Browsing by Author "Leble, Vladimir"
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- Asymmetry of red blood cell motions in a microchannel with a diverging and converging bifurcationPublication . Leble, Vladimir; Lima, Rui A.; Dias, Ricardo P.; Fernandes, Carla S.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiIn microcirculation, red blood cells (RBCs) flowing through bifurcations may deform considerably due to combination of different phenomena that happen at the micro-scale level, such as: attraction effect, high shear and extensional stress, all of which may influence the rheological properties and flow behavior of blood. Thus, it is important to investigate in detail the behavior of blood flow occurring at both bifurcations and confluences. In the present paper, by using a micro-PTV system, we investigated the variations of velocity profiles of two working fluids flowing through diverging and converging bifurcations - human red blood cells suspended in dextran 40 with about 14% of haematocrit level (14Hct) and pure water seeded with fluorescent trace particles. All the measurements were performed in the center plane of rectangular microchannels using a constant flow rate of about 3.0×10-12 m3/s. Moreover, the experimental data was compared with numerical results obtained for Newtonian incompressible fluid. The behavior of RBCs was asymmetric at the divergent and convergent side of the geometry, whereas the velocities of tracer particles suspended in pure water were symmetric and well described by numerical simulation. The formation of a red cell-depleted zone immediately downstream of the apex of the converging bifurcation was observed and its effect on velocity profiles of RBCs flow has been investigated. Conversely, a cell-depleted region was not formed around the apex of the diverging bifurcation and as a result the adhesion of RBCs to the wall surface was enhanced in this region.
- Flow of red blood cells in capillary networksPublication . Couto, Ana Rita; Teixeira, Lúcia; Leble, Vladimir; Lima, Rui A.; Ribeiro, António E.; Dias, Ricardo P.In the present work we have studied the flow of red blood cells through a column packed with soda lime glass spheres with diameter of 337.5 micron (pore diameter 150 micron). The ratio between the average velocity of the RBCs and the average velocity of the carrying fluid (physiological saline) was close to 0.9. The RBCs migrated faster through the column than the carrying fluid mainly due to a hydrodynamic chromatographic effect.
- Flow of red blood cells through microchannel with a confluencePublication . Leble, Vladimir; Lima, Rui A.; Fernandes, Carla S.; Dias, Ricardo P.Micro-visualization techniques have been used to investigate the in vitro blood flow through straight glass capillaries. Although the glass microchannels present certain similarities to in vivo microcirculation, it is also clear that these kind of in vitro experiments differ from microvessels in several respects, such as: elasticity of microvessels, effect of the endothelial surface layer and microvascular networks composed with short irregular vessel segments which are linked by numerous bifurcations and convergences. Thus it was not surprising that several studies on blood flow in glass microtubes and in microvessels have yielded conflicting results with respect to blood viscosity and flow resistance. The main purpose of this work is to improve our understanding about the effect of a confluence on the rheological properties of in vitro blood. The flow behaviour of both pure water (PW) and dextran 40 (Dx40) containing about 14% (14Hct) of human red blood cells (RBCs) will be investigated by means of a confocal micro-PTV system. The experimental measurements obtained will be compared numerically by using the commercial finite element software package POLYFLOW® and different constitutive models to describe the rheology of the blood, namely: constant viscosity, power-law model and Carreau model.
- Flow visualization of trace particles and red blood cells in a microchannel with a diverging and converging bifurcationPublication . Leble, Vladimir; Fernandes, Carla S.; Dias, Ricardo P.; Lima, Rui A.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiThis paper aims to investigate the effect of both diverging and converging bifurcations on the flow behaviour of pure water (PW) and red blood cells (RBCs). A confocal micro-PTV system is used to visualize and measure the flow characteristics of the working fluids. The results show no formation of a cell-free layer (CFL) around the apex of the bifurcation. In contrast, there is a clear formation of a triangular CFL just downstream of the confluence apex. As a result, this triangular CFL seems to play an important role on the in vitro blood flow characteristics at this region.
- Motions of trace particles and red blood cells in a PDMS microchannel with a converging bifurcationPublication . Leble, Vladimir; Dias, Ricardo P.; Lima, Rui A.; Fernandes, Carla S.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiThis paper presents microflow visualizations of both pure water and red blood cells (RBCs) in a converging bifurcation. The visualizations are a combination of results obtained from a confocal micro-PTV system and an image analysis technique known as “Zproject” from ImageJ. Our preliminary qualitative results suggest that the cell-free layer that is formed in middle of the microchannel (after confluence apex) may play an important role on RBCs trajectories.