Under the influence of mechanical environment, bone structure is formed and maintained by adaptive remodeling that involves osteoclastic resorption and osteoblastic formation. In the mechanotransduction system in osteoblasts, it is believed that intracellular calcium plays a fundamental role and cytoskeletal actin filament is a crucial component for the signal transduction process. To clarify the role of actin filament in deformation-induced Ca²⁺ signaling, osteoblast-like cells (MC3T3-E1) with different actin filament densities controlled by cytochalasin D were subjected to tensile strain in vitro. The change in intracellular Ca²⁺ concentration labeled by fluo-3 was observed using a confocal laser-scanning microscope. As a result, the disruption of the actin filament was found to significantly suppress the deformation-induced Ca²⁺ response that was regulated according to the degree of actin filament organization. This result indicates that the actin filament is indispensable for the quantitative regulation of Ca²⁺ signaling in response to a mechanical stimulus in osteoblasts.

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An experiment was carried out to investigate the morphological response of mechanically stimulated myoblasts that were cultured on a collagen-coated silicone ribbon and were subjected to tension for 6 hours. Images of the cells were taken by a CCD camera and input into a computer every 10 minutes for 8 hours. Both morphological change represented by a shape index (SI) and cumulative migration of the cells were measured every hour. An increase of the SI and decrease of the migration velocity were observed during tensile loading. Considering the cell structure, it is considered that hydrodynamic force of the cytosol would act on cytoskeletons due to the deformation of the cell. The fluid-structure interaction analysis was carried out to estimate the stress of the filament, where the actin filament and cytosol were modeled as an elastic cylinder and viscous fluid, respectively. The results of the calculation suggested that the rounding of the cell might not be caused by the break of the filament due to the hydrodynamic force.

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The clathrin-coated pits, vesicles and chained vesicles on the inner surface of the plasma membrane facilitate the cell to transport specific extracellular macromolecules. This cellular process is strongly involved with large mechanical deformations of the plasma membrane accompanied by changes in membrane curvature. The assembly of the clathrin coat is thought to provide curvature into the membrane. Hence, effects of in-plane shear elasticity due to these coat structure may be significant on the vesicular mechanics. In this study, large deformation mechanics of plasma membrane chained vesicles in cells have been formulated based on minimization of bending and in-plane shear strain energy of the membrane. Effects of outer surrounding cytoplasmic flat membrane upon mechanically stable shapes of the vesicles were revealed, while effects of in-plane shear elasticity were partly discussed.

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The advantages of microencapsulated cells over those of suspended cells were evaluated for improving viability in cryopreservation. Rat pheochromocytoma (PC12) cells were selected as the test biological cells and then microencapsulated in alginate-polylysine-alginate membranes. These microencapsulated PC12 cells were frozen by differential scanning calorimetry (DSC) at various cooling rates, from 0.5 to 10°C/min. Their latent heat was measured during freezing from 4 to −80°C. The post-thaw viability was evaluated by dopamine-concentration measurement and by trypan blue exclusion assay. Results showed that at cooling rates of 0.5 and 1°C/min, the latent heat of microencapsulated PC12 cells was lower than that of suspended cells. This lower latent heat is caused by the fact that the extra-microcapsule froze and the intra-capsule remained unfrozen due to the formation of ice crystals in the extra-capsule space. The post-thaw viability of microencapsulated PC12 cells was improved when the cooling rate was 0.5 or 1°C/min, compared with that of suspended cells. Therefore, in microencapsulated PC12 cells, maintaining the intra-microcapsules in an unfrozen state during freezing reduces the solution effect and thus improves the post-thaw viability.

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The application of dynamics observed in organisms is very instructive in the field of engineering. We noted the utility of eukaryotic flagellar motion for propulsion in water, and made an enlarged propulsion mechanism modeled on the active sliding of microtubules in eukaryotic flagella. Active sliding between two rows of electromagnets on flexible beams corresponding to the active sliding of microtubules was used. Cyclic two-dimensional bending movement and positive thrust force of the propulsion mechanism were generated in water. We discussed the influence of the bending frequency, the number of waves, and the sliding length on the thrust force.

