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Guided excitation in patterned cardiomyocytes was analysed by extracellular recording of field potentials with a commercial device of multi-electrode array (MEA). In order to define fibronectin patterns on the MEA surface, microcontact printing was performed with a microscope-based alignment system. Cardiomyocytes were harvested from neonatal rats and then cultured on the patterned device. After 3days, cell stripes were formed, allowing guided excitation along each of the cell stripes. Increasing the culture time from 3 to 5days improved the beating repeatability without changing the quality of the electric conduction. More detailed analyses revealed that the excitation propagation along a cell stripe was sensitive to the cell coupling defects which could be modified by adding drugs in the culture medium during the early stage of the pattern formation. Our results suggest that extracellular recordings with patterned MEAs are reliable for quantitative analyses of guided excitation of cardiomyocytes.

Recent development of tissue engineering techniques allows creating and maintaining almost indefinitely networks of excitable cells with desired architecture. We coupled the network of live excitable cardiac cells with a common computer by sensitizing them to light, projecting a light pattern on the layer of cells, and monitoring excitation with the aid of fluorescent probes (optical mapping). As a sensitizing substance we used azobenzene trimethylammonium bromide (AzoTAB). This substance undergoes cis-trans-photoisomerization and trans-isomer of AzoTAB inhibits excitation in the cardiac cells, while cis-isomer does not. AzoTAB-mediated sensitization allows, thus, reversible and dynamic control of the excitation waves through the entire cardiomyocyte network either uniformly, or in a preferred spatial pattern. Technically, it was achieved by coupling a common digital projector with a macroview microscope and using computer graphic software for creating the projected pattern of conducting pathways. This approach allows real time interactive photocontrol of the heart tissue.

We observed the photophoresis of smoke particles in a small focal laser beam under micro-gravity, exerted in an airplane, to avoid air convectional flow due to buoyancy. We measured the motion of smoke particles and found that the particles exhibit negative photophoresis under the suppression of the convection. Based on the distribution of velocity of negative photophoresis, it is shown that the photophoretic velocity is proportional to the laser power applied for the particle. We discuss the mechanism in terms of the radiometric force.

This paper presents an in vitro system for cardiac tissue engineering based on cardiomyocytes cultured on electrospun polymethylglutarimide (PMGI) nanofibrous meshes either imprinted on solid substrate or suspended in space. Special care was taken over the ability to control the tissue architecture. The electrospinning process allowed nano-scale diameter PMGI fibers with different positioning density to be collected in a random or in an aligned way that defines the general configuration of the mesh. Micro-imprinted on solid substrate nanofibers guarantee aligned cell growth, when the distance between them is 30 μm or less. Suspended in 3D space, nanofibers define the overall architecture of the tissue, depending on orientation and positioning density of the nanofibers. As a result, cardiac cells proliferated into contractile tissue filaments, open-worked tissue meshes and continuous anisotropic cell sheets. Alignment of the cells was characterized by elongation of the cell shape and orientation of the α-actin filaments supported by the FFT data. The advantage of this method is its ability to maintain both three-dimensionality and structural anisotropy.

Cardiomyocyte tissue culture allows visualization of excitation waves with the aid of potential-sensitive and Ca ++ -sensitive dyes similar to experiments with the real heart tissue, but it provides much lower level of intrinsic complexity. It also offers a tool to create desirable structure of the tissue: geometry, controllable inhomogeneities, gradients, etc. In our study we show the ways to create patterned tissue and experimental examples of the processes of origination of spiral waves in cultured cardiomyocytes. We also show the method to control the excitation waves in the cardiomyocyte tissue by adding the AzoTAB and varying the wavelength and intensity of illumination.

We performed single-DNA observation to measure double-strand breaks caused by γ-ray irradiation. To analyze the efficiency of the breakage reaction in a semi-quantitative manner, we used T4 DNA, 166 kbp. The efficiency of γ-ray-induced breakage for compact DNA in the presence of spermidine (3+) was ∼1/25 of that for elongated DNA. This finding suggests that the primary protective effect of polyamines is due to the compaction of DNA.

