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Biorheology is an international interdisciplinary journal that publishes research on the deformation and flow properties of biological systems or materials. It is the aim of the editors and publishers of
Biorheology to bring together contributions from those working in various fields of biorheological research from all over the world. A diverse editorial board with broad international representation provides guidance and expertise in wide-ranging applications of rheological methods to biological systems and materials.
The aim of biorheological research is to determine and characterize the dynamics of physiological processes at all levels of organization. Manuscripts should report original theoretical and/or experimental research promoting the scientific and technological advances in a broad field that ranges from the rheology of macromolecules and macromolecular arrays to cell, tissue and organ rheology. In all these areas, the interrelationships of rheological properties of the systems or materials investigated and their structural and functional aspects are stressed.
The scope of papers solicited by
Biorheology extends to systems at different levels of organization that have never been studied before, or, if studied previously, have either never been analyzed in terms of their rheological properties or have not been studied from the point of view of the rheological matching between their structural and functional properties. This biorheological approach applies in particular to molecular studies where changes of physical properties and conformation are investigated without reference to how the process actually takes place, how the forces generated are matched to the properties of the structures and environment concerned, proper time scales, or what structures or strength of structures are required.
Biorheology invites papers in which such 'molecular biorheological' aspects, whether in animal or plant systems, are examined and discussed. While we emphasize the biorheology of physiological function in organs and systems, the biorheology of disease is of equal interest. Biorheological analyses of pathological processes and their clinical implications are encouraged, including basic clinical research on hemodynamics and hemorheology.
In keeping with the rapidly developing fields of mechanobiology and regenerative medicine,
Biorheology aims to include studies of the rheological aspects of these fields by focusing on the dynamics of mechanical stress formation and the response of biological materials at the molecular and cellular level resulting from fluid-solid interactions. With increasing focus on new applications of nanotechnology to biological systems, rheological studies of the behavior of biological materials in therapeutic or diagnostic medical devices operating at the micro and nano scales are most welcome.
Abstract: Simultaneous measurements of load, deformation and diameter were performed on stretched collagen fiber bundle from rat tail tendon using a dynamic, electronically controlled stretch system and a novel computer based electroptical set-up. A parallel analysis of glycosaminoglycan (GAG) concentration in the bathing solution was carried out to determine whether stretching affects GAG exudation from the bundle. Results show that the bundle diameter does change under stretch in a manner which depends on strain and time. The diameter decreases with time under constant axial strain, implying loss of fluid from the structure. Results of GAG analysis showed that stretching accelerate…their exucation to the external bath. The data from cyclic stretch tests show that low (0.5%) strain produces monotonically decreasing diameter from cycle to cycle. Yet at higher strain level (4%) under sufficiently long rest periods between cycles, the diameter increases monotonically with cycling to above its original level, implying damage to restraining elements in the bundle which maintain its structural integrity. Simultaneous load and diameter data show mutually different trends, indicating that variation in the bundle’s hydration (diameter) in itself does not have a significant effect on the bundle’s axial response.
Keywords: Collagen bundle, in-vitro stretch, effect on hydration
vol. 25, no. 4, pp. 591-603, 1988
Abstract: A cone and plate viscometer was modified to permit the continuous study of platelet response during shear stress exposure times on the order of one second to 180 seconds. Platelets may be stimulated by uniform, controlled shear stress alone or with the addition of chemical platelet agonists. The time course of platelet aggregation is interpreted from alterations in the apparent optical density of the platelet suspension. The rate and extent of platelet dense granule release is estimated from the intensity of the luminescent reaction of platelet released ATP with firefly luciferase and luciferin. Intracellular calcium ion concentration is determined as…a function of shear exposure time through the fluorescence intensity of indo-15− , a membrane-permeant pentacarboxylate calcium ion chelator.
Abstract: Blood from non-inbred obese-hyperglycaemic ob/ob -mice or normoglycaemic controls was fixed in glutaraldehyde and embedded in plastic on glass slides. In vertically oriented red blood cells (RBCs) the diameter, central thickness, and toroidal thickness were measured at the diametrical cross section. For each RBC, the area, volume, and cross-sectional profile were calculated and used to analyze the mechanical properties of the corpuscle. In both types of mice, the diameter correlated positively with the central thickness and negatively with the toroidal thickness, suggesting a variation not only in size but also in biconcavity; the smaller the diameter, the more biconcave the…disc. However, ob/ob -mouse RBCs were both larger and more biconcave than those in control mice. These differences in size and shape are suggested to explain why ob/ob -mouse RBCs exhibit a decreased deformability in filtration experiments.
Abstract: The Hemorheometer has been adapted to allow the recording of the flow rate during the filtration process. For newtonian fluids, the flow rate variation versus time through the pores is well approximated by Poiseuille’s law. For dilute red blood cell suspensions, the same analysis can be applied by introducing the concept of “apparent filtration viscosity” which is higher than the usual Viscosity measured by Couette viscometry. The apparent filtration viscosity parameter is related to the deformations undergone by red blood cells as they pass through the narrow pores. Apparent filtration viscosity can be used to obtain a precise determination of…the erythrocyte deformability. Measurements per-formed / for a given blood sample, with pores of different diameters (5μ m, 8μ m and 12μ m) show that the error on the value of apparent filtration viscosity is less than 3 %. As a result, the sensitivity of the filtration method allows to discriminate among normal blood samples. High concentrations of erythrocytes or leucocytes are found to modify the apparent filtration viscosity. These factors are apparent in the recorded filtration curves. Their effects on filtration measurements can be easily estimated.
