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

Living cells are composed of active materials, in which forces are generated by the energy derived from metabolism. Forces and structures self-organize to shape the cell and drive its dynamic functions. Understanding the out-of-equilibrium mechanics is challenging because constituent materials, the cytoskeleton and the cytosol, are extraordinarily heterogeneous, and their physical properties are strongly affected by the internally generated forces. We have analyzed dynamics inside two types of eukaryotic cells, fibroblasts and epithelial-like HeLa cells, with simultaneous active and passive microrheology using laser interferometry and optical trapping technology. We developed a method to track microscopic probes stably in cells in the presence of vigorous cytoplasmic fluctuations, by using smooth three-dimensional (3D) feedback of a piezo-actuated sample stage. To interpret the data, we present a theory that adapts the fluctuation-dissipation theorem (FDT) to out-of-equilibrium systems that are subjected to positional feedback, which introduces an additional nonequilibrium effect. We discuss the interplay between material properties and nonthermal force fluctuations in the living cells that we quantify through the violations of the FDT. In adherent fibroblasts, we observed a well-known polymer network viscoelastic response where the complex shear modulus scales as G* ∝ (-iω)3/4. In the more 3D confluent epithelial cells, we found glassy mechanics with G* ∝ (-iω)1/2 that we attribute to glassy dynamics in the cytosol. The glassy state in living cells shows characteristics that appear distinct from classical glasses and unique to nonequilibrium materials that are activated by molecular motors.

DOI： 10.1126/sciadv.1700318

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

Nature is full of power-law interactions, e.g., gravity, electrostatics, and hydrodynamics. When sources of such fields are randomly distributed in space, the superposed interaction, which is what we observe, is naively expected to follow a Gauss or Levy distribution. Here, we present an analytic expression for the actual distributions that converge to novel limits that are in between these already-known limit distributions, depending on physical parameters, such as the concentration of field sources and the size of the probe used to measure the interactions. By comparing with numerical simulations, the origin of non-Gauss and non-Levy distributions are theoretically articulated.

DOI： 10.1103/PhysRevLett.117.030602

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

The cytoskeleton is a network of crosslinked, semiflexible filaments, and it has been suggested that it has properties of a glassy state. Here we employ optical-trap-based microrheology to apply forces to a model cytoskeleton and measure the high-bandwidth response at an anterior point. Simulating the highly nonlinear and anisotropic stress-strain propagation assuming affinity, we found that theoretical predictions for the quasistatic response of semiflexible polymers are only realized at high frequencies inaccessible to conventional rheometers. We give a theoretical basis for determining the frequency when both affinity and quasistaticity are valid, and we discuss with experimental evidence that the relaxations at lower frequencies can be characterized by the experimentally obtained nonaffinity parameter.

DOI： 10.1103/PhysRevE.89.042711

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

DOI： 10.1039/c0sm00925c

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

DOI： 10.1103/PhysRevLett.102.168102

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

Cells actively probe mechanical properties of their environment by exerting internally generated forces. The response they encounter profoundly affects their behavior. Here we measure in a simple geometry the forces a cell exerts suspended by two optical traps. Our assay quantifies both the overall force and the fraction of that force transmitted to the environment. Mimicking environments of varying stiffness by adjusting the strength of the traps, we found that the force transmission is highly dependent on external compliance. This suggests a calibration mechanism for cellular mechanosensing.

DOI： 10.1103/PhysRevLett.102.168102

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

DOI： 10.1126/science.1134404

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

Cells both actively generate and sensitively react to forces through their mechanical framework, the cytoskeleton, which is a nonequilibrium composite material including polymers and motor proteins. We measured the dynamics and mechanical properties of a simple three-component model system consisting of myosin II, actin filaments, and cross-linkers. In this system, stresses arising from motor activity controlled the cytoskeletal network mechanics, increasing stiffness by a factor of nearly 100 and qualitatively changing the viscoelastic response of the network in an adenosine triphosphate-dependent manner. We present a quantitative theoretical model connecting the large-scale properties of this active gel to molecular force generation.

DOI： 10.1126/science.1134404

Language：Others   Publisher：arXiv  

Soft jammed solids exhibit intriguing mechanical properties, while their
linear response is elusive. In particular, foams and emulsions generally reveal
anomalous viscous loss with the loss and storage modulus following $G^{\prime
\prime} \propto \sqrt{\omega}$ and $G^{\prime} \propto \omega^0$. In this
study, we offer a comprehensive microscopic understanding of this behavior.
Using microrheology experiment, we measured $G^* = G^{\prime} + i G^{\prime
\prime}$ of concentrated emulsions in a wide range of frequencies. In theory,
we applied a linear response formalism for microrheology to a soft sphere model
that undergoes the jamming transition. We find that the theory quantitatively
explains the experiments without the need for parameter adjustments. Our
analysis reveals that the anomalous viscous loss results from the boson peak,
which is a universal vibrational property of amorphous solids and reflects the
marginal stability in soft jammed solids. We discuss that the anomalous viscous
loss is universal in systems with various interparticle interactions as it
stems from the universal boson peak, and it even survives below the jamming
density where thermal fluctuation is pronounced and the dynamics becomes
inherently nonlinear.

DOI： 10.48550/ARXIV.2402.00291

arXiv

researchmap

Other Link： http://arxiv.org/pdf/2402.00291v1

Language：Others   Publisher：arXiv  

We investigate dense suspensions of swimming bacteria prepared in a
nutrient-exchange chamber. Near the pellet concentration, nonthermal
fluctuations showed notable agreement between self and collective behaviors, a
phenomenon not previously observed at equilibrium. The viscosity of active
suspensions dramatically decreased compared to their inactive counterparts,
where glassy features, such as non-Newtonian viscosity and dynamic
heterogeneity, disappeared. Instead, the complex shear modulus showed a
power-law rheology,$G^*(\omega)\propto\left(-i\omega\right)^\frac{1}{2}$,
indicating the role of bacterial activity in driving the system towards a
critical jamming state.

