In this article, we discuss a mechanical model for structural and remodeling analysis / simulation of cancellous bone, that takes into account tissue microstructure and residual stress. A three-dimensional lattice continuum is used as a structural model of cancellous bone with trabecular architecture, and its mechanical behavior is investigated concerning the dependence of structural parameters on the apparent mechanical properties of the tissue. Assuming the local uniform stress state to be an optimal stress state realized at the remodeling equilibrium, a remodeling rate equation is proposed to express the stress regulation process at the microstructural level for the three-dimensional lattice continuum. In terms of the lattice continuum, a vertebral body is modeled based on quantitative measurements of the trabecular architecture of the cancellous bone, and a remodeling simulation is conducted under the conditions of repetitive bending with compression. By comparison of the obtained distributions of the residual stress and the volume fraction with the experimental observations, the validity of the proposed model in predicting the adaptive remodeling of cancellous bone using a three-dimensional lattice continuum is demonstrated.

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The wear behavior of a cobalt-chromium-molybdenum alloy sliding against itself under a mixed or boundary lubricating condition was studied in pin-on-plate reciprocating tests with respect to metal-on-metal joint prostheses. Phospholipid L-α DPPC (dipalmitoyl phosphatidylcholine) and proteins (mixture of albumin and γ-globulin) ordinarily reduced the wear rate. However, the wear rate of the pin bearing surface which was rubbed on the same contact zone was increased by the proteins. These two contrasting results were explained by the difference in the role of the adsorbed film of proteins on the bearing surface, which served as either a protective layer to reduce wear or a blockade layer to increase wear.

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Optical tomography will be a new modality of non-invasive diagnosis in medicine and biology, and is expected to image the distribution of optical properties in human bodies by measuring transmitted light at skin surfaces. In the process of developing optical tomographic imaging systems for diagnosis of disease and study of brain functions of human heads, we need realistic optical phantoms which anatomically and optically simulate human heads with complicated and multi-layered structures. In this study, we have fabricated optical phantoms based on MRI images of a human head. The phantoms had a multi-layered structure with different optical properties at five layers; i.e., skin, skull, cerebrospinal fluid layer, gray matter and white matter. Also the phantoms which were mainly made of solid resin had dynamic parts to simulate the temporal variation of physiological functions in brain. The optical properties of the liquid circulating through the dynamic part can be changed to simulate the change in oxygenation states. The material of the skin layer was a soft rubber in order to achieve a good contact with optical fibers. The fabricated optical head phantom was checked by X-ray CT to see whether air bubbles were trapped or not, and to measure the size and cavity in the phantom.

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To observe the remodeling process in bone adapted to mechanical stimuli, a microcomputed tomography (micro CT) system with a high spatial resolution was utilized. The rat fifth caudal vertebrae (C5) were subjected to daily axial or offset loads. Morphological alterations of C5 were measured periodically and non-invasively with the micro CT between daily mechanical stimuli for 14 days. The finite element (FE) models were built from the binary cross-sectional images of cortex and trabecular bone architecture of C5. Von Mises stresses were calculated by applying the contact pressures from the rigid-body spring model (RBSM) analyses to the FE-models as boundary conditions. The transformations of cortex and the increases of the cortical area were observed in the loaded rats. FE-analyses in the offset loaded rat indicated that von Mises stress distributed uniformly under the analytical offset loaded condition. This fact suggests that the C5 would adapt to the offset loads applied externally by morphological alterations.

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A layer-structured finite element model is introduced for an artery, which consists of passive and active elements and is applicable to a variety of boundary-value problems. Constitutive equations are formulated for each type of element in the finite element model. The passive element is expressed as an incompressible isotropic hyperelastic material. The active element develops an active stress in the circumferential direction. To validate the model, we carried out numerical simulations, i.e., the pressure-diameter relationships and stress distributions at mean transmural pressure in the passive and active states, and the opening angle change with activation. The results of numerical simulation showed significant changes in the mechanical behavior of the vessel with activation. It also showed that a large contraction occurred at a higher level of activation for a higher level of constant pressure, and that the tendency of opening angle change was consistent with the experimental one reported in the literature.

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A mathematical model is formulated for activated muscles under stretching. "Yielding", which is characterized as the decrease in the rate of muscle force during stretching, is reported in the literature for activated cat soleus muscles. We hypothesize that such "yielding" mainly results from the change of an active state that is determined by step functions of activation stimulus which reflects the properties of muscle conditions. The activation stimulus increases when the muscle begins to be stretched, and it decreases after a short duration at the start of stretching and when the stretching is stopped. The effect of velocity and stimulation rate is expressed by determining the change of activation stimulus systematically. The simulation results show that the "yielding" is described by a simple frame of the model. The model might be applied to simulate the behavior of activated muscles during stretching such as walking and sports.

