Enhanced axial migration of a deformable capsule in pulsatile channel flows

We present a numerical analysis of the lateral movement of a deformable spherical capsule in a pulsatile channel flow, with a Newtonian fluid in an almost inertialess condition and at a small confinement ratio a0/R=0.4, where R and a are the channel and capsule radius. We find that the speed of the axial migration of the capsule can be accelerated by the flow pulsation at a specific frequency. The migration speed increases with the oscillatory amplitude, while the most effective frequency remains basically unchanged and independent of the amplitude. Our numerical results form a fundamental basis for further studies on cellular flow mechanics, since pulsatile flows are physiologically relevant in human circulation, potentially affecting the dynamics of deformable particles and red blood cells, and can also be potentially exploited in cell focusing techniques.journal articl

Editorial for the Special Issue on Advances in Microfluidics for Quantifying Cell Mechanics and Biotransport

Ito H, Takeishi N. Editorial for the Special Issue on Advances in Microfluidics for Quantifying Cell Mechanics and Biotransport. Micromachines. 2022; 13(7):1127. https://doi.org/10.3390/mi1307112

Capture of microparticles by bolus flow of red blood cells in capillaries

Previous studies have concluded that microparticles (MPs) can more effectively approach the microvessel wall than nanoparticles because of margination. In this study, however, we show that MPs are not marginated in capillaries where the vessel diameter is comparable to that of red blood cells (RBCs). We numerically investigated the behavior of MPs with a diameter of 1 μm in various microvessel sizes, including capillaries. In capillaries, the flow mode of RBCs shifted from multi-file flow to bolus (single-file) flow, and MPs were captured by the bolus flow of the RBCs instead of being marginated. Once MPs were captured, they rarely escaped from the vortex-like flow structures between RBCs. These capture events were enhanced when the hematocrit was decreased, and reduced when the shear rate was increased. Our results suggest that microparticles may be rather inefficient drug carriers when targeting capillaries because of capture events, but nanoparticles, which are more randomly distributed in capillaries, may be more effective carriers.Takeishi, N., Imai, Y. Capture of microparticles by bolus flow of red blood cells in capillaries. Sci Rep 7, 5381 (2017). https://doi.org/10.1038/s41598-017-05924-

Flow of a circulating tumor cell and red blood cells in microvessels

Quantifying the behavior of circulating tumor cells (CTCs) in the blood stream is of fundamental importance for understanding metastasis. Here, we investigate the flow mode and velocity of CTCs interacting with red blood cells (RBCs) in various sized microvessels. The flow of leukocytes in microvessels has been described previously; a leukocyte forms a train with RBCs in small microvessels and exhibits margination in large microvessels. Important differences in the physical properties of leukocytes and CTCs result from size. The dimensions of leukocytes are similar to those of RBCs, but CTCs are significantly larger. We investigate numerically the size effects on the flow mode and the cell velocity, and we identify similarities and differences between leukocytes and CTCs. We find that a transition from train formation to margination occurs when (R-a)/tR≈1, where R is the vessel radius, a is the cell radius, and tR is the thickness of RBCs, but that the motion of RBCs differs from the case of leukocytes. Our results also show that the velocities of CTCs and leukocytes are larger than the average blood velocity, but only CTCs move faster than RBCs for microvessels of R/a≈1.5-2.0. These findings are expected to be useful not only for understanding metastasis, but also for developing microfluidic devices.Takeishi N., Imai Y., Yamaguchi T., et al. Flow of a circulating tumor cell and red blood cells in microvessels. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 92, 6, 063011. https://doi.org/10.1103/PhysRevE.92.063011

