Hiroaki Ito

Chiba University · Department of Physics

Large deformability of erythrocytes in microvasculature is a prerequisite to realize smooth circulation. We develop a novel tool for the three-step “Catch-Load-Launch” manipulation of a human erythrocyte based on an ultra-high speed position control by a microfluidic “robotic pump”. Quantification of the erythrocyte shape recovery as a function of...

Active force generation in living organisms, which is mainly involved in actin cytoskeleton and myosin molecular motors, plays a crucial role in various biological processes. Although the contractile properties of actomyosin have been extensively investigated, their dynamic contribution to a deformable membrane remains unclear because of the cellul...

Actomyosin actively generates contractile forces that provide the plasma membrane with the deformation stresses essential to carry out biological processes. Here, we reconstituted a model system with a cell-sized soft interface that exhibits anomalous curvature-radius dependent deformation caused by actomyosin cortex underneath the closed interface...

In this study, we physically modeled the influence of endotoxin-induced sepsis symptoms on human red blood cells (RBCs) by quantifying the impact of endotoxins on the cell mechanics by the analysis of Fourier-transformed mean square amplitude of shape fluctuation, called flicker spectroscopy. With the aid of a microfluidic diffusion chamber, we non...

Recently, the transfer method has been shown to be useful for preparing cell-sized phospholipid bilayer vesicles, within which desired substances at desired concentrations can be encapsulated, with a desired asymmetric lipid composition. Here, we investigated the transfer process of water-in-oil (W/O) droplets coated by phospholipid monolayers acro...

We investigated self-sustained oscillation in a collapsible channel, in which a part of one rigid wall is replaced by a thin elastic wall, and synchronization phenomena in the two channels connected in parallel. We performed a two-dimensional hydrodynamic simulation in a pair of collapsible channels which merged into a single channel downstream. Th...

Revealing the ion distributions on a charged lipid membrane in aqueous solution under the influence of long-range interactions is essential for understanding the origin of the stability of the bilayer structure and the interaction between biomembranes and various electrolytes. However, the ion distributions and their dynamics associated with the ph...

Dynamic lateral transport of lipids, proteins, and self-assembled structures in biomembranes plays crucial roles in diverse cellular processes. In this study, we perform a coarse-grained molecular dynamics simulation on a vesicle composed of a binary mixture of neutral and anionic lipids to investigate the lateral transport of individual lipid mole...

A density oscillator is a fluid system in which oscillatory flow occurs between different density fluids through the pore connecting them. We investigate the synchronization in coupled density oscillators using two-dimensional hydrodynamic simulation and analyze the stability of the synchronous state based on the phase reduction theory. Our results...

Biological membranes are functionalized by membrane-associated protein machinery. Membrane-associated transport processes, such as endocytosis, represent a fundamental and universal function mediated by membrane-deforming protein machines, by which small biomolecules and even micrometer-size substances can be transported via encapsulation into memb...

We execute a numerical simulation on active nematics with particles interacting by excluded volume effect. The system with rhomboidal particles and that with elliptical particles are considered in order to investigate the effect of the direct contact of particles. In our simulation, the void regions, where the local number density is almost zero, a...

A density oscillator is a fluid system in which oscillatory flow occurs between different density fluids through the pore connecting them. We investigate the synchronization in coupled density oscillators using two-dimensional hydrodynamic simulation and analyze the stability of the synchronous state based on the phase reduction theory. Our results...

Since the cellular process of endocytosis enables uptake of biomacromolecules interacting with the cell surface by outside-in vesicle fission, endocytosis-like membrane deformation is an ideal methodology for the incorporation of micrometer-size biomacromolecules into vesicles. However, such endocytosis-like vesicle fission, which requires expansio...

Microfluidics is a powerful tool to precisely control fluids as well as to manipulate suspended small particles in a micrometer-sized space [...]

A flame exhibits a limit-cycle oscillation, which is called "flame flickering" or "puffing," in a certain condition. We investigated the bifurcation structure of the flame oscillation in both simulation and experiment. We performed a two-dimensional hydrodynamic simulation by employing the flame sheet model. We reproduced the flame oscillation and...