We report the vectorial transport of a material object to a desired location by chemical waves generated in an excitable medium (Belousov−Zhabotinsky reaction). The transportation route is determined by the excitable waves induced at a certain point on the excitable medium. This study realized direct coupling between a chemical reaction and vectorial motion; such transduction of energy is generally found in biological motility but has been difficult to achieve in artificial model systems. We discuss the future possible application of these findings to the fabrication of a chemical machine that works under the self-management of motion in response to external stimuli.

To identify the optimum conditions for the optical trapping of a droplet under microgravity, we theoretically analyzed the efficiency of trapping with counter laser beams. We found that the distance between the two foci is an important parameter for obtaining stable trapping conditions. We also performed an optical trapping experiment with counter laser beams under microgravity. The experimental results correspond well to the theoretical prediction.

It has been reported that an oil droplet on a glass surface moves spontaneously in an oil-water system. This motion of an oil droplet can be understood as the spreading of a reactive droplet, which is induced by the interfacial tension gradient at the glass surface. In this paper, we focus on the spontaneous motion of an oil droplet climbing up stairs. We found that an oil droplet tends to move tip the stairs rather than to step down. We describe some of the mechanisms of this unique behavior.

金沢大学大学院自然科学研究科計算科学, 金沢大学理学部, Chemical control of the spontaneous motion of a reactive oil droplet moving on a glass substrate under an aqueous phase is reported. Experimental results show that the self-motion of an oil droplet is confined on an acid-treated glass surface. The transient behavior of oil-droplet motion is also observed with a high-speed video camera. A mathematical model that incorporates the effect of the glass surface charge is built based on the experimental observation of oil-droplet motion. A numerical simulation of this mathematical model reproduced the essential features concerning confinement of oil droplet motion within a certain chemical territory and also its transient behavior. Our results may shed light on physical aspects of reactive spreading and a chemotaxis in living things. © 2005 The American Physical Society.

The optical levitation of a liquid droplet in the gas phase was investigated under a time-dependent change in the gravitational acceleration in an airplane following a specific flight profile. Through multiple trials under a linear increase in effective gravitational acceleration, we performed an experiment on the optical trapping of a droplet from 0.3 g 0 to 0.9 g 0 , where g 0 = 9.8 m/s 2 . During this change in the effective gravitational acceleration, the trapping position of a droplet with a radius of 14 μm was found to be lowered by ca. 100 μm. The essential feature of the change in the trapping position was reproduced by a theoretical calculation under the framework of ray optics. To the best of our knowledge, this study is the first to report on optical levitation under a time-dependent gravitational change.

We report the rhythmic growth and disappearance of a micrometer-sized water droplet under stationary nonequilibrium conditions, with a periodicity of ~ 1 s. Under a supersaturated vapor, a micro water droplet nucleates on a glass plate, grows and then disappears when the growing droplet touches a larger water sink, and this cycle repeats in a rhythmic manner. We discuss the rhythmic phenomenon as a kind of limit cycle oscillation.

The generation of convective flow by a chemical wave was studied experimentally on a mm-sized droplet of Belousov–Zhabotinsky (BZ) reaction medium. A propagating chemical wave causes a transient increase in interfacial tension, and this local change in interfacial tension induces convection. The observed flow profile was reproduced with a numerical simulation by introducing the transient increase in interfacial tension to a modified Navier–Stokes equation coupled with a chemical kinetic equation; a modified Oregonator. We also observed the periodic motion of a BZ droplet floating on an oil phase. Such periodic motion is attributed to the rhythmic change in interfacial tension. The observed periodic convective motion coupled with a chemical reaction is discussed in relation to chemo-mechanical energy transduction under isothermal conditions.