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The motion of a microorganism with a flagellum is investigated with a view to applying its propulsion mechanism to the hydrodynamic driving of micromachines in the future. Using the boundary element method for the Stokes flow, the speed of advance and the power consumption of the microorganism are numerically determined. Optimizations are performed on six nondimensional parameters that describe the shape of the flagellum and two nondimensional parameters that represent the shape of the cell body. The optimum shape agrees well with the shape of the actual microorganism except for the cross-sectional shape of the flagellum. Low power consumption and high speed of advance are predicted when the cross section of the flagellum is elliptic with its major axis in the radial direction of the flagellar spiral.

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In the present study, we observed the motion of the bacterium, Vibrio alginolysicus, which swims by rotating a single helically shaped flagellum, by means of a dark-field microscope with a CCD camera system. We took measurements of the speed and the rotation rate as well as the size of individual bacteria. Next, we predicted the swimming speed by means of the boundary element method to analyse the bacterium’s motion and compared the calculated speed with the observed one. There was a close correlation between them not only qualitatively but also qauntitatively. Furthermore, we evaluated the torque of the flagellar motor, by coupling the computational and the experimental results. The torque was estimated to be of the order of 0.1-1 pNμm.

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Blood flow in a large artery is commonly analyzed by means of constitutive equations. However, it is not appropriate to use constitutive equations for small arteries because of the heterogeneity of the blood. In this paper, a new method to model an erythrocyte using beads and springs is proposed as an alternative way to analyze the blood flow, which is called a deformable erythrocyte model. The behavior of a single erythrocyte is computed under a constant shear field. The rotating attitude of the erythrocyte model and rheological property of the blood are discussed. The results show that the deformable erythrocyte model can appropriately simulate the tank tread motion of an erythrocyte and the shear-thinning property under high-shear-rate conditions. It is, therefore, considered that the present model is able to consistently express the blood flow characteristics.

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Responses of endothelial cells to shear stress due to blood flow are basically heterogeneous. One of the reasons of the heterogeneity may be variation of the shear stress at individual cell level. In this study, we presented a method of three-dimensional cell shape measurement by confocal laser scanning microscopy, and determination of shear stress distribution on the surface of the cell by particle tracking velocimetry with a scale-up model. Thereby, shear stress distribution on the surface of statically cultured cells and flow-exposed cells was determined. From the results of two examples, it has been shown that the shear stress distribution on a cell had close correlation not only with the surface geometry of the cell but also with that of surrounding cells, and varied from cell to cell. The subcelluar distribution of the shear stress may provide important information to clarify the mechanisms of the mechanotransduction of endothelial cells.

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Over 90% of subarachnoid hemorrhages are caused by rupture of a cerebral aneurysm. Medical statistics indicate that cerebral aneurysm occurs predominantly in arteries which branch off with sharp curvature, where flow and wall shear stress change abruptly. In this paper, a system for analysis of flow in the cerebral artery is constructed. In this system, numerical simulation is conducted for geometry, which is extracted from computed tomographic angiography of the cerebral artery. The boundary conditions are modeled from measured data and are prescribed to simulate hemodynamics in the real situation. This system investigates effects of geometry on wall shear stress distribution and the flow pattern in the artery. Wall shear stress was found to be concentrated in specific areas due to effects of curvature.

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The flow past cells adherent to the bottom plate of a parallel-plate channel is numerically analyzed in the zero-Reynolds-number limit, and the effect of the neighboring adherent cells on the drag force exerted on an adherent cell is examined. The cells are modeled as rigid spherical particles and they are assumed to be attached to the channel wall regularly in a square array. It is found that, when the size ratio of the cell-to-channel height is smaller than approximately 0.2, the drag force exerted on an adherent cell is well approximated by a linear function of the size ratio, almost independently of the separation distances between neighboring cells except for the cases of very narrow spacing. For larger size ratios, the drag force on an adherent cell in channel flow is generally smaller than the corresponding value in tube flow, but both values vary considerably, depending on the size ratios and the separation distances.

