In this study, a formula describing on the flattening phenomenon when a bending moment acts on a box beam was derived considering the cross-sectional deformation. Calculation results obtained using the derived formula were then compared with results acquired using the finite element method (FEM). The case of a bending moment acting on a box beam composed of four thin plates that permits cross-sectional deformation along the longitudinal direction was investigated with the following assumptions: the boundaries of these plates is are simply supported, an equally distributed load acts on these plates, and the width along the neutral line of the plates is retained after deformation. Furthermore, on the basis of the coupling of the deflections of adjacent plates and the thin plate theory, the moment of inertia of cross section was obtained as a function of the curvature of the box beam. A formula relating the bending moment to the curvature is was then derived. Calculation results from this derived formula were compared with FEM results modeling only the cross section using generalized plane strain elements. For box beams with a square cross section, the maximum moments and curvatures calculated from the derived formula were within 5% of the FEM results. This indicates that it is important to consider the reduction in the cross section that accompanies the bending of the plates. Regarding general box beams with a rectangular cross section, the influence of the aspect ratio of the cross section was found to be considerably larger in the FEM results than in the derived formula. The reason for this difference may be that plates do not satisfy the abovementioned assumptions regarding the boundary and load conditions of the plates; however, confirming this remains a task for future work.
Generally in Japan, high skilled UT engineer performed examination and high reliability of examination results are achieved. However, it is not confirmed how high skill and actual probability of detection (POD). In the performance demonstration (PD) system in US, there are determined that the number of defect, minimum number of detection, number of unflawed area and allowable false detection, but it is not considered the defect size. In this study, based on the signal detection theory, the actual POD was estimated by the signal amplitude (defect size) and observed reflection position of field experience data. It was confirmed that the POD is decreased with a less than 3.2 mm depth. The estimated POD for each crack depth well matches the result of laboratory experience data. The probability of failure for piping system was calculated based on this estimated POD, it was lower than 10-7 in case of stress corrosion cracking (SCC) on low carbon stainless steel piping SCC, and it was lower than 10-3 in case of SCC on sensitized stainless steel 304. In order to keep the probability of failure is 10-3 or less, it is only necessary that the POD is 0.95 or greater for large crack as 3.2 mm depth or more. Based on these result, this paper proposed the acceptance criteria for qualification test as training graduation.
Structural integrity of cracked pipes is assessed by predicting crack growth. In the fitness-for-service code of the Japan Society of Mechanical Engineers (JSME), the crack growth is predicted using stress intensity factor at the deepest and surface points. A semi-elliptical crack is assumed not to become deeper than a semi-circular crack. However, in reality, the stress corrosion cracking initiated at nickel alloy welds stops growing at the fusion line and becomes deeper than a semi-circular crack. Furthermore, crack shape is close to a rectangular shape rather than a semi-elliptical shape. In this study, validity of the JSME code procedure was discussed for predicting the growth of stress corrosion cracking at nickel alloy welds. Crack growth was simulated by finite element analysis together with an auto meshing technique. Various residual stress distributions and retardation of the crack growth at the fusion line were considered in the simulation. It was demonstrated that the growth prediction procedure prescribed in the JSME code brought about a conservative prediction even if the crack became deeper than the depth of a semi-circular shape crack. It was revealed that, when the growth to the surface direction was retarded at the fusion line, the change in crack size in the depth direction could be predicted conservatively by the current JSME procedure. It was suggested that, when the retardation at the fusion line is assumed in the growth prediction, the crack shape should be modelled by a rectangular shape.
Our group has developed a 3D gel printer called "SWIM - ER" (Soft and Wet Industrial Material - Easy Realizer). Here we are aiming to improve the gel material used in the SWIM-ER system for problems related to free forming and mechanical strength. The composition of the high strength gel material with low viscosity and easy modeling was clarified by adjusting the concentration of the crosslinking agent of 1st gel against the problem that the viscosity of the material is too high and it was difficult to shape. We tried tear tests in addition to various evaluation tests, tensile tests, compression tests. We thought that we can estimate and evaluate dissipation and diffusion of fracture energy by microscopic observation of specimens after tear tests.