DOI： 10.48550/ARXIV.2401.15658

arXiv

researchmap

Other Link： http://arxiv.org/pdf/2401.15658v2

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

We investigate the fluctuating dynamics of colloidal particles in weakly crosslinked F-actin networks with optical-trap-based microrheology. Using the dual-feedback technology, embedded colloidal particles were stably forced beyond the linear regime in a manner that does not suppress spontaneous fluctuations of particles. Upon forcing, a particle that was stably confined in a cage made of the network's crosslinks started to intermittently jump to the next caging microenvironments. By investigating the statistics of the jump dynamics, we discuss how heterogeneous relaxations observed in equilibrium systems became homogeneous when similar jumps were activated under constant forcing beyond the linear regime.

DOI： 10.1103/physreve.108.034601

Web of Science

Scopus

PubMed

researchmap

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevE.108.034601/fulltext

Language：Japanese   Publisher：日本バイオマテリアル学会  

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)

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Biophysical Society of Japan General Incorporated Association  

Nonthermal Fluctuation Accelerates Molecular Motor Kinesin

DOI： 10.2142/biophys.63.86

CiNii Research

researchmap

Language：Japanese   Publisher：Japan Oil Chemists' Society  

<p>Microrheology (MR) using optical trapping and laser interferometry is particularly useful for biological samples whose rheology remarkably depends on time and length scales. However, it has been challenging to measure samples like living cells that exhibit large fluctuations (flow) and can be damaged by laser light. Recently, with the feedback control of the optical-trapping force and the probe position, it has become possible to conduct precise, minimally invasive MR measurements of soft matter and living samples. In this paper, after explaining these latest techniques, we will present examples of measurements: the linear viscoelasticity within living cells, and the force-induced nonlinear fluctuations in the in vitro cytoskeleton.</p>

DOI： 10.5650/oleoscience.23.491

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Cold Spring Harbor Laboratory  

<jats:title>Abstract</jats:title><jats:p>Active microrheology was conducted in living cells by applying an optical-trapping force to vigorously-fluctuating tracer beads with feedback-tracking technology. The complex shear viscoelastic modulus<jats:italic>G</jats:italic>(<jats:italic>ω</jats:italic>) =<jats:italic>G</jats:italic>′(<jats:italic>ω</jats:italic>) –<jats:italic>iG</jats:italic>″(<jats:italic>ω</jats:italic>) was measured in HeLa cells in an epithelial-like confluent monolayer. We found that<jats:italic>G</jats:italic>(<jats:italic>ω</jats:italic>) ∝ (−<jats:italic>iω</jats:italic>)<jats:sup>1/2</jats:sup>over a wide range of frequencies (1 Hz &lt;<jats:italic>ω</jats:italic>/2<jats:italic>π</jats:italic>&lt;10 kHz). Actin disruption and cell-cycle progression from G1 to S and G2 phases only had a limited effect on<jats:italic>G</jats:italic>(<jats:italic>ω</jats:italic>) in living cells. On the other hand,<jats:italic>G</jats:italic>(<jats:italic>ω</jats:italic>) was found to be dependent on cell metabolism; ATP-depleted cells showed an increased elastic modulus<jats:italic>G</jats:italic>′(<jats:italic>ω</jats:italic>) at low frequencies, giving rise to a constant plateau such that<jats:italic>G</jats:italic>(<jats:italic>ω</jats:italic>) =<jats:italic>G</jats:italic><jats:sub>0</jats:sub>+<jats:italic>A</jats:italic>(−<jats:italic>iω</jats:italic>)<jats:sup>1/2</jats:sup>. Both the plateau and the additional frequency dependency ∝ (−<jats:italic>iω</jats:italic>)<jats:sup>1/2</jats:sup>of ATP-depleted cells are consistent with a rheological response typical of colloidal jamming. On the other hand, the plateau<jats:italic>G</jats:italic><jats:sub>0</jats:sub>disappeared in ordinary metabolically active cells, implying that living cells fluidize their internal states such that they approach the critical jamming point.</jats:p><jats:sec><jats:title>Statement of Significance</jats:title><jats:p>Intracellular mechanical properties were measured using optical-trap-based microrheology. Despite expectations to the contrary, shear viscoelasticity was hardly affected by reorganization of cytoskeletal structures during cell-cycle progression (G1 to S and G2 phases), nor by artificial disruption of the actin cytoskeleton induced by chemical inhibitors. Rather, the mechanics of cell interiors is governed by the glassy cytoplasm. Cells depleted of ATP solidified, whereas living cells that maintained metabolic activities were more fluid-like. Instead of a completely fluid response, however, we observed a characteristic power-law viscoelasticity<jats:italic>G</jats:italic>(<jats:italic>ω</jats:italic>) ∝ (−<jats:italic>iω</jats:italic>)<jats:sup>1/2</jats:sup>over the whole range of frequencies measured. Based on our current understanding of jamming rheology, we discuss how cells fluidize their internal state in a way that pushes the system towards the critical jamming transition.</jats:p></jats:sec>

DOI： 10.1101/2022.09.02.506288

Scopus

PubMed

researchmap

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

The movement of single kinesin molecules was observed while applying noisy external forces that mimic intracellular active fluctuations. We found kinesin accelerates under noise, especially when a large hindering load is added. The behavior quantitatively conformed to a theoretical model that describes the kinesin movement with simple two-state reactions. The universality of the kinetic theory suggests that intracellular enzymes share a similar noise-induced acceleration mechanism, i.e., active fluctuations in cells are not just noise but are utilized to promote various physiological processes.

DOI： 10.1103/PhysRevLett.127.178101

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

Soft matter consists of meso-scale (nm~{mu}m) structures that are formed by
weak interactions and reorganized under thermal fluctuations. The resulting
complex relaxation phenomena may be probed with microrheology, by observing the
movement of embedded probe particles. Because of the softness of the material,
however, perturbations to the probe that are inevitably added during
microrheology experiments prevent direct translation of those movements to
rheological properties. In this study, we conducted optical-trap-based
microrheology with significantly reduced mechanical perturbations; dual
feedback technology allowed us to apply well-determined optical-trapping forces
to a fluctuating embedded probe and precisely measure its response and
fluctuations with high spatiotemporal resolution. We demonstrate the improved
performance of this technique by studying an reconstituted network of actin
cytoskeletal filaments, observing their slow dynamics, homogeneous thermal
fluctuations as well as activated hopping between mesoscale microenvironments.