The oscillatory flow of water draining from an upside-down plastic bottle with a thin pipe attached to its head is studied as an example of a dissipative structure generated under far-from-equilibrium conditions. Mode bifurcation was observed in the water/air flow: no flow, oscillatory flow, and counter flow were found when the inner diameter of the thin pipe was changed. The modes are stable against perturbations. A coupled two-bottle system exhibits either in-phase or anti-phase self-synchronization. These characteristic behaviors imply that the essential features of the oscillatory flow in a single bottle system can be described as a limit-cycle oscillation.

In conventional primary cultures, cardiac cells prepared from a newborn rat undergo spontaneous formation of cell clusters after several days. These cell clusters may be non-homogeneously distributed on a flat surface and show irregular beating which can be recorded by calcium ion imaging. In order to improve the cell cluster homogeneity and the beating regularity, patterned topographic features were used to guide the cellular growth and the cell layer formation. On the substrate with an array of broadly spaced cross features made of photoresist, cells grew on the places that were not occupied by the crosses and thus formed a cell layer with interconnected cell clusters. Accordingly, spatially coordinated regular beating could be recorded over the whole patterned area. In contrast, when cultured on the substrate with broadly spaced but inter-connected cross features, the cardiac cell layer showed beatings which were neither coordinated in space nor regular in time. Finally, when cultured on the substrate with narrowly spaced features, the cell beating became spatially coordinated but still remained irregular. Our results suggest a way to improve the rhythmic property of cultured cardiac cell layers which might be useful for further investigations.

The photoinduced motion of an oil droplet on an aqueous solution under local irradiation by a green laser is reported. The results showed that a repulsive force is generated on pure water, while an attractive force is observed with an aqueous solution containing a surfactant. The driving force is discussed in terms of a thermal Marangoni effect. The switching on the photothermal effect is interpreted by taking into account the advection caused by the spatial gradient of the surface tension under local heating by a laser. A numerical model revealed that the geometrical profile of the surface tension around the droplet determines the mode of advection around the droplet and causes switching in the direction of migrations.

Self-movement in an oil/water system generated by chemically driven Marangoni instability was studied. Repetitive changes in the interfacial tension were monitored for a two-phase system, in which the oil phase was a nitrobenzene solution of iodine and potassium iodide and the aqueous phase contained cationic surfactant. Our findings show that inversion of the contact angle induced by a sudden increase in tension is essential for inducing marked acceleration in the self-motion of the oil droplet. The self-motion continues for 30−60 min and then terminates. The movement starts again with the addition of iodine to the oil droplet after an induction period necessary for “digestion” of the nutrient, i.e., the iodine.

本稿では,水・油・界面活性剤から成る系における自発的な界面運動について記述している。化学種の濃度が水相と油相間で非平衡である時,界面で様々な自励振動が見られる。今回は,その自励振動のうち,特に界面張力の周期的な増加に注目し,界面張力変化と界面運動との相関について説明した。界面張力が急激に増加すると接触角も急激に変化し,その結果界面張力間のバランスが崩れて運動が起こることを明らかにした。また,油水系では界面運動の駆動力は水相と油相間での界面活性剤の濃度勾配である。すなわち,等温条件下で化学的なエネルギーから機械的な運動を直接取り出している系であると言える。これは,例えば筋肉におけるエネルギー変換の機構と比較すると1)非平衡状態で起こり,2)熱エネルギーを介さない化学→機械エネルギーの直接変換系であり,3)空間的に非対称性を取り入れることによって運動方向の制御が可能である,といった点などにおいて共通性があり,生物の運動のメカニズムを探索する上で有効であると考えている。

We report here the repulsive/attractive motion of an oil droplet floating on an aqueous phase caused by the application of a stimulant gas. A cm-sized droplet of oleic acid is repelled by ammonia vapor. In contrast, a droplet of aniline on an aqueous phase moves toward hydrochloric acid as a stimulant. The mechanisms of these characteristic behaviors of oil droplets are discussed in terms of the spatial gradient of the interfacial tension caused by the stimulant gas.