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The effects of smooth muscle cells on the mechanical response of arterial walls were investigated for the common carotid arteries in culture. Tubular segments obtained from male Japanese White rabbits were cultured for 6 days in the unloaded state in DMEM+20% FBS. Prior to culture, half of the specimens were soaked in liquid nitrogen (liq-N₂) for 20-40 seconds to kill cells in their walls. The mechanical response of the two groups following culture was examined using the pressure-diameter test and ruorphometry of the cultured segments. The arterial segments cultured without liq-N₂ treatment had significantly smaller outer diameter than their uncultured counterparts over 80mmHg (P<0.02), and also their wall thickness was significantly reduced (P<0.005). These changes were not significant for the segments treated with liq-N₂. These results suggest that mechanical response observed in the cultured arteries are attributable to active remodelling of arterial wall caused by smooth muscle cells.

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The present study is concerned with the elucidation of spondylolysis observed in the lower lumbar vertebrae. A three-dimensional finite element model is constructed by taking account of L3, L4 and L5 vertebrae, the sacrum, the ilium, intervertebral disks and spinal ligaments. The mechanical properties of the ligaments and the annulus fibrosus of intervertebral disks are modeled using nonlinear elastic materials. To evaluate the effects of material nonlinearity, corresponding linear elastic materials are also introduced. The motions of extension, flexion and axial rotation are simulated by using nonlinear and corresponding linear elastic materials. The results show that the extension motion is the most dangerous and that spondylolysis is most frequently observed in L5. A comparison of nonlinear and linear analyses clarifies that the material nonlinearity of soft tissues plays an important role in reducing the extension force, flexion load and axial rotation moment.

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This paper deals with the determination of fracture mechanics parameters, such as critical stress intensity factor, K_c, and critical strain energy release rate, G_c, of compact bone. Haversian bone samples taken from fresh bovine femurs were machined into small compact tension (CT) specimens with various initial crack lengths and thicknesses, and then tested under quasi-static mode I loading condition at room temperature. Factor K_c was determined following the ASTM standard E399-90, and the compliance method was used for the determination of G_c. The values of K_c and G_c were larger in the specimens with transversely oriented initial cracks than in those with longitudinally oriented initial cracks. Both K_c and G_c were dependent on initial crack length as well as specimen thickness, and these fracture characteristics could be interpreted by a hypothesis based on the observation of damage accumulation, or microcracking ahead of the main crack front.

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We present a precise method of measuring the displacement of soft tissue using a probe with a compliant needle. The displacement vector is set using two needles which are fixed in the tissue. The new method was applied to measure the displacement of a porcine meniscus in the transverse plane under joint load. The meniscus moved 0.5-1mm outward under joint load of 600 N in 2 seconds. Then, slow displacement due to creep deformation followed. The results show approximate agreement with previous predictions by computer simulation and strain measurement.

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A mathematical model for various types of arteries in the active state is proposed with the incorporation of an activation parameter, an inelastic strain and stiffening of elasticity. The total stress is divided into a passive stress and an active stress. The passive stress is expressed by an incompressible isotropic strain energy density function. The active stress is expressed as a fiber stress of smooth muscles with the use of the activation parameter and an isometric force-length relationship. The inelastic strain corresponds to the deformation between the reference configuration and the unloaded configuration. Stiffening of elasticity is considered mainly for elastic-type arteries. The simulation results show that the model adequately describes the pressure-diameter relationships in the physiological range. The stress analyses of the arterial walls show that the circumferential stress changes to compressive stress in the active state with a strong contraction and a lower transmural pressure of the vessel.

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The possibility of wear control in Metal-on-Metal artificial joints has been investigated by using a uni-directional sliding tester and a reciprocating pin-on-plate tester. The mechanism to reduce the amount of wear was the promotion of oxidization of bearing surfaces by means of externally applied magnetic field. Bearing materials were austenitic stainless steel (SUS304, SUS316) which are paramagnetic materials. In uni-directional wear tests of SUS304 sliding on SUS304 and SUS316 on SUS316 in atmosphere of air, the reduction in the amount of wear was observed by means of magnetic filed, if the influence of the magnetic field horizontal to the surfaces, which enhances wear rate, could be avoidable. The magnetic field, however, deteriorated the wear characteristic or obstructed the severe to mild transition in the tests where sliding materials were SUS304 on SUS316 and SUS316 on SUS304. The influence of magnetic field, which reduces the amount of wear of SUS316 on SUS316, was confirmed in water-based lubrication (distilled water, saline solution with and without proteins) and reciprocated sliding. The influences of magnetic field were varied by the constituents of lubricant (chlorine ion, proteins).