DOI： 10.48550/ARXIV.2106.05119

Language：Japanese  

Optical leverage in laser particle tracking

DOI： 10.11470/jsapmeeting.2021.1.0_786

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

The actin cytoskeleton in living cells generates forces in conjunction with myosin motor proteins to directly and indirectly drive essential cellular processes. The semiflexible filaments of the cytoskeleton can respond nonlinearly to the collective action of motors. We here investigate mechanics and force generation in a model actin cytoskeleton, reconstituted in vitro, by observing the response and fluctuations of embedded micron-scale probe particles. Myosin mini-filaments can be modeled as force dipoles and give rise to deformations in the surrounding network of cross-linked actin. Anomalously correlated probe fluctuations indicate the presence of rapid local compression or draining of the network that emerges in addition to the ordinary linear shear elastic (incompressible) response to force dipoles. The anomalous propagation of compression can be attributed to the nonlinear response of actin filaments to the microscopic forces, and is quantitatively consistent with motor-generated large-scale stiffening of the gels.

DOI： 10.1039/c9sm02362c

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

Optical trapping and laser interferometry enable the non-invasive manipulation of colloids, which can be used to investigate the microscopic mechanics of surrounding media or bound macromolecules. For efficient trapping and precise tracking, the sample media must ideally be homogeneous and quiescent whereas such conditions are usually not satisfied in vivo in living cells. In order to investigate mechanics of the living-cell interior, we introduced (1) the in-situ calibration of optical trapping and laser interferometry, and (2) 3-D feedback control of a sample stage to stably track a colloidal particle. Investigating systematic errors that appear owing to sample heterogeneity and focal offsets of a trapping laser relative to the colloidal probe, we provide several important caveats for conducting precise optical micromanipulation in living cells. On the basis of this study, we further improved the performance of the techniques to be used in cells, by optimizing the position sensitivity of laser interferometry and the stability of the feedback simultaneously.

DOI： 10.3390/app10144970

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

Optical trapping and laser interferometry enable the non-invasive manipulation of colloids, which can be used to investigate the microscopic mechanics of surrounding media or bound macromolecules. For efficient trapping and precise tracking, the sample media must ideally be homogeneous and quiescent whereas such conditions are usually not satisfied in vivo in living cells. In order to investigate mechanics of the living-cell interior, we introduced (1) the in-situ calibration of optical trapping and laser interferometry, and (2) 3-D feedback control of a sample stage to stably track a colloidal particle. Investigating systematic errors that appear owing to sample heterogeneity and focal offsets of a trapping laser relative to the colloidal probe, we provide several important caveats for conducting precise optical micromanipulation in living cells. On the basis of this study, we further improved the performance of the techniques to be used in cells, by optimizing the position sensitivity of laser interferometry and the stability of the feedback simultaneously.

DOI： 10.3390/app10144970

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

DOI： 10.1007/s12551-020-00643-2

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

Molecular motors are nonequilibrium open systems that convert chemical energy to mechanical work. Their energetics are essential for various dynamic processes in cells, but largely remain unknown because fluctuations typically arising in small systems prevent investigation of the nonequilibrium behavior of the motors in terms of thermodynamics. Recently, Harada and Sasa proposed a novel equality to measure the dissipation of nonequilibrium small systems. By utilizing this equality, we have investigated the nonequilibrium energetics of the single-molecule walking motor kinesin-1. The dissipation from kinesin movement was measured through the motion of an attached probe particle and its response to external forces, indicating that large hidden dissipation exists. In this short review, aiming to readers who are not familiar with nonequilibrium physics, we briefly introduce the theoretical basis of the dissipation measurement as well as our recent experimental results and mathematical model analysis and discuss the physiological implications of the hidden dissipation in kinesin. In addition, further perspectives on the efficiency of motors are added by considering their actual working environment: living cells.

DOI： 10.1007/s12551-020-00684-7

Language：English  

DOI： 10.1007/s12551-020-00643-2

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

Molecular motors are nonequilibrium open systems that convert chemical energy to mechanical work. Their energetics are essential for various dynamic processes in cells, but largely remain unknown because fluctuations typically arising in small systems prevent investigation of the nonequilibrium behavior of the motors in terms of thermodynamics. Recently, Harada and Sasa proposed a novel equality to measure the dissipation of nonequilibrium small systems. By utilizing this equality, we have investigated the nonequilibrium energetics of the single-molecule walking motor kinesin-1. The dissipation from kinesin movement was measured through the motion of an attached probe particle and its response to external forces, indicating that large hidden dissipation exists. In this short review, aiming to readers who are not familiar with nonequilibrium physics, we briefly introduce the theoretical basis of the dissipation measurement as well as our recent experimental results and mathematical model analysis and discuss the physiological implications of the hidden dissipation in kinesin. In addition, further perspectives on the efficiency of motors are added by considering their actual working environment: living cells.

DOI： 10.1007/s12551-020-00684-7

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

Measuring Dissipation of Molecular Motor Kinesin

DOI： 10.2142/biophys.59.300

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

Nonequilibrium energetics of single molecule translational motor kinesin was investigated by measuring heat dissipation from the violation of the fluctuation-response relation of a probe attached to the motor using optical tweezers. The sum of the dissipation and work did not amount to the input free energy change, indicating large hidden dissipation exists. Possible sources of the hidden dissipation were explored by analyzing the Langevin dynamics of the probe, which incorporates the two-state Markov stepper as a kinesin model. We conclude that internal dissipation is dominant.

DOI： 10.1103/PhysRevLett.121.218101

Language：English  

DOI： 10.1016/j.bpj.2017.11.2783

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

Severity of sour environment determined in accordance with ISO15156-2 or NACE MR0175 for carbon and low-alloy steels has been proposed. The critical line of each region which was indicated as regions 0, 1, 2 and 3 was thought to be determined based on experimental sulfide stress cracking (SSC) results of API grade N80 and P110. SSC or hydrogen induced cracking (HIC) occurs if hydrogen concentration entering into steel from the environment exceeds the critical hydrogen concentration in steel. The severity of sour environment was introduced and proposed based on equal hydrogen concentration entering into steel from the environment from the viewpoint of HIC.

