This paper presents a formulation to identify muscle activities from the variation in shapes of organs during swallowing. We assume that each organ consists of a three-dimensional hyperelastic body, and the contraction movement of the muscle is caused by a contractive inelastic stress in the organ. A function distributed in the organ domain to control the magnitude of the inelastic stress is chosen as a design variable in the same manner as the density in the topology optimization problem of density variation type. The identification problem is formulated as a problem of determining the design variable that minimizes an objective cost function defined by the squared L² norm of the reaction force in the normal direction on the boundary when an enforced displacement to fit the varied boundary of the organ and the inelastic stress modeling the muscle activity are applied. The finite deformation problem of the hyperelastic body is analyzed using the finite element method. The direction of the muscle fiber is assumed to be the direction of the minimum principal stress obtained as the solution to the finite deformation problem. The solution to the identification problem is presented based on a scheme using the H¹ gradient method for the topology optimization problem of density variation type. A numerical example using a previously developed model of the tongue is introduced to demonstrate the effectiveness of the proposed approach.

Although cardiac strain has been used as a practical mechanical indicator to estimate cardiac functions, measurement of strain is still difficult due to the need for operator proficiency and special equipment to perform echocardiography and magnetic resonance imaging (MRI). Hence, a modified indicator that can be calculated more easily at the bedside is needed to assess cardiac function based on cardiac morphology. The circumferential strain of the left ventricular (LV) wall and the contraction potential energy were numerically investigated in this study using a thick-walled cylindrical model under different myocardial thicknesses, stiffnesses, and diastolic pressures for given specific ejection fractions (EFs) or end-diastolic volumes. The LV wall was modeled as a visco-hyperelastic, continuous material. We proposed the modified ejection fraction (mEF), which is the product of EF and the contractility percentage of the internal volume within the epicardium, as an indicator of circumferential strain. Calculated peak circumferential strain was better estimated by mEF than EF. Furthermore, the contraction potential energy correlated well with circumferential strain and mEF. Our results regarding mEF are consistent with those obtained in 7 previous clinical studies. mEF may be a useful and practical indicator of the reduced contraction potential energy of the local myocardium and of heart failure, regardless of imaging modalities and vendors.

Actin filaments play significant roles in many essential cellular processes including muscle contraction, cell motility, vesicle and organelle movement, cell signaling, and mechano-sensing mechanism of cells. However, one of the important cellular processes, the mechano-sensing mechanism of cells, is still debatable. To elucidate these mechanisms of cellular processes, it is important to observe the remodeling of the F-actin structure in cells. Although there are many reports about the remodeling of the F-actin structure during cellular processes, it needs to consider that the intracellular and extracellular proteins are fluctuating with thermal energy. We assumed that these small fluctuations affect the mechano-transduction in cells. We focused on an F-actin small fluctuation and tried to observe that in a living cell. Here, we propose the analyzing method of F-actin fluctuation in a living cell using the quasi super-resolution technique. To visualize F-actin filaments in living cells, Lifeact-GFP plasmid vector was transfected to NIH3T3 cells. Ten images of F-actin in living cells were taken every second under static culture conditions. First, we analyzed the small fluctuation of F-actin in living cells with Gaussian smoothed images. In this analysis, the amplitude of F-actin fluctuation was approximately 0.2 to 0.3 μm, which is almost the same as the optical resolution. Therefore, we have reconstructed the F-actin image in cell from a cross-sectional fluorescent profile with the quasi super-resolution technique. We analyzed the fluorescent profile at several points along one F-actin filament, and the X and Y coordinates were picked up from the peak fluorescent in each fluorescent profile. From these X and Y coordinates in images, F-actin filament was approximated as a quadratic curve. We reconstructed the F-actin filament each time. The obtained spatial resolution was 0.08 μm which was 2.5 times higher than the optical resolution. In quasi super-resolution images, the fluctuation amplitude of F-actin was 0.42 to 0.53 μm in the peripheral region and 0.27 μm in the center region. The frequency of F-actin fluctuation in both center and peripheral regions was approximately 3 Hz. The F-actin fluctuation was irregular, and several fluctuation patterns were observed. These phenomena might be caused due to the influence of restriction of the cytoskeletal network.

