The objectives of this study were to solve computationally the arm stroke in the crawl swimming which maximized the swimming speed for different maximum joint torque conditions, and to investigate the maximum joint torque dependency of the crawl swimming with the optimized arm stroke. In the optimizing calculation, the swimming human simulation model, SWUM, was used for the simulation of the crawl swimming. The maximum joint torque characteristics, which were constructed in the previous study, were imposed as the constraint condition. In order to investigate the maximum joint torque dependency of the optimized arm stroke, four levels of maximum joint torque were prepared. The following findings were obtained from the results of optimization: The maximum swimming speed was realized by shortening the stroke cycle as much as possible although this shortening brought a lower propulsive efficiency as well as a lower stroke length. In a constant maximum joint torque condition, the swimmer does not push the water by turning the palm to the side in the latter half of the underwater stroke at the stroke cycle which brings the maximum swimming speed. The locus of the hand was relatively straight. At the slightly longer stroke cycle, the swimmer pushed the water until the end of the underwater stroke. The locus of the hand was still relatively straight. At the sufficiently longer stroke cycle, the swimmer also pushed the water until the end of the underwater stroke. The locus of the hand, however, became more curved and therefore became a so-called ‘S-shaped’ stroke.
In this study, for a better understanding of arterial functions, we examine the effects of active stresses, which are generated by contractile units included in smooth muscle cells, on the stress distribution in the arterial wall. Thus far, it is widely recognized that active stress generation is regulated by mechanical and chemical operations, i.e., both smooth muscle stretch and intracellular calcium ion concentration. Based on this fact, we develop an arterial wall model with active stresses that couples the mechanical and chemical ones suitable for the finite element method. By using this coupled model within the framework of finite element analysis, we calculate the stress distribution including active stresses at a prescribed intracellular calcium ion concentration. The results show that as the intracellular calcium ion concentration increases, the effect of active stress appears continuously, i.e., stress distribution could be considered as a continuous function of the intracellular calcium ion concentration. To obtain stress distributions at the prescribed intracellular calcium ion concentration, which is assumed to be reached as a result of active calcium ion transport under various in vivo conditions, are meaningful as a preliminary step in developing advanced models considering the active calcium ion transport systems.
In previous published research, the deployment of flow-diversion increases the intra-aneurysmal pressure by 20 mmHg in the case with a pre-aneurysm stenosis. The purpose of this study is to learn the influence to the aneurysm when a pre-aneurysm stenosis exists which may threaten people's health even more severely. In the present research, idealized models of straight and curved blood vessels with both aneurysm and pre-aneurysm stenosis were established, with altering the degree of stenosis, the distance between stenosis and aneurysm and the curvature of parent artery. As the degree of stenosis increases, the reattachment length increases in straight vessels. Different positions of reattachment points to aneurysm neck affect the flow pattern inside the aneurysm. In the model with higher degree of stenosis and smaller distance between stenosis and aneurysm, the flow pattern and the direction of vortexes inside the aneurysm are affected by the recirculation after stenosis. Driven by inertial force, reattachment length decreases as the curvature of the parent artery increases, and stream inside the aneurysm is affected only when the distance between stenosis and aneurysm is short enough. In all models, the pressure drop inside the aneurysm increases as the degree of stenosis increases, creating a lower pressure environment in the aneurysm.
In this study, the differential pressure distribution on the wing surface of an insect-like ornithopter was measured directly. Three microelectromechanical system (MEMS) differential pressure sensors were attached to a wing surface in the spanwise direction. The wing length, flapping frequency, and total weight of the ornithopter were 110 mm, 15 Hz, and 7.1 g, respectively. The attachment points corresponded to 25%, 50% and 75% of the wing length and 20% of the length of the wing chord. The ornithopter took off in anterosuperior mode without yawing or rolling. At takeoff, the flapping motion of the wing induced a periodic differential pressure between the upstroke and downstroke. The average values of the maximum differential pressures were 23.5 ± 3.5 Pa, 45.2 ± 3.4 Pa, and 96.7 ± 10.0 Pa at the wing root (WR), wing center (WC), and wing tip (WT), respectively. The maximum differential pressures shifted from the WT to WR in the spanwise direction. These results reflected the aerodynamic forces acting on the insect-like ornithopter during takeoff.
