It is difficult to experimentally observe the influence of differences in individual skin properties of human fingers on tactile perceptions. During subjective experiments, many parameters, such as skin properties, the transmittance of nerve signals, and individual feelings are intricately mixed; therefore, it is difficult to identify which elements are affected and to what extent. It has not been determined how age-related changes in the stiffness of skin influence tactile perceptions. We developed a two-dimensional cross-section human fingertip finite element model based on previous studies. Then, we estimated the influence of age-related changes in skin stiffness on Merkel cells and tactile perceptions by using finite element analysis. Age-related changes in skin stiffness were described by changing skin material properties in the model. Simulations using a model involving the fingertip being contacted with a rigid flat plate or a 2-point indenter were performed. Using a rigid flat plate and standard skin material properties, the contact width between the finger pad and the object was 5 mm. Meanwhile, the width changed from 5 mm to 4 mm when using a model of age-related changes of skin. Using a rigid 2-point indenter, the difference in the peak-to-valley of the Mises distribution around the Merkel cells indicated 2-point discrimination. Besides, the difference decreased by approximately 43% with changes in skin stiffness. These results indicated that age-related changes in skin stiffness influenced tactile perceptions.
Severe head injuries—and even deaths—have been reported in the practice of judo, often resulting from inexperience in using the appropriate falling technique (ukemi). In this study, we developed a novel head protector that protects the head and suppresses the neck extension during impact with the mat. The head protector was fabricated for this purpose and consists of a head support structure and shock-absorbing materials. The effectiveness of the head protector was tested experimentally with an apparatus with head and neck components that were based on a Hybrid III dummy. Several configurations of the support structure characteristics and the shock-absorbing materials were evaluated. The proposed head protector was capable of reducing the head angular velocity variation range—which is an important evaluation index for the onset of acute subdural hematoma —by 29% using the devices alone, by 21% using shock-absorbing materials alone, and by 47% using a combination of both. These results show that the proposed structures are highly effective in suppressing extensions at the cervical-thoracic joint (C7-T1), whereas the shock-absorbing materials are highly effective in suppressing rotations at the atlanto-occipital joint (O-C1). It is concluded that wearing the proposed head protector—which combines both effects—can reduce the risk of severe head injuries, even those resulting from severe impacts such as those associated with the judo ukemi practice.
Intraplaque hemorrhage (IPH), bleeding in a plaque, is caused by a neocapillary rupture in an atherosclerotic plaque. We used contrast-enhanced ultrasonography to diagnose carotid atherosclerotic plaques before carotid endarterectomy (CEA), a surgical operation to remove an arterial intimal layer including a plaque lesion. We found lumenward (inward) deformation in some cases of ruptured plaques with IPH. The aim of this study was to evaluate the mechanical effects of infiltrated blood in the lipid core on the luminal shape of the ruptured plaque in the short-axis view. We created a finite element model of a carotid artery bifurcation with a ruptured plaque based on a sample obtained from CEA. As physiological loads, we assigned pressures on the surfaces of the lumen and the lipid core, the sum of a gradual pressure drop in the artery obtained from computational fluid dynamics analysis and a uniform pressure, and a constant longitudinal stretch. In the simulation, the fibrous cap in the ruptured model became almost flat in the short-axis view with lumenward deformation, being less deformed than that observed in ultrasonography. The simulation results show that inward deformation of the fibrous cap is correlated with an equal pressure in the lumen and the lipid core. In comparison, a hyperelastic model of soft unruptured plaque reproduced a round lumen. A better understanding of contrast-enhanced ultrasonography images from a mechanical perspective may facilitate the morphological identification of plaque rupture with IPH.
Improving the process of cell injection during hepatocyte transplantation requires an understanding of the causal relationships that shear, direct contact cells with a solid surface, and cell deformation have on cell viability loss. A linear shear model was used to model this loss of cell viability during their movement on a solid surface as part of the injection step of hepatocyte transplantation. Rat hepatocytes were studied under linear shear using two parallel plates, with a ”tight” condition that had a 25 μm gap, and a ”loose” gap condition with a > 25 μm gap, to determine the effects of cell deformation, and simulate cell viability loss during injection. Cell morphology and deformation were also observed using time-lapse images. Direct contact with a solid surface is deleterious for cells, and live cells became deformed under shear stress until they lost viability. The cell size could decrease or increase during deformation, and a loss of viability could occur due to a loss of membrane integrity or cell rupture. The space limitations in the tight gap could prevent cell expansion, which delayed the process of cell viability loss. In summary, preventing the direct contact of hepatocytes with a solid surface is recommended to improve the cell injection process during transplantation.
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.
The cart-type friction measurement device developed by the authors facilitates measurement of both the static coefficient of friction (SCOF) and the dynamic coefficient of friction (DCOF) between the shoe and the floor simultaneously, as well as measurement with variation in sliding velocity. However, whether slip–resistance evaluation using this cart-type friction measurement device corresponds to the actual slip and fall risks is unclear. To investigate the validity of evaluation of slip resistance between the shoe and the floor by using the SCOF and DCOF values measured with a cart-type friction measurement device, we aimed to investigate the relationship between the slip angle in a ramp test and the coefficient of friction (COF) values between the test safety shoe and the 10 test floor sheets contaminated with a glycerol solution. The results indicate that the SCOF values and the DCOF values corresponding to sliding velocity lower than 0.3 m/s are highly correlated with the slip angle in the ramp test, which suggests that the cart-type friction measurement device can simulate the slip between the shoe and the floor in the ramp test under such sliding velocity conditions. Because the ramp test has been used widely to assess the slip resistance of floors and because the slip angle is highly correlated to the risk of slip-induced falls during level walking, the results suggest that the cart-type friction measurement device is valid and effective for assessing the slip resistance between the shoe and the floor. This study provides new information about the evaluation of slip resistance and indicates that the cart-type friction measurement device will contribute toward the prevention of slip-induced fall accidents.
A sufficient number of functional live hepatocytes delivered to a recipient is necessary for cell therapy. Preventing cell viability loss during the cell injection process is important to improve the clinical outcomes of hepatocyte transplantation. The critical location of cell viability loss is important to identify the causal relationship between the viability loss and cell injection process. In this study, the critical location of cell viability loss was determined experimentally in a rectangular microchannel by microscopic high-speed camera observations. Live hepatocyte distributions were investigated upstream and downstream, and measured on three planes, top, center, and bottom, under horizontally or vertically supplied conditions of the syringe orientation. Sedimented and uniform dispersion conditions of the live hepatocyte distribution at upstream of the microchannel were classified according to observations at horizontal and vertical syringe orientations, respectively. Higher hepatocyte viability loss was found under the sedimented condition. The results suggested that the critical location of hepatocyte viability loss was on the bottom plane of the microchannel. Furthermore, physical causes of the hepatocyte viability loss were found by micro-scale observations of the cell velocity and diameter during the cell injection process. This information may contribute to development of a guideline for the cell injection process to improve hepatocyte transplantation.