The system that consists of a ball bouncing off a sawtooth-shaped table vibrating vertically is considered. The horizontal motion in this system is caused by the table shape, and we plotted the mean horizontal velocity as a function of the asymmetry of the table shape. The ball is transported in the direction which the gentler slopes face. To give...

A flame exhibits a limit-cycle oscillation, which is called "flame flickering" or "puffing", in a certain condition. We investigated the bifurcation structure of the flame oscillation in both simulation and experiment. We performed a two-dimensional hydrodynamic simulation by employing the flame sheet model. We reproduced the flame oscillation and...

Droplet-based microfluidics is a powerful tool for producing monodispersed micrometer-sized droplets with controlled sizes and shapes; thus, it has been widely applied in diverse fields from fundamental science to industries. Toward a simpler method for fabricating microparticles with front–back asymmetry in their shapes, we studied anisotropic gel...

Enhancers regulate gene expressions in a tissue‐ and pathology‐specific manner by altering its activities. Plasma levels of atrial and brain natriuretic peptides, encoded by the Nppa and Nppb, respectively, and synthesized predominantly in cardiomyocytes, vary depending on the severity of heart failure. We previously identified the noncoding conser...

We investigated the phase separation of dioleoylphosphatidylserine (DOPS) and dipalmitoylphosphatidylcholine (DPPC) in giant unilamellar vesicles in hypotonic solution using fluorescence and confocal laser scanning microscopy. Although phase separation in charged lipid membranes is generally suppressed by the electrostatic repulsion between the cha...

Observations and analyses of a microscopic object are essential processes in various fields such as chemical engineering and life science. Microfluidic techniques with various functions and extensions have often been used for such purposes to investigate the mechanical properties of microscopic objects such as biological cells. One of such extensio...

We investigated the spontaneous deformation and fission of a tetradecane droplet containing palmitic acid (PA) on a stearyltrimethylammonium chloride (STAC) aqueous solution. In this system, the generation and rupture of the gel layer composed of PA and STAC induce the droplet deformation and fission. To investigate the characteristics of the dropl...

The system in which a small rigid ball is bouncing repeatedly on a heavy flat table vibrating vertically, so-called the bouncing ball system, has been widely studied. Under the assumption that the table is vibrating with a piecewise polynomial function of time, the bifurcation diagram changes qualitatively depending on the order of the polynomial f...

Self-propelled droplets made of organic materials can be an influential candidate for understanding cell migration from the viewpoint of non-equilibrium physics, and have attracted significant attention with regard to soft-matter-type rovers. Since self-propelled droplets are soft enough to be easily deformed, they should be useful as chemically ar...

A density oscillator exhibits limit-cycle oscillations driven by the density difference of the two fluids. We performed two-dimensional hydrodynamic simulations with a simple model and reproduced the oscillatory flow observed in experiments. As the density difference is increased as a bifurcation parameter, a damped oscillation changes to a limit-c...

The system in which a small rigid ball is bouncing repeatedly on a massive at table vibrating vertically, so-called the bouncing ball system, has been widely studied. Under the assumption that the table is vibrating with a piecewise polynomial function of time, the bifurcation diagram changes qualitatively depending on the order of the polynomial f...

Structural heart disease is the most common congenital anomaly, affecting almost 1% of live births [1]. Approximately 25% of newborns with congenital heart disease (CHD) require surgical or trans-catheter intervention in the first year of life [2]. Artificial materials such as polytetrafluoroethylene are used for the surgical repair of CHD, but the...

Hydrodynamic instabilities often cause spatio-temporal pattern formations and transitions between them. We investigate a model experimental system, a density oscillator, where the bifurcation from a resting state to an oscillatory state is triggered by the increase in the density difference of the two fluids. Our results show that the oscillation a...

We investigated the spontaneous deformation and fission of a tetradecane droplet containing palmitic acid (PA) on a stearyltrimethylammonium chloride (STAC) aqueous solution. In this system, the generation and rupture of the gel layer composed of PA and STAC induce the droplet deformation and fission.To investigate the characteristics of the drople...

Abstract Active microfluidics for the applications to cellular deformability measurements is an emerging research field ranging from engineering to medicine. Here, we review conventional and microfluidic methods, and introduce an on-chip cell manipulation system with the design principle of fast and fine cell manipulation inside a microchannel. In...

