Monocyte accumulation in the arterial intima is a hallmark in early atherosclerosis. Monocyte extravasation involves sequential processes including rolling, adhesion, and transmigration across vascular endothelial cells (ECs), where abundant mechanical interactions between these two cells exist. Platelet-endothelial cell adhesion molecule-1 (PECAM-1) is a junctional protein expressed on both cells, and participates in paracellular transmigration via homophilic binding between these cells, while PECAM-1 binds homophilically between neighboring ECs in the absence of monocytes. During monocyte transmigration, PECAM-1-bearing membrane can be recruited to the transmigration spot from intracellular pools. The mechanism by which PECAM-1 binding between ECs in control state is switched to that between monocytes and ECs during transmigration, and its relationship with recruited PECAM-1 remain unclear. In this study, we built an experimental model in vitro for studying molecular behavior of PECAM-1 during monocyte transmigration. A plasmid vector containing PECAM-1 tagged with green (GFP) or red (DsRed) fluorescent protein was constructed, and separately transfected into ECs. The mixture of both transfectants in culture achieved a monolayer that contains an intercellular PECAM-1 boundary between PECAM-1-GFP- and PECAM-1-DsRed-expressing cells which is visualized as yellow in merged image. Using this model together with confocal laser scanning microscope-based system, molecular behavior of PECAM-1 on neighboring ECs during monocyte transmigration was observed in live cells. This model can be essential to directly visualize binding/dissociation state of PECAM-1 between neighboring ECs during monocyte trans-endothelial migration in relation to mechanical monocyte-EC interactions.

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We evaluated mechanical states in an atheromatous artery and correlated these values with both lipoprotein retention in a regionally thickened wall and the rupture of a luminal plaque. We used two specimens of common carotid arteries dissected at autopsy; one specimen had diffuse intimal thickening and the other had an atherosclerotic plaque. Mechanical properties were identified by cyclic inflation tests. Stress-released geometries were obtained ring specimens via a radial cut. Finite element (FE) analyses were performed on the stress-released geometry, postulating two incompressible isotropic hyperelastic models for the vascular tissues and a lipid pool. Stress/strain values and their variations were obtained under a constant axial stretch of 1.07 and intraluminal pressures ranging from 10 to 16 kPa. Light microscopy was also performed on stained specimens. Results from the FE analysis showed that the variation in maximum principal stress was ‹ 10 kPa in the deep intimal layer of a regionally thickened wall. Maximum principal stress and variation concentrated at 655 kPa and 281 kPa, respectively, at a shoulder in the plaque cap region. Maximum principal strain variation in the region of the atheromatous plaque was much lower than in the corresponding region of the artery with intimal thickening. Low stress/strain variations are likely to retain the lipid pool after formation in the thickened wall region, where the convection force seems to be very low. Both concentrations of stress and variations in stress are likely to cause a rupture at the plaque cap shoulders, which are one of the reported sites.

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Coronary arterial flow can be described in terms of an intramyocardial pump that displaces blood backward and forward during systole and diastole, which is termed diastolic predominant flow. When the diastolic predominant flow runs through the stenotic arteries, the geometric characteristics and mechanical properties of these arteries may influence the flow. We have developed an experimental system to represent this diastolic predominant flow phenomenon. To produce a stenosis model, polyvinyl alcohol hydrogel was shaped into various forms of diseased coronary stenosis. The mechanical properties of this stenosis model are similar to human coronary arteries. We then examined the effects of stenosis severity, stiffness, and curvature on flow and pressure. A change in curvature had only a minimal affect on flow, while stenosis severity and the stiffness parameter significantly influenced diastolic predominant pulsatile flow.

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The objective of this study was to construct a fluid force model for the dive start. The fluid force model is incorporated into a swimming human simulation model SWUM, which has been developed by the authors. In order to identify the fluid force coefficients in the model, dive starts performed by actual swimmers were filmed and reproduced by the simulation model. The fluid force coefficients were determined so that the swimmers’ movement in the simulation agreed with that of the experiment as much as possible. From simulations using the identified fluid force coefficients, it was found that simulation results of normal and ‘intentionally bad form’ trials for one subject agreed well with the experimental ones. This suggests that the proposed fluid force model would be valid to reproduce dive starts of various forms. For trials of another subject, the discrepancy between simulation and experiment becomes somewhat larger. This error can be reduced, however, by tuning the fluid force coefficients. This indicates that tuning the fluid force coefficients is effective to improve the accuracy of the simulation, and that the proposed model for the fluid forces will be valid for other swimmers.