The technique of rapid evaluation of fatigue limit using infrared thermography has been paid attention during the past 30 years. This technique is beneficial because it also makes possible to detect the location of fatigue damage in real structures. In this technique, the second harmonic of temperature variation during cyclic loading is often used as a measure of the temperature evolution to evaluate the fatigue limit. The source of the second harmonic has been already investigated quantitatively for the load amplitude above the fatigue limit but has not been investigated very well for the load amplitude below the fatigue limit. In this research, five factors (second harmonic caused by energy dissipation, applied load signal, photoelectric current of infrared sensor, quantization error and specimen movement) were examined quantitatively to examine the source of the second harmonic below the fatigue limit. Experiments were conducted for double edge notched specimens of type 304 stainless steel. As a result, it was found that the second harmonic of temperature variation below the fatigue limit is mainly caused by loading equipment. In conclusion, it is suggested that the fatigue limit should be evaluated by fitting curves considering the second harmonic proportional to the square of the load amplitude.
In order to design a rotating shaft, it is necessary to investigate the fatigue characteristics under the variable amplitude loading by using a rotating bending fatigue machine. However, the stress amplitude cannot be changed frequently in a commercial rotating bending fatigue machine. Therefore, the automatic loading apparatus was manufactured in order to perform the fatigue test under the repeated two-step variable amplitude loading by using the commercial rotating bending fatigue machine. In this apparatus, the load was changed by loading or unloading the weight using air pressure. The high stress amplitude and the low stress amplitude were alternately applied to the specimen in the rotating bending fatigue test under repeated two-step variable amplitude loading. Rotating bending fatigue tests were performed using heat-treated 0.45%C steel specimens. Before the fatigue tests, the performance test of the automatic loading apparatus was conducted and it was found that the apparatus was available for fatigue tests. Next, the fatigue tests under the repeated two-step variable amplitude loading were carried out based on the results in the Hi-Lo two-step loading fatigue test and then the cumulative fatigue was investigated. The total fatigue lives to failure of low stress amplitude under the repeated two-step variable amplitude loading are almost same as lives under the Hi-Lo two-step loading, but they have the longer lives as the low stress amplitudes decrease. Finally, the life prediction method for the specimens subjected to repeated two-step variable amplitude loading was proposed. The results estimated based on the proposed method were in good agreement with the experimental ones.
In order to ensure the safety of passengers in the event of an accident, side member and crash box are mounted on automobiles. Cylindrical tubes, rectangular pipes and hat-shaped members have been examined as structural members that subjected to an axial compressive load. However, these structures have problems that the initial peak load is very high and the load rapidly decreases due to buckling during crushing. To solve the problems, we proposed a cellular solid with mimetic woody structure as a new structural member. Some woods have no initial sharp peak load and have a plateau region which the load is constant in the relationship between the load and the displacement, when the impulsive load are applied to them. We considered that those features were suitable for structural members like a side member or a crash box. The basic cell was a square block with a side length of 10 millimeters and it had a hole in the center. The cellular solid was constituted by combining some basic cells. Therefore, a homogeneous cellular solid was fabricated by making small holes in the aluminum cube. From results obtained from the impact crushing test and simulation by the FEM software LS-DYNA®, it was demonstrated that the proposed cellular solid had crushing characteristics similar to the wood, and the energy absorption characteristics were influenced by the shape and arrangement of the cells. As a result, it was shown that the results of experiment and analysis substantially corresponded. Since the load during crushing depended on the shape and arrangement of the cells, the possibility of controlling the energy absorption characteristics was shown.
In the present study, flow in an ion-drag electrohydrodynamic (EHD) micropump was numerically simulated, and electric charge density on the emitter was modeled through the simulation. The simulation was performed for an ion-drag EHD micropump developed and experimentally tested by Kazemi et al. (Journal of Microelectromechanical Systems, Vol.18, No.3 (2009), pp.547-554.). Two models of charge density on the emitter were tested. First, one model was tested in which charge density was distributed uniformly on the emitter. The simulated discharge pressure generated in the micropump was proportional to both applied voltage and charge density. The experimental discharge pressure was reproduced by considering the change of charge density with applied voltage. Next, the other model was tested in which charge density was distributed depending on electric field on the emitter. The model was more realistic than the former because of consideration of electric field distribution on the emitter. The model also reproduced the experimental discharge pressure.