A density oscillator exhibits limit-cycle oscillations driven by the density difference of the two fluids. We performed two-dimensional hydrodynamic simulations with a simple model, and reproduced the oscillatory flow observed in experiments. As the density difference is increased as a bifurcation parameter, a damped oscillation changes to a limit-...

Hydrodynamic instabilities often cause spatio-temporal pattern formations and transitions between them. We investigate a model experimental system, a density oscillator, where the bifurcation from a resting state to an oscillatory state is triggered by the increase in the density difference of the two fluids. Our results show that the oscillation a...

During intraerythrocytic development, the human malaria parasite Plasmodium falciparum alters the mechanical deformability of its host cell. The underpinning biological processes involve gain in parasite mass, changes in the membrane protein compositions, reorganization of the cytoskeletons and its coupling to the plasma membrane, and formation of...

We use a coarse-grained molecular dynamics simulation to investigate the interaction between neutral or charged nanoparticles (NPs) and a vesicle consisting of neutral and negatively charged lipids. We focus on the interaction strengths of hydrophilic and hydrophobic attraction and electrostatic interactions between a lipid molecule and an NP. A ne...

The deformability of a red blood cell (RBC) is one of the most important biological parameters affecting blood flow, both in large arteries and in the microcirculation, and hence it can be used to quantify the cell state. Despite numerous studies on the mechanical properties of RBCs, including cell rigidity, much is still unknown about the relation...

We use a coarse-grained molecular dynamics simulation to investigate the interaction between charged nanoparticles (NPs) and a vesicle consisting of neutral and negatively charged lipids. We focus on the interaction strengths of hydrophilic/hydrophobic attraction and electrostatic interactions between a lipid molecule and an NP. A neutral NP passes...

Blood viscosity depends on density of red blood cells (RBCs), which deform and interact to each other through the long-ranged hydrodynamic flow field. However, a direct experimental evidence for the correlation between macroscopic fluid properties of blood and these microscopic dynamics is still lacking. In this paper we will experimentally examine...

Red blood cells (RBCs) are subjected to intermittent deformation stress when they flow inside blood vessels throughout the body. We modeled such various deformation pattern using a microfluidic constriction channel mounted on an on-chip cell manipulation system, and measured viscoelastic responses of a RBC. Here we fabricated a microchannel with th...

A microfluidic channel is one of the best tools for the evaluation of red blood cell (RBC) deformability in a short time with just a tiny amount of sample blood. We have proposed a novel method to evaluate both viscosity and elasticity of a RBC in a microfluidic channel. For more precise evaluation of stress exerted on a RBC in a realistic situatio...

This paper proposes an on-chip density mixer that can achieve even density in a target chamber with a swirling flow enhanced by an air chamber. The system is composed of a main channel, a target chamber where two liquids with different densities are included, an isolated air chamber, and an external vibration pump driven by a piezo actuator at the...

In cell culture, the pH of the culture medium is one of the most important conditions. However, the culture medium may have non-uniform pH distribution due to activities of cells and changes in the environment. Although it is possible to measure the pH distribution with an existing pH meter using distributed electrodes, the method involves direct c...

Bubbles with diameter of several hundred nanometers are known as nanobubbles. Oxygen nanobubbles are reported to increase the growth rate of animals such as fishes. The goal of this study is to understand how oxygen nanobubbles affect cell culture in microscopic view. We visualized the behavior of fibroblasts in the culture media with and without o...

We found a new phenomenon of changing RBC color and named it "Chameleon Effect". When a RBC is compressed in a construction channel, the RBC dramatically changes its transparency level with the increase of loading time. Since it is well known that there are close relationships between diseases and the deformability of RBC, we focused on the correla...

This paper proposes a method for automatic evaluation of red blood cell using a microfluidic chip. The evaluation is based on cell velocity and deformation through parallel microchannels. In conventional works, the evaluation is performed by a human analyst for reliability, but it takes enormous time and manpower. By the proposed method， we not onl...

We propose a new method for quantifying red blood cell (RBC) deformability based on the combination of a microfluidic constriction channel and a “robotic pump”, which enable real-time high speed, precise manipulation of a RBC inside the channel. By the manipulation of a RBC around the narrow path, we applied deformation for a specified time. After...