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Ultrasonic techniques were developed to study the characteristics for contact mechanics of an artificial hip joint. Total Hip Replacement model was used to determine contact pressure distribution on an artificial aceptabular cup subjected to compressive load ranged from 196 N to 588 N in four femur positions. The contact pressure was found to be non-uniform and reaches more than 6 MPa. It was shown that the tendency of the pressure distribution is in agreement with that obtained by the computer simulation. Some preliminary results were also presented to illustrate the effect of the direction and the magnitude of the load applied to a femoral head on the contact pressure distribution on the aceptabular cup and to evaluate the contact mechanism of the artificial hip joint.

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Local elastic moduli in the wall of porcine thoracic aortas were measured in the axial, circumferential, and radial directions by the pipette aspiration method. The local elastic moduli in the three directions were found to be independent of wall position. Then, histological analysis using color classification based on Mahalanobis' generalized distance was performed to quantitatively assess the correlation between elastic moduli and histology. Porcine thoracic aortas had a typical layered structure. The area fraction values, i.e., the percentage area of three structural components, elastin, collagen fibers and smooth muscle cells, were almost uniform in the wall. On the other hand, the moduli in bovine aortas reported previously decreased significantly from the inner to the outer sides of the wall. The histological structure was not homogeneous, that is, large clusters of smooth muscle cells existed in the outer side. These results suggest that the intramural distributions of elastic moduli are closely correlated with the histological structure.

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In this paper, a new method has been proposed to theoretically analyze the forces on the toe, ankle and knee joints using a musculoskeletal model of the lower limb. It was shown that when a human being jumps down vertically from a height of 0.3 meters without an active shock absorbing motion, the maximum force on the knee joint could reach up to 11.2 times his weight. Moreover, the optimal motion of the lower limb muscles during a vertical landing on a hard surface was obtained by converting the multi-degree-of-freedom and nonlinear optimal control problem to a parameter optimization problem. Detailed investigations were performed in three cases to minimize the forces on the toe, the ankle and the knee joints. By this optimal motion, it is possible to reduce the forces on the toe and the lower limb joints by half. It was determined that the forces on the toe would be involved in the performance function. Furthermore, the forces on the toe and the activation level of the lower limb muscles predicted by parameter optimization agreed well with the experimental results.

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Epidemiological studies have suggested that because of their frequent exposure to mechanical vibration, bus and truck drivers are especially susceptible to disc disorders. It has been reported that drivers of such vehicles are subjected to low-frequency vibration up to 6 Hz. The intervertebral disc regulates the viscoelastic properties of spinal segments. The intradiscal pressure will play an important role in the mechanical response of a spinal segment to vibrations. While previous studies have made direct in vivo measurements of intradiscal pressure under static conditions, no data has been reported on intradiscal pressure response to vibration loading under either in vivo or ex vivo conditions. The present study is to measure the intradiscal pressure response to cyclic loading in a physiological saline solution simulating in vivo conditions. The effect of mean load, amplitude and frequency of cyclic loading on the intradiscal pressure response was examined using calf lumbar spinal segments. The experiment employed mean loads of 20, 60, and 100 N with amplitudes of 10, 15, and 20 N and compared the low-frequency effects of 0.05, 0.5 and 5 Hz. The mean load was applied for one hour before the cyclic loading test, in order to consider the equilibrium intradiscal pressure. Therefore, it was confirmed that the relationships of load versus displacement, and load versus intradiscal pressure were affected by the mean load and the frequency of cyclic loading.

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Orthodontic treatment is based on the remodeling of the alveolar bone in response to externally applied orthodontic force to a tooth. The rate of bone resorption is, therefore, one of the essential factors for understanding tooth movement during orthodontic treatment. There is the basic concept of differential force in orthodontics that the application of an optimal force enables the canine to be moved without moving the molar that is used as an anchor for retracting the canine. In this paper, the resorption rates of the alveolar bone around the molar and the canine were estimated from the clinical measurements of tooth movement and the stress analyses of tooth roots using a 3-D finite element model. The model consisted of an orthodontic spring, the canine, the second premolar, and the first and second molars. The bone resorption rate to a unit stress at the molar was found to be about 0.5 micron / (kPa·day) and almost the same as that of the canine. This result suggests that the concept of differential force can be explained simply by differences in the geometry of the roots of moved and fixed teeth.

