Biorheology - Volume 38, issue 5-6

Authors: Pennati, Giancarlo

Article Type: Research Article

Abstract: The umbilical cord is a complex and fascinating structure that connects the fetus to the placenta and encases the umbilical vessels. The response of its tissues to mechanical loading due to fetal movements and uterine contractions is not well understood. The aim of this study is the evaluation of the mechanical properties of the main components of the human umbilical cord. Fresh umbilical cord specimens were collected from neonates born at term of the gestation and submitted to compliance tests. Furthermore, uniaxial tensile and stress‐relaxation tests were performed on samples of umbilical vein and Wharton's jelly. Both materials exhibited nonlinear …stress–strain response with increasing strain, increasing the elastic modulus (Ehigh about 10–20 times Elow ) and significant viscoelastic behavior. In addition, anisotropy of the vein was observed. Although the circumferential properties of the vein (mean Ehigh about 2.4 MPa) were similar to those after birth, the longitudinal stiffness of both materials was higher (mean Ehigh over 10 MPa) and comparable to that of the ligaments. These findings suggest a mechanism of protection acting against excessive elongations of the cord, which could cause undue restriction of the umbilical vessel area and interference with the fetal blood circulation. Show more

Citation: Biorheology, vol. 38, no. 5-6, pp. 355-366, 2001

Authors: Zeng, Yanjun | Huang, Kun | Xu, Chuanqing | Zhang, Jing | Sun, Guangci

Article Type: Research Article

Abstract: This study investigated the changes in biorheological characteristics of skin after expansion. Expanders were implanted into the back of eight adult dogs, and after an eight‐week expansion the expanded and the non‐expanded control skins were transferred to an adjacent site. The expanded specimens and their controls were obtained at 3, 6, 12 and 24 weeks after transfer, and their biorheological characteristics and histological changes were studied. The characteristics of the stress–relaxation, the stress–strain relationship and tensile strength of the expanded and control specimens were measured. The tests demonstrated that during the initial stage after transfer, the biorheological properties of experimental …specimens differed significantly from those of their controls. However, the differences between expanded and control specimens began to lessen gradually with increasing recovery time. When the recovery time reached 24 weeks or longer, the experimental skin exhibited the same mechanical properties as the control skin. Histological examination of expanded specimens showed thickened epidermis and thinned dermis. But there were no significant histological differences between expanded skins and their controls after 24 weeks. Show more

Keywords: Skin expansion, biorheological characteristics, stress relaxation, stress–strain, tensile strength, histological examination

Citation: Biorheology, vol. 38, no. 5-6, pp. 367-378, 2001

Authors: Mo, Yunqian | Nishinari, Katsuyoshi

Article Type: Research Article

Abstract: The extensional viscosity and the steady shear viscosity of sodium type hyaluronan (NaHA) in water with sodium chloride and/or sucrose and in DMSO solvent were measured. The extensional viscosities for HA in aqueous solution (0.05, 0.1, 0.3 w/v%) were constant at lower extensional rates, and then became strain thinning above a critical extensional rate. However, on adding sodium chloride, the extensional viscosity decreased and became strain thickening at higher extensional rates. Sodium ions shield the electrostatic repulsion between carboxyl residues of HA molecules and constrict the coil dimensions. The strain thickening of HA solution in the presence of sodium chloride …at higher extension rates is due to the coil stretching. The addition of sucrose increased the extensional viscosity and shifted the critical extensional rate to lower strain rates. With increasing strain (shear) rates, extensional (shear) viscosities for HA aqueous solutions remained constant up to a critical extension (shear) rate; but they showed no plateau and decreased linearly in DMSO. It is clear that molecular interaction of HA in DMSO is stronger than that in aqueous solution. This should be attributed to the different conformations of HA in DMSO and in aqueous solutions. Show more

Keywords: Extensional viscosity, strain thickening, coil stretch, hyaluronan, steady shear viscosity

Citation: Biorheology, vol. 38, no. 5-6, pp. 379-387, 2001

Authors: Neu, Björn | Armstrong, Jonathan K. | Fisher, Timothy C. | Bäumler, Hans | Meiselman, Herbert J.