In order to apply the multi-particle collision dynamics (MPCD) method to a magnetic particle suspension, we have elucidated the dependence of the translational and rotational Brownian motion of magnetic particles on the MPCD parameters that characterize the MPCD simulation method. We here consider a three-dimensional system composed of magnetic spherical particles in thermodynamic equilibrium. The diffuse reflection model has been employed for treating the interactions between fluid and magnetic particles. In the diffuse reflection model, the interactions between fluid and magnetic particles are transferred into the translational motion more strongly than into the rotational motion of magnetic particles. The employment of relatively small simulation time steps gives rise to a satisfactory level of the translational Brownian motion. The activation level of the Brownian motion is almost independent of both the size of the unit collision cell and the number of fluid particles per cell. Larger values of the maximum rotation angle induce stronger translational and rotational Brownian motion, but in the present magnetic particle suspension the range of θmax≲π/2 seems to be reasonable. We may conclude that the MPCD method with the simple diffuse reflection model is a feasible simulation technique as the first approximation for analyzing the behavior of magnetic particles in a suspension. If more accurate solutions regarding the aggregate structures of magnetic particles are required, the introduction of the scaling coefficient regarding the interactions between fluid and magnetic particles can yield more accurate and physically reasonable aggregate structures in both a qualitative and quantitative meanings.
In the present study we have performed lattice Boltzmann simulations of an electro-conjugate fluid in order to elucidate the mechanism for inducing a strong microjet between positive and negative electrodes in the situation of a high external electric field. It has been assumed that charges are injected from the surface of a positive electrode where electric fields are significantly concentrated. The mechanism due to these injected charges has mainly been assessed as an essential factor for the occurrence of a strong microjet. In the present numerical simulations, the lattice Boltzmann equations and the basic equation for charge densities have simultaneously been solved for obtaining the flow field and the charge density distribution, respectively. The main results obtained here are summarized as follows. A strong microjet is possibly generated between the positive and the ground electrodes in the situation where Coulomb forces are much more dominant than viscous forces. A microjet starts to occur at the position of the injected charges, grows along with the fluid flow, collides with the ground electrode, and flows away from the electrode in an oblique direction relative to the center line connected between the electrodes. The flow rate induced due to the occurrence of a strong microjet increases approximately in proportion to the increasing external electric field strength. From good agreement with the corresponding experimental result in regard to the velocity vectors of a microjet, we may conclude that the mechanism for inducing a strong microjet in an electro-conjugate fluid is the interaction between the injected charges from the positive electrode and a high external electric field.
Close contact melting of solid phase on hot circular cylinders horizontally arranged in line was studied analytically. The analytical results were compared with experiment. Momentum and energy equations were treated on the assumption that nonlinear term in momentum equation can be neglected because of low velocity in thin melted liquid layer. Functional correlation between the height of a solid phase and time during melting was obtained with the use of approximated temperature profile in the liquid layer by polynomial function inserted in integrated energy equation. The result shows that decreasing rate of the solid height is almost in inversely proportional to the 1/4-th power of the ratio of diameters. Comparison between the analysis and the experiments shows good agreement. The melting time of ices on horizontal circular cylinders was considerably shortened compared with those on flat plates.
