Language：Others  

DOI： 10.1038/s41598-023-40774-6

Language：Japanese  

細胞内部が周囲力学環境から受ける様々な応力と,細胞質内のモーターたんぱく質・酵素から受ける力により,どのように変形し流動するかを知るためには,細胞質のレオロジーを明らかにする必要がある.細胞内部は生体高分子ゲルとして振る舞う細胞骨格と,その間隙を埋めるリポソーム,たんぱく質や核酸からなる高濃度コロイド懸濁液からなる.これまで,細胞の機械的特性を調べる上で,細胞骨格が注目されてきたが,骨格間隙の細胞質レオロジーは未解明であった.本稿では,当研究グループにて得られた細胞質レオロジーについての知見を細胞内レオロジーの測定法と共に紹介する.(著者抄録)

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.bpj.2023.04.011

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.2142/biophysico.bppb-v19.0036

Language：Others   Publishing type：Research paper (scientific journal)  

Abstract

A network of semiflexible biopolymers, known as the cytoskeleton, and molecular motors play fundamental mechanical roles in cellular activities. The cytoskeletal response to forces generated by molecular motors is profoundly linked to physiological processes. However, owing to the highly nonlinear mechanical properties, the cytoskeletal response on the microscopic level is largely elusive. The aim of this study is to investigate the microscopic mechanical response of semiflexible biopolymer networks by conducting microrheology (MR) experiments. Micrometer-sized colloidal particles, embedded in semiflexible biopolymer networks, were forced beyond the linear regime at a variety of conditions by using feedback-controlled optical trapping. This high-bandwidth MR technology revealed an affine elastic response, which showed stiffening upon local forcing. After scaling the stiffening behaviors, with parameters describing semiflexible networks, a collapse onto a single master curve was observed. The physics underlying the general microscopic response is presented to justify the collapse, and its potentials/implications to elucidate cell mechanics is discussed.

DOI： 10.1088/1367-2630/ac6902

Language：English   Publishing type：Research paper (scientific journal)  

Cell adhesion on biomaterial surfaces has been extensively studied from the perspective of the adsorption properties of adhesive ligands, while recent research on mechanobiology has been revealing a critical role of the mechanical properties of the extracellular milieu in the control of cell adhesion, such as the stiffness and viscoelasticity of the matrix. Although the effects of the lateral mobility of an adhesive ligand have been intensively investigated in a model substrate with water-soluble polymer layers, less is known about those in the setting of lateral deformability of hydrophobic condensed polymer layers. In this study, to help clarify this issue, we used PNIPAAm-grafted substrates with a well-controlled degree of graft-polymerization (DGP) as a typical hydrophobic condensed polymer surface at a cell culture temperature of 37 degrees C. We observed a clear negative correlation between cell spreading and DGP of PNIPAAm regardless of the amount of fibronectin adsorbed on the substrates, which was found to be attributable to the lateral deformability of a condensed PNIPAAm layer based on lateral force microscopic analysis. The surface-lateral-deformation-induced modulation in stability and maturation of focal adhesion of the cells is discussed in relation to the matrix-strain-induced alteration of the density distribution of adsorbed adhesive ligands.

DOI： 10.1038/s41428-021-00577-w

Language：Japanese   Publishing type：Research paper (scientific journal)  

Dynamics of Cell Shaping and Migration on the Matrix with Cell-scale Stiffness-heterogeneity

DOI： 10.2142/biophys.61.152

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.bpj.2020.11.617

Language：English   Publishing type：Research paper (scientific journal)  