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In this study, a device is developed for the measurement and adjustment of resultant graft tension of the anterior cruciate ligament (ACL) reconstructed knee in vitro. This device is attached to the tibial surface at the distal end of the drill hole for ACL reconstruction. It measures the graft tension via a suture coming from the graft and fixed at one end of the device positioned on the axis of the drill hole, by using strain gauges. A hollow bolt-nut pair at the end of suture fixation site provides a level adjusting mechanism for the initial tension adjustment of the graft. The calibration test showed a good linearity and sensitivity, and the effect of the device is examined through the knee extension test and the anterior-posterior (A-P) drawer test for four human cadaveric knees. The graft tension observed by the device showed the ACL / graft tension characteristics that is consistent with those in past reports by several authors, and it is confirmed that the developed device enables us to study the graft tension under the practical situation of ACL reconstruction quantitatively.

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Direct measurements of blood flow and pressures are not attempted in long-term clinical use of artificial hearts due to difficulties, such as blockage by thrombus formation at the transducer and invasive location of the transducer. We developed a technique for a beat-by-beat basis on-line estimation of blood flow and aortic and left atrial pressures for use with a portable closed-loop pneumatic artificial heart drive system. This technique is based on non-invasive measurements of the driving conditions and physical models of the actuator and pump system. In vitro tests showed sufficient linear correlations between the actual pressures and stroke volume and their estimates on a beat-by-beat basis. This is an indication of in vivo success in the realtime computational technique.

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Behavior of transient blood flow behind artery stenosis and its relationship with wall shear stress (WSS) has been numerically analyzed using a computational fluid dynamic modeling of unsteady, incompressible flow in a 2D constricted channel. A train of propagating vortex waves was detected downstream the constriction and, it was found that the nature of this vortex wave correspond to a steep, adverse pressure gradient. Investigation of Strouhal number dependence shows that wavelength and total length of the vortex wave are inversely proportional to the Strouhal number, and the strength of both the primary wave and the secondary disturbance flow increase with increasing Strouhal number. Variation in geometry of stenosis indicates that the vortex wave is dramatically reduced to a jet-stream when the stenosed height exceeds a critical value of about 70% unperturbed depth of the channel, but it shows robustness to the changes in length. The time-dependent WSS gives an extreme value almost six times larger at systole compared to that related to the mean flow but a low and oscillating feature with a mean value approximately one tenth at diastole.

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A flow visualization study of a centrifugal blood pump was conducted to find the shear and velocity profiles in the back gap between the impeller and the casing. For a wide range of Reynolds numbers and specific speeds, it was found that high shear exists only in the boundary layers of the moving and stationary walls. The velocity profile was essentially laminar. It was also found that the total thickness of the high shear regions is 0.3-0.6mm for conditions of artificial heart and the thickness is determined only by Reynolds number. Hence, it can be concluded that reducing the impeller velocity is the only way to reduce wall shear stress and that increasing the gap width is not effective.

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Conventional mechanical mitral valves close rapidly, which is one of the reasons for the attendant hemolysis and the closing click. Safer mechanical valves which close more slowly will be realized if the occluder (opening and closing movement element) starts closing withont any backflow. A new self-closing occluder was designed by adjusting the center of gravity of the occluder. Blood flow becomes nearly zero for around 250 msec from the middle of left ventricular relaxation. The valve is expected to start closing by gravity during the nearly zero flow periods. Thus, the time from the maximally open state to complete closure should be designed to be no more than 250 msec. In this paper, a new design process for a self-closing occluder was proposed. A new prototype occluder made of aluminum alloy was produced by optimizing the center of gravity, torque by gravity and moment of inertia. The prototype occluder with a piano wire as the rotational axis was mounted on an acrylic resin base. The closing motion of the valve was measured by a high-speed video camera (125 pictures per second). The calculation and measurement of the closing motion were carried out, and qualitative agreement was observed with the motion in air. The time from the maximally open state to complete closure by gravity in glycerin solution as a blood substitute was 208 msec, which is thought to be satisfactory available for the cases requiring mitral valve replacement. The results showed the validity of the proposed design process.