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To investigate the effect of the changes in water filtration velocity on the structure of an arterial wall, measurements of water filtration velocity and microscopic observation of histological specimens of the rabbit common carotid arteries were carried out by surgically removing the adventitia of the arteries and harvesting them at different times postoperatively. It was found that by removal of the adventitia, water filtration velocity at the arterial wall increased temporarily, and then as healing of the adventitia progressed, it decreased gradually until water filtration velocity attained almost the same value as that obtained with intact arteries. Intimal thickening was observed in those vessels harvested at 7 and 14 days postoperatively. Furthermore, it was shown by theoretical calculations that the concentration of low-density lipoprotein, which is a main carrier of cholesterol in blood, was locally elevated at the luminal surface of the segment where water filtration velocity was increased by removal of the adventitia. These results indicate that the change in water filtration velocity at the vessel wall brings about certain changes in the structure of the vessel wall.

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The characteristics of a pulsatile flow through stenosis are already well known, however, mass transport around stenosis is not yet well understood. In this study, mass transport in the pulsatile flow between flat plates with asymmetric stenosis is analyzed numerically. The effects of the pulsation and asymmetry of the stenosis on the mass transport are investigated. Flow pattern, concentration pattern and the distribution of the wall concentration are obtained. It is found that an asymmetry of the stenosis increases the wall concentration downstream of the stenosis. In the asymmetric stenosis case, the wall concentration downstream of the stenosis recovers at a lower pulsatile frequency than the symmetric stenosis case.

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Spatiotemporal maps of the velocity of intraventricular blood flows obtained with color M-mode Doppler (CMD) echocardiography are used to assess the diastolic function of the left ventricle (LV). However, theoretical basis for that is unclear. Hence, we studied the relationship between flow patterns in the LV and the shapes of aliasing areas that appear in CMD echocardiograms by means of computational fluid dynamics using an axisymmetric model of the LV. The results showed that a ring vortex formed in the early stage of expansion and grew larger while shifting its center towards the apex of the LV, occupying a large annular space between the mainflow along the long axis and the lateral wall of the LV and constricting the mainflow. Due to that, fluid elements in the mainflow increased their velocities and proceeded further deeper into the LV with high velocities, which appeared to be an elongated shape of the aliasing area in the CMD echocardiogram. From these results it was concluded that the shape of the aliasing area in a CMD echocardiogram shows the change in the velocity of the mainflow affected by the growth and migration of a ring vortex formed in the LV.

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The effect of a locally disturbed flow on intimal thickening was studied by creating a moderate axisymmetric stenosis (mean diameter reduction: 26%) in common carotid arteries of the rabbit and feeding a cholesterol-rich diet. In eight of nine specimens obtained from four rabbits, intimal thickening occurred at the distal side of the stenosis, mainly in a restricted region which extended from the apex of the stenosis to the distal end, the point of the maximum thickness locating approximately a half of the vessel diameter downstream of the apex of the stenosis. The result was compared with the distributions of wall shear stress and surface concentration of low-density lipoproteins (LDL) which were calculated using a theoretical model of blood flow and LDL transport through the stenosed artery. It was found that the site of intimal thickening well corresponded to the region where wall shear stress was relatively low and surface concentration of LDL was locally elevated. These results suggest that blood flow plays an important role in the localized pathogenesis and development of intimal thickening by locally augmenting concentration polarization of LDL at a blood/endothelium boundary.