Stiffness-gradient-induced cellular taxis, so-called durotaxis, has been extensively studied on a substrate with a single broad or steep stiffness gradient. However, in actual living tissues, cells should sense cell-scaled heterogeneous elasticity distribution in the extracellular matrix. In this study, to clarify the effect of the cell-scale heterogeneity of matrix-elasticity on durotaxis, we examined the motility of different types of cells on microelastically-striped patterned gels with different cell-sized widths. We found that cells accumulated in stiff regions with specific width on cell-type-dependency, even when a stiffness gradient is too small to induce usual durotaxis with a monotonic stiffness gradient. Fibroblast cells accumulated in a wide stiff region of multicellular size, while mesenchymal stem cells localized in a narrow stiff region of single-cell size. It was revealed that durotactic activity is critically affected not only with the cell type but also with the cell-scale heterogeneity of matrix-elasticity. Based on the shape-fluctuation-based analysis of cell migration, the dynamics of the pseudopodia were found to play a key role in determining the behaviors of general durotaxis. Our results suggest that design of cell-scale heterogeneity of matrix-elasticity is pivotal in controlling directional cell migration, the spontaneous cell-patterning, and development of the tissue on the biomaterials surfaces.

DOI： 10.1016/j.biomaterials.2019.119647

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1247/csf.19040

Language：English   Publishing type：Research paper (scientific journal)  

In general, cells move on a substrate through extension and contraction of the cell body. Though cell movement should be explained by taking into account the effect of such shape fluctuations, past approaches to formulate cell-crawling have not sufficiently quantified the relationship between cell movement (velocity and trajectory) and shape fluctuations based on experimental data regarding actual shaping dynamics. To clarify this relationship, we experimentally characterized cell-crawling in terms of shape fluctuations, especially extension and contraction, by using an elasticity-tunable gel substrate to modulate cell shape. As a result, an amoeboid swimmer-like relation was found to arise between the cell velocity and cell-shape dynamics. To formulate this experimentally-obtained relationship between cell movement and shaping dynamics, we established a persistent random deformation (PRD) model based on equations of a deformable self-propelled particle adopting an amoeboid swimmer-like velocity-shape relationship. The PRD model successfully explains the statistical properties of velocity, trajectory and shaping dynamics of the cells including back-and-forth motion, because the velocity equation exhibits time-reverse symmetry, which is essentially different from previous models. We discuss the possible application of this model to classify the phenotype of cell migration based on the characteristic relation between movement and shaping dynamics.

DOI： 10.1038/s41598-018-23540-x

Language：English  

DOI： 10.1016/j.bpj.2016.11.2328

Language：English   Publishing type：Research paper (scientific journal)  

In vertically vibrated dense suspensions, several localized structures have been discovered, such as heaps, stable holes, expanding holes, and replicating holes. Because an inclined free fluid surface is difficult to maintain because of gravitational pressure, the mechanism of those structures is not understood intuitively. In this paper, as a candidate for the driving mechanism, we focus on the boundary condition on a solid wall: the slip-nonslip switching boundary condition in synchronization with vertical vibration. By applying the lubrication approximation, we derived the time evolution equation of the fluid thickness from the Oldroyd-B fluid model. In our model we show that the initially flat fluid layer becomes unstable in a subcritical manner, and heaps and convectional flow appear. The obtained results are consistent with those observed experimentally. We also find that heaps climb a slope when the bottom is slightly inclined. We show that viscoelasticity enhances heap formation and climbing of a heap on the slope.

DOI： 10.1103/PhysRevE.92.053016

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/srep08546

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)  

Granular materials often segregate under mechanical agitation such as flowing, shaking, or rotating, in contrast to an expectation of mixing. It is well known that bidisperse mixtures of granular materials in a partially filled rotating cylinder exhibit monotonic coarsening dynamics of segregation. Here we report the steady oscillation of segregated axial bands under the stationary rotation of a nearly filled coaxial cylinder for O(103) revolutions. The axial bands demonstrate steady back-and-forth motion along the axis of rotation. Experimental findings indicated that these axial band dynamics are driven by global convection throughout the system. The essential features of the spatiotemporal dynamics are reproduced with a simple phenomenological equation that incorporates the effect of global convection.