To improve the coefficient of performance (COP) in air-conditioning systems, the liquid-solid phase change temperature of the cold energy storage material should be approximately 10°C. Tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate possesses the qualities of an efficient cold storage material. TBAB aqueous solutions form a clathrate hydrate at temperatures between 5 and 12°C, depending on the concentration. The temperature region is well suited to air conditioning systems. A 20 wt% TBAB solution has a latent heat of fusion of approximately 220 kJ/kg, and its clathrate hydrate suspension is a slurry with sufficient fluidity. The objective of this study is to examine the dynamic characteristics of the formation of TBAB clathrate hydrate. The schlieren system was used for simultaneous measurement of crystal growth and concentration field in TBAB aqueous solution. Results showed that the concentration diffusion layer of the leading edge of TBAB clathrate hydrate crystal moved with the crystal growth. Based on the measured spread rate and thickness of the diffusion layer, the diffusion coefficient of the TBAB molecule in the vicinity of solid-fluid interface was estimated.
Heterogeneous nucleation of droplets on a solid surface with and without nanostructures was investigated by the classical molecular dynamics simulations. The simulations investigated effects of the nanostructures on the condensation processes and the nucleation rates. The calculation system was consisted of the fluid molecules(Ar) and the solid atoms(Pt) which interact through the 12-6 Lennard Jones(LJ) potential function, and a liquid membrane existed in the vicinity of the upper solid surface at the initial condition. Then, we changed the temperature of the lower solid wall to a lower value, which enabled us to investigate the nucleation processes in the vicinity of the lower solid surface with and without the nanostructures under a constant pressure. The potential functions between the fluid molecules and solid atoms were also assumed to be the LJ form, and the energy scale parameter between fluid molecules and solid atoms was changed to simulate a hydrophobic surface. The results showed that clusters tend to be formed near the side walls of the nanostructures and grow between the nanostructures. It was also shown that the nucleation rate is influenced by morphology of the nanostructures; the nucleation rate increases with the increase of the height of the nanostructures and with the decrease of the spacing between the nanostructures. Furthermore, the results revealed that there is a positive correlation between the nucleation rate and the heat flux measured at the lower solid wall.
Microscopic visualization experiments and simple numerical calculations using Darcy's law have been conducted for soot (PM) deposition in hexagonal channel diesel particulate filters (HEX DPFs) made of aluminum titanium oxide. In the HEX DPFs, a flow rate of the conventional wall-through flow crossing over a wall between inlet and outlet channels (an Inlet/Outlet wall) changes drastically during surface pore filtration, because a part of working gas with soot is distributed to an Inlet/Inlet wall as a bypass flow which is introduced into a wall between inlet and inlet channels (an Inlet/Inlet wall), then turning toward the direction parallel to its wall surface, and finally exiting into the outlet channel. In this case, the thickness of soot deposited on the surface of the Inlet/Inlet wall becomes thinner for the dependence on the distance from the outlet channel. On the other hand, during soot cake layer filtration, since the difference between both superficial flow velocities for Inlet/Inlet and Inlet/Outlet walls become smaller, growth rates of soot cake layers are almost uniform on both wall surfaces. Consequently, the thickness of soot deposited on the Inlet/Inlet wall has a distribution from the minimum height at the center of the channel width to the maximum around the edge.
To develop a heat flux sensor for internal combustion engines, two metal substrate thin film resistance sensors have been developed as prototypes by using MEMS (Micro-Electro-Mechanical Systems) technologies. In our previous study, a thin film heat flux sensor on a Si chip was developed for combustion fields. To apply the thin film sensor to the engine, a metal substrate sensor technology has to be developed. To begin with, a flat plate shape sensor with a SUS substrate was made in order to confirm the fabrication process and the performance of the metal substrate MEMS sensor. Heat fluxes were successfully measured in laminar premixed combustion fields, and it was confirmed that the SUS substrate flat plate shape sensor has sufficient performance in temporal resolution, measurement noise and temperature durability against requirements. Secondly, a plug shape sensor using an AC8A substrate was produced to be introduced to an engine. The heat from the sensor sidewall has to be taken into account due to the small size of the plug shape sensor, the analytical model for the heat flux calculation was extended to a two dimensional cylindrical system. Heat flux measurement tests under high load conditions with the plug shape sensor were conducted in a rapid compression and expansion machine. As a result, the sensor endured the harsh environment with the maximum pressure of 9.1 MPa and the heat flux load of 8.9 MW/m2. Furthermore, the measurement noise was estimated to 11.0 kW/m2, which was a quite low level compared with a commercially available heat flux sensor. Although the issue in the fabrication process remains, the prospects for introducing the MEMS heat flux sensor in internal combustion engine were obtained.