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This paper describes the fundamental investigations for developing new technology using shock waves and bubbles, such as drug delivery systems (DDS) and bioprocess for environmental protection. To understand the fundamental phenomena, the coupling oscillation problems between the deformations of the cell including a bubble and the flow when underwater shock waves propagating are analyzed using computational fluid dynamics (CFD) and optical visualization. For this analysis, the cell is modeled as a liquid droplet including a gas bubble. The effects of (1) the differences of acoustic impedance between internal and surrounding fluid and (2) the boundary motion of the cell on the flow field (density) are discussed using ALE (Arbitrary Lagragian-Eulerian) computational method. The result shows that the effects of the differences of the acoustic impedance and the existence of a bubble in a cell are large for the deformation process of the cell itself. For the optical visualization, deformation process of a bubble near the elastic wall is observed as a model of cell membrane by shock waves to analyze the behavior of the bubble in the cell or microcapsule. From this result, it is suggested that there should be optimized or critical point to have large deformation of the bubble while changing initial position and initial diameter of the bubble in the cell and relative curvature of the wall (cell diameter), which may be enough to have large deformation to cracking the cell membrane. From these two results, it is found that if the proper parameters are selected, there are possibilities to make the large deformation enough to crack the cell membrane efficiently comparing with that has no bubbles when the shock waves and bubbles are applied to the fields of DDS or bioprocess.

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The efficiency of axial gas dispersion during ventilation with high-frequency oscillations (HFO) can be improved by manipulating the oscillatory flow waveform such that intermittent oscillatory flow occurs. To clarify the augmentation of axial gas transfer during intermittent oscillatory flow, we measured the axial and secondary velocity profiles during intermittent oscillatory flow through a model human central airway. We used a rigid model of human airways consisting of asymmetrical bifurcations up to third generation. Velocities in the axial and radial directions were measured with two-color laser-Doppler velocimetry. Secondary flow was accelerated at the beginning of the stationary period, particularly in the trachea, which resulted in enhanced gas transport during intermittent oscillatory flow.

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Total sacrectomy is the most efficient surgical treatment for preventing the recurrence of malignant sacral tumors. This treatment requires a reconstructed structure as a replacement for the sacrum, which can support the weight of the upper body. On the other hand, large components cannot be used to reconstruct the structure because of the risk of infection. Therefore, the reconstructed structures of the sacrum must be designed under the severe requirement of the ability of support a heavy weight with minimum structural components. Although several designs of reconstructed structures, in which the lumber vertebrae are connected to the pelvis by metal rods, bars and screws, have been proposed, the size and layout of the instruments have depended on only constraints due to operative procedures, not mechanical considerations. The reliability of the reconstructed structures has been proved empirically, but quantitative evaluations of rigidity and mechanical stress have not been sufficient. In this study, finite-element analyses of two types of reconstruction, which are applied in clinical use, were carried out to obtain stress distribution and total deformation. Advantages and disadvantages of the reconstructed structures were discussed by comparing the results. Furthermore, an improved reconstructed structure was proposed and its mechanical effectiveness was examined by finite-element analysis and a model experiment.

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A hypothesis that the thoracic idiopathic scoliosis is buckling phenomenon of the fourth mode induced by the growth of thoracic vertebral bodies was presented in the previous work by the authors using numerical simulations with finite element model of the spine. If the hypothesis is acceptable, sensitivity function with respect to the critical growth of thoracic vertebrae on the maximization problem of buckling load with the fourth buckling mode gives us useful information to improve and develop treatments for the idiopathic scoliosis. The numerical results analyzed by the finite element method demonstrated that the sensitivity function is high at the articular capsules of the intervertebral joints, the intervertebral disks, the costotransverse joints and the constovertebral joints around the apex of the curvature in the case of the thoracic idiopathic scoliosis.

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An experimental system using the thermoelastic stress analysis method and a synthetic femur was utilized to perform reliable and convenient mechanical biocompatibility evaluation of hip prosthesis design. Unlike the conventional technique, the unique advantage of the thermoelastic stress analysis method is its ability to image whole-surface stress (Δ(σ₁+σ₂)) distribution in specimens. The mechanical properties of synthetic femurs agreed well with those of cadaveric femurs with little variability between specimens. We applied this experimental system for stress distribution visualization of the intact femur, and the femurs implanted with an artificial joint. The surface stress distribution of the femurs sensitively reflected the prosthesis design and the contact condition between the stem and the bone. By analyzing the relationship between the stress distribution and the clinical results of the artificial joint, this technique can be used in mechanical biocompatibility evaluation and pre-clinical performance prediction of new artificial joint design.

