Masaki Sano

• Professor
• Professor (Full) at Shanghai Jiao Tong University

Many internal organs in multicellular organisms comprise epithelia which enclose fluid-filled cavities referred to as lumens. Lumen formation is regulated by a wide range of processes, including epithelial polarization, secretion, exocytosis and actomyosin contractility. While these mechanisms have shed light on lumen growth, what controls lumen sh...

Organoids are ideal systems to predict the phenotypes of organs. However, there is currently a lack of understanding regarding the generalized rules that enable use of simple cellular principles to make morphological predictions of entire organoids. Therefore, we employed a phase field model with the following basic components: the minimum conditio...

Many internal organs in the body harbor a fluid-filled lumen. The mechanisms of lumens initiation and fusion have been reported as dependent on organ-type during organogenesis. In contrast, the physics of lumen suggests that force balance between luminal pressure and cell mechanics could lead to conserved rules which may unify their self-organisati...

Organoids are ideal systems to predict the phenotypes of organs. However, there is currently a lack of understanding regarding the generalized rules that enable use of simple cellular principles to make morphological predictions of entire organoids. Therefore, we employed a phase field model with the following basic components: the minimum conditio...

Formation of fluid filled lumen by epithelial tissues is a fundamental process for organ development. How epithelial cells regulate the hydraulic and cortical forces to control lumen morphology is not completely understood. Here, we quantified the mechanical role of tight junctions in lumen formation using genetically modified MDCKII cysts. We foun...

Lumens, liquid-filled cavities surrounded by polarized tissue cells, are elementary units involved in the morphogenesis of organs. Theoretical modeling and computations, which can integrate various factors involved in biophysics of morphogenesis of cell assembly and lumens, may play significant roles to elucidate the mechanisms in formation of such...

We study the polar collective dynamics of Janus colloidal particles fueled by an AC electric field. When the density is high enough, the polar interactions between the particles induce a polar orientationally ordered state, which exhibits features reminiscent of the Vicsek model such as true long-range order and giant number fluctuations. Independe...

We study the polar collective dynamics of Janus colloidal particles fueled by an AC electric field. When the density is high enough, the polar interactions between the particles induce a polar orientationally ordered state which exhibits features reminiscent of the Vicsek model such as true long-range order and giant number fluctuations. Independen...

Emergence and collapse of coherent motions of self-propelled particles are affected more by particle motions and interactions than by their material or biological details. In the reconstructed systems of biofilaments and molecular motors, several types of collective motion including a global-order pattern emerge due to the alignment interaction. Me...

The physico-chemical processes supporting life’s purposeful movement remain essentially unknown. Self-propelling chiral droplets offer a minimalistic model of swimming cells and, in surfactant-rich water, droplets of chiral nematic liquid crystals follow the threads of a screw. We demonstrate that the geometry of their trajectory is determined by b...

Chirality is an essential evolutionary-conserved physical aspect of swimming microorganisms. However, the role of chirality on the hydrodynamics of such microswimmers is still being elucidated. Hydrodynamic theories have so far predicted that, under a torque-free condition satisfied in the system of microswimmers, a rotlet dipole generating a twist...

Active matter consists of self-propelled elements exhibits fascinating collective motions ranging from biological to artificial systems. Among wide varieties of active matter systems, reconstituted bio-filaments moving on molecular motor turf interacting purely by physical interactions provides the fundamental test ground for understanding biologic...

Macroscopic ordering is key in multicellular behaviors, but its predictive understanding has been challenging since the dynamics are typically out of equilibrium. Here we show that mouse neural progenitor cells cultured on dish present features of an active nematic system, resembling the patterns of liquid crystal but with the cells rapidly gliding...

We recently reported the experimental realization of a chiral artificial microswimmer exhibiting helical self-propulsion [T. Yamamoto and M. Sano, Soft Matter 13, 3328 (2017)]. In the experiment, cholesteric liquid crystal (CLC) droplets dispersed in surfactant solutions swam spontaneously, driven by the Marangoni flow, in helical paths whose hande...