Porous metal fin was used as boiling heat transfer plate of phase change devices. The number of cells of the porous metal fin is 8 ppi, and the pore diameter of the porous metal fin is 3.1 mm. On the boiling heat transfer surfaces, the porous metal fin and the bass plate are brazed. Three samples of boiling heat transfer plates with the porous metal fin were made as prototype. For HFE7000 and HFE7100 made by 3M Company as working fluid, the boiling heat transfer coefficient of the boiling heat transfer plate with porous metal fin with surface roughing process by ultrasonic wave is 15 kW/m2･K. And the vale is 2.5 times of the boiling heat transfer coefficient of the flat plate without fin. Predicting method of the boiling heat transfer coefficient to which the expansion ratio of effective area for the flat plate was added to correlation of the boiling heat transfer coefficient of Stephan’s equation. The boiling heat transfer coefficient in the heat transfer plate with surface roughing process by ultrasonic wave can be put in order by ± 10 %.
Heat insulation by a wall material which has low heat capacity and heat conductivity is one of the effective ways to reduce heat transfer. By the heat insulated coating, wall temperature is fluctuated following the behavior of in-cylinder gas temperature, which decreases the gap between gas and wall temperature. In order to suppress wall heat transfer in wide engine operation range, Model Based Development is required. In this study, wall heat transfer mechanism under wall temperature fluctuated condition by heat insulation was investigated by simultaneous measurement of wall heat flux and flow behavior in wall boundary layer in RCEM. As a result, it was clarified that turbulent energy was influenced by wall temperature behavior, which impact on heat transfer coefficient. In addition, non-dimensional velocity distribution in wall boundary layer was not changed drastically by wall temperature behavior. In terms of modeling under heat insulated condition, wall heat flux was able to be predicted well by wall heat transfer model taking into account of density change in wall boundary layer.
A variety of robots has been studied and developed for undersea exploration. One of the applications for undersea exploration is mining of undersea resources such as methane hydrate and rare metal by Autonomous Underwater Vehicle (AUV). To extend active duration time of the robot in the sea, a system through which the AUVs recharge autonomously batteries is a key technology. Our reseach group has confirmed in a pool environment the dual-eye visual servoing system made a pole attached to the vehicle dock into a hole. This experiment simulates situation where the vehicle approaches recharging station under deep sea. But previous studies were conducted with ROV (Remotely Operated Vehicle) that is controlled by remote computer instead of human operator. In those experiments, power cables affected performance of control accuracy. Therefore the performance of visual feedback with AUV named Tuna-Sand2 that is compeletely indepent from cables or wires and has a general structure of modernized AUV system, has been verified to confirm the practicability of dual-eye dockig system.
Recently, electrical welfare vehicles driven by two motors employing free casters are widely used by patients and elders. However, as the user is not able to drive the vehicle well on the uneven rough roads, it is necessary to apply a new mechanism to drive on the rough road in order to expand driving area. The skid steer vehicle (SSV) has been used because of its high traveling ability on the rough road. However, the SSV has disadvantage that is, the driving assistance is required because its steering is highly affected by the road condition. The aim of this study is to design a driving assistance system of SSV for patients and elders by using Model Error Compensator (MEC) that suppresses the modeling error. The proposed controller consists of MEC, Extended Kalman Filter (EKF) that reduces sensor noise and system noise, and estimator of on-line cornering power of SSV. The effectiveness of the proposed system using on-line cornering power estimator is confirmed by the outdoor driving experiments. And the improvement of the driving assistance is evaluated by the correlation of the joystick manipulation comparing the paved and the dirt roads.