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

Living cells are composed of active materials, in which forces are generated by the energy derived from metabolism. Forces and structures self-organize to shape the cell and drive its dynamic functions. Understanding the out-of-equilibrium mechanics is challenging because constituent materials, the cytoskeleton and the cytosol, are extraordinarily heterogeneous, and their physical properties are strongly affected by the internally generated forces. We have analyzed dynamics inside two types of eukaryotic cells, fibroblasts and epithelial-like HeLa cells, with simultaneous active and passive microrheology using laser interferometry and optical trapping technology. We developed a method to track microscopic probes stably in cells in the presence of vigorous cytoplasmic fluctuations, by using smooth three-dimensional (3D) feedback of a piezo-actuated sample stage. To interpret the data, we present a theory that adapts the fluctuation-dissipation theorem (FDT) to out-of-equilibrium systems that are subjected to positional feedback, which introduces an additional nonequilibrium effect. We discuss the interplay between material properties and nonthermal force fluctuations in the living cells that we quantify through the violations of the FDT. In adherent fibroblasts, we observed a well-known polymer network viscoelastic response where the complex shear modulus scales as G* proportional to (-i omega)(3/4). In the more 3D confluent epithelial cells, we found glassy mechanics with G* proportional to (-i omega)(1/2) that we attribute to glassy dynamics in the cytosol. The glassy state in living cells shows characteristics that appear distinct from classical glasses and unique to nonequilibrium materials that are activated by molecular motors.

DOI： 10.1126/sciadv.1700318

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

Feedback-tracking microrheology, developed to study nonequilibrium mechanics of active materials, revealed glassy cell dynamics.

DOI： 10.1126/sciadv.1700318

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

We investigate the hydrodynamic fluctuations in suspensions of swimming microorganisms (Chlamydomonas) by observing the probe particles dispersed in the media. Short-term fluctuations of probe particles were superdiffusive and displayed heavily tailed non-Gaussian distributions. The analytical theory that explains the observed distribution was derived by summing the power-law-decaying hydrodynamic interactions from spatially distributed field sources (here, swimming microorganisms). The summing procedure, which we refer to as the physical limit operation, is applicable to a variety of physical fluctuations to which the classical central limiting theory does not apply. Extending the analytical formula to compare to experiments in active swimmer suspensions, we show that the non-Gaussian shape of the observed distribution obeys the analytic theory concomitantly with independently determined parameters such as the strength of force generations and the concentration of Chlamydomonas. Time evolution of the distributions collapsed to a single master curve, except for their extreme tails, for which our theory presents a qualitative explanation. Investigations thereof and the complete agreement with theoretical predictions revealed broad applicability of the formula to dispersions of active sources of fluctuations.

DOI： 10.1103/PhysRevE.95.030601

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

The cytoskeleton is a network of crosslinked, semiflexible filaments, and it has been suggested that it has properties of a glassy state. Here we employ optical-trap-based microrheology to apply forces to a model cytoskeleton and measure the high-bandwidth response at an anterior point. Simulating the highly nonlinear and anisotropic stress-strain propagation assuming affinity, we found that theoretical predictions for the quasistatic response of semiflexible polymers are only realized at high frequencies inaccessible to conventional rheometers. We give a theoretical basis for determining the frequency when both affinity and quasistaticity are valid, and we discuss with experimental evidence that the relaxations at lower frequencies can be characterized by the experimentally obtained nonaffinity parameter.

DOI： 10.1103/PhysRevE.89.042711

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

DOI： 10.1016/j.bpj.2013.11.973

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

DOI： 10.1016/j.bpj.2013.11.3218

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

Analytical and numerical calculations are presented for the mechanical response of fiber networks in a state of axisymmetric prestress, in the limit where geometric nonlinearities such as fiber rotation are negligible. This allows us to focus on the anisotropy deriving purely from the nonlinear force-extension curves of individual fibers. The number of independent elastic coefficients for isotropic, axisymmetric, and fully anisotropic networks are enumerated before deriving expressions for the response to a locally applied force that can be tested against, e.g., microrheology experiments. Localized forces can generate anisotropy away from the point of application, so numerical integration of nonlinear continuum equations is employed to determine the stress field, and induced mechanical anisotropy, at points located directly behind and in front of a force monopole. Results are presented for the wormlike chain model in normalized forms, allowing them to be easily mapped to a range of systems. Finally, the relevance of these findings to naturally occurring systems and directions for future investigation are discussed.

DOI： 10.1103/PhysRevE.88.022717

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

Many cells express a membrane-coupled external mechanical layer, the pericellular matrix (PCM), which often contains long-chain polymers. Its role and properties are not entirely known, but its functions are believed to include physical protection, mechanosensing, chemical signalling or lubrication. The viscoelastic response of the PCM, with polysaccharides as the main structural components, is therefore crucial for the understanding of its function. We have here applied microrheology, based on optically trapped micrometre-sized colloids, to the PCM of cultured PC3 prostate cancer cells. This technology allowed us to measure the extremely soft response of the PCM, with approximately 1 mu m height resolution. Exogen-ously added aggrecan, a hyaluronan-binding proteoglycan, caused a remarkable increase in thickness of the viscoelastic layer and also triggered filopodia-like protrusions. The viscoelastic response of the PCM, however, did not change significantly.

DOI： 10.1098/rsif.2011.0825

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

Many cells express a membrane-coupled external mechanical layer, the pericellular matrix (PCM), which often contains long-chain polymers. Its role and properties are not entirely known, but its functions are believed to include physical protection, mechanosensing, chemical signalling or lubrication. The viscoelastic response of the PCM, with polysaccharides as the main structural components, is therefore crucial for the understanding of its function. We have here applied microrheology, based on optically trapped micrometre-sized colloids, to the PCM of cultured PC3 prostate cancer cells. This technology allowed us to measure the extremely soft response of the PCM, with approximately 1 µm height resolution. Exogenously added aggrecan, a hyaluronan-binding proteoglycan, caused a remarkable increase in thickness of the viscoelastic layer and also triggered filopodia-like protrusions. The viscoelastic response of the PCM, however, did not change significantly.

