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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: The mechanical effects resulting from the normal transmural delay of electrical depolarization of the myocardium are investigated. An activation sequence having a finite radial propagation velocity is introduced into the equations of ventricular mechanics. The resulting system of coupled integral equations is solved using a perturbation method based on the small ratio of transmural propagation time to cardiac period. Numerical calculations are performed using cavity pressure and volume waveforms characteristic of the canine left ventricle (LV), for both simultaneous and delayed activation of fiber layers. The results show that a finite transmural electrical propagation velocity tends to: (i) equalize the…transmural distribution of sarcomere length during systole; (ii) equalize the transmural distribution of fiber external work/vol; and (iii) insignificantly affect myocardial tissue pressure. Calculations are also performed to investigate the mechanical effects resulting from the application of an externally applied moment that prevents LV torsion. Those results are highly dependent on the transmural distribution of sarcomere length in the stress-free reference state (unloaded diastole). When we assume a uniform distribution, then normal torsion acting with normal activation delay tends to: (i) increase the magnitude of fiber strain in the subendocardium and decrease it in the subepicardium; (ii) equalize the transmural distribution of fiber external work/vol; and (iii) lower myocardial tissue pressure. The normally occurring transmural delay of activation tends to lessen endocardial O2 demand, while the normally occurring torsion further lessens that demand and improves O2 supply.
Abstract: Described is a special purpose cone-plate viscometer that is capable of acceleration or deceleration through a step change in speed in less than 0.7s. The speed of the rotating cone is controlled by a microcomputer which can be programmed to generate speed vs time ramp functions of variable slope. Prior calibration of motor power required to shear Newtonian fluids of known viscosity at various speeds provides the basis for determination of apparent suspension viscosity and enables the viscometer automatically to compensate for changing sample viscosity during shear. The viscometer was used to carry out a series of preliminary studies in…which platelet-rich plasma (PRP) was subjected to continuous and pulsatile shear stress at 37°C. Shear-induced platelet aggregation (SIPAG) was significantly greater in response to pulsatile versus continuous shearing except at the lowest applied stress (10 dyn/cm2 ). Increases ranged from about 40 percent at a stress amplitude of 25 dyn/cm2 to nearly 55 percent at dyn/cm2 . This increasing trend with stress amplitude might be interpreted as a positive correlation between SIPAG and the loading rate. Dense granule release, as indicated by serotonin release, was dependent on both stress amplitude and number of pulses even at the higher stress where SIPAG was independent of pulse number.
Keywords: platelets, pulsatile shear stress
vol. 25, no. 3, pp. 449-459, 1988
Abstract: To study the effect of fluid shear stress on cultured endothelial cells, we have developed an apparatus for the stress creation, which consists of a stainless steel disk driven by an electric DC motor and a stage to place a culture dish and to adjust the distance between the disk and the dish. When the disk is rotated, a concentric fluid movement occurs in the culture medium in the dish and exerts the shear stress on the endothelial cells cultured on the bottom of the dish. A theoretical analyses concerning the induced concentric flow velocity predicted that when the angular…velocity of the disk rotation (ω ) is slow enough to maintain a Reynolds’ number of the order of 10, the exerted wall shear stress τ w on the endothelial cell monolayer is given for a constant as τ w = μ r ω / d where μ is the viscosity of the medium, d the distance from the plate to the monolayer and r the radial distance from the center of the dish. When ω is varied in a sinusoidal mode τ w also becomes sinusoidal, thus allowing to apply a pulsatile stress. In vitro experiments carried out to examine the validity of the theoretical results, using a suspension of polystyrene as a tracer with the ordinary culture medium and 99% ethanol, revealed excellent agreement of the measured velocity profiles with the predicted ones. The results demonstrated that the present apparatus can create both the steady and pulsatile wall shear stress on the culture cell layer as expected, unless Reynolds’ number greatly exceeds the level of 10.
Abstract: Both the transmission of light through a confined layer of blood and the reflection from the surface of that layer have been utilized for studying the rheology of erythrocyte aggregates. The two methods do not necessarily provide the same information. The light reflected from the blood layer relates to the rheological behavior of erythrocytes near the blood surface, whereas the light transmitted relates more to the properties of blood in bulk. This investigation makes direct comparison between the transmitted and reflected light methods with regard to the kinetics of aggregation in thin and thick layers of blood as well as…following shear flow excitation steps of different sizes. Also, the transmission and reflection for static blood layers of varying thicknesses were determined. The kinetics of aggregation from transmitted and reflected light measurements are compared both graphically and by equations containing multiple characteristic aggregation times. The number of characteristic times required for accurate description increases with the time over which the aggregation process is monitored. The first 40 seconds of the aggregation process are precisely described by two characteristic times. For normal blood the characteristic times from reflection measurements are shorter than those from transmission measurements.