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Swimming motion of a singly flagellated bacterium close to a rigid surface was numerically investigated. The cell’s attitude and its distance from the surface were calculated by integrating the velocity and angular velocity determined by the boundary element analysis at an instant. A diagram indicating the transition of the cell’s state that was defined as a couple of the pitch angle and the distance was obtained. Four separated regions exist on the diagram for an average size cell. When the absolute of the pitch angle is bigger than a certain threshold value, the cell monotonically leaves from the surface, or approaches and touches the surface. With a moderate pitch angle, the state for forward motion converges to a point, while the state for backward motion diverges since the state of backward motion conversely follow the same transition path. The observed asymmetry between forward and backward motions is explained according to the diagram.

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In recent years, the distributions of vehicle types include a substantial number of Sport Utility Vehicles (SUVs). Pedestrian injury distribution of SUVs is different from that of passenger cars and head, torso, and lower extremities are most frequently injured body regions of pedestrian impacted with SUV. Therefore, kinematics of pedestrian and mechanism of injuries of pedestrian, who is impacted by SUV, are emerging research area. In this paper, the kinematics and lower extremity injuries of pedestrian were simulated by using a human FE model “Total Human Model for Safety” (THUMS) and SUV FE model. The result by the simulation was validated with test result and showed generally good correlations. Kinematics of whole pedestrian and mechanism of injuries of lower extremities of pedestrians impacted by SUV were discussed.

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The first objective of this study was to develop a musculoskeletal simulation model to analyze the muscle load of a pregnant woman. The second objective of this study was to investigate the muscle load on the Erector Spinae numerically using the developed simulation model. An experiment to validate the simulation was also conducted. The following findings were obtained: In the simulation of a standing non-pregnant woman, the muscle force is relatively small when the bending angle of the body is -20 to 0 degrees, while it gradually increases as the bending angle increases from 0 degrees. In the simulation of a pregnant woman, on the other hand, the muscle force increases monotonously for the entire range of the bending angle. In the simulation of a straight standing pregnant woman, the muscle force becomes 2 to 4 times larger than a nonpregnant woman. The validity of the simulation was confirmed since the experimental values of the muscle force were almost within the range of the simulated values. In the simulation of a seated pregnant woman, the muscle force becomes significantly smaller than that in the case of a standing pregnant woman when the backrest of the seat is lent back more than 10 degrees. The ratio becomes less than 0.5 when the backrest is lent back more than 20 degrees.

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A double-sensor difference based algorithm to estimate segment rotation angles in 2 directions for lower limb segment orientation analysis in 3-dimensional (3D) space was presented. The results of the simulation suggest that the accuracy of the calculated angles correlate strongly with the range of the rotation angles. In order to achieve higher precision of the calculated angles in a range of -60° to 60°, a switching algorithm containing arcsine or arccosine according to the value of the angle was presented. Then, to qualitatively verify the method in practical application, a prototype of a wearable sensor system using only one kind of inertial sensor (accelerometer) was developed. The system was first tested on a board with one freedom of rotation in the sagittal plane. Then it was tested on the thigh of a volunteer to obtain the pitch and yaw angles for lower limb segment orientation. In the experiment, two accelerometers were used to measure the actual accelerations on the thigh. The volunteer swung his lower limb in the work space of an optical motion analysis system to obtain the orientation angles of the thigh as reference. It was assumed that there was very little trunk sway or skin artifacts and no significant internal/external rotation of the leg. The results show that, without integration and switching between different sensors, using only one kind of sensor (accelerometer), the prototype is suitable for ambulatory analysis of lower limb segment orientation in two directions.

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In human swimming, there are many situations in which the target of the analysis is not only the swimmer but also other swimmers or other equipment, such as synchronized swimming by multiple swimmers, swimming with fins, and so on. The objective of this study was to extend the swimming human simulation model SWUM so that it could handle the dynamic behavior of multiple rigid bodies and could freely describe the mechanical interactions among the rigid bodies. In this paper, the outline of SWUM is described first. The extension to the multi agent/object simulation and its implementation are explained next. Finally, its validity and usefulness are examined by discussing three examples of analysis. The first example was synchronized swimming by three swimmers. From the simulation results, it was found that the three swimmers gradually gathered, and finally the swimmers' upper limbs stably formed a hexagon. The second example was monofin swimming. The monofin was divided into five rigid plates in this simulation in order to represent its elastic deformation. From the simulation results, it was found that the swimmer accelerated at the moments of downward and upward kicks. The third example was the shooting motion in water polo. From the simulation results, it was found that the ball was smoothly released and flew in an appropriate direction. Since reasonable results were obtained in these examples of analysis, the validity and usefulness of the extension were confirmed.

