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.
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.
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.
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.
Although the blood flow velocity in a left ventricle (LV) has been considered to be sufficiently fast to prevent thrombus formation, internal wall structures, such as trabeculae carneae (TC) and papillary muscle, recently received attention as possible causes of reduced near-wall blood flow. As a fundamental consideration of this problem, this study established a method for constructing an unsteady LV model from magnetic resonance (MR) images and investigated the effect of a few simplified TC structures on the blood flow in the model. The LV model at arbitrary time steps was constructed by deforming a computational mesh generated from MR images at a reference time step. The validity of the proposed construction scheme was confirmed by comparison with the configuration of an LV model extracted from MR images. Numerical analysis was performed for the unsteady blood flow in LV models with and without two simplified TC structures. The flow field in the model with the internal structure differed from that in the model without the internal structure near the wall, and flow separation caused by the internal structure decreased wall shear stress on the rear of the internal structure. The computational results provide fundamental information for the complex interaction between the internal structures and the blood flow in an LV.