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

Dynamic networks designed to model the cell cytoskeleton can be reconstituted from filamentous actin, the motor protein myosin and a permanent cross-linker. They are driven out of equilibrium when the molecular motors are active. This gives rise to athermal fluctuations that can be recorded by tracking probe particles that are dispersed in the network. We have here probed athermal fluctuations in such "active gels'' using video microrheology. We have measured the full distribution of probe displacements, also known as the van Hove correlation function. The dominant influence of thermal or athermal fluctuations can be detected by varying the lag time over which the displacements are measured. We argue that the exponential tails of the distribution derive from single motors close to the probes, and we extract an estimate of the velocity of motor heads along the actin filaments. The distribution exhibits a central Gaussian region which we assume derives from the action of many independent motor proteins far from the probe particles when athermal fluctuations dominate. Recording the whole distribution rather than just the typically measured second moment of probe fluctuations (mean-squared displacement) thus allowed us to differentiate between the effect of individual motors and the collective action of many motors.

DOI： 10.1039/c0sm00925c

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

Many active materials and biological systems are driven far from equilibrium by embedded agents that spontaneously generate forces and distort the surrounding material. Probing and characterizing these athermal fluctuations are essential to understand the properties and behaviors of such systems. Here we present a mathematical procedure to estimate the local action of force-generating agents from the observed fluctuating displacement fields. The active agents are modeled as oriented force dipoles or isotropic compression foci, and the matrix on which they act is assumed to be either a compressible elastic continuum or a coupled network-solvent system. Correlations at a single point and between points separated by an arbitrary distance are obtained, giving a total of three independent fluctuation modes that can be tested with microrheology experiments. Since oriented dipoles and isotropic compression foci give different contributions to these fluctuation modes, ratiometric analysis allows us characterize the force generators. We also predict and experimentally find a high-frequency ballistic regime, arising from individual force-generating events in the form of the slow buildup of stress followed by rapid but finite decay. Finally, we provide a quantitative statistical model to estimate the mean filament tension from these athermal fluctuations, which leads to stiffening of active networks.

DOI： 10.1103/PhysRevE.81.041910

Language：Japanese  

21pEF-3 Nonequilibrium Mechanics of Life

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

Many cells cover themselves with a multifunctional polymer coat, the pericellular matrix (PCM), to mediate mechanical interactions with the environment. A particular PCM, the endothelial glycocalyx (EG), is formed by vascular endothelial cells at their luminal side, forming a mechanical interface between the flowing blood and the endothelial cell layer. The glycosaminoglycan (GAG) hyaluronan (HA) is involved in the main functions of the EG, mechanotransduction of fluid shear stress and molecular sieving. HA, due to its length, is the only GAG in the EG or any other PCM able to form an entangled network. The mechanical functions of the EG are, however, impaired when any one of its components is removed. We here used microrheology to measure the effect of the EG constituents heparan sulfate, chondroitin sulfate, whole blood plasma and albumin on the high-bandwidth mechanical properties of a HA solution. Furthermore, we probed the effect of the hyaldherin aggrecan, a constituent of the PCM of chondrocytes, and very similar to versican (present in the PCM of various cells, and possibly in the EG). We show that components directly interacting with HA (chondroitin sulfate and aggrecan) can increase the viscoelastic shear modulus of the polymer composite.

DOI： 10.1088/1478-3975/6/2/025014

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

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

We report measurements of the frequency-dependent shear moduli of aging colloidal systems that evolve from a purely low-viscosity liquid to a predominantly elastic glass or gel. Using microrheology, we measure the local complex shear modulus G* (ω) over a very wide range of frequencies (from 1 Hz to 100 kHz). The combined use of one- and two-particle microrheology allows us to differentiate between colloidal glasses and gels-the glass is homogenous, whereas the colloidal gel shows a considerable degree of heterogeneity on length scales larger than 0.5 μm. Despite this characteristic difference, both systems exhibit similar rheological behaviors which evolve in time with aging, showing a crossover from a single-power-law frequency dependence of the viscoelastic modulus to a sum of two power laws. The crossover occurs at a time t0, which defines a mechanical transition point. We found that the data acquired during the aging of different samples can be collapsed onto a single master curve by scaling the aging time with t0. This raises questions about the prior interpretation of two power laws in terms of a superposition of an elastic network embedded in a viscoelastic background.

DOI： 10.1103/PhysRevE.78.061402

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

Quantitatively measuring the mechanical properties of soft matter over a wide range of length and time scales, especially if a sample is as complex as typical biological materials, remains challenging. Living cells present a further complication because forces are generated within these nonequilibrium materials that can change material properties. We have here developed high-bandwidth techniques for active one- and two-particle microrheology to tackle these issues. By combining active micromanipulation of probe particles with an optical trap with high-resolution tracking of thermal motions of the very same particles by laser interferometry, we can both measure the mechanical properties of and, at the same time, identify nonequilibrium forces in soft materials. In both simple liquids and equilibrium cytoskeletal actin networks, active microrheology (AMR) proves to be less noise sensitive than and offers extended bandwidth (0.1 - 100 kHz) compared to passive microrheology (PMR), which merely tracks thermal motions. We confirm high-frequency power-law dynamics in equilibrium actin networks with two-particle AMR and also discuss low-frequency local mechanical response near probe particles which shows up in one-particle AMR. The combination of AMR and PMR allowed us to quantify nonthermal force fluctuations in actin networks driven by myosin motor proteins. Our approach offers a new direct way to investigate the nonequilibrium dynamics of living materials.

DOI： 10.1021/ma801218z

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

We have investigated the validity of the fluctuation-dissipation theorem (FDT) and the applicability of the concept of effective temperature in a number of non-equilibrium soft glassy materials. Using a combination of passive and active microrheology to measure displacement fluctuations and the mechanical response function of probe particles embedded in the materials, we have directly tested the validity of the FDT. Our results show no violation of the FDT over several decades in frequency (1-10⁴ Hz) for hard-sphere colloidal glasses and colloidal glasses and gels of Laponite. We further extended the bandwidth of our measurements to lower frequencies (down to 0.1 Hz) using video microscopy to measure the displacement fluctuations, again without finding any deviations from the FDT.

DOI： 10.1209/0295-5075/84/20006

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

The endothelial glycocalyx (EG) is a complex biopolymer network produced by vascular endothelial cells that forms a layer with Multiple functions at the luminal side of blood vessels. The EG acts as an anti-adhesive protection layer, as a molecular sieve, as a chemical sensor site, and as a mechanotransducer of fluid shear stress to the underlying cell layer. A major component involved in these processes is the highly hydrated glycosaminoglycan (GAG) hyaluronan (HA). Here we used laser interferometry to measure the broadband mechanical response of reconstituted HA Solutions at close to physiological conditions. HA showed rheological behavior consistent with that of a flexible polymer. The elastic behavior observed for entangled HA networks showed reptational relaxation with a large distribution of time scales, which disappeared quickly (15 min) with the addition of hyaluronidase (HAase). We conclude that the broadband mechanical probing of model systems (HA solutions) provides quantitative data that are crucial to understand the mechanical response of the EG in vivo and its role in mechanosensing.

