Insect wings change its shape dynamically through the interactions of the structure, and the aerodynamic and inertial forces when flapping, which can greatly affect its aerodynamic performances. While the detailed change of the wing shape has been extensively measured with high-speed photogrammetry, its implications on the flapping wing aerodynamics are poorly understood. In order to clarify the linking between the wing deformation and the flapping wing aerodynamics, the aerodynamic effect of the wing deformation in terms of the twist, the camber and the spanwise bending have been systematically investigated by means of the computational fluid dynamic analyses of a hovering hawkmoth with artificially deformed flapping wings. With the appropriate magnitude and phase, the twist and the camber are found to enhance the aerodynamic efficiency of flapping wing by redirecting the aerodynamic force vector on the wing so as to reduce the drag or increase the lift. The spanwise bending can increase the aerodynamic force without the redundant increase in aerodynamic power by appropriately adjusting the speed of the wing. We specified the magnitude and the phase of deformation that give the highest efficiency in the range of the study, and pointed out that, while the twist and the camber can enhance the efficiency, the deformation beyond the optima can reduce the aerodynamic efficiency drastically. The results in this study revealed the aerodynamic contributions of each kind of wing deformation, and will be of great implications for the design of bio-inspired micro air vehicles.
In this study, a hybrid electromagnetic and mechanical stimulation system that can apply an alternative current magnetic field (ACMF) and tensile strain fields on PC12 cells was developed to enhance nerve axonal extension. For the ACMF stimulation system, we used a frame to facilitate uniform ACMF application and in situ microscopic observation. We optimized the design of the frame based on analytical results. We verified that the developed ACMF stimulation system can generate a uniform magnetic field. Further, we designed a uniaxial stretch stimulation system. The cell culture area of the stretch stimulation system was made of a nonmagnetic material. The strain in the stretch stimulation region was confirmed to be uniform, with acceptably small deviations. Next, the effectiveness of axonal extension enhancement was validated by adopting two stimulation methods, ACMF and stretch, separately or in combination, hereafter referred to as ACMF, stretch, and hybrid conditions. PC12 cells seeded on the silicone sheets were cultured for 96 h under the three stimulation conditions. The enhancement rate of the hybrid condition was higher than the enhancement rates of ACMF stimulation and stretch stimulation. The effects of stretch stimulation on axonal extension appeared immediately after beginning the stimulation, while the effects of ACMF stimulation took longer to appear. These results revealed that there are different mechanisms of cell environment stimulation of the axonal extension of PC12 cells and that hybrid stimulation is the most effective stimulation method of those studied.
Approximately one in three people over 65 years of age fall each year. The resulting physiological and psychological trauma can lead to physical deconditioning, social isolation and early mortality. Recent research has reported balance recovery can be trained in a single session resulting in dramatic reductions in fall rates. However, most previous research has used repeated exposures to a single hazard in a fixed location and not controlled for reductions in walking speed. It follows, that the biomechanical mechanisms important for reactive balance recovery (in the absence of anticipatory adjustments) are probably not well understood. Here, we investigated the biomechanics of successful reactive balance recovery following the first exposures to unexpected trip and slip hazards in different locations. Ten healthy adults (29.1±5.6 years) completed 32 walks at fixed speed, cadence and step length over a custom 10-meter walkway while being exposed to randomly presented and located slip and trip hazards. Balance recovery kinematics were assessed using a VICON motion analysis system. Repeated exposures to unexpected hazards induced significant reductions (p≤0.05) in anteroposterior (AP) trunk sway following the trips (26.7° to 14.3°; Cohen’s d -1.24) and slips (32.7° to 19.0°; Cohen’s d -0.93). During recovery from unexpected trips, reduced AP trunk sway was strongly correlated with a more posterior centre-of-mass position relative to the stepping foot (r=0.91) and a longer step length (r=-0.71). During recovery from unexpected slips, reduced AP trunk sway was moderately correlated with slower slipping speed (r=0.54) and a less posterior centre-of-mass position relative to the stance (slipping) foot (r=-0.39). The biomechanical mechanisms required for the successful reactive balance recovery from trips and slips were different. Future experimental protocols to optimize reactive balance recovery for fall prevention should therefore use progressive exposures to both slip and trip hazards using specialized equipment and determine if similar biomechanical mechanisms are observed in young and elderly people at risk of falls.
Osteoblasts change their intracellular calcium ion concentration in response to mechanical stimuli. Although it has been reported that osteoblasts sense and respond to stretching of a substrate on which osteoblastic cells have adhered, the details of the dynamic characteristics of their calcium signaling response remain unclear. Motion artifacts such as loss of focus during stretch application make it difficult to conduct precise time-course observations of calcium signaling responses. Therefore, in this study, we observed intracellular calcium signaling responses to stretch in a single osteoblastic cell by video rate temporal resolution. Our originally developed cell-stretching microdevice enables in situ observation of a stretched cell without excessive motion artifacts such as focus drift. Residual minor effects of motion artifacts were corrected by the fluorescence ratiometric method with fluorescent calcium indicator Fluo 8H and fluorescent cytoplasm dye calcein red-orange. We succeeded to detect the intracellular calcium signaling response to stretch by video rate temporal resolution. The results revealed a time lag from stretch application to initiation of the intracellular calcium signaling response. We compared two time lags measured at two different cell areas: central and peripheral regions of the cell. The time lag in the central region of the cell was shorter than that in the peripheral region. This result suggests that the osteoblastic calcium signaling response to stretching stimuli initiates around the central region of the cell.