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Dolphins swim by vertical oscillation of their tail fins which have been considered to play an important role for generating thrust. The propulsive performance of the tail fin relates with the structure and the mechanical properties of the tail fin. Our objectives are to investigate the structure and the bending properties of the central part of the tail fin of a dolphin. A sample of the tail fin was anatomized to investigate the vertebrae structure and tendons insertions, and the bending tests were carried out on the central part of the tail fin at the state with tensions on the tendons. Our results demonstrated that there were three kinds of tendons in the tail fin, that is, the epaxial tendon I, the epaxial tendon II and the hypaxial tendon. The epaxial tendons Is inserted into each tail vertebra, the epaxial tendon IIs inserted into five tip tail vertebrae, and the hypaxial tendons inserted on the chevron bones and tail vertebrae. In the bending test, it was found the tension which was acted on the epaxial tendon IIs produced larger bending deformation and made the central part of the tail fin stiffer than the same tension which was acted on the epaxial tendon Is or hypaxial tendons.

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Twist drills are often used to prepare implant sites for the internal fixation of fractures, and the stability of the fixation, which depends directly on how securely the implants are held, depends on the quality of the bone around the pilot holes after implant site preparation. To optimize the design of surgical drills, this study evaluated the effects of the drill design elements (thinning, and the helix and point angles) on drilling characteristics (thrust force and temperature increase and duration) when drilling bone. We used mature porcine femurs because porcine bone resembles human bone, and measured the thrust force and bone temperature at three points during the drilling test using drills with different designs and a standard surgical drill. We found that types X, N, and R thinning were effective in reducing the thrust force, and a quick helix was effective in reducing temperature increase and duration when drilling cortical bone. However, no obvious relationship was observed between the drill design elements and the drilling characteristics, perhaps because the cutting system of a drill is complex. In the future, creating a more efficient evaluation method to overcome the complexity of the cutting system and examining the relationship between the drill design elements and the drilling characteristics should be carried out to improve the drilling performance of bone.

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The objective of this study was to develop a simulation model for monofin swimming which considers the mechanical interaction between the monofin and swimmer. For this objective, the swimming human simulation model SWUM was extended to the monofin swimming. In order to identify the bending stiffness and damping coefficient of the monofin, the static and dynamic bending tests of a monofin were conducted. From the identification process, it was found that the simulation using the identified parameters reproduced the experiment well. This suggests the validity of the modeling of the monofin itself. The body geometry and joint motion of the swimmer were acquired from the experiment using a subject swimmer. In order to identify the fluid force coefficients of the monofin, the fluid force acting on the monofin was measured in the experiment which was conducted in a circulating water tank. The simulation with the identified parameters reproduced the experiment well. This suggests the validity of the fluid force model for the monofin. From the simulation of monofin swimming using the identified model parameters, it was found that the whole behavior of the swimmer and monofin in the simulation agrees well with that in the experiment, especially for the bending motion of the monofin. The velocities averaged in one kicking cycle in the simulation and experiment also agreed within a 10% error. These results sufficiently suggest the validity of the developed simulation model.

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Particle image velocimetry (PIV) and computational fluid dynamics (CFD) modelling of blood flow through a carotid artery bifurcation has been carried out in order to assess the role of haemodynamics in atherosclerosis and validate a novel wall shear stress (WSS) measurement method via detailed quantitative data analysis. Velocity and WSS data, obtained by PIV was compared against CFD-predicted data obtained for the same geometry and boundary conditions. The results demonstrate that both methods are capable of capturing essential flow characteristics, and are in good agreement. The axial velocity data clearly show the important flow features such as skewed velocity profiles and a low-momentum region near the sinus outer wall, although with slight errors between the two techniques in the order of 6.1-13.7%. The secondary velocity plots and three-dimensional particle traces reveal complex flow features within the sinus, such as Dean vortices and helicoidal flow. WSS data obtained by both techniques reveal the presence of a low-momentum and reversed-flow regions, and show agreement with errors in the order of 1% in the common carotid artery and 0.9-9.8% in the sinus. The error sources in both the experimental and numerical methodology are discussed and recommendations for future applications are made.