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We investigated the hydrogel of poly (vinyl alcohol) (PVA) which possesses elastic behavior similar to the blood vessel. In this study, drag reduction on the polymer hydrogel tube surface was experimentally investigated at steady flow condition. A transparent PVA hydrogel tube was prepared from the solution of PVA, dimethyl sulfoxide (DMSO) and water by repetitive cooling method and the surface of the hydrogel tube was modified with poly (acrylic-acid) (PAA). Monodisperse polystyrene particles (7.21 μm in diameter) were used as a tracer of fluid flow and the flow was observed by CCD camera under a microscope. The wall shear stress (WSS) was determined from near-wall velocity gradient obtained by particle-tracking (PT) method and drag reduction was calculated from the WSS. Microscopic investigations have shown that the drag reduction on the hydrogel surface depends on the chemical nature of the hydrogel surface, which was varied with changing pH of flow liquid. Maximum drag reduction was obtained with water (flow), when the PAA of modified surface is in the dissociated condition.

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In this study, damage of living tissue cells (red blood cells and cancer cells) and experimental cell models (microcapsules) by plane shock waves is carried out experimentally. In addition, the effects of physical condition on the degree of damage are evaluated by constructing an appropriate mathematical model. To explain these phenomena, the red blood cells and the microcapsules are modeled mathematically as two spherical elastic shells filled with liquid. The fundamental equations express the oscillation of the spherical elastic shell in response to the incident pressure wave in the surrounding fluid. Frequency responses of the elastic shell model of two living tissue cells with mutual interaction in water are analyzed. From the results of this analysis, the effects of (1) the rise time of shock waves, (2) the distance between cells on shock-induced damage, (3) the concentration of suspended cells and (4) the incideuce angle of shock waves are discussed. It is found that effects of these parameters are large in certain cases.

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The aortic blood flow is characterized by the intermittent entry flow in a strongly curved tube because of the presence of stationary diastolic period. In this study we measured the axial and secondary velocity of intermittent flow in a strongly curved tube simulating the blood flow in an aortic arch (the ratio of the tube radius to the radius of curvature=1 / 3, Dean number=79l) by Laser Doppler Velocimeter. In order to reveal the effect of diastolic period (t_d) on the flow development, t_d ranges from 0.4 to 2.0 sec, whereas the systolic period remains constant (0.4 sec). During the deceleration phase of the systolic period, reversed axial flow starts to appear near the inner wall. This reversed axial flow becomes significant at the end of systolic phase and causes to induce the new secondary flow development. For t_d=0.4 sec flow does not diminish completely until the end of the diastolic period and affects the flow development in the following systolic period. This secondary flow augmentation in the beginning of diastolic phase is remarkable in the entry region of curved tube.

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Murray derived an Optimum condition for a vascular system by applying a concept of minimum work. Murray's law states that the diameter of a blood vessel is proportional to the cube root of the flow rate within it, and the cube of the diameter of the parent vessel is equal to the sum of the cubes of the diameter of the daughter vessels at an arterial bifurcation. We tested the applicability of Murray's law to our experimental data on the diameters of and flow rates in major arteries of four mongrel dogs in order to elucidate the physiological principles governing arterial architecture. It was found that our experimental data on major arterial bifurcations of the dog fitted Murray's law not exactly but reasonably well, and the relationship between the diameter of parent vessel and that of its daughter vessels at an arterial bifurcation was best expressed by a modified expression of Murray's law given by Σ D_di³=0.95×D_p³.

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It is we11 accepted that hemodynamics plays an important role in atherogenesis in man. However, the precise mechanisms have not been elucidated yet. Recently, Karino et al. hypothesized that flow-dependent concentration polarization of low-density lipoproteins (LDL) may occur at a blood / endothelium boundary, leading to a high risk of atherogenesis in regions of low wall shear rate where the concentration of LDL builds up. In this study, we attempted to experimentally confirm their predictions by optically measuring the concentration profile of polystyrene latex microspheres in a suspension flowing through a dialysis tube. It was found that the surface concentration of microsphere certainly increases with decreasing the flow rate and it occurs even under the condition of a very low water filtration velocity encountered in normal arteries in vivo, giving a strong support to the hypothesis proposed by Karino et al.

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Three-dimensional unsteady blood flow through an artery with a small side branch was numerically analyzed using the finite-element method. Our main focus was on the model in which the angle between the trunk and the small side branch was larger than 90 deg. This arterial geometry is generally observed in a real arterial system. For this study, the arterial wall was assumed to be rigid and the non-Newtonian effect of blood was not taken into consideration. The calculation results are summarized as follows. 1) The branch angle does not have a strong effect on the flow rate through the side branch. 2) In the case of a large branch angle, the still-standing stagnation point appears near the outer wall of the small side branch. Moreover, this still-standing stagnation point has an effect of increasing the values of wall shear stress gradient (WSSG).