Human motion is very flexible for performing various tasks but has low speed and low precision; therefore, support and assistance of human motion by robots is desirable in some situations. In this study, in order to achieve such functions, we developed a new portable module for accurately controlling the position of a human hand and constructed a high-speed, high-accuracy positioning control system using image tracking via a high-speed vision system. In order to evaluate its performance, we executed tracing tests of constant position, circular or linear trajectory. Finally, we performed the task of catching a falling small ball, as a significantly difficult positioning task. Although this task was nearly impossible to perform with the human hand alone, the success rate was dramatically improved by using the proposed method.
This paper presents experiments and an analysis of the self-excited vibration of a plate supported by air pressure. In the analysis, the unsteady fluid force acting on the plate is calculated based on the basic equation of a two-dimensional gap flow between the plate and a chamber surface. The basic equation considers the effect of air compressibility in the chamber. The characteristic equation of the system is derived from the plate motion coupled with the unsteady fluid force acting on the plate. The instability condition and vibration frequency are predicted through the root locus of the system with changing air flow rate supplied to the chamber. The experiment consists of a plate supported by the air pressure supplied from a slit on the upper surface of the chamber, where the vibration characteristics are examined. The influence of the slit width and chamber volume on the instability condition of the self-excited vibration is clarified comparing the analytical result with experiments. Moreover, the local work done by the unsteady fluid force acting on the plate (bottom surface) is shown in this paper, and the instability mechanism is discussed. Lastly, the influence of slit width on the unsteady fluid force is addressed by the block diagram showing the phase relationship of pressure fluctuation and plate displacement.
An instability mechanism of flutter generated on a rectangular flexible sheet in an axial fluid flow is investigated through the energy-transfer quantifications. The work done by unsteady fluid force acting on the fluttering sheet surface is calculated based on a three dimensional flutter analysis utilized the Doublet-point method and finite element method. Then the work done by fluid force is divided to three terms caused by fluid added mass, damping and stiffness by applying Roger's approximation, and influence of each term on stability is clarified. As a result, it is clarified that the work caused by fluid added stiffness is dominant for excitation of flutter. Lastly, the influence of the work caused by interaction of natural vibration modes of the sheet which are dominant for flutter on stability is investigated, and the instability mechanism of flutter is discussed.
In this paper, we present a simultaneous optimization method of shape and topology for designing a light-weight plate and shell structure. The free-form optimization method for shells and SIMP method are respectively employed for shape and topology optimization, and combined effectively. Shape and fictitious homogenized-density variations are used as the design variables, and simultaneously determined in one iteration of the convergence process. With this method, the optimal topology is determined in the variable design surface optimized by shape optimization. Compliance is used as the objective functional, and minimized under the volume constraint. The optimal design problem is formulated as a distributed-parameter optimization problem, and the sensitivity functions with respect to shape and density variations are theoretically derived. Both the optimal shape and density variations are determined by the H1 gradient method, where the sensitivity functions are applied as the Robin condition to the design surface. With the proposed method, the optimal lighter and stiffer shell structure with smooth surface can be obtained without any design parameterization and numerical instabilities such as checkerboard and zigzag-shape problems.
To apply the germanium (Ge) thin film for various electronic devices, energy band structure should be controlled by carbon (C) and/or Tin (Sn) doping. It is important to understand the stable atomic configurations of C and Sn atoms near the (001) surface of a Ge thin film. In this study, first principles calculation based on density functional theory was performed to obtain the formation energies and the thermal equilibrium concentrations of C and Sn atoms near the surface of Ge thin film. The results of the analysis are threefold. First, C and Sn atoms are most stable at the first atomic layer of the Ge thin film, and the surface does not affect the stability of C or Sn atoms deeper than the fifth layer. Second, C and Sn atoms at the second to fourth layer increase the thermal equilibrium concentration of newly arrived C and Sn atoms at the surface during film growth. Third, in the case of mono-doping, formation energy of C (Sn) at the (001) surface increases with increasing concentration of surface C (Sn). In the case of co-doping at C/Sn concentration ratio of 1:1, the increases of formation energies are suppressed in comparison to the case of mono-doping. It is concluded from these results that co-doping enhances the incorporation of C and Sn atoms in the Ge thin film. Furthermore, the doped atom near Si surface becomes more stable than that in the Si bulk, and it is more remarkable in comparison to Ge.