Keywords: Erythrocyte aggregation, light transmission, light reflection, kinetics of aggregation, optical attenuation in blood, characteristic aggregation times
vol. 25, no. 3, pp. 471-487, 1988
Abstract: Ciliary metachronism and motility were examined optically in tissue cultures from frog palate e:Rithelium as. a func.tion of extracellular ATP concentration in the range of 10−7 –10−3 M. The main findings were: a) upon addition of ATP the metachronal wavelength increased by a factor of up to 2. b) the velocity of the metachronal wave increased by a factor of up to 5. c) the frequency of ciliary beating increased by a factor of up to 2–3, the increase being temperature insensitive in the range of 15°C–25°C. d) the area under the 1-second FFT spectrum decreased by a factor of…up to 2.5. e) the energy of the metachronal wave is increased by a factor of up to 9.5. f) all the spectrum parameters are subject to influence by ATP, as also by ADP and AMP. However, there are pronounced differences in the various responses to them. Based on these findings, physical aspects of the rate increase of particle transport caused by addition of extracellular ATP are explained. A plausible overall chemical mechanism causing pronounced changes in ciliary motility is discussed.
Abstract: The sedimentation potential or the Dorn effect occurs when heavy particles fall in a liquid. An electrode near the bottom of the vessel acquires a potential difference with respect to another identical electrode placed near the upper surface of the solution. The Boycott phenomenon enhances the sedimentation in inclined vessels. In this investigation, fixed erythrocytes at 2–3% concentration were studied. The shapes include discs, oblate spheroids, spheres and spindles. From the sedimentation potentials, the zeta potentials were calculated and compared with those determined by laser Doppler velocity. By using a technique of reduced. variables, it is shown that all of…the data could be placed on a single curve, combining particle flexibility, shape, concentration and angle of inclination.
Abstract: Membrane fluidity and osmotic sensitivity were examined in DPPC liposomes treated with phospholipase A2 (PL.A2 ) in the presence of Ca2+ or Mg2+ . The amount of liposome phospholipid hydrolyzed differed with the two ions. Embedded DPH, a rod-like fluorescent probe, was employed in the determination of membrane fluidity. Membrane fluidity decreased according to the degree of phospholipid hydrolization in liposomes by PL.A2 . The reciprocal value of absorption at 450 nm was measured as the index of osmotic sensitivity of liposomes. Intact sonicated liposomes showed osmotic insensitivity. PL.A2 -treated liposomes in which about 40 % of total…phospholipid was hydrolyzed showed osmotic sensitivity. No change in the membrane fluidity was obtained when PL.A2 -treated liposomes were exposed to hypertonic or hypotonic solution. These results suggested that the motion of the acyl-chain of phospholipids and free fatty acids was resisted in PL.A2 -treated liposomes. The resistance may be due to a phase separation between phospholipids and free fatty acids. The pore for water permeation might be induced in the border between phase-separated domains in PL.A2 -treated liposomes.
Abstract: We have measured the density and ultrasonic velocity (usv) of swine red blood cell (RBC) suspensions in the wide osmolarity range from 300 mOsm to 1400 mOsm in saline solution. The cellular density and compressibility of RBC at each osmolarity were obtained using the fact that the density and the compressibility are additive by volume. The osmolarity dependence of hematocrit was also measured at a constant number concentration of RBC in the range of 300 mOsm to 1700 mOsm. The cellular density and the cellular compressibility of RBC as well as the inverse of hematocrit were expressed well into one…unique exponential type equation f ( π ) = a [ 1 − b exp ( − c π ) ] with a common value for the coefficient c = 0.0025 against the osmolarity π . The results were analyzed with a simple consideration based only upon the contribution of free water inside the erythrocyte through the volume concentration ϕ of the free water in it. According to this theoretical analysis, the density and the compressibility of the free water were found to be 0.990 g/cm3 and 4.59 × 10−11 cm2 /dyne which agree closely with 0.998 g/cm3 and 4.59 × 10−11 cm2 /dyn of pure water at 20°C within the experimental error.