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It is pointed out that mass transport in an artery, such as LDL transport, influences the progression of stenosis severely. Mass transport in blood flow through a stenosed tube is analyzed numerically. Flow is assumed to be periodic, incompressible and axisymmetric. Non-Newtonian viscosity of blood and movement of arterial wall are considered. The effect of pulsation, non-Newtonian property of blood and wall movement on mass transport is investigated. Flow pattern, concentration pattern and distribution of concentration gradient on the wall are obtained. It is found that the effect of the vortex on mass transport on the wall changes drastically with Schmidt number. In low Schmidt number flow the strength of vortex and its center position are important. Therefore, time-mean mass transport on the wall has maximum value at certain frequency because of the vortex enhancement. On the other hand, whether the vortex downstream of the stenosis flows away or not becomes important in high Schmidt number flow.

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Stability of a Starling resistor type collapsible tube circuit is studied on the basis of one-dimensional distributed parameter model ignoring the effect of flow separation at the collapsed part of the tube. The governing equations are spatially discretized into 201 ordinary differential equations with respect to time. The stability of the circuit is examined by the characteristic equation of linearized governing equations. Transition of the stability with the flow rate is indicated as loci of the eigenvalues. The spatially discretized nonlinear equations are numerically solved by Runge-Kutta scheme and the theoretical amplitudes and frequencies of self-excited oscillations qualitativeIy agree well with experimental results.

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Propagation of isolated pressure wave through a thin-walled collapsible tube filled with a viscous incompressible fluid is calculated numerically. One-dimensional continuity equation, equation of motion including a wall friction term, and the tube law obtained experimentally are used as basic equations. The pressure waveforms at three locations along the collapsible tube calculated by the present method are compared with those obtained by the experiment. It is shown that the tube law obtained experimentally needs to be modified such that slope is discontinuous at a point where locally two-dimensional buckling of the collapsible tube occurs. The viscous effect is evaluated using an equivalent Womersley number α for the isolated wave. Incorporation of the wall friction term with high accuracy is necessary in the case of small α in one-dimensional flow calculation. The propagation velocity can be approximately calculated using the Moens-Korteweg velocity corresponding to a tube with circular cross-section.

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The purpose of this study is to reveal(1)the effect of shear stress on the albumin uptake area and its content per unit area, and(2)the energy dependence of albumin uptake into endothelial cells. The uptake of the fluorescent labeled albumin was visualized with a confocal laser scanning microscope. The uptake into the endothelial cells is inhibited completely at 4°C or by 1 μM p-trifluoromethoxy-phenylhydrozone (FCCP), which is a potent energy metabolism inhibitor. This result indicates that albumin uptake is an energy-dependent, active transport. At 10 dyn / cm², at 5 μm the uptake area increases by 363% and the albumin content per unit area increases by 192%. At 60 dyn / cm², at 3 μm the area decreases by 21% and the albumin content decreases by 54%. It is, therefore, considered that the effect of shear stress on the uptake area is more dominant than on the albumin content per unit area.

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It has been recognized that the structure and function of the endothelial monolayer is affected by the applied mechanical stress. Microscopic observation of changes in cell morphology during the imposition of shear stress is necessary to identify the specific mechanism which mediates the cellular response to shear stress. In this study we observed the morphology and migration of individual cultured cells with the wall shear stress of 3 and 5 Pa under an optical microscope. We traced the particular group of cells under view, and examined the behavior of these particular cells during the imposition of shear stress. It was concluded that the initial orientation and shape of cells affect the process of receiving the external shear stress stimulus. The behavior of the individual cell depends on the geometry of surrounding cells. Thus, the external shear stress stimulus results in the "small grouping behavior", primarily due to the biological and mechanical interaction among cells.

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This study is concerned with the wing structure and aerodynamic characteristics of a dragonfly in flight. The structural properties of dragonfly wings were studied through measurements of certain morphological parameters. The scanning electron microscopic observation showed the morphological characteristics of the dragonfly wing. Dragonflies were examined in a small low-turbulence wind tunnel. In the experiment on the measurements of wing flapping, an optical displacement detector was used to measure the displacement of the dragonfly wing. In the experiment on the measurements of the velocity fluctuation, a hot-wire anemometer was used to measure the velocity field. The spectrum of dragonfly flight was revealed by the measurements of velocity fluctuation.

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The application of dynamics in organisms to the field of engineering is very instructive. To make an artificial micropropulsion mechanism in liquid, a simulation study of a propulsion mechanism modeled on the sliding mechanism of microtubules in flagella was carried out. In the simulation, sliding condition between two microtubules formed a bending wave. Both the movement and the thrust force of the propulsion mechanism were calculated. The characteristics of thrust force with change in microtubule distance and sliding length were discussed.