We found that a focused laser can generate microscopic phase separation in an oil/water system. An oil droplet emerges and grows at the focus of the laser in a water-rich homogeneous medium. In contrast, in an oil-rich homogeneous phase, water droplets spring out in a successive manner from the focus of the laser, move away, and disappear in the surroundings, forming a flower-like pattern. The mechanism of this dynamic phase separation is discussed under the framework of the mean field theory.

A water droplet, which was formed as a nucleation center from an aerosol of ammonium chloride, was trapped by a converged c.w. IR laser (λ = 1064 nm) using a 100× objective lens, and the successive growth of the droplet was observed under supersaturated water vapor. The size of the droplet increased linearly with time and its maximum radius was 5.7 μm at a laser at 5 mW, indicating that the axial trapping efficiency Q was 0.46. This efficiency is much greater than those reported previously; for example, according to Ashkin and Dziedzic [Science 1975, 187, 1073], Q = 0.08 for a glycerol droplet of radius 6 μm at 40 mW (λ = 514.5 nm).

The geometry of excitation wave front may play an important role on the propagation block and spiral wave formation. The wave front which is bent over the critical value due to interaction with the obstacles may partially cease to propagate and appearing wave breaks evolve into rotating waves or reentry. This scenario may explain how reentry spontaneously originates in a heart. We studied highly curved excitation wave fronts in the cardiac tissue culture and found that in the conditions of normal, non-inhibited excitability the curvature effects do not play essential role in the propagation. Neither narrow isthmuses nor sharp corners of the obstacles, being classical objects for production of extremely curved wave front, affect non-inhibited wave propagation. The curvature-related phenomena of the propagation block and wave detachment from the obstacle boundary were observed only after partial suppression of the sodium channels with Lidocaine. Computer simulations confirmed the experimental observations. The explanation of the observed phenomena refers to the fact that the heart tissue is made of finite size cells so that curvature radii smaller than the cardiomyocyte size loses sense, and in non-inhibited tissue the single cell is capable to transmit excitation to its neighbors.

An oscillatory system called a plastic bottle oscillator is studied, in which the downflow of water and upflow of air alternate periodically in an upside-down plastic bottle containing water. It is demonstrated that a coupled two-bottle system exhibits in- and antiphase synchronization according to the nature of coupling. A simple ordinary differential equation is deduced to interpret the characteristics of a single oscillator. This model is also extended to coupled oscillators, and the model reproduces the essential features of the experimental observations.

Self-movement of an oil–water system induced by chemically-driven Marangoni instability was studied. Depending on the shape of the vessel and the amount of oil and water solutions, various modes of movement were generated, such as random, rotational, and ameba-like. The most significant finding is the realization of a spatially directed mechanical movement. The mechanism of such chemomechanical transduction is discussed in relation to an imbalance of the interfacial tension due to a nonlinear oscillation at the interface.

International audience; Liquid droplets can be manipulated in a controlled fashion along trajectories of any desired shape (such as a heart, see picture) by using light to create a wavelength-dependent interfacial tension gradient at a liquid/liquid interface. In this new phenomenon, the "chromocapillary effect", an interfacial flow generates droplet motion in the direction opposite to the gradient.

Directed motion of an oil droplet floating in an aqueous solution is generated by using a laser beam. Interestingly, the direction of the droplet motion can be switched between forward and backward by changing the optical path of the laser through the droplet. This motion is caused above a certain critical power of the laser, and above this value the velocity increases almost linearly with the power. The mechanism of this directed motion is explained as follows: the oil droplet is locally heated by a narrow laser beam, this local heating induces a specific mode of convection inside the droplet, and this generated convective motion produces translational directed motion of the droplet.

