet adhesion in addition to the shear effect. Show more

Keywords: Platelet adhesion, flow chamber, hemodynamic stresses

DOI: 10.3233/BIR-1997-34203

Citation: Biorheology, vol. 34, no. 2, pp. 111-126, 1997

Authors: Peters, G.W.M. | Meulman, J.H. | Sauren, A.A.H.J.

Article Type: Research Article

Abstract: This paper deals with the mechanical characterization of brain tissue which behaves a., a viscoelastic material. We focus on the linear viscoelastic behavior, which should apply for small strains at any strain rate, and demonstrate the applicability of the time/temperature superposition principle. This principle allows the opportunity to extend the range of shear rates for which the material is characterized, and makes the results applicable to impact conditions. This characterization of the linear behavior forms the basis for a further nonlinear characterization of the tissue.

Keywords: Brain tissue, viscoelasticity, time/temperature superposition principle, dynamic modulus, relaxation modulus

DOI: 10.3233/BIR-1997-34204

Citation: Biorheology, vol. 34, no. 2, pp. 127-138, 1997

Authors: Lanel, B. | Barthès-Biesel, D. | Regnier, C. | Chauvé, T.

Article Type: Research Article

Abstract: Wound healing is promoted by dressings that maintain a moist environment. Specifically, hydrocolloid dressings allow excess fluid to escape without permitting wound desiccation. However, the fluid handling capacity of hydrocolloid dressings depends on many factors such as the physicochemical properties of the gel formulation, and the design of the dressing. We measured the moisture uptake kinetics of different hydrocolloid dressings by placing the gel side of a sample in contact with water. The time evolution of the thickness was measured by means of a video camera linked to a computer. The theory of Tanaka and Fillmore (1979) was used to …predict the kinetics of uniaxial swelling of a cylindrical gel sample. The model allows to associate to an experimental curve a total thickness increase hf - h0 (where hf and h0 are respectively the final and initial thickness) and a characteristic time τ . The model also relates hf - h0 and τ to the physicochemical composition of the dressing, and to the initial thickness h0 . The influence of h0 is discussed by means of experiments performed on dressings with different initial thickness. Show more

Keywords: Gels, kinetics of swelling, hydrocolloid dressings, absorption of liquid

DOI: 10.3233/BIR-1997-34205

Citation: Biorheology, vol. 34, no. 2, pp. 139-153, 1997