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Articular cartilage has high water content and biphasic property. The structures of the tissue are inhomogeneous and anisotropic. Furthermore, the mechanical behavior of cartilage shows depth-dependence. Therefore it is necessary to consider not only the average tissue property but also the local one to explain mechanical and functional behavior. Previously, we created two-dimensional biphasic finite element (FE) cartilage tissue models considering the depth-dependence of elastic modulus distribution based on experimental results. As a result, this finding indicates that the depth-dependence of elastic modulus has a remarked influence on the deformed profile. In this study, the effectiveness of collagen fiber network in addition to the depth-dependent elastic modulus of cartilage tissue is evaluated. By creating of cartilage tissue models using axisymmetric biphasic elements and spring elements, we analyzed the unconfined compressive behaviors of articular cartilage specimens and compared the FE analyses to experimental results. Every FE model has depth-dependence of elastic modulus based on our previous formula, while the Poisson's ratio and permeability of solid phase were assumed as constant in literature data. To compare experimental result with finite element analysis (FEA), boundary conditions for FEA were given to correspond to the compression test. As a result, total load capacity and deformed profiles immediately after compression of FEA simulation on eventual model corresponded to experimental results by controlling spring constant. Furthermore, local strain of axial direction in FEA results for eventual model and experimental ones show the same tendency about time-dependent change. Then, we considered intrinsic fluid flow of eventual model.

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In this study, we investigated whether ultrasound wave stimulation could accelerate the bone-bonding ability of bio-active titanium alloy in vitro. Titanium alloy (α+β-Ti-6Al-4V) processed in chemical and heat treatments was used as a specimen, and soaked in simulated body fluid (SBF) under pulsed ultrasound wave for the planned time periods. The surface of samples was observed using scanning electron microscopy (SEM), energy dispersive spectroscopy, X-ray diffraction to assess the state of bone-like hydroxyapatite formation. SEM images showed that a richer and finer layer of bone-like hydroxyapatite covered the titanium surface in the ultrasound wave group as compared with the non-ultrasound group. The measurements of mass of specimens also indicated the efficiency of ultrasound waves for hydroxyapatite formation. These findings suggest that the nucleation and crystallization of apatite on bio-active material surfaces might be promoted by micro-moving and cavitation of low-intensity pulsed ultrasound waves. We propose that pulsed ultrasound stimulation has a great potential for further improvement of osseointegration and osteoconductivity for medical bio-active implants.

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The objective of this study was to propose the walking in water for ACL injury rehabilitation program by simulation. For this objective, the simulator which can compute the body load considering the fluid force and force acting on the ACL was utilized. The optimal walking forms for three rehabilitation phases were then computed by the simulation. From the simulation analysis, the form for the first phase of rehabilitation was obtained as “bend the knee all through the swing phase”. This form can prevent the ACL from loading the force. The form for the second phase was obtained as “bend the knee greatly and stretch the ankle first, then bend the hip keeping the knee bent and the foot stretched in the swing phase”. By this form, the muscles around the knee joint can be trained without loading force on the ACL. The form for the last phase was obtained as “keep the thigh backward and the ankle stretched first, then bend the hip joint quickly and greatly in the swing phase”. By this form, the muscles around the knee joint can be trained to the utmost.

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An approach using physical-sensor difference and virtual-sensor difference based algorithm to visually and quantitatively confirm lower limb posture was proposed and a wearable sensor system was developed. Flexion/extension (FE) and abduction/adduction (AA) hip joint angles and FE knee joint angle were estimated for orientations of the lower limb segments; the knee and ankle joint trajectories were calculated using the segmental orientation angles and lengths to estimate the positions of lower limb joints. In the wearable sensor system, an accelerometer on the hip and two MAG³s (inertial sensor module) on the thigh were in grouped to measure the data for estimating the thigh orientation and knee joint position using the double-sensor difference based algorithm. Two MAG³s on the thigh and shank near the knee joint were in grouped to measure the data for estimating the knee joint angle and ankle joint position using the virtual-sensor difference based algorithm. Compared with the camera motion capture system, the correlation coefficients in five trials were above 0.89 for the hip FE angle, higher than 0.9 for the hip AA angle and better than 0.88 for the knee FE angle. There was no integration of acceleration or angular velocity for the joint rotations and positions in this method. The developed wearable sensor system was able to visually and quantitatively confirm the lower limb posture with fewer sensors and higher accuracy than with other methods. It can be used as a substitute for the camera system for patient gait posture analysis in daily life.

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