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Previous studies in both fields of automotive safety and orthopedic surgery have hypothesized that immobilization of the shoulder caused by the shoulder injury could be related to multiple rib fractures, which are frequently life threatening. Therefore, for more effective occupant protection, it is important to understand the relationship between shoulder injury and multiple rib fractures in side impact. The purpose of this study is to develop a finite element model of the human shoulder in order to understand this relationship. The shoulder model included three bones (the humerus, scapula and clavicle) and major ligaments and muscles around the shoulder. The model also included approaches to represent bone fractures and joint dislocations. The relationships between shoulder injury and immobilization of the shoulder are discussed using model responses for lateral shoulder impact. It is also discussed how the injury can be related to multiple rib fractures.

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The purpose of this study was to clarify the dynamic changes in contact pressure distribution and three-dimensional ankle joint motion before and after lateral ligament injuries. Five fresh and frozen intact cadaveric ankles were examined. Each ankle was mounted on a specially designed frame that preserved five degrees of freedom motion. The direct linear transformation technique was used to measure the three-dimensional ankle motion, and a pressure-sensitive conductive rubber sensor was inserted into the talocrural joint space to determine the contact pressure distribution. The contact area on the talus for intact ankle moved anteriorly and laterally with increasing dorsiflexion. An area of high pressure was observed in the medial aspect of the articular surface after the ligament was cut. Supination significantly increased after a combined anterior talofibular ligament (ATF) and calcaneofibular ligament (CF) were cut in comparison with after only an ATF was cut, and no significant differences were observed in motional properties under each experimental condition.

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Excessive repetitive impacts in human walking lead to lower extremity orthopaedic disorders such as degenerative joint disease and prosthetic loosening. In this study, two planar models, corresponding to free or fixed ankle joints, were used to examine movements of the knee and ankle joints that affect foot impact forces and their attenuation during level walking. A kinetic approach was used to describe the relationship between the landing style of the leg and the impact at heel contact. Human subjects with free and fixed ankle joints were studied to verify the models. Free and fixed ankle groups showed a significant difference with regard to acceleration (p<0.005). The attenuation capacity of acceleration for healthy subjects with a freed ankle joint was 59.9±12.1 (mean ±SD)%, while the capacity for the same subjects with a fixed joint was 27.4±28.9%. The movements of the knee and ankle joints at landing on the ground played important roles in attenuating impulsive force.

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The shape of the tympanic membrane(TM) is often changed due to middle-ear diseases or middle-ear surgery. Although it is assumed that this change in shape affects the sound transmission of the middle ear, the degree of this effect remains unclear. In this study, three-dimensional finite-element models of the middle ear with different depths of the conical-shaped portion of the TM were established, and the effects of the depth, Young’s modulus and thickness of the TM on middle-ear sound transmission were analyzed. The efficiency of sound transmission was found to decrease when the depth of the conical-shaped portion of the TM decreased because of a decline in the efficiency of transmission of the vibration of the TM to the ossicles. The transfer function was also influenced by the Young’s modulus and thickness of the TM. Thus, when substitutional materials, whose Young’s modulus or thickness was appropriately greater than those of the normal TM, were used in TM reconstruction, the efficiency improved, even if its shape was flat.

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The wing apparatus of Hymenoptera was observed with a scanning electron microscope, and the structure and function of insect wings were studied. The measurements of displacement of extrinsic skeleton vibration produced by wing flapping of a wasp were made by an optical displacement detector system. The free flight of the wasp was analyzed by a three dimensional motion analysis system. The results of a series of measurements revealed the flight characteristics of Hymenoptera, such as the wing tip velocity, wing path, wave form of extrinsic skeleton vibration, and so forth.