Deformation of a red blood cell in a narrow rectangular microchannel

The deformability of a red blood cell (RBC) is one of the most important biological parameters affecting blood flow, both in large arteries and in the microcirculation, and hence it can be used to quantify the cell state. Despite numerous studies on the mechanical properties of RBCs, including cell rigidity, much is still unknown about the relationship between deformability and the configuration of flowing cells, especially in a confined rectangular channel. Recent computer simulation techniques have successfully been used to investigate the detailed behavior of RBCs in a channel, but the dynamics of a translating RBC in a narrow rectangular microchannel have not yet been fully understood. In this study, we numerically investigated the behavior of RBCs flowing at different velocities in a narrow rectangular microchannel that mimicked a microfluidic device. The problem is characterized by the capillary number Ca, which is the ratio between the fluid viscous force and the membrane elastic force. We found that confined RBCs in a narrow rectangular microchannel maintained a nearly unchanged biconcave shape at low Ca, then assumed an asymmetrical slipper shape at moderate Ca, and finally attained a symmetrical parachute shape at high Ca. Once a RBC deformed into one of these shapes, it was maintained as the final stable configurations. Since the slipper shape was only found at moderate Ca, measuring configurations of flowing cells will be helpful to quantify the cell state.Takeishi, Naoki, Hiroaki Ito, Makoto Kaneko, and Shigeo Wada. 2019. "Deformation of a Red Blood Cell in a Narrow Rectangular Microchannel" Micromachines 10, no. 3: 199. https://doi.org/10.3390/mi1003019

Haemorheology of dense suspension of red blood cells under oscillatory shear flow

We present a numerical analysis of the rheology of a suspension of red blood cells (RBCs) for different volume fractions in a wall-bounded, effectively inertialess, oscillatory shear flow. The RBCs are modeled as biconcave capsules, whose membrane is an isotropic and hyperelastic material following the Skalak constitutive law, and the suspension examined for a wide range of applied frequencies. The frequency-dependent viscoelasticity in the bulk suspension is quantified by the complex viscosity, defined by the amplitude of the particle shear stress and the phase difference between the stress and shear. Our numerical results show that deformations of RBCs wekaly depend on the shear frequency, and the normal stress differences, membrane tension and amplitude of the shear stress are reduced by the oscillations. The frequency-dependent complex viscosity is nevertheless consistent with the classical behavior of non-Newtonian fluids, where the real part of the complex viscosity $\eta^\prime$ decreases as the frequency increases, and the imaginary part $\eta^{\prime\prime}$ exhibit a maximum value at an intermediate frequency. Such local maximum frequency is the same in both dense and dilute conditions. The effect of the viscosity ratios between the cytoplasm and plasma, volume fractions of RBCs, and oscillatory amplitudes represented by a capillary number on the complex viscosity are also assessed

Leukocyte margination at arteriole shear rate

We numerically investigated margination of leukocytes at arteriole shear rate in straight circular channels with diameters ranging from 10 to 22 lm. Our results demonstrated that passing motion of RBCs effectively induces leukocyte margination not only in small channels but also in large channels. A longer time is needed for margination to occur in a larger channel, but once a leukocyte has marginated, passing motion of RBCs occurs continuously independent of the channel diameter, and leukocyte margination is sustained for a long duration. We also show that leukocytes rarely approach the wall surface to within a microvillus length at arteriole shear rate.Takeishi, N., Imai, Y., Nakaaki, K., Yamaguchi, T., Ishikawa, T., Leukocyte margination at arteriole shear rate, Physiol Rep, 2 ( 6), 2014, e12037, doi: 10.14814/phy2.1203