Keywords: Red Blood Cell, Deformability, Filtration, Viscosity
vol. 25, no. 4, pp. 639-649, 1988
Abstract: Experiments with a continuous centrifuge reveal that the separation of leukocytes (WBCs) and platelets from erythrocytes (RBCs) is maximized at a lower than normal RBC concentration or hematocrit (HCT). Conventional hindered settling models are unsatisfactory in the explanation of this behavior because they do not adequately account for differences in cell size, density, deformability and electrical charge on the membrane surface. In this paper a new approach is taken where an effective porosity is used to account for the differences in the micro-environment of each particle type. Introduction of effective porosities into various sedimentation equations is useful in allowing better…prediction of the optimum separation conditions observed in experimental data. Further adjustment of parameters is necessary for some models to shift optimums in settling curves to align with experimental trends.
Keywords: Blood Cell Sedimentation and Separation, Effective Porosity, Continuous Centrifugation
vol. 25, no. 4, pp. 651-662, 1988
Abstract: One of the most rapid methods to determine cell counts in whole blood is by way of layer thickness measurements of the buffy coat. The purpose of this study was to determine the separation and purity of blood cells in the different layers of the buffy coat. Blood samples were centrifuged at 10,000 g in microhematocrit tubes with an inserted float to expand the buffy coat region. Whole blood from normal laboratory individuals separates by density into four regions: platelets, a layer of lymphocyte and monocytes, granulocytes and erythrocytes. A thin band of highly swollen red cells was discovered between…the buffy coat layers of many normal volunteers and patients. Stereo logical analysis of electron micrographs showed that mixing of formed elements within the layers is less than 2% with the exception of some erythrocytes, which can make up a higher volume fraction in the lymphocyte/monocyte and granulocyte layers. The red cell column contains about 95.7% erythrocytes and is depleted of platelets and leukocytes. In approximately 5% of hospital blood samples, the granulocyte-erythrocyte interface was feathered and undetectable, and a significantly higher volume fraction of red cells was found among the granulocytes. Cell mass density determinations indicate that the erythrocytes in these abnormal granulocyte layers have a lowered mass density, overlapping with that of the granulocytes.
Abstract: The rate of onset of erythrocyte flow orientation at normal concentration has not previously been established. Reflectivity of blood and resuspended non-aggregated red cells at normal (41%) and elevated (60%) hematocrit has been used to examine this process. Video recordings were made before, during, and after shearing by bob motion in a cylinder-in-cylinder viscometer at shear rates ranging from 4 to 100 inverse seconds. Unaggregated erythrocytes in PBS, already more reflective than blood before shearing, became even more reflective during shearing even at the lowest shear rate studied. The time required for the increased reflectivity to stabilize was observed to…be inversely proportional to shear rate for both blood and resuspended red cells. Reflection became constant after a total shear strain (bob shear rate x time) from 4 to 10 at all shear rates studied. Onset of increased reflection expressed in total shear strain units (an index of overall bob movement) was independent of shear rate in the absence of aggregation. When red cells were studied in native plasma, reflectivity increased as much as 30% during shearing, but always remained below unaggregated red cell reflectivity for the same hematocrit and shear rate. Greater reflectivity of unaggregated red cells persisted after cessation of shearing, while blood’s reflectivity dropped progressively over several seconds to its pre-shearing value. The geometry chosen for study and insensitivity to light source composition indicate that specular reflection by red cells near the cup’s inner surface is responsible for the increased light return during flow. Maximal rate of rise in reflectivity at all shear rates studied was observed to coincide with blood’s previously reported transient shear stress overshoot and to correspond with an overall bob motion that would rotate suspended particles approximately 45°. The close relation of both reflectivity increase and shear stress overshoot to such modest overall bob movement indicates that an efficient flow-mediated rotation of either individual or aggregated erythrocytes from initially random positions toward an orientation in the shear plane characterizes flow onset.
Abstract: By the evaluation of the strain and stress distributions in the vicinity of a stenosis, it is suggested that the bending moment generated by the axial force acting on a stenosis is one of the causes of the post-stenotic dilatation. The conditions which enhance this bending moment are investigated and it is expected that the present mechanism is specially effective for the artery where the ratio of wall thickness to radius is very small. Lastly, the concrete numerical value of this bending moment is evaluated and it is shown that the bending moment generated by this mechanism is large enough…to cause the post-stenotic dilatation.
Keywords: post-stenotic dilatation, strain-stress analysis, shell theory
vol. 25, no. 4, pp. 685-695, 1988
Abstract: A disposable clinical whole blood viscometer which can produce viscosity measures over a wide range of shear rates in a single rapid determination has been developed and is currently under test. The design is based upon the time varying flow of blood through a capillary. The flow is driven by the pressure in a fixed volume air chamber and transmitted to the sample through a compliant membrane. The time varying pressure in the air chamber is measured by a suitable transducer. The instantaneous shear stress of the blood in the capillary is proportional to the air pressure, while the instantaneous…shear rate is proportional to the pressure-time derivative. Proper design ensures that the system operates as a first order dynamic system with flow resistance entirely determined by the nonlinear sample viscosity. By constructing the air chamber in two parts coupled by a quick disconnect fitting the design can allow for the blood-containing part of the instrument to be discarded, eliminating handling and cleaning of blood contacted components. The entire determination is completed in less than a minute, so that anticoagulants are not necessary. Tests on a prototype show that the instrument gives results in excellent agreement with those obtained on a cone-plate rheogoniometer.
Keywords: blood, clinical, viscometer, disposable
vol. 25, no. 4, pp. 697-712, 1988