DOI： 10.1021/bm800381z

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

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

DOI： 10.1016/j.jbiomech.2008.01.035

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

We have directly observed short-time stress propagation in viscoelastic fluids using two optically trapped particles and a fast interferometric particle-tracking technique. We have done this both by recording correlations in the thermal motion of the particles and by measuring the response of one particle to the actively oscillated second particle. Both methods detect the vortexlike flow patterns associated with stress propagation in fluids. This inertial vortex flow propagates diffusively for simple liquids, while for viscoelastic solutions the pattern spreads superdiffusively, depending on the shear modulus of the medium.

DOI： 10.1103/PhysRevE.77.061508

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

We present techniques based on optical trapping of micron-sized particles as probes and detecting their motion with sub-nanometer accuracy at 100 kHz bandwidth that can measure viscoelastic properties of biomaterials and cells on micrometer scales.

DOI： 10.1364/aoe.2008.sap1

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

There is increasing evidence that cell function and mechanical properties are closely related to morphology. However, most in vitro studies investigate flat adherent cells, which might not reflect physiological geometries in vivo. Osteocytes, the mechanosensors in bone, reside within ellipsoid containment, while osteoblasts adhere to flatter bone surfaces. It is unknown whether morphology difference, dictated by the geometry of attachment is important for cell rheology and mechanosensing. We developed a novel methodology for investigating the rheology and mechanosensitivity of bone cells under different morphologies using atomic force microscopy and our two-particle assay for optical tweezers. We found that the elastic constant of MLO-Y4 osteocytes when flat and adherent (>1 kPa) largely differed when round but partially adherent (<1 kPa). The elastic constant of round suspended MLO-Y4 osteocytes, MC3T3-E1 osteoblasts, and primary osteoblasts were similarly <1 kPa. The mechanosensitivity of round suspended MLO-Y4 osteocytes was investigated by monitoring nitric oxide (NO) release, an essential signaling molecule in bone. A preliminary observation of high NO release from round suspended MLO-Y4 osteocytes in response to ∼5 pN force is reported here, in contrast with previous studies where flat cells routinely release lesser NO while being stimulated with higher force. Our results suggest that a round cellular morphology supports a less stiff cytoskeleton configuration compared with flat cellular morphology. This implies that osteocytes take advantage of their ellipsoid morphology in vivo to sense small strains benefiting bone health. Our assay provides novel opportunities for in vitro studies under a controlled suspended morphology versus commonly studied adherent morphologies.

DOI： 10.1016/j.jbiomech.2008.01.031

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

We have developed a high-bandwidth technique for active 2-particle microrheology (AMR) with which we can probe linear and nonlinear responses of soft materials. Micron-sized colloidal probe particles are driven by an oscillating optical trap, and the resulting correlated motions of neighboring particles are detected by laser interferometry. Lack-in detection at the driving frequency and at its second harmonic makes it possible to measure the linear and the non-linear response of the embedding medium at the same time. We demonstrate the sensitivity of the method by detecting a second-harmonic response in water which is of purely geometric origin and which can be fully understood within linear hydrodynamics.

DOI： 10.1117/12.739441

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

We provide a direct experimental test of the fluctuation-dissipation theorem (FDT) in an aging colloidal glass. The use of combined active and passive microrheology allows us to independently measure both the correlation and response functions in this nonequilibrium situation. Contrary to previous reports, we find no deviations from the FDT over several decades in frequency (1 Hz-10 kHz) and for all aging times. In addition, we find two distinct viscoelastic contributions in the aging glass, including a nearly elastic response at low frequencies that grows during aging.

DOI： 10.1103/PhysRevLett.98.108302

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

Dynamics of nano-sized colloidal particles in a swollen lyotropic lamellar phase of a nonionic surfactant has been studied by three methods of microrheology. By electrophoretic microrheology (EPM), we find two relaxation processes respectively relating to the fluctuation of membranes and topological defects in lamellar structure. By direct tracking of particles under a microscope and manipulating them with an optical tweezers, we obtained detailed information on diffusion of a particle at low frequencies. We observed the jump-trap motion of a particle and the non-Newtonian rheological behavior at low frequencies.

DOI： 10.1080/15421400701739170

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

Cells both actively generate and sensitively react to forces through their mechanical framework, the cytoskeleton, which is a nonequilibrium composite material including polymers and motor proteins. We measured the dynamics and mechanical properties of a simple three-component model system consisting of myosin II, actin filaments, and cross-linkers. In this system, stresses arising from motor activity controlled the cytoskeletal network mechanics, increasing stiffness by a factor of nearly 100 and qualitatively changing the viscoelastic response of the network in an adenosine triphosphate-dependent manner. We present a quantitative theoretical model connecting the large-scale properties of this active gel to molecular force generation.