We study the active dynamics of self-propelled asymmetrical colloidal particles (Janus particles) fueled by an AC electric field. Both the speed and the direction of the self-propulsion and the strength of attractive interaction between the particles can be controlled by tuning the frequency of the applied electric field and the ion concentration o...

We study the active dynamics of self-propelled asymmetrical colloidal particles (Janus particles) fueled by an AC electric field. Both the speed and the direction of the self-propulsion and the strength of attractive interaction between the particles can be controlled by tuning the frequency of the applied electric field and the ion concentration o...

Cultured stem cells have become a standard platform not only for regenerative medicine and developmental biology but also for biophysical studies. Yet, the characterization of cultured stem cells at the level of morphology and macroscopic patterns resulting from cell-to-cell interactions remain largely qualitative. Here we report the collective mot...

Significance Commanding the swimming of micrometric objects subjected to thermal agitation is always challenging for both artificial and living systems. Now, artificial swimmers can be designed with self-propelling force that can be tuned at will. However, orienting such small particles to an arbitrary direction requires counterbalancing the random...

Even though making artificial micrometric swimmers has been made possible by using various propulsion mechanisms, guiding their motion in the presence of thermal fluctuations still remains a great challenge. Such a task is essential in biological systems, which present a number of intriguing solutions that are robust against noisy environmental con...

Cultured stem cells have become a standard platform not only for regenerative medicine and developmental biology but also for biophysical studies. Yet, the characterization of cultured stem cells at the level of morphology and macroscopic patterns resulting from cell-to-cell interactions remain largely qualitative, even though they are the simplest...

We study the collective dynamics of long, filamentous, non-tumbling bacteria swimming in a very thin fluid layer. The strong confinement induces nematic alignment upon collision, which, for large enough density of cells, gives rise to global nematic order. We show that this homogeneous but fluctuating phase, observed on the largest experimentally-a...

We study the collective dynamics of elongated swimmers in a very thin fluid layer by devising long, filamentous, non-tumbling bacteria. The strong confinement induces weak nematic alignment upon collision, which, for large enough density of cells, gives rise to global nematic order. This homogeneous but fluctuating phase, observed on the largest ex...

We report the first experimental realization of a chiral artificial microswimmer exhibiting the helical motion. We found that a cholesteric liquid crystal droplet with a helical director field swims in a helical path driven by the Marangoni flow in an aqueous surfactant solution. We confirmed that the handedness of the droplet determines that of th...

We report the first experimental realization of a chiral artificial microswimmer exhibiting the helical motion. We found that a cholesteric liquid crystal droplet with a helical director field swims in a helical path driven by the Marangoni flow in an aqueous surfactant solution. We confirmed that the handedness of the droplet determines that of th...

We run numerical simulations of strongly confined suspensions of model spherical swimmers called "squirmers". Because of the confinement, the Stokeslet dipole singularity generated by the particles is quickly screened and the far-field flow is dominated by the source dipole singularity for all the different kinds of squirmers. However, we show that...

Transition from laminar to turbulent flow drastically changes the mixing, transport, and drag properties of fluids, yet when and how turbulence emerges is elusive even for simple flow within pipes and rectangular channels. Unlike the onset of temporal disorder, which is identified as the universal route to chaos in confined flows, characterization...

To elucidate mechanisms of mesoscopic turbulence exhibited by active particles, we experimentally study turbulent states of non-living self-propelled particles. We realize an experimental system with dense suspensions of asymmetrical colloidal particles (Janus particles) self-propelling on a two-dimensional surface under an AC electric field. Veloc...

For biophysical understanding of cell motility, the relationship between mechanical force and cell migration must be uncovered, but it remains elusive. Since cells migrate at small scale in dissipative circumstances, the inertia force is negligible and all forces should cancel out. This implies that one must quantify the spatial pattern of the forc...

We consider random walks of active deformable particles (ADP) that can move by actively deforming their shape from a sphere. A theory is developed by assuming that the equation of velocity includes a coupling with active random deformation. It is shown that the model exhibits a truncated power-law distribution of velocity, whose exponent is determi...

We report a quantitative measurement of traction stress exerted by dividing eukaryotic cells. The stress field was highly dynamic and sequentially changed as follows: (1) strong and localized as two spots, (2) weak and broadly distributed, and (3) strong and localized as four spots. At the final stage of cytokinesis, the dividing cells exerted stro...