The purpose of this study was to investigate age-related changes in the passive resisting moments at the hip. The changes in the passive resisting moments were hypothesized to occur due to age-related changes in muscle stiffness. Two groups of healthy men participated in this study: young men (approximately 24 years of age) and old men (approximately 68 years of age). Subjects were positioned in a left lateral decubitus position with their left limb supported on a table. With a subject relaxed, an experimenter slowly moved the subject’s limb by pulling or pushing the handle attached to the lower limb via a load cell. The subject’s hip was moved in passive range of flexion-extension motions. The joint kinematics, measured by a motion capture system, and load cell readings were used to compute the passive resisting moments-joint angle curves at the hip. The passive resisting moments at the hip were found to considerably depend on the adjacent knee angle. The maximal resisting moments, when the hip was extended, were larger for the older group than for the younger group. The measured resisting moments were finally validated against the resisting moments calculated by a musculoskeletal computer model for the same movements. The computer model was able to predict measured tendencies of the moments at the hip. However, further adjustments of the computer model are required to represent the aging effects precisely.
The endothelial cells lining our cardiovascular system are constantly affected by shear stress, which can alter both the morphology and biological activity of the cells. Methods to study the basic shear stress response by creating stable flow profiles on the macro scale are well established, but they do not allow the generation of controlled high precision flow profiles. The emergence of microfluidic devices has enabled well-defined individual cellular response studies on endothelial cells in scale-relevant tools. However, so far, no shear stress studies on clonal heterogeneity have been published. We have developed a novel bioassay system to study several shear stress conditions in parallel on clonal expanded single cells. The device consists of a silicon/glass microwell slide with integrated polydimethylsiloxane microchannels, which delivers shear stress to cells in a well-controlled manner using micropumps. The flow behavior of the device was numerically characterized by computational fluid dynamics analysis, which confirmed that the desired fluid-imposed shear stress was obtained. Bovine aortic endothelial cells were cultured in the microwells for 24 hours and then subjected to a fluid shear stress of up to 2.0 Pa for 6 hours. The results showed that alignment and elongation of the endothelial cells along the flow direction were dependent on the level of shear stress applied. It was demonstrated that multiple experimental conditions can be examined simultaneously within a single device and the compartmentalized structure of the microwell slide can be used to ensure physical separation of cells in individual wells. Moreover, it was shown that the device could reduce consumption of expensive reagents and enable screening of rare samples.
Noninvasive quality evaluation methods that make it possible to monitor culture processes are ideal for tissue-engineered cartilage made of autologous chondrocytes and collagen gel. However, usual methods are quite invasive because the products are examined chemically and observed histologically with dye. Here we employed second-harmonic-generation (SHG) microscopy, which can be used to observe collagen without any preparation such as staining or fixing. We demonstrated SHG imaging of tissue-engineered cartilage composed of rabbit chondrocytes and type I collagen gel. Our results showed that aggregations of round cells that produced type II collagen were observed as spherical dark spaces in the SHG images. The volumes of these spaces were related to the numbers of cells in the aggregations. These results indicate that we can estimate the number of the matrix-producing cells by SHG imaging. Because SHG microscopy is a noninvasive method, it is suitable for evaluating the quality of tissue-engineered cartilage and also for quality control during the manufacturing process.
Without being able to evaluate blunt thoracic trauma in terms of an acceptable injury criterion, it is not possible to develop or validate non-lethal projectiles, bullet proof vests and chest protectors for sports personnel etc. In order for the assessment of the blunt trauma caused by high speed projectiles, a novel design of a mechanical surrogate of the thorax (Mechanical THOrax for Trauma Assessment: MTHOTA) was conceptualized. An iterative impact analyses in the virtual testing environment were carried out by impacting the finite element model of the mechanical thorax with 37 mm diameter, 100 mm long wooden baton weighing 140 grams (20 m/s and 40 m/s impact speeds) and 37 mm diameter, 28.5 mm long wooden baton weighing 30 grams with 60 m/s impact speed. From the output of every simulation, force dynamic response (force-time), deflection dynamic response (deflection-time) and force-deflection response were elicited and compared with the corresponding human response corridors developed by Wayne State University's researchers. By suitably changing the design parameters of the mechanical surrogate, simulation iterations were continued till the responses were correlated with the human response corridors. Values of viscous criterion (VCmax), product of maximum chest deflection and the rate at which chest deforms, obtained from MTHOTA were in very good agreement with those obtained from the cadaveric test data. The methodology, concept and validation of the MTHOTA have been presented in this paper.