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

We show the intracellular upregulation of NO production after mechanical stimulation, an essential chemical signal in bone remodeling. This is done in real time using the fluorescent chromophore DAR-4M AM. Differences in cellular response to mechanical stimulation of different regions of a single cell were observed.Introduction: Osteocytes are the most abundant bone cells that are believed to be the mechanosensors of bone, responding to mechanical stresses in interstitial fluid flow through the canaliculi. Under mechanical load, chemical signals such as NO play a key role in the activity of osteoblasts/osteoclasts that regulate bone remodeling. Despite the importance of NO in signaling, its real-time detection has proved challenging. This is largely because of the short NO half-life (typically similar to 0.1-5 s). Here, we show the upregulation of intracellular NO production in single osteocytes under localized mechanical stimulation.Materials and Methods: We used the chromophore DAR-4M AM for NO detection. This is loaded into surface-attached MLO-Y4 osteocyte-like and MC3T3-E1 osteoblast-like cells that are subjected to a localized mechanical stimulation using optical tweezers or a microneedle tip. DAR-4M AM is membrane-permeable and chelates NO, forming a stable, fluorescent compound, which is visible with a rhodamine filter.Results: Nonstimulated MLO-Y4 and MC3T3-E1 cells showed basal NO production levels, as indicated by a gradual increase in their fluorescence intensity. Localized mechanical stimulation of single MC3T3-E1 cells and MLO-Y4 cells by optical tweezers (150-550 pN, 0.5-3 Hz, 1 minute) showed a nearly 15-30&#37; increase, whereas MLO-Y4 cells stimulated by a microneedle (10-20 nN, 1 minute) showed nearly 15-16&#37; increase relative to their nonstimulated state. Furthermore, stimulation of a single cell process by a microneedle resulted in a 2-10&#37; increase in the fluorescence intensity.Conclusions: NO is essential for mechanically induced bone remodeling and is a meaningful parameter for measuring bone cell activation after mechanical loading. Here we show NO upregulation in individual bone cells after a localized mechanical stimulation. We also show that both the cell body and the cell processes might be involved in mechanosensing. This technique allows characterization of the mechanosensitivity of different parts of a single osteocyte. This opens up the possibility to uncover the complexities and function of single osteocytes in the dynamic process of bone remodeling.

DOI： 10.1359/jbmr.060720

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

The dynamics of nanosized colloidal particles dispersed in a hyper-swollen lyotropic lamellar phase of a nonionic surfactant has been studied by ac electrophoretic light scattering and direct tracking of particles under a microscope. The frequency spectrum of electrophoretic mobility shows two relaxation processes. These are originated from the hindrance of free diffusion of particles by the interaction between membranes and particles. By direct tracking measurement, we find that particles jump from site to site where they stay for a long time. This trap-jump process greatly decreases the mobility at low frequencies.

DOI： 10.1088/0953-8984/17/31/021

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

Dynamics of nano-sized colloidal particles dispersed in a dilute lyotropic lamellar phase of a nonionic surfactant has been studied experimentally by ac electrophoretic light scattering and direct tracking under a microscope. The obtained frequency spectrum of complex electrophoretic mobility shows two relaxation processes at about 1 kHz (HF relaxation) and a few Hz (LF relaxation). These relaxations are due to the hindrance of free diffusion of particles by the hierarchical local static and dynamical structures of lamellar phase. From the direct tracking of fluorescent-labeled particles under a microscope, we find that particles show jump from sites to sites where they stay for a long time. This trap-jump process extremely decreases their mobility at low frequencies.

DOI： 10.1080/15421400590956324

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

Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility micro*(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately 1 kHz (high frequency relaxation, HF) and 1 Hz (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.

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

Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility [Formula presented] of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately [Formula presented] (high frequency relaxation, HF) and [Formula presented] (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.

DOI： 10.1103/PhysRevE.70.011509

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

The dielectric response in lyotropic lamellar and sponge phases made up of a nonionic surfactant and water was measured. A Maxwell-Wagner relaxation influenced by the charge accumulation at the interface between membrane and water was observed. Overall, results give some basic information for understanding the dynamic electrical properties of other complex systems composed of lipid membranes.

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

We study the dielectric response in lyotropic lamellar and sponge phases made up of a binary mixture of a nonionic surfactant and water. A single relaxation is observed in both phases within the measured frequency range of 10-10(7) Hz. This relaxation originates from the obstruction of electric current by insulating membranes. In the sponge phase, it depends on surfactant concentration and conductivity of solvent. The observed dependence is well-described quantitatively by the equivalent electric circuit of the sponge structure, including the effect of accumulation of ions at the interface between water and membrane. In the lamellar phase, there is little dependence of dielectric relaxation on surfactant concentration. This is presumably due to the fact that submicrometer-sized defects play a more important role in the electrical property in this phase than the lamellar structure in smaller length scales does. Our results offer some basic information to study more complicated systems composed of charged membranes in aqueous solution.

DOI： 10.1103/PhysRevE.67.061505

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

We study the dielectric response in lyotropic lamellar and sponge phases made up of a binary mixture of a nonionic surfactant and water. A single relaxation is observed in both phases within the measured frequency range of 10-10(7) Hz. This relaxation originates from the obstruction of electric current by insulating membranes. In the sponge phase, it depends on surfactant concentration and conductivity of solvent. The observed dependence is well-described quantitatively by the equivalent electric circuit of the sponge structure, including the effect of accumulation of ions at the interface between water and membrane. In the lamellar phase, there is little dependence of dielectric relaxation on surfactant concentration. This is presumably due to the fact that submicrometer-sized defects play a more important role in the electrical property in this phase than the lamellar structure in smaller length scales does. Our results offer some basic information to study more complicated systems composed of charged membranes in aqueous solution.

Language：English  

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

We study the dielectric response in lyotropic lamellar and sponge phases made up of a binary mixture of a nonionic surfactant and water. A single relaxation is observed in both phases within the measured frequency range of [Formula presented] This relaxation originates from the obstruction of electric current by insulating membranes. In the sponge phase, it depends on surfactant concentration and conductivity of solvent. The observed dependence is well-described quantitatively by the equivalent electric circuit of the sponge structure, including the effect of accumulation of ions at the interface between water and membrane. In the lamellar phase, there is little dependence of dielectric relaxation on surfactant concentration. This is presumably due to the fact that submicrometer-sized defects play a more important role in the electrical property in this phase than the lamellar structure in smaller length scales does. Our results offer some basic information to study more complicated systems composed of charged membranes in aqueous solution.

DOI： 10.1103/PhysRevE.67.061505

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

DOI： 10.1103/physrevlett.87.088104

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

We measured the complex electrophoretic mobility μ*(ω) of nanometer-sized particles dispersed in a lyotropic lamellar phase, and observed two relaxation processes corresponding to the two characteristic lengths of lamellar structure. Faster relaxation is caused by the distortion field of lamellar phase induced by the colloidal particles, and slower relaxation is presumably due to the defects in lamellar structure. Since the dynamic transport property is strongly influenced by the microscopic circumstances as shown in this paper, this method is referred to as electrophoretic microrheology.