We provide a comprehensive report on scale-invariant fluctuations of growing interfaces in liquid-crystal turbulence, for which we recently found evidence that they belong to the Kardar-Parisi-Zhang (KPZ) universality class for 1+1 dimensions [Phys. Rev. Lett. 104, 230601 (2010); Sci. Rep. 1, 34 (2011)]. Here we investigate both circular and flat i...

We propose a route to spatiotemporal chaos, in which the system is assumed to have spatial reflection antisymmetry and field-translation symmetry. The lowest-order nonlinear equation that satisfies these symmetries is explored with the weak nonlinear analysis around the bifurcation point. We conclude that the nonlinear term ${$\partial${}}_{x}^{2}u...

We consider a one-dimensional brownian motion under nonequilibrium feedback control. Generally, the fluctuation-dissipation theorem (FDT) is violated in driven systems under nonequilibrium conditions. We find that the degree of the FDT violation is bounded by the mutual information obtained by the feedback system when the feedback protocol includes...

Stochastic motion of a point - known as Brownian motion - has many successful applications in science, thanks to its scale invariance and consequent universal features such as Gaussian fluctuations. In contrast, the stochastic motion of a line, though it is also scale-invariant and arises in nature as various types of interface growth, is far less...

Supplementary Movie 2

Supplementary Information

Supplementary Movie 1

We consider a geometrical model of a broken interface showing self-propelling motion. This model is constructed to comprise a static solution with a spontaneous curvature. Furthermore, by introducing a nonlocal interaction force into the geometrical model, we show that the static solution causes spontaneous drift motion even when the nonlocal force...

We consider the thermodynamics of chemical coupling from the viewpoint of free energy transduction efficiency. In contrast to an external parameter-driven stochastic energetics setup, the dynamic change of the equilibrium distribution induced by chemical coupling, adopted, for example, in biological systems, is inevitably an autonomous process. We...

We study self-propulsion of a half-metal coated colloidal particle under laser irradiation. The motion is caused by self-thermophoresis: i.e. absorption of laser at the metal-coated side of the particle creates local temperature gradient which in turn drives the particle by thermophoresis. To clarify the mechanism, temperature distribution and a th...

In 1929, Leo Szilard invented a feedback protocol in which a hypothetical intelligence called Maxwell's demon pumps heat from an isothermal environment and transduces it to work. After an intense controversy that lasted over eighty years; it was finally clarified that the demon's role does not contradict the second law of thermodynamics, implying t...

We investigate growing interfaces of topological-defect turbulence in the electroconvection of nematic liquid crystals. The interfaces exhibit self-affine roughening characterized by both spatial and temporal scaling laws of the Kardar-Parisi-Zhang theory in 1+1 dimensions. Moreover, we reveal that the distribution and the two-point correlation of...

The kinetics of granular gases, including both freely cooling and steadily driven systems, is studied experimentally in quasi-two-dimensional cells. Under microgravity conditions achieved inside an aircraft flying parabolic trajectories, the frictional force is reduced. In both the freely cooling and steadily driven systems, we confirm that the vel...

This is a comprehensive report on the phase transition between two turbulent states of electroconvection in nematic liquid crystals, which was recently found by the authors to be in the directed percolation (DP) universality class [K. A. Takeuchi, Phys. Rev. Lett. 99, 234503 (2007)]. We further investigate both static and dynamic critical behaviors...

DOI:https://doi.org/10.1103/PhysRevLett.103.089901

This is a comprehensive report on the phase transition between two turbulent states of electroconvection in nematic liquid crystals, which was recently found by the authors to be in the directed percolation (DP) universality class [K. A. Takeuchi et al., Phys. Rev. Lett. 99, 234503 (2007)]. We further investigate both static and dynamic critical be...

We have studied the morphological diversity and change in bacterial colonies, using the bacterial species Escherichia coli, as a function of both agar concentration Ca and nutrient concentration Cn. We observed various colony patterns, classified them into four types by pattern characteristics and established a morphological diagram by dividing it...