Keywords: Ultrasonic velocity, Red blood cell, Cellular compressibility, Osmotic behavior
vol. 25, no. 3, pp. 527-537, 1988
Abstract: Hartert’s thromboelastography has been used in the diagnosis of abnormal blood clotting for more than 20 years. From a thromboelastogram three parameters are obtained, viz, the reaction time ‘r’, the rate of formation of fibrin clot ‘k’ , the maximum elasticity of thrombus ‘amax ’. It is desirable, however, to know the equation that describes the thromboelastogram both in the period in which the complex modulus increases with time because of coagulation, and in the period in which the complex modulus decreases with time because of fibrinolysis. The parameters of the equation could then be used as a diagnostic criterion;…yielding information on the mechanism of coagulation and fibrinolysis. Based on our experimental results on human blood in normal and abnormal subjects, we found that the complex modulus of thromboelastograms can be expressed by the sum of two terms, one describing the increase of the complex modulus during coagulation, G 1 = G 1 ′ ( − τ 1 / t ) , the other describing the decrease of the complex modulus during fibrinolysis, G 2 = G 2 ′ ( − τ 2 / t − D ) when t > D. G2 = 0 when t < D. The compound complex modulus from coagulation to fibrinolysis is G = G 1 − G 2 . Here t is the clotting time, and G 1 ′ , G 2 ′ , τ 1 , τ 2 , and D are five constants to be identified. These five constants can be used for diagnostic and prognostic purposes.
Abstract: Erythrocyte sedimentation rate was measured in a physiological saline solution as a function of both the tube diameter d and the initial suspension length ı 0 . All the sedimentation curves in the vertical tubes were found to overlap over the range 1 mm < d < 7 mm and 100 mm < ı 0 < 330 mm, within the precision of 8 %. The sedimentation curves in the tilted tubes fit well to an exponential equation of ı = a [ 1 − exp ( −…bt ) ] , where ı and t are the medium length along the tube and the elapsed time from sample injection respectively: At fixed tilt angle θ and ı 0 . a was roughly constant and b was roughly proportional to l/d, while at fixed θ and d, a was linearly proportional to to and b was constant. The initial slope ESR ( θ ) = ( d ı / dt ) t → 0 = ab was represented by a unique straight line as a function of ı 0 /d for each fixed tilt angle. The experimental results were compared with some recent theories.
Abstract: The authors (1987), and Chuong and Fung (1986) have shown that the strain and stress distributions in the arterial wall should be more uniform than those calculated on the basis of the conventional assumption that there is no stress over the cross-section of the arterial wall when all external force is removed (zero initial stress hypothesis). Instead of this assumption, the authors have proposed a new hypothesis that the circumferential strain uniformly distributes through the wall thickness at a physiologically normal loading, and named it ‘uniform strain hypothesis’. Their results suggest the validity of the thin-walled theory in the vascular…mechanics. This paper shows that if the uniform strain hypothesis is applied, the thin-walled theory can be used to accurately determine the constants included in the strain energy density function which describes the mechanical properties of the arterial wall. There were, however, significant differences in the values of the constants between the thin-walled theory and the thick-walled theory if assuming the conventional zero initial stress hypothesis.
Keywords: artery, uniform strain hypothesis, strain energy density function
vol. 25, no. 3, pp. 555-565, 1988
Abstract: We studied the distribution of the early atherosclerotic lesions in the curving sites of the human internal carotid arteries composed of the carotid siphon portion (part I) and carotid canal portion (part II). These early atherosclerotic lesions included a localized cloudy thickening with pallor, slight elevation, a non-fibrotic lesion and gray-white or yellowish-white, firm, elevated fibrous plaques. These lesions had the same pattern-distribution in each curving artery. Both were located in the distal regions from the middle of the inner curva ture of parts I and II, where eddying fluid motions and directional change in the wall shear stress were…considered to occur. In part I, there was a localized cloudy thickening in the younger subjects (average age: 22.8 years) rather than fibrous plaques (average age: 63.3 years). A positive correlation between the extent of the surface areas involved with fibrous plaques and the age of subjects was found in parts I and II. The extent of the surface areas involved with fibrous plaques was significantly greater in part I (26.9%) than in part II (7.85%). The radius of curvature was shorter in the former than in the latter. These results suggest that hemodynamic factors associated with flow in the curving sites of arteries may be important for the localization and progression of atherosclerotic lesions.