Article Type: Research Article

Abstract: Poly(ethylene glycol), abbreviated as PEG, was covalently attached to the surface of human red blood cells (RBC) and the effects of such coating on the regions near the cell's glycocalyx were explored by means of cell electrophoresis. RBC electrophoretic mobilities were measured, in polymer‐free buffers of various ionic strengths, as functions of PEG molecular mass (3.35, 18.5, 35.0, 35.9 kDa), geometry, (linear or 8‐arm branched) and polymer/RBC ratio during attachment. The results indicate marked decreases of the mobility (up to 85%) which were affected by polymer molecular mass and geometry. Since PEG is neutral and its covalent attachment only removes …positively‐charged amino groups on the cell membrane, such decreases of mobility likely reflect structural changes near and within the RBC glycocalyx. Experimental results were analyzed using an extended “hairy sphere” model to consider friction and thickness of the polymer layer. Calculated polymer layer thickness increased with molecular mass for linear PEGs and was less extended for a branched PEG of similar molecular mass. Friction within the polymer layer increased with polymer/RBC ratio and for the linear PEGs was inversely related to molecular mass; friction was greatest for the branched PEG. Our results are consistent with the effects of attached PEGs on RBC aggregation and surface antigenic site masking, and suggest the usefulness of electrophoretic mobility techniques for studies of bound neutral polymers. Show more

Citation: Biorheology, vol. 38, no. 5-6, pp. 389-403, 2001

Authors: Kayar, E. | Mat, F. | Meiselman, H.J. | Baskurt, O.K.

Article Type: Research Article

Abstract: Red blood cell (RBC) deformability and aggregation characteristics were investigated in an experimental model of ischemia‐reperfusion injury. Ischemia was produced in rat hind limb by occluding the femoral artery for 10 minutes, followed by reperfusion. Blood samples were obtained either following the ischemia or 15 minutes after reperfusion. RBC deformability measured by ektacytometry was found to be significantly impaired immediately after the end of ischemic period in the blood samples obtained from femoral vein of the ischemic limb, while there was no significant difference after 15 minutes of reperfusion. In contrast, RBC aggregability was found to be decreased only after …the reperfusion period and this alteration was not only limited to the blood returning from the ischemic limb but was also observed in the samples obtained from non‐ischemic, contralateral hind limb, indicating a systemic alteration. RBC electrophoresis studies suggested that the altered aggregability might be related to altered RBC surface properties including increased RBC surface charge density. Show more

Citation: Biorheology, vol. 38, no. 5-6, pp. 405-414, 2001

Authors: Sharan, Maithili | Popel, Aleksander S.

Article Type: Research Article

Abstract: A two‐phase model for the flow of blood in narrow tubes is described. The model consists of a central core of suspended erythrocytes and a cell‐free layer surrounding the core. It is assumed that the viscosity in the cell‐free layer differs from that of plasma as a result of additional dissipation of energy near the wall caused by the red blood cell motion near the cell‐free layer. A consistent system of nonlinear equations is solved numerically to estimate: (i) the effective dimensionless viscosity in the cell‐free layer (β), (ii) thickness of the cell‐free layer (1−λ) and (iii) core hematocrit (Hc …). We have taken the variation of apparent viscosity (μapp ) and tube hematocrit with the tube diameter (D) and the discharge hematocrit (HD ) from in vitro experimental studies [16]. The thickness of the cell‐free layer computed from the model is found to be in agreement with the observations [3,21]. Sensitivity analysis has been carried out to study the behavior of the parameters 1−λ, β, Hc , B (bluntness of the velocity profile) and μapp with the variation of D and HD . Show more