DOI： 10.1103/PhysRevLett.87.088104

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

DOI： 10.1103/physreve.63.046302

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

DOI： 10.1021/la000821h

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

DOI： 10.1143/jjap.39.l1197

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

DOI： 10.1021/la9903954

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

Responsible for pages：生体の科学 Vol.72 No.3 2021年 06月号 特集 生物物理学の進歩——生命現象の定量的理解へ向けて ■Ⅰ．分子レベル 「生きている細胞の非平衡力学」   Language：Japanese   Book type：Scholarly book

Responsible for pages：第4章 解析技術 1. 液滴混み合い状態としての細胞内レオロジー   Language：Japanese   Book type：Scholarly book

Responsible for pages：総ページ数：221p   Language：Japanese  

Language：English   Book type：Scholarly book

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京, 学士会館   Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.10

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.4

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学西新プラザ   Country：Japan  

Event date： 2019.4

Language：English  

Venue：Yokohama   Country：Japan  

Mechanics of living cell interior are governed by cytoskeletons and cytosol. They are extraordinarily heterogeneous and their physical properties are strongly affected by the internally generated forces. In order to understand the out-ofequilibrium mechanics, we have developed a method of microrheology using laser interferometry and optical trapping technology. This method allowed us to probe mechanics and dynamics in living cells with a high spatio-temporal resolution. Microscopic probes in cells are stably trapped in the presence of vigorous cytoplasmic fluctuations, by employing smooth 3D feedback of a piezo-actuated sample stage. To interpret the data, we present a theory that adapts the fluctuation-dissipation theorem (FDT) to out-of-equilibrium systems. We discuss the interplay between material properties and non-thermal force fluctuations in the living cells that we quantify through the violations of the FDT.

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ボストン アメリカ   Country：Japan  

Event date： 2018.12

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学西新プラザ   Country：Japan  

Event date： 2018.7

Language：English   Presentation type：Oral presentation (general)  

Venue：ダブリン アイルランド   Country：Ireland  

Event date： 2018.5

Language：English   Presentation type：Oral presentation (general)  

Venue：ハイデルベルグ ドイツ   Country：Germany  

Event date： 2018.4 - 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：ダブリン アイルランド   Country：Japan  

Event date： 2014.2

Language：English  

Venue：Moscone Convention Center, San Francisco, USA   Country：United States  

Event date： 2014.2

Language：English  

Venue：oscone Convention Center, San Francisco, USA   Country：United States  

Event date： 2014.2

Language：English  

Venue：Kavli Institute for Theoretical Physics, University of California, Santa Barbara, USA   Country：United States  

Event date： 2014.2

Language：English   Presentation type：Oral presentation (general)  

Venue：Kavli Institute for Theoretical Physics, University of California, Santa Barbara, USA   Country：United States  

Event date： 2013.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Davao City, Philippines   Country：Japan  

Event date： 2013.9

Language：English  

Venue：Rome, Italy   Country：Italy  

Event date： 2013.9

Language：English  

Country：Italy  

Event date： 2008.10 - 2008.11

Language：English  

Venue：Shanghai   Country：China  

We present techniques based on optical trapping of micron-sized particles as probes and detecting their motion with sub-nanometer accuracy at 100 kHz bandwidth that can measure viscoelastic properties of biomaterials and cells on micrometer scales.

Event date： 2007.8

Language：English  

Venue：San Diego, CA   Country：United States  

We have developed a high-bandwidth technique for active 2-particle microrheology (AMR) with which we can probe linear and nonlinear responses of soft materials. Micron-sized colloidal probe particles are driven by an oscillating optical trap, and the resulting correlated motions of neighboring particles are detected by laser interferometry. Lock-in detection at the driving frequency and at its second harmonic makes it possible to measure the linear and the non-linear response of the embedding medium at the same time. We demonstrate the sensitivity of the method by detecting a second-harmonic response in water which is of purely geometric origin and which can be fully understood within linear hydrodynamics.

Event date： 2003.11

Language：English  

Venue：Sendai   Country：Japan  

Transport of nano-sized colloidal particles in a dilute lyotropic lamellar phase of a nonionic surfactant has been studied by AC electrophoretic light scattering. The frequency dispersion of complex electrophoretic mobility shows two relaxation processes at about 1kHz (HF relaxation) and a few Hz (LF relaxation). These relaxations are originated from the hindrance of diffusion of particles in characteristic local structures of lamellar phase. The HF relaxation is found to relate the local deformation of membranes induced by particles. The LF one relates the confinement of a particle within persistence length of lamellar orientation.

Event date： 1998.10

Language：English  

Venue：Sendai, Miyagi, Jpn   Country：Other  

Ripplon light scattering technique was applied for the investigation of the mechanical properties of the surface of surfactant solution. The velocity and damping constant of the ripplon were measured for decyl-alcohol solution under periodical modulation of the surface area and the dynamic surface tension was obtained in the frequency range of 10^-3-10^-1 Hz. The relaxation of surface elasticity due to the adsorption and desorption of the surfactant molecules was successfully observed.

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Language：Japanese  

Country：Japan  

Dynamics of Bilayer Membranes in the Sponge Phase of Non-Ionic Micelles
We have studied the sponge phase (L_3) of binary mixture of C_<12>E_5 and water by the dynamic light scattering technique. At the concentration above 2w&#37;, an almost single relaxation related with the cooparative diffusion of membranes is detected. The dynamic correlation lengh is evaluated from the diffusion constant to be a little larger than that obtained for the L_α phase. At the concentration below 2w&#37;, we can find the crossover behavior Γ∝q^2 to Γ∝q^3 in the dispersion relation between the inverse correlation time Γ and the scattering wavenumber q.

Language：Japanese  

Country：Japan  

A.C. Electrophoresis of charged colloidal particles

Language：Japanese  

Country：Japan  

Dynamics of the fluctuation in colloidal crystals

Language：Japanese  

Country：Japan  

Wide Band Spectroscopy of Complex Electrophoretic Mobility in Colloidal Suspension

Language：Japanese  

Country：Japan  

21pVA-4 Nonequilibrium mechanics and dynamics of active cytoskeletons

Language：Japanese  

Country：Japan  

30pVC-1 High resolution probing of active cellular traction

Language：Japanese  

Country：Japan  

28pVC-16 Non-equilibrium fluctuation in active cytoskeltons

Language：Japanese  

Country：Japan  

26pPSA-42 Non-equilibrium fluctuation in active cytoskeltons

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagoya   Country：Japan  

Language：English  

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Visiting lecture

researchmap