Axial and nonaxial migration of red blood cells in a microtube

Human red blood cells (RBCs) are subjected to high viscous shear stress, especially during microcirculation, resulting in stable deformed shapes such as parachute or slipper shape. Those unique deformed RBC shapes, accompanied with axial or nonaxial migration, cannot be fully described according to traditional knowledge about lateral movement of deformable spherical particles. Although several experimental and numerical studies have investigated RBC behavior in microchannels with similar diameters as RBCs, the detailed mechanical characteristics of RBC lateral movement—in particular, regarding the relationship between stable deformed shapes, equilibrium radial RBC position, and membrane load—has not yet been fully described. Thus, we numerically investigated the behavior of single RBCs with radii of 4 µm in a circular microchannel with diameters of 15 µm. Flow was assumed to be almost inertialess. The problem was characterized by the capillary number, which is the ratio between fluid viscous force and membrane elastic force. The power (or energy dissipation) associated with membrane deformations was introduced to quantify the state of membrane loads. Simulations were performed with different capillary numbers, viscosity ratios of the internal to external fluids of RBCs, and initial RBC centroid positions. Our numerical results demonstrated that axial or nonaxial migration of RBC depended on the stable deformed RBC shapes, and the equilibrium radial position of the RBC centroid correlated well with energy expenditure associated with membrane deformations.Takeishi N, Yamashita H, Omori T, Yokoyama N, Sugihara-Seki M. Axial and Nonaxial Migration of Red Blood Cells in a Microtube. Micromachines. 2021; 12(10):1162. https://doi.org/10.3390/mi1210116

Development of a mesoscopic framework spanning nanoscale protofibril dynamics to macro-scale fibrin clot formation

Thrombi form a micro-scale fibrin network consisting of an interlinked structure of nanoscale protofibrils, resulting in haemostasis. It is theorized that the mechanical effect of the fibrin clot is caused by the polymeric protofibrils between crosslinks, or to their dynamics on a nanoscale order. Despite a number of studies, however, it is still unknown, how the nanoscale protofibril dynamics affect the formation of the macro-scale fibrin clot and thus its mechanical properties. A mesoscopic framework would be useful to tackle this multi-scale problem, but it has not yet been established. We thus propose a minimal mesoscopic model for protofibrils based on Brownian dynamics, and performed numerical simulations of protofibril aggregation. We also performed stretch tests of polymeric protofibrils to quantify the elasticity of fibrin clots. Our model results successfully captured the conformational properties of aggregated protofibrils, e.g., strain-hardening response. Furthermore, the results suggest that the bending stiffness of individual protofibrils increases to resist extension.Takeishi Naoki, Shigematsu Taiki, Enosaki Ryogo, Ishida Shunichi, Ii Satoshi and Wada Shigeo 2021Development of a mesoscopic framework spanning nanoscale protofibril dynamics to macro-scale fibrin clot formationJ. R. Soc. Interface.182021055420210554 http://doi.org/10.1098/rsif.2021.055

MRP3 as a novel resistance factor for sorafenib in hepatocellular carcinoma

The mechanism of resistance of hepatocellular carcinoma (HCC) to sorafenib is unknown and no useful predictive biomarker for sorafenib treatment has been reported. Accordingly, we established sorafenib-resistant HCC cells and investigated the underlying mechanism of resistance to sorafenib. Sorafenib-resistant cell lines were established from the HCC cell line PLC/PRF5 by cultivation under continuous exposure to increasing concentration of sorafenib. The IC50 values of the 2 resistant clones PLC/PRF5-R1 and PLC-PRF5-R2 were 9.2±0.47 μM (1.8-fold) and 25±5.1 μM (4.6-fold) respectively, which were significantly higher than that of parental PLC/PRF5 cells (5.4±0.17 μM) (p<0.01 respectively), as determined by MTT assay. Western blot analysis of signal transduction-related proteins showed no significant differences in expression of AKT/pAKT, mTOR/pmTOR, or ERK/pERK between the 2 resistant clones versus parent cells, suggesting no activation of an alternative signal transduction pathway. Likewise, when expression of membrane transporter proteins was determined, there were no significant differences in expression levels of BSEP, MDR1, MRP2, BCRP, MRP4 and OCT1 between resistant clones and parent cells. However, the expression levels of MRP3 in the 2 resistant clones were significantly higher than that of parent cells. When MRP3 gene was knocked down by siRNA in PLC-PRF5-R2 cells, the sensitivity of the cells to sorafenib was restored. In the analysis of gene mutation, there was no mutation in the activation segment of Raf1 kinase in the resistant clones. Our data clearly demonstrate that the efflux transporter MRP3 plays an important role in resistance to sorafenib in HCC cells