Keywords: Mathematical model, two‐phase blood flow, energy dissipation, relative viscosity, bluntness

Citation: Biorheology, vol. 38, no. 5-6, pp. 415-428, 2001

Authors: Bozzo, Jordi | Tonda, Raúl | Hernández, María‐Rosa | Alemany, Mònica | Galán, Ana‐María | Ordinas, Antonio | Escolar, Ginés

Article Type: Research Article

Abstract: We investigated whether ghosts behaved similarly to intact erythrocytes to maintain regular primary hemostasis under flow conditions. To this end we performed perfusion experiments with whole blood in which erythrocytes were replaced by pink ghosts, and platelet interaction with the subendothelial surface of a damaged vessel was morphometrically evaluated. The same objective was sought by means of studies with a platelet function analyzer (PFA‐100TM instrument). Perfusions performed with control blood reconstituted with intact erythrocytes gave rise to 0.4±0.2% contact but not spread platelets, 10.8±3.4% adhering and spread platelets, 16.3±4.6% platelets in thrombi, with 27.5±7.4% of the surface covered. Even …though the average diameter of the ghosts was smaller than that of intact erythrocytes (5.3 μm vs. 7.7 μm), the values obtained in perfusions performed with ghosts were similar to those of the erythrocyte controls. Studies performed with the PFA‐100TM analyzer were consistent with those observed in perfusion studies. The viscosity of control blood was compared with that of blood reconstituted with ghosts. At shear rates lower than 450 s−1 , the viscosity of the ghost samples was higher than that of the controls, but the difference progressively decreased as shear rate increased up to 750 s−1 (3.61±0.15 and 3.71±0.17 cP, respectively). In conclusion, the results of our study showed that ghosts behaved similarly to intact erythrocytes in maintaining a normal platelet interaction with digested subendothelium, under conditions of moderate shear rate and constant hematocrit (40%). The rheological activity of ghosts, bodies that are metabolically less active, was sufficient for them to satisfactorily act as substitutes for intact erythrocytes in our system. Show more

Keywords: Erythrocytes, ghosts, platelets, perfusion

Citation: Biorheology, vol. 38, no. 5-6, pp. 429-437, 2001

Authors: Jagger, Justin E. | Ellis, Christopher G. | Sibbald, William J. | Eichelbrönner, Otto

Article Type: Research Article

Abstract: Reductions in red blood cell membrane deformability (RBCD ) may perturb microcirculatory blood flow and impair tissue O2 ‐availability. We investigated the effect of assay temperature on the distribution of RBCD in endotoxin (LPS) incubated and control RBCs. Fresh blood from healthy rats was incubated with and without the presence of LPS for 6 hrs. An index of red blood cell membrane deformability, δ, was measured via the micropipette aspiration technique at 25°C and 37°C at 0, 2 and 6 hrs of incubation. The ATP content of RBC was measured by the luciferin–luciferase technique. At 25°C, LPS caused a …significant decrease in mean δ after 2 and 6 hours incubation compared to controls (−10.0%, p=0.03 and −24.0%, p=0.03, respectively) characterized by a left shift in the distribution (skewness: −1.4). However, at 37°C a significant decrease in δ was only detected after 6 hrs of LPS incubation (−13.8%, p=0.01, compared to −5.1%, p=0.7 at 2 hours) and lacked the left shifted distribution (skewness: 0.2). No significant difference in ATP content of RBCs was observed between groups. We have shown that LPS incubation results in a significant decrease in RBCD and that room temperature measurement of physical membrane properties may exaggerate the differences between normal and perturbed RBCs. Show more

Citation: Biorheology, vol. 38, no. 5-6, pp. 439-448, 2001

Article Type: Abstract

Citation: Biorheology, vol. 38, no. 5-6, pp. 449-466, 2001

Article Type: Other

Citation: Biorheology, vol. 38, no. 5-6, pp. 467-470, 2001