Bone grinding with miniature ball-end diamond wheels, called diamond burs by surgeons, is widely used for surgical resection of bones, especially in orthopedic surgery and neurosurgery. During bone resection, a considerable amount of grinding heat is generated, which can cause thermal injury to adjacent tissues, including nerves. To address this problem, several types of countermeasures such as irrigation, namely coolant supplying methods, have been developed; however, the existing measures cannot suppress the excessive heat generation. To solve this problem, our previous studies proposed surgical diamond grinding wheels with titanium dioxide (TiO2) particles deposited surfaces for preventing strong loading of bone swarf on the wheel surfaces due to hydrophilicity of TiO2 and found that such wheels reduced the grinding-induced temperature elevation. However, in the experiments, pure water was used as coolant instead of saline, which is typically used in surgery. Then the grinding performances of the wheels under a saline supply were investigated. The experimental results revealed that sodium ion in saline promoted the strong loading on the wheel surface through Maillard reaction and, as a result, the grinding-induced temperature increased rapidly and finally exceeded the threshold for thermal injury. Based on our findings, new grinding wheels with fluorine-treated surfaces were developed in the hopes of promptly shedding of the adhesion of bone swarf on the wheel surface. These wheels significantly and stably suppressed bone temperature elevation compared with commercial and previously developed wheels.
A parallel-piped flow channel with micro-striped patterns has been designed to study the effect of the shear field on the myoblast in vitro. The micro-pattern was manufactured with the photolithography technique and used for the scaffold of the cell culture in the flow chamber placed in the incubator on the microscope. Variation was made on the angle between the stripe of the pattern and the flow direction: 0, 45, and 90 degrees. After cultivation for 4 hours, C2C12 (mouse myoblast cell line) adhered on the micro-pattern was exposed to the shear flow for 4 hours. The wall shear stress is estimated from the parabolic velocity profile in the medium between the parallel walls. With the experimental system, the following tendencies of responses (deformation, orientation, and migration) of each cell was observed. Under the wall shear stress of < 3 Pa, each cell deforms to the round shape at first, and extends again along the stripe-pattern. Orientation of each cell is collapsed during exposure to the wall shear stress of 3 Pa, and is recovered after stopping exposure to the shear field. The results show that the experimental system is available to investigate quantitatively the effect of mechanical stress field on the oriented cell.
Mechanical stimulation affects cell behaviors (proliferation, orientation, migration and differentiation) in vivo, and a lot of models of experiments on mechanical stimulation in vitro have been reported. The development of control technique on cell is important in the field of regenerative medicine. Recently, skeletal myoblasts have been applied for cardiac repair. In the previous study, C2C12 (mouse myoblast cell line) made orientation perpendicular to the streamlines in the donut shape flow channel. In the present study, C2C12 has been cultured in the Couette type of the shear field between the rotating disk and the stationary culture plate to study quantitatively the effect of shear stress (for 24 hours, < 2 Pa) on orientation of myoblasts in vitro. The time lapse image of myoblasts shows that C2C12 tilts perpendicularly against the flow direction at the wall shear stress of 2 Pa and that C2C12 tends to migrate to the lower wall shear stress region of 0.4 Pa.
It is already known that micro gravity affects astronaut’s body. In contrary, hyper-gravity might affect myoblasts. In the present study, mouse muscle cells (C2C12) were cultured four five hours in hyper-gravitational environment (50 G, 100 G) using the centrifugal machine placed in the incubator. Cells were observed at the incubator microscope for 24 hours after stopping centrifugation. The contour of each cell at the time-lapse images was approximated to the ellipsoid and several parameters were calculated: the angle, the area, and the aspect ratio. Each cell tends to shrink from the extended shape under hyper-gravitational environment. The directions of the major axis at 50% of cells tilt to the parallel direction to the hypergravity. After 24 hours, 51% of cells tilt to the perpendicular direction of the hypergravity in the 50 G group. The result shows that the history of hyper-gravitational environment affects the shape of cells.