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We have developed Visual Sensing System that monitors respiration for 24 hours non-restrictively. The principle of this system is inter-image subtraction. The gray scale levels of pixels on a ROI (region of interest) of a current frame are subtracted from those of a previous frame to make respiration patterns in time domain. Compared with conventional restrictive methods, this method is more convenient for long respiration monitoring since it does not restrain patients' bodies. In this paper, we explain some methods to enhance the system performance. We first explain methods that improve accuracy of detecting respiration patterns by setting a threshold and an interval for inter-image subtraction most adaptively. We then explain an authenticity judgement method that judges the authenticity of respiration patterns by comparing frequency characteristics of current periodic movements with those of normal respiration using Fast Fourier Transform and by comparing gray scale histograms of the current and the previous frames. We lastly explain an emergency message and a data sending method that sends emergency messages and respiration data to host computers using a socket function when abnormality in respiration is detected. Though the algorithms are simple, we achieved a high precision in extracting respiration patterns and also satisfied the needs of patients living at distant places.

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Muscle contraction results from the relative sliding motion between thick myosin and thin actin filaments. Actomyosin is a molecular machine that converts chemical energy produced by the hydrolysis of ATP into kinetic energy. The investigation of the contractile mechanism of muscles at the atomic / molecular level was motivated by the determination of the structures of actin and myosin head S1 monomers by X-ray diffraction analyses. In order to clarify microscopic kinetic function and material heterogeneity, the molecular structural analysis of actomyosin was carried out using the molecular mechanics simulation code "AMBER". The 3-D molecular structures of actomyosin employ three models which consist of three kinds of myosin head S1 (with ATP, with ADP, and without nucleotide) and F-actin itself to reveal the fundamental micromechanism of activation in the motility assay. The minimum-energy conformations of actomyosin in the three models were determined from molecular mechanics analyses. The differences in atomic coordinates and potential energy distributions show the existence of local packing and microstructural heterogeneity. Then, molecular fluctuations were studied by molecular dynamics analysis. The fluctuations reveal the dynamic properties at the atomic level and thc possibility of change in the mesoscale structure as well as the emergence of the sliding motion of the entire molecule.

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The objective of the present study is to clarify the dynamic behavior of the middle ear by measuring the middle ear vibration directly. The velocity amplitudes of the tympanic membrane and ossicles of guinea pigs are measured before and after the manipulation of the cochlea and bulla using a laser Doppler velocimeter coupled to a compound microscope. The frequency characteristics of the middle ear vibration after the manipulation are different from those before it. These differences are explained by considering mass and damping components of the cochlear impedance and mass and stiffness components of the bulla's impedance.

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In this study, the unfolding of corrugated simple leaves such as hornbeam or common alder leaves, was observed. Based on the observation, a series of numerical models with various crease interval ratios, a^* (=a₂ / a₁, a₁:the distance from a valley crease to a crest crease, a₂:the distance from a crest crease to a valley crease) were considered to investigate the effect of a^* on the unfolding manner of corrugated leaves. By using vector analysis and transformation of coordinates with the models, numerical simulatioins for the unfolding of corrugated leaves were performed. A number of characteristic values such as angles between lamina elements and the movements of creases (valley creases run along main veins) were calculated during unfolding. The relationship between a^* and the kinetic energy of leaves during unfolding was also examined. It was found that the difference in unfolding manner between hornbeam and common alder leaves may be caused by the difference in the crease interval ratio in a leaf, a^*, i.e., a^* &ap; 1.0 in hornbeam leaves and a^* &ap; 1.3 in common alder leaves. It can be understood that hornbeam leaves with a relatively small vein diameter could choose a^*=1.0 to reduce the volume of fully folded leaves, while common alder leaves with a large vein diameter had to choose a value of a^*≠1.0 to avoid the increase in local volume due to the overlap of veins.

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The feasibility of using thermophysical properties to evaluate extracellular freezing processes favorable for cryopreservation was demonstrated by determining the correlation between the thermal state and the viability of cells and tissue. We measured the eftective thermal conductivity of Medaka embryos (Oryzias latipes) during extracellular freezing using the self-heated thermistor technique⁽1). The insulated test chamber (8×8×12mm) had a 2.5-mm-diameter thermistor bead installed in the bottom. The effective thermal conductivity was measured at -10°C for various cooling rates (from 0.1 to 10°C / min) for embryos in 1.92 mol / kg DMSO, and measured from 6 to -20°C for a cooling rate of 1°C / min for embryos in 0-2.56 mol / kg DMSO. We used the hatching rate to evaluate the viability of the embryos. The effective thermal conductivity was strongly correlated with the hatching rate, increasing as the hatching rate decreased. This demonstrates that thermophysical properties of biological materials can be used as indices for evaluating the freezing process of such materials.