The non-equilibrium distribution of colloids in a polymer solution under a temperature gradient is studied experimentally. A slight increase of local temperature by a focused laser drives the colloids towards the hot region, resulting in the trapping of the colloids irrespective of their own thermophoretic properties. An amplification of the trappe...

Long-term measurement of the morphological dynamics of cell shape.We measured a single WT vegetative cell for 3.3 h and then calculated the autocorrelation function of Amp(θ, t) at each time window (500 s). Six examples of autocorrelation function are shown on the left side of Amp(θ, t). We found that the ordered pattern dynamically changes; for in...

Multiple pseudopodia due to loss of PTEN. Typical pten&minus cells in VEG state. White arrowheads represent irregular pseudopodia. Scale bar is 10 µm. The number indicates time of measurement [second]. (0.04 MB PDF)

Trajectory of centroid and angular dynamics of cell movement Upper column: trajectory of each ordered pattern. Red asterisk represents the start point. Middle column: the angular dynamics of cell movement of each ordered pattern. Lower column: the corresponding ordered patterns (0.69 MB PDF)

Elongating WT starved cell. (0.23 MB MOV)

pten-vegetative cell exhibiting a random membrane dynamics. (0.36 MB MOV)

LY294002-treated WT vegetative cell exhibiting a random membrane dynamics. (0.69 MB MOV)

Supplementary results and discussions (0.10 MB DOC)

Act(&theta, t) : a reliable measure of F-actin accumulation. (A) We employed Act(&theta, t) instead of the measure of I(r, &theta, t) along cell membrane because F-actin accumulates nearby cell membrane but not on the edge of cell membrane (see Figure 5A). To test the reliability of Act(&theta, t), we compared it with the largest intensity of F-act...

Clustering analysis of autocorrelation function. We first subject autocorrelation function (ACF) to Fourier transform to obtain the three parameters, AS, AL, and AR. We then conduct clustering analysis of ACF based on the obtained parameters. We show the clustering tree of wild-type vegetative cells. (0.37 MB PDF)

Elongating WT vegetative cell. (0.27 MB MOV)

Rotating WT vegetative cell. (0.36 MB MOV)

PI3K inactivation reduces the amplitude of pseudopodia. Average power spectra of cell morphology. Upper: WT cells (red solid line), WT+LY294002 cells (green dash line) and pi3k1/2&minus cells (green solid line). Lower: pten&minus cells (red) and pten&minus+LY294002 cells (green). Left is VEG state and right is STA state. The individual power spectr...

Oscillating WT vegetative cell. (0.24 MB MOV)

Oscillating WT starved cell. (0.37 MB MOV)

pten-starved cell exhibiting a random membrane dynamics. (0.28 MB MOV)

Characterization of the centre of mass displacements. (A) Average mean square displacement along the trajectory as a function of time and (B) autocorrelation function of instantaneous velocity for WT (red), pten&minus (blue) and pi3k1/2&minus (green) in both the VEG and STA states. All curves of the MSD fit a decaying power-law. We adopt time inter...

Rotating WT starved cell. (0.24 MB MOV)

pi3k1/2-vegetative cell exhibiting a random membrane dynamics. (0.43 MB MOV)

pi3k1/2-starved cell exhibiting a random membrane dynamics. (0.71 MB MOV)

LY294002-treated WT starved cell exhibiting a random membrane dynamics. (0.66 MB MOV)

LY294002-treated pten-vegetative cell exhibiting a random membrane dynamics. (0.28 MB MOV)

LY294002-treated pten-starved cell exhibiting a random membrane dynamics. (0.27 MB MOV)

Single-molecule manipulation techniques have given experimental access to unfolding intermediates of proteins that are inaccessible in conventional experiments. A detailed characterization of the intermediates is a challenging problem that provides new possibilities for directly probing the energy landscape of proteins. We investigated single-molec...

The kinetics of the freely evolving granular gas is studied experimentally in a quasi‐2D cell under normal gravity condition and microgravity condition by parabolic flights. Since the frictional force is highly reduced under microgravity condition, we successfully realized the ideal state of the freely evolving granular gas. For large t and under m...