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An interlaminar peeling test was conducted for an A. dichotoma beetle fore-wing with the interlaminar reinforcement mechanism being investigated. The load-displacement curves indicated the presence of many load peaks with the number of load peaks being equal to the number of trabeculae found in the chitin fiber laminae. This result suggested that each trabecula fracture contributed to a single load peak, which then combined to provide the interlaminar strength. The increment of interlaminar strength due to the trabecular in the chitin fiber laminae was approximately 30 times in a local region and 3 times in a whole region larger compared to that of the chitin fiber laminae without trabeculae. The chitin fibers were found to be connected between the chitin fiber laminae with the trabeculae being curved and continuous, whilst the trabeculae bonded chitin fiber laminae were distributed in two dimensions within the chitin fiber lamina plane. Furthermore, a strong reinforcement mechanism in nature was clarified with a model for the reinforcement mechanism being proposed.

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The purpose of our study is to investigate the effect of the caudal fin behavior resulting from the caudal muscle-skeletal structure of tuna on the propulsive force. A propulsion system by tuna-like fin stroke using two air rubber artificial muscles and a multi-joint bending mechanism (a tuna-like bending mechanism) modeled on the antagonism muscles and the caudal skeletal structure of tuna was developed. In order to realize instructed oscillation of a wing, a method of continuous path follow-up control of a wing in water was discussed in regard to the control of the internal pressure of the artificial muscles. It was found that the optimum control method for the tuna-like bending mechanism was the pressure control of the artificial muscles with both feedforward and pressure feedback compensations. The propulsion performance on a deformable wing using the propulsion system was discussed.

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A new method is proposed to investigate kinematics and dynamics of locomotion without any limitation of laboratorial conditions. This method enables simple measurements and numerical kinematical calculations with small body-mounted instruments utilizing accelerometers and gyroscopes. Temporal parameters of gait are determined by classification of accelerations and angular velocities. Joint angles, joint moments, and energy consumptions as mechanical works are estimated assuming rigid-body dynamics in sagittal plane. The method is verified by comparing the results of video-based motion capture system and force plates as conventional standards, evaluating accuracy for normal level walking at four cadences. No significant differences are observed between the results of the proposed method and those from the conventional method. It confirms the validity of the proposed method for healthy subjects and the method can provides free mobility in the investigation of locomotive dynamics beyond the gait laboratory.

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We have been developing exoskeletal robots in order to realize the human motion support (especially for physically weak people). In this paper, we propose a 2-DOF exoskeletal robot and its method of control to support the human shoulder motion. In this exoskeletal robot, the flexion-extension and abduction-adduction motions of the shoulder are supported by activating the arm holder of the robot, which is atached to the upper arm of the human subject, using wires driven by DC motors. A fuzzy-neuro controller is designed to control the robot according to the skin surface electromyogram(EMG) signals in which the intention of the human subject is reflected. The proposed controller controls the flexion-extension and abduction-adduction motion of the human subject. The effectiveness of the proposed exoskeletal robot has been evaluated experimentally.

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For the technical improvement for brass instrument players it is important to obtain the detailed control parameters for embouchure building. While many investigators have reported the preliminary data on the muscle behavior, the precise aspects are unrevealed so far. The purpose of the present paper is to study dynamic perioral muscle behavior of French horn players and to investigate their lip valve function by measuring the contact pressure on teeth buccal surface during playing. It was shown from the experimental results that the advanced players contracted depressor angulioris and levator angulioris especially for high tone playing. It is considered that the combined contraction by these muscles contributes to forming smaller lip aperture being suitable to produce higher tones. Inversely a strong contraction of m. buccinator, which is widely believed to work to give hard tension to player’s lip, was observed insignificantly in the advanced players.

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The contraction and relaxation of muscles located below the skin play an important role to maintain a constant internal body temperature. In this paper, we propose a new temperature control system modeled after the functions of the muscles located below the skin. The most important feature of this system is that the precise control of internal temperature is achieved by the operation of flow rate allotment. Moreover, we used digital adaptive control to improve the performance and flexibility of this system. To verify the validity of this system, the experiments were carried out and it was shown that this system can control the internal temperature within the range of ±0.02°C.

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