Blood is composed of red blood cells, leukocytes and platelets, which are dispersed in plasma. These particulate components have different size and stiffness. In blood flow, red blood cells are found to flow in the center of vessels. On the other hand, leucocytes and platelets are observed in the vicinity of wall of vessels. This phenomenon is called ‘margination’. In this study, we simulate the behavior of binary droplet dispersion with size and surface tension differences under Couette flow, in order to investigate the mechanism of margination. We found that large floppy droplets migrate toward the center of channel, whereas small stiff droplets marginate near the wall of channel.
As is well-known, the mechanical properties of surimi gels are improved by incubation at moderate temperatures (low temperature setting: LTS) prior to high temperature treatment (high temperature setting: HTS). In this study we investigated the effect of the setting temperature on the mechanical properties of surimi gels. To this end, the temporal development of the dynamic modulus during the setting process was investigated at various temperatures. The dynamic modulus of the surimi paste increased with time at low temperature treatment (5 and 10°C). However, this trend reversed at higher temperatures (25 and 30°C). The mechanical properties of the thermal gel, which was heated to 90°C after LTS, were also investigated. In this case, the sample treated at 10°C prior to HTS showed the most rigid property. The protein extracted from both the set surimi paste and thermal gel was analyzed by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). This analysis revealed a relatively high actin content in the thermal gel set at 10°C. Two important findings emerged from the study; the setting temperature at which the gel acquires its most desirable textural properties is not the commercial setting temperature, and actin appears to play an unexpected role in the gelling mechanism.
The present study examined expressions of type I collagen and MMP-1 mRNA of bovine tenocytes in response to elevation in intracellular tension/traction forces induced by either mechanical or chemical stimulation. Tenocytes were cultured in the following conditions: micropillars with the Young’s modulus of 75 kPa in a normal culture medium, in the presence of 1 nM calyculin A in the medium or under 4 or 8% static tensile strain in the normal medium. In all the treatments, cell traction forces were increased significantly from the levels of corresponding control tenocytes. However, these increases in traction forces were not associated with statistically significant increase in type I collagen gene expression. Because our treatments induced the increase in traction forces equidirectionally, it is speculated that highly directional increase in traction forces, associated with an elongated cell shape, is required to induce marked upregulation of type I collagen mRNA expression in tenocytes.
The present study is concerned with the flow of blood in an artery with an overlapping mild stenosis. To account for the slip at stenotic wall, hematocrit, pulsatility of flow and inclination of the tube, blood has been represented by a fluid whose viscosity varies with radial coordinate and hematocrit. The expression for the flow characteristics, namely, the wall shear stress, the shear stress at the critical height of the stenosis, the pressure drop and the resistance to flow (impedance) have been derived and represented graphically with respect to different flow parameters. The resistance to flow increases with the hematocrit and critical height of the stenosis but decreases with slip at wall. With respect to any parameter, the shear stress at the critical height possesses the characteristics similar to that of the impedance.
Making use of the poroelastic theory for hydrated polymeric matrices, the ultrasound (US) propagation in a gel medium filled by spherical cells is studied. The model describes the connection between the poroelastic structure of living tissues and the propagation behavior of the acoustic waves. The equation of fast compressional wave, its phase velocity and its attenuation as a function of the elasticity, porosity and concentration of the cells into the gel external matrix are investigated. The outcomes of the theory agree with the measurements done on Alginic acid gel scaffolds inseminated by porcine liver cells at various concentrations. The model is promising in the quantitative non-invasive estimation of parameters that could assess the change in the tissue structure, composition and architecture.
Many food products based on gelatin contain sugar. Although the effect of sugars on physical properties of gelatin gels has been intensively investigated, aging of gelatin gels containing sugars has not been studied in detail. In the present study, vacuum-ultraviolet circular dichroism (VUVCD) was applied to the study of the aging of gelatin gels with and without sugars and the aging process measured by VUVCD was compared with that measured by rheology and polarimetry. The storage modulus G’ and reduced ellipticity θ/θ0 in the aging process were correlated with each other, indicating VUVCD is a useful tool for detecting the conformation change of gelatin molecules. On the other hand, the behavior of optical rotation Δα was different with that of either G’ or θ/θ0, suggesting that the optical rotation does not represent the conformation change accurately in the case of gelatin gels containing sugars. The relationship between G’ and a fraction χ of helix amount estimated from VUVCD data showed that the critical helix fraction χc for gelation is slightly increased by the addition of sugars, suggesting a change in the network structure.
Quartz crystal microbalance (QCM) is widely used for the investigation of human blood mechanical properties, and shows high sensitivity for monitoring select dynamic processes, including red blood cell sedimentation and aggregation, coagulation, plasma protein absorption, as well as evaluating the bio-compatibility/affinity of different materials, etc. The present study provides a critical analysis of the challenges associated with data modelling and data interpretation, with respect to a QCM-based experimental setup. Here, the modelling approach selected for use is based on the analysis of the interactions that occur between an oscillating QCM surface and different blood components adhering to the surface. The resultant mathematical model overcomes these challenges by presenting simple, interpretable output parameters for monitoring experimental erythrocyte sedimentation in whole blood (WB), platelet aggregation in platelet rich plasma (PRP) and fibrin polymerisation in platelet poor plasma (PPP).
We study concentration dependence of the critical shear rate of a layer orientation transition in lyotropic triblock copolymer lamellar phase. Theory predicts that suppression of undulation fluctuation by shear triggers the transition. The critical shear rate at high polymer concentration is in reasonable agreement with theory. However, experimental results at low polymer concentrations show different behavior from the prediction. Violation of the theory is attributed to defective nature of the lamellar phase, in which creation of defects prevents the suppression of the undulation fluctuation.