DOI:https://doi.org/10.1103/PhysRevE.77.059902

We evaluate the energy dissipation rate of an optically driven Brownian particle in a polymer solution utilizing the generalized version of Harada and Sasa's equality [Phys. Rev. Lett. 95, 130602 (2005)] by Deutsch and Narayan [Phys. Rev. E 74, 026112 (2006)]. The irreversible work of a small system is estimated from readily obtainable quantities....

In the absence of stimuli, most motile eukaryotic cells move by spontaneously coordinating cell deformation with cell movement in the absence of stimuli. Yet little is known about how cells change their own shape and how cells coordinate the deformation and movement. Here, we investigated the mechanism of spontaneous cell migration by using computa...

We experimentally investigate the critical behavior of a phase transition between two topologically different turbulent states of electrohydrodynamic convection in nematic liquid crystals. The statistical properties of the observed spatiotemporal intermittency regimes are carefully determined, yielding a complete set of static critical exponents in...

The authors present a method to control the conformation of DNA by using temperature gradient. The conformations of one end tethered and two ends tethered DNA are measured in different temperature gradients up to 3 K/μm. The results show that temperature gradient can exert force on a single DNA and create internal tension within it. The magnitude o...

In this article, we proposed a mathematical model which show several types of collective motions, and validated it. Firstly we constructed a model in which each element obeys the Newton equation with resistive and interactive force and has a degree of freedom of the heading vector which is parallel to the element axis, in addition to its position a...

On the basis of topological arguments, it is shown that phase jump lines arise in two-dimensional cellular patterns. A phase jump line either ends at a phase singularity with a half-integer topological charge or it has no endpoints. As a simple model equation which exhibits such lines, a set of amplitude equations describing resonant interaction be...

We experimentally investigate the critical behavior of a phase transition between two topologically different turbulent states of electrohydrodynamic convection in nematic liquid crystals. The statistical properties of the observed spatiotemporal intermittency regimes are carefully determined, yielding a complete set of static critical exponents in...

The thermodynamic formalism for dynamical systems with many degrees of freedom is extended to deal with time averages and fluctuations of some macroscopic quantity along typical orbits, and applied to coupled map lattices exhibiting phase transitions. Thereby, it turns out that a seed of phase transition is embedded as an anomalous distribution of...

We observe a new type of behavior in a shear-thinning yield stress fluid: freestanding convection rolls driven by vertical oscillation. The convection occurs without the constraint of container boundaries, yet the diameter of the rolls is spontaneously selected for a wide range of parameters. The transition to the convecting state occurs without hy...

Measurement of energy dissipation in small nonequilibrium systems is generally a difficult task. Recently, Harada and Sasa [Phys. Rev. Lett. 95, 130602 (2005)] derived an equality relating the energy dissipation rate to experimentally accessible quantities in nonequilibrium steady states described by the Langevin equation. Here, we show an experime...

This paper reports collective behaviors of multirobot system with simple dynamics and interactions. The model for collective motion is described by fundamental kinetics and the dynamics of the heading which each element has as a degree of freedom. Firstly, we shows the system based on this model realizes various types of behavior according to the s...

Measurement of energy dissipation in small nonequilibrium systems is generally a difficult task. Recently, Harada and Sasa [Phys.Rev.Lett. 95, 130602(2005)] derived an equality relating the energy dissipation rate to experimentally accessible quantities in nonequilibrium steady states described by the Langevin equation. Here, we show the first expe...

Biological processes are governed by complex networks ranging from gene regulation to signal transduction. Positive feedback is a key element in such networks. The regulation enables cells to adopt multiple internal expression states in response to a single external input signal. However, past works lacked a dynamical aspect of this system. To addr...

The thermodynamic formalism for dynamical systems with many degrees of freedom is extended to deal with time averages and fluctuations of some macroscopic quantity along typical orbits, and applied to coupled map lattices exhibiting phase transitions. Thereby, it turns out that a seed of phase transition is embedded as an anomalous distribution of...

We report observations of stable, localized, linelike structures in the spatially periodic pattern formed by nematic electroconvection, along which the phase of the pattern jumps by pi. With increasing electric voltage, these lines form a gridlike structure that goes over into a structure indistinguishable from the well-known grid pattern. We prese...