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The application of dynamics in organisms to the field of engineering is very instructive. We noted the utility of eukaryotic flagellar motion for the propulsion of micromachines in liquid. We proposed a micropropulsion mechanism modeled on the active sliding of microtubules in eukaryotic flagella. Three microtubules were used to generate a three-dimensional bending wave of the micropropulsion mechanism. Both the movement and the thrust force of the micropropulsion mechanism were simulated.

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A new simultaneous measuring system using Magnetic Resonance Imaging (MRI) and microdialysis was developed. Because MRI and microdialysis have complementary measuring advantages, the combination of the two methods can provide less invasiveness, high detection sensitivity and multimodality for in vivo biomedical measurement. Using the MRI-Microdialysis simultaneous measuring system, preliminary experiments were performed to examine the rapid effect which MRI has on rat brain metabolism and to analyze the acute physiological response of the brain to oxidative stress. The changes in 5-hydroxyindoleacetic acid (5HIAA), noradrenaline levels in the striatum and 5HIAA, L-aspartic acid and L-asparagine levels in the hypothalamus area were not significant when compared to normal changes in the absence of the MRI sequence. There were no significant changes in 5-HIAA and glutamine levels during the oxidative stress;however, the intensity of the MR image was increased. The increase suggested that a decrease in paramagnetic molecules occurred during the oxidative stress period in the brain.

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The procedure to determine controlling parameters of prefreezing and freezing processes of biological tissues are discussed. In the prefreezing process, the concentration of cryoprotectant is raised stepwise to avoid exceeding osmotic stress. The rate of increase of the concentration of cryoprotectant can be chosen by considering the relaxation time of the swell of a biological cell. On the other hand, during the freezing process, the initial concentration of the cryoprotectant and the cooling rate must be determined to avoid exceeding osmotic stress and injury caused by freezing. Optimum parameters can be obtained by estimating the normalized volume of the cell. The maximum possible size of a biological tissue to be cryopreserved can be estimated from the effective thermal diffusivity of the tissue.

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Vascular endothelial cell vesicles are attached to both luminal and abluminal surfaces of the endothelium and contribute to the transport of specific macromolecules between the external environment and the cell. The vesicles have mostly flask-like or chained bead-like shapes, while they appear free within the cytoplasm. The existence of a transendothelial channel, which is considered to be involved in specific transport systems, is also reported. In this study, the generation mechanism of vascular endothelial chained vesicles and the transendothelial channel is theoretically investigated based on a method proposed by J.C. Luke (1982). A system of nonlinear differential equations is derived according to the variational principle and is reduced to a two-point boundary value problem. The equations are solved using the shooting method along with the Newton-Raphson and Runge-Kutta methods. The computed shape of the vesicle suggests that the chained vesicles and the cylindrical transendothelial channel are the most dynamically stable shape which can be formed in vascular endothelial cells.

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An ultrasonic CT method was researched for measuring indirectly the interior temperature distribution from a series of sound speed projections, which were taken at several different orientations relative to a phantom body. First, we compared three popular reconstruction algorithms to minimize a required number of projections. Then, phantom made of agar was placed in a water bath, and a series of sound speed projections was measured when a pair of ultrasonic detectors were both translated and rotated. We could obtain the temperature distribution in phantom by subtracting the sound speed before heating from the sound speed after heating. When bone or gas is in the area of measurement, projections include a data missing part. If the missing part was small, we could obtain approximately the reconstructed image by modifying the projections.

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The permeability and endothelial cell morphology in rat aortae were measured. Using FITC-albumin as a tracer, the permeability was measured on the lateral sides of ascending aota (immediately before the brachiocephalic artery, A), aortic arch (immediately after the left subclavian artery, C) and thoracic aorta (E), and on their medial sides, B, D and F, respectively. By silver staining endothelial cell morphology was observed in the same portions where the permeability was measured. The permeabilities in A and B of the ascending aorta were higher than those of the aortic arch and thoracic aorta. The cell morphology in A and B was almost the same as in other portions. However, the deviation values of the cell orientation to the axis of the blood vessel in A and B were higher than those in other portions. These results indicate that a complex blood flow in the ascending aorta affected the orientation of endothelial cells and might induce the changes in the permeability through endothelial cells.

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