Cellular tissue made of smooth muscle cells becomes stiffer after applying cyclic pressure during the culture, and we call the procedure of applying such cyclic pressure as “Cell Exercise”. In conventional approaches, the pressure is applied using pressurized air, and consequently, the carbon dioxide in the air dissolve into the culture solution an...

This paper reports a novel method of using air column to temporarily change microfluidic structure for cell seeding and culture in a microfluidic chamber. In conventional on-chip culture system, the medium flow has to be carefully controlled to prevent from excessive shear stress that washes out cells. We propose a method to directly seed cells int...

In cell culture, the pH of culture liquid is one of the most important conditions. However, culture liquid may have pH-gradient because of dissolved CO2 especially when we apply pressure to cells, and it may affect cells. In order to confirm existence of pH-gradient, we propose a method for 3D pH measurement using the color change of phenol red. Th...

We observed an interesting phenomenon of coupled vortices in a microfluidic channel with different driving pressure. We call this phenomenon “Virtual Vortex Gear”, as the vortices transmitting like a set of gear. The channel has an elbow and a circular chamber outside the bend point. In addition to the phenomenon, we can also control the flow into...

Muscles are the engine of our body, and actomyosin is the engine of a cell. Both muscle and the actomyosin use the same proteins, namely, actin, and myosin, which are the pair of cytoskeleton and motor proteins generating a force to realize deformation. The properties of force generation by actomyosin at a single-molecule level have been studied fo...

Physical interactions of four major green tea catechin derivatives with cell membrane models were systemically investigated. Catechins with galloyl moiety caused the aggregation of small unilamellar vesicles and an increase in the surface pressure of lipid monolayers, while those without did not. Differential scanning calorimetry revealed that, in...

An interesting phenomenon of microfluidic vortices rotating and transmitting like a set of gears has been experimentally observed and is named “Virtual Vortex Gear”. We found that the vortices could be serially induced by increasing the driving pressure. Every two closed by vortices were having opposite directions of the swirling. The relation betw...

Red blood cell responses during a long-standing load were experimentally investigated. With a high-speed camera and a high-speed actuator, we were able to manipulate cells staying inside a microfluidic constriction, and each cell was compressed due to the geometric constraints. During the load inside the constriction, the color of the cells was fou...

An on-chip deformability checker is proposed to improve the velocity-deformation correlation for red blood cell (RBC) evaluation. RBC deformability has been found related to human diseases, and can be evaluated based on RBC velocity through a microfluidic constriction as in conventional approaches. The correlation between transit velocity and amoun...

A high-resolution cell manipulation system is presented for investigating red blood cell deformation under long-standing load in this paper. Because the low Reynolds number in microfluidic system, cell position can be manipulated by controlling the flow in a microchannel. A high-speed vision system is embedded in the system for providing cell prese...

Biomembranes, which are mainly composed of neutral and charged lipids, exhibit a large variety of functional structures and dynamics. Here, we report a coarse-grained molecular dynamics (MD) simulation of the phase separation and morphological dynamics in charged lipid bilayer vesicles. The screened long-range electrostatic repulsion among charged...

Regeneration of a tissue fragment of freshwater polyp Hydra is accompanied by significant morphological fluctuations, suggesting the generation of active forces. In this study, we utilized a two fingered micro-robotic hand to gain insights into the mechanics of regenerating tissues. Taking advantage of a high force sensitivity (∼1 nN) of our micro-...

We report a centrifugal microfluidic method called the droplet-shooting and size-filtration (DSSF) method for the production of cell-sized liposomes with controlled lipid compositions. The DSSF method involves the generation of large and small droplets from the tip of a glass capillary and the selective transfer of small droplets through an oil-wat...

We investigated the effect of charge on the membrane morphology of giant unilamellar vesicles (GUVs) composed of various mixtures containing charged lipids. We observed the membrane morphologies by fluorescent and confocal laser microscopy in lipid mixtures consisting of a neutral unsaturated lipid [dioleoylphosphatidylcholine (DOPC)], a neutral sa...

The spontaneous formation of a thread-like pattern with negatively charged lipids on an oil/water interface is reported. An analysis of the time-dependent change at the interface observed by fluorescence microscopy revealed that the thread-like pattern is generated through a two-step mechanism. First, inverted lipid micelles in the bulk-oil phase g...