Spontaneous motion of an oil droplet driven by chemical nonequilibricity is reported. It is shown that the droplet undergoes regular rhythmic motion under appropriately designed boundary conditions, whereas it exhibits random motion in an isotropic environment. This study is a novel manifestation on the direct energy transformation of chemical energy into regular spatial-motion under isothermal conditions. A simple mathematical equation including noise reproduces the essential feature of the transition from irregularity into periodic regular motion. Our results will inspire the theoretical study on the mechanism of molecular motors in living matter, working under significant influence of thermal fluctuation., Comment: 4 pages, 4 figures

The generation of convective flow by a chemical wave was studied experimentally on Belousov‐Zhabotinsky (BZ) reaction medium. A propagating chemical wave causes a transient increase in interfacial tension, which induces convection in the bulk phase. The observed flow profile was reproduced with a numerical simulation by coupled equation of a Navier‐Stokes equation including interfacial tension with the chemical kinetics, named Oregonator. The present experimental system serves as a model toward the deeper understanding on the mechanism of direct coupling of chemical energy with mechanical motion.

Rhythmic bursting on the order of seconds in a cluster of plastic beads under continuous irradiation of a focused neodymium-doped yttrium aluminum garnet (Nd:YAG) laser beam (1064 nm) is reported. The oscillatory instability is induced as a result of competition between trapping and scattering forces, where both forces are induced by the focused laser beam. Above a critical power of the laser beam, mode bifurcation from the stationary state into periodic bursting is observed. Our model employing ordinary differential equations reproduces the essential aspects of the experimental results.

A new kind of cool chemical engine is reported. It is shown that spatially directed mechanical movement is generated with a simple experimental system composed with oil, water and an aluminum rotor. The spontaneous movement is driven by rhythmic oscillation of interfacial tension accompanied with the repetitive change of the contact angle. The rhythmic change of the interfacial tension is induced through the high nonlinearity of the transportation process of the surfactant molecules through the interface in a far-from-equilibrium condition on the concentration of the surfactant.

Spontaneous motion of a solid/liquid composite induced by a chemical Marangoni effect, where an oil droplet attached to a solid soap is placed on a water phase, was investigated. The composite exhibits various characteristic motions, such as revolution (orbital motion) and translational motion. The results showed that the mode of this spontaneous motion switches with a change in the size of the solid scrap. The essential features of this mode-switching were reproduced by ordinary differential equations by considering nonlinear friction with proper symmetry.

Giant liposomes were formed spontaneously from neutral phospholipids in an aqueous solution containing MgCl2. Based on both dark-field microscopy and transmission electron microscopy, we concluded that these giant liposomes are unilamellar.

It is shown that the optimal path in a two-dimensional vector field is deduced by the use of chemical wave in the Belousov-Zhabotinsky reaction (BZ reaction). We also reproduced our experimental result in a numerical simulation based on a two-variable reaction-diffusion equation. The present result provides a simple model for the future application of excitable media to parallel computing, i.e., an excitable medium serves as a self-organized parallel processor.

We report the potential for photocontrol of cardiac excitation ranging from the cellular to the tissue level using the photo-sensitive compound, azobenzene trimethyammonium bromide (AzoTAB). Cells and heart tissue were collected from rats & incubated with 0.1-0.5 mM AzoTAB. Under illumination with blue light (>440 nM) and in the thermally relaxed state, the trans-isomer of AzoTAB reversibly reduced the occurrence of spontaneous activity and decreased the speed of propagating waves in cardiac myocyte monolayers, to the point of complete suppression. Illumination of near-UV light (∼365 nm) changed the tertiary structure of AzoTAB to its cis-isomer form and restored monolayer excitability. In isolated atrial preparations, spontaneous activations were suppressed in the presence of AzoTAB. The activity returned after the tissue was illuminated with UV light. We conclude that AzoTAB mediated sensitization offers the potential for controlling cardiac excitation waves either uniformly or in a preferred spatial pattern. The combination of photocontrol with optical mapping techniques allows one to control and observe wave excitation patterns simultaneously without physical manipulation.