Phase-contrast magnetic resonance imaging (PC-MRI) allows us to acquire biofluid flow velocity maps, whereas MRI data is restricted by spatiotemporal resolution limitations and contains theoretically inevitable errors. Although various approaches to estimating actual velocity from MR velocity maps using the mass and momentum conservation laws have been proposed, practically reasonable methodologies are still not well established. This study investigates a practical strategy for estimating physically consistent velocities from MR velocity maps based on variational optimal boundary control through examples of the 2D steady Stokes flow as an incompressible viscous fluid. We defined a minimization problem of the sum of squared residuals between MR and the estimated velocity at all pixels (voxels) considering the image data structure with respect to the Dirichlet boundary velocity condition subject to flow governing equations based on variational formulations. This optimization problem is treated as an unconstrained optimization problem by deriving the Lagrange functional, including the cost function, regularization term, and constraint conditions. The optimality condition is computed using the adjoint variable method in a finite element manner. The boundary velocity profile is iteratively updated by the optimality condition using gradient-based optimization until convergence. Numerical examples for 2D Poiseuille flow with noise-free and noisy reference data demonstrated good convergencies of the cost function minimization. The estimated flow velocities were in excellent agreement with reference data. Finally, we demonstrated the viability of the velocity estimation using the actual MR velocity of the cerebrospinal fluid flow. The proposed approach with further considerations specialized for the MRI may be feasible in providing physically consistent velocity profiles in a versatile target of the biofluid flow.

Elderly people often use a cane to walk; it is an important part of their daily life. The cane must be made of a light weight material of high stiffness. In addition, stress relaxation on impact is required to make the cane easy to grasp. All these factors are affected by the shape design. Therefore, an effective shape design considering the stress relaxation on impact load and the weight of the cane is important. Traditionally, straight-type canes are widely used in the market. In this study, a bioinspired shape design methodology is proposed to produce canes. The basis vector method is used, and a multi-objective design optimization for minimizing the total volume and the maximum stress is performed. A sequential approximate optimization is then adopted to determine the Pareto optimal solutions. The superiority of the proposed method over the straight-type cane is confirmed through numerical results. The optimal cane shapes have more than 90% lower impact stress than the straight-type canes. Finally, a prototype of the optimized cane is produced using the braiding technology. Carbon fiber reinforced plastic is the selected cane material owing to its light weight and high stiffness.

The high sensitivity of mammalian hearing is achieved by cochlear amplification. The basis of this amplification is the motility of outer hair cells (OHCs), which are sensory cells in the inner ear. This motility may be due to voltage-dependent conformational changes of the motor protein prestin, which is densely embedded in the lateral membrane of OHCs. However, the membrane structure of prestin has not yet been elucidated. Therefore, the membrane structure of prestin was herein investigated by force spectroscopy using an atomic force microscope (AFM). The gene of prestin fused with an Avi-tag at its C terminus was transfected into Chinese hamster ovary (CHO) cells and the inside-out plasma membrane was isolated. The Avi-tag was enzymatically biotinylated and attached to a streptavidin-coated AFM cantilever via biotin-streptavidin binding. Prestin was then pulled out from the plasma membrane and the relationship between the force applied to the protein and the extension distance, i.e., the force-extension (FE) curve, was assessed. The curves obtained showed saw-toothed patterns. An attempt was then made to analyze these curves using the worm-like chain model. The force caused by stretching of the intracellular C terminus and that due to the extraction of one or several transmembrane domains were identified. The present results imply that the C terminus and the subsequent transmembrane domains of prestin correspond to those of the previously reported model with 12 transmembrane domains.

A numerical approach is one of feasible ways to discover the biomechanics of hallux valgus deformity with various osteotomy and fixation strategies. In the present study, two types of finite element models for analyzing the biomechanical performances of hallux valgus treatment with plate fixations were developed including the single first metatarsal bone model and the musculoskeletal lower extremity model. There are four types of plate fixations that were used to correct the deformity of hallux valgus. The strengths and limitations of both the single first metatarsal bone model and the musculoskeletal lower extremity model were evaluated and discussed. The results revealed that the single metatarsal bone models can be used to quickly predict the biomechanical performances of different hallux valgus treatments. Additionally, the musculoskeletal lower extremity models can be used to predict the biomechanical performances of different hallux valgus treatments under a physiological loading. The plate fixations with the insertion of all locking screws revealed better osteotomy fixation stability and lower risk of the implant failure compared to the other fixations. Additionally, the plate fixations with the insertion of six bone screws had lower risk of the metatarsal bone failure compared to the plate fixations with the insertion of four bone screws. The six holes plate with the insertion of six locking screws was the best treatment among the four treatment strategies. The numerical models and simulation techniques developed in the present study can provide useful information for understanding the biomechanics of hallux valgus treatments.

The cerebellum has a unique morphology characterized by fine folds called folia. During cerebellar morphogenesis, folia formation (foliation) proceeds with granule cell (GC) proliferation in an external granular layer, and subsequent cell migration to an internal granular layer (IGL). GC migration is guided along Bergmann glial (BG) fibers, whose orientation depends on the deformation of cerebellar tissue during folia formation. The aim of this study is to investigate the contribution of the fiber-guided GC migration on folia formation from a mechanical viewpoint. Based on a continuum mechanics model of cerebellar tissue deformation and GC dynamics, we simulated foliation process caused by GC proliferation and migration. By changing migration speeds, we showed that the fiber-guided GC migration caused the non-uniform accumulation of GCs and folia lengthening. Furthermore, the simulation of impaired GC migration under pathological conditions, where GCs did not migrate along BG fibers, revealed that fiber-guided GC migration was necessary for folia lengthening. These simulation results successfully recapitulated the features of physiological and pathological foliation processes and validated the mechanisms that guidance of GC migration by BG fibers causes folia lengthening accompanied by non-uniform IGL. Our computational approach will help us understand biological and physical morphogenesis mechanisms, facilitated by interactions between cellular activities and tissue behaviors.