Ascertaining a person's motion intentions through muscle activity is important for controlling various assistive devices for people with disabilities. Several techniques have been proposed for estimating the extent of intended joint angle motion using skin deformation information derived from muscle contractions. The objective of this study is to verify our signal processing procedure for estimating intended wrist joint angle with skin deformation information in able-bodied subjects and subjects with an upper-limb amputation. Skin deformation was measured with a tactile sensor consisting of 48 distance sensors over a large measurement area. The root-mean-square error (RMSE) of the measured and estimated angles are evaluated offline using multiple linear regression in one individual with an upper-limb amputation and five able-bodied participants. In all tests, subjects undertook a wrist flexion and extension task guided by visual feedback, measured in real time. Sensors are selected in descending order of the standard deviation of each sensor's value. Strong relationships occur between the position and displacement of the area of greatest skin deformation and the intended wrist joint angle in all subjects. The minimum RMSE was 8.19° for the individual with an upper-limb amputation using 48 sensors as input, and 2.24° for able-bodied individuals using 16 sensors. One-way repeated-measures analysis of variance showed that at least 16 sensors are needed to reliably record skin deformation. Skin deformation analyzed with multiple linear regression is a plausible means of estimating intended wrist joint angle in persons with an upper-limb amputation. Even when a limited number of sensors (≥16) are used, continuous joint angle can be estimated reliably. These findings will inform the design of assistive devices that must noninvasively determine muscle activity.
Cells in our body utilize a variety of adaptor proteins for transmitting context specific signals that arise from the cellular microenvironment. Adaptor proteins lack enzymatic activity and typically perform their function by acting as scaffolds that bind other signaling proteins. While most adaptor proteins are functionally modulated by biochemical alterations such as phosphorylation, a subset of adaptor proteins are functionally modulated by a mechanical alteration in their structure that makes cryptic sites available for binding to downstream signaling proteins. α-catenin is one such adaptor protein that localizes to cadherin-based cell adhesions by binding the membrane-localized cadherin-β-catenin complex at one side and the cytosolic F-actin on the other side. An increase in actomyosin tension is directly relayed to α-catenin resulting in a change in its conformation making cryptic binding sites accessible to its interacting partners. Here, I describe an updated view of the mechanical regulation of α-catenin in the context of cellular adhesion, including the role of cadherin clustering in its activation.
Insect wings change its shape passively by the aerodynamic and inertial forces when flapping, which can greatly affect its aerodynamic performances. In order to confirm the importance of the fluid-structure interaction in flapping wing aerodynamics, we performed computational fluid-structure interaction analyses of a hovering hawkmoth with ‘virtual’ vacuum conditions that can adjust the effect of the aerodynamic force on the deformation of flapping wings. It is turned out that the large part of the wing deformation, such as the wing twist, is induced by the inertial force as reported previously, but the adjustment of the wing deformation by the aerodynamic force can greatly affect the kinematics and the aerodynamics of flapping wings. While the wing deformation, regardless of the contribution of the aerodynamic force, can increase the aerodynamic power, force and efficiency of flapping wings, the wing deformation adjusted in response to the unsteady aerodynamics of flapping wings can further enhance the aerodynamic performance. These results not only reveal the influence of the wing deformation on the aerodynamic performance of flapping wings, but also point out the great importance of the fluid-structure interaction in the aerodynamics of insect flight and the design of bio-inspired micro aerial vehicles.
Dental plaque on the surfaces of implants causes peri-implantitis and periodontitis. Although the plaque needs to be removed from the surfaces, it is difficult to clean it from the screw section of an implant, as this is roughened to improve biocompatibility. Recently, a method using a cavitating jet was proposed to clean dental plaque. In this paper, the geometry of a Venturi type nozzle for a cavitating jet is optimized by measuring the cavitation impact using a PVDF (Polyvinylidene Fluoride) sensor. The cleaning performance of a cavitating jet using this nozzle is compared with that of a normal water jet. The results show that the optimum divergence angle is 15 deg or 20 deg, depending on the injection pressure. The effect of temperature on the impact power was also investigated, and it was found that the impact power increases with water temperature and saturates at 40-50 °C. It was demonstrated that a cavitating jet using the optimized Venturi type nozzle can remove dental plaque from the screw section of an implant and that the area cleaned by the cavitating jet is greater than that cleaned by a normal water jet.
Determination of left-right asymmetry of the body plan is achieved in the early embryo. At the 4-6 somite stage, a cavity structure, called a node, is observed in the ventral midline surface, in which hundreds of cilia rotate. Nodal cilia are typically tilted toward the posterior and rotate in the clockwise direction, resulting in the generation of leftward flow in the node. Such leftward flow acts as a trigger of left-specific gene expression, and fluid mechanics plays a role in left-right symmetry breaking. To understand the cilia-driven nodal flow, it is necessary to determine the hydrodynamic interactions among rotating cilia, as ciliary motions interact with each other through fluid motion. In this study, we numerically investigated the elastohydrodynamic synchronization of two rotating cilia, as well as the flow field. The ciliary motion was determined by the balance of cytoskeletal elastic force, motor protein-induced active force, and fluid viscous force. According to the geometric clutch hypothesis, the frequency of rotating cilia is controlled by the bending curvature. Owing to hydrodynamic interactions, bending deformations of two cilia become time-dependent, and the rotation is finally locked in anti-phase regardless of the relative position and initial phase difference. By locking in the reverse phase, the average propulsion flow rate becomes 2-3 times larger than in-phase beating. The results of this study form a basis for understanding cilium-driven nodal flow.