DOI： 10.1103/PhysRevE.91.010201

Language：English   Publishing type：Research paper (scientific journal)  

In vertically vibrated starch suspensions, we observe bifurcations from stable holes to replicating holes. Above a certain acceleration, finite-amplitude deformations of the vibrated surface continue to grow until void penetrates fluid layers, and a hole forms. We studied experimentally and theoretically the parameter dependence of the holes and their stabilities. In suspensions of small dispersed particles, the circular shapes of the holes are stable. However, we find that larger particles or lower surface tension of water destabilize the circular shapes
this indicates the importance of capillary forces acting on the dispersed particles. Around the critical acceleration for bifurcation, holes show intermittent large deformations as a precursor to hole replication. We applied a phenomenological model for deformable domains, which is used in reaction-diffusion systems. The model can explain the basic dynamics of the holes, such as intermittent behavior, probability distribution functions of deformation, and time intervals of replication. Results from the phenomenological model match the linear growth rate below criticality that was estimated from experimental data. © 2013 American Physical Society.

DOI： 10.1103/PhysRevE.88.053007

Language：English   Publishing type：Research paper (scientific journal)  

How can localized, steady deformed structures be formed in the free surface of a fluid layer? For example, in vertically vibrated dense suspensions, heaping and stable holes are stable structures that are sustained against large gravitational pressure. Here we propose a new model of heaping induced by a boundary condition on a solid wall. We found that a flat fluid layer becomes unstable and forms heaps when we impose a boundary condition that shows slip/non-slip switching in synchronization with vertical vibration. The obtained onset acceleration, bifurcation type and flow of the heaps are consistent with those observed experimentally. Furthermore, we found that heaps can drift and climb a slope when the bottom is slightly inclined. This result indicates that our model can be applied to the migration of localized structures. © Copyright EPLA, 2012.

DOI： 10.1209/0295-5075/100/14001

Language：English   Publishing type：Research paper (scientific journal)  

We find self-replicating holes on the surface of a vertically vibrated potato starch suspension. Above certain acceleration, the finite-amplitude deformation of the surface grows to form a hole that penetrates the fluid layer. The circular shape of the hole is not stable, and the hole begins to replicate just like the self-replicating spots in chemical reaction-diffusion systems. At high acceleration, these holes exhibit spatiotemporal chaos. By assessing the statistical properties in a steady state, we show that fluctuation in the number of holes can be understood by a master equation. © 2011 American Physical Society.

DOI： 10.1103/PhysRevLett.107.088301

Language：Others  

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.1063/1.3180032

Language：English   Publishing type：Research paper (scientific journal)  

Surface instabilities in vertically vibrated suspensions of various powders dispersed in silicone oil are investigated in quasi-two-dimensional (2D) and quasi-one-dimensional (1D) systems. As vibration acceleration exceeded a critical value, the flat surface became unstable against a finite-amplitude perturbation. We found an expanding hole or viscous fingerlike pattern in the quasi-2D system and segregation between dried and wet areas in the quasi-1D system. We show that these instabilities are accompanied by convectionlike flow at their rim and in the quasi-1D system, the height of the convectionlike flow can be scaled by acceleration, vibration frequency, diameter of the dispersed powder, mean density of the suspension, and viscosity of silicone oil. We propose a simple model that accounts for the scaling and concentric motion of the convectionlike flow. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevE.79.066308

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.1

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2013.6 - 2013.7

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Country：Other  

A model for heap formation in vibrated gravitational suspensions

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Mode bifurcations of a swimming droplet driven by Faraday wave

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Swimming droplets driven by surface wave

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Language：Japanese  

19pAD-9 Bifurcation of the holes in dense suspensions

Language：Japanese  

24aGA-3 A model of heaping using slip on the wall in vertically vibrated slurries

Language：Japanese  

28aTF-2 Surface instability induced by slip on the wall in vertically vibrated slurries

Language：Japanese  

23pTD-13 Dynamics of deformation of self-propelled holes in dense suspensions

Language：Japanese  

20pEJ-8 Pattern dynamics in vertically vibrated wet granular matter II

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26aQC-7 Pattern dynamics in vertically vibrated wet granular matter

Language：Japanese  

27aTB-8 Convection like flow in vertically vibrated wet granular matter

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20aVA-1 Instability of vertically vibrated paste surface II

Language：Japanese  

25pWF-1 Instability of vertically vibrated paste surface

Language：English  

Water Behavior in Capillary Tubes under Microgravity