The present study focused on freestyle swimming by swimmers with unilateral transradial deficiency. It has not been clarified yet whether the deficient limb should move so as to match the tempo of the intact upper limb, or if it should move as fast as possible to produce thrust by itself. The objective of this study was to solve the theoretically ideal deficient limb’s strokes in freestyle for a swimmer with unilateral transradial deficiency by using the optimizing simulation. The method of the optimizing simulation of arm strokes considering muscle strength characteristics was developed in a previous study. This method was utilized to solve the deficient limbs’ strokes in the present study. Actual swimming by a participant was reproduced by simulation first. Since the resultant swimming speed of the simulation was in the range of the experimental speed, the validity of the simulation was confirmed. Next, optimizing simulations were conducted for the case of maximum shoulder joint torque multiplied by 1.0, 0.85 and 0.72. From these results, a significant increase in the swimming speed was found for the optimized cases. It was also suggested that the contribution by the deficient limb to propulsion can be increased by up to 15% of the intact limb. The optimized stroke was found to have a later timing and faster motion than the original stroke. This motion was realized by the principle that more joint torque can be exhibited in adduction than in flexion when the joint angular velocity was high.

Osteocyte plays a central role as a commander in the bone to modulate bone remodeling processes. While the osteocyte is known to be differentiated from osteoblasts, understanding in mechanism of the osteocyte differentiation remained still poor. The aim of this study is to elucidate the osteocyte differentiation capability using three-dimensional (3D) cell culture technique. We first fabricated a self-organized spheroid reconstructed by mouse osteoblast-like cells by adjusting the number of subcultured cells in the round-bottom well. Compared to a conventional two-dimensional (2D) monolayer model, the 3D spheroid exerted greater osteocyte gene expressions in vitro within 2 days. As a result of the size-dependent experiment, there might be an appropriate cell-cell and cell-ECM interaction for osteoblast-like cells to induce the osteocytogenesis in the form of 3D spheroid culture. Moreover, the present model showed that the spheroid further exerted the prolonged osteocyte differentiation capability after a long period of incubation, 7 days. In conclusion, we characterized the self-organized osteocytic spheroids reconstructed by osteoblast-like cells and further suggested the potential application of the spheroid as a new in vitro tissue-engineered osteocytic model.

While rovers are of importance for Mars exploration in terms of various surveillance, surface rovers may encounter great challenges due to rough terrain and complex turbulent environment on Mars partly because aerial vehicles have difficulties to stay airborne due to the extremely low atmospheric density. Flights of surface rovers on Mars share the aerodynamic similarity with insect flights on earth in terms of low Reynolds number flow regime. Motivated by that insects can achieve remarkable flapping-wing aerodynamic performance in force production, flight stability and maneuverability under highly unsteady environments, we here proposed a bumblebee-inspired flapping-wing design for Mars surface rovers. We developed a power-efficient aerodynamic model by combining a surrogate model and a bioinspired dynamic flight simulator for hovering flight in a parametric space comprising wing shape and wing kinematics to explore feasible design points and some optimal solution with the power output minimized. Our results indicate that an enlarged wing model inspired by bumblebees is capable of sustaining hovering flight on Mars with a set of aspect ratios and wing kinematics and an optimal design point is found to correspond with a power output of 0.0509W, which may provide a novel and feasible biomimetic design for flapping-wing aerial vehicles on Mars.

Recent research has shown that enhanced focal adhesion between cells and extracellular matrix (ECM) and intracellular actin polymerization can accelerate cellular functions like proliferation and differentiation. It is a desirable and necessary technique to modulate cellular functions in the desired lineage in tissue engineering. Previously, we have shown that topographical effects of micropatterns on a cell culture substrate promoted osteogenic differentiation of mesenchymal stem cells (MSCs) without administration of osteogenic growth factors. In this study, bone marrow mesenchymal stem cells from rats were cultured with combined biophysical stimuli, such as surface topography of biomaterials and uniaxial tensile stress and induced osteogenic differentiation. We evaluated MSCs by assessment of alkaline phosphatase (ALP). We demonstrated that a polydimethylsiloxane substrate with microgroove patterns (2 μm of ridge thickness, 1 μm of depth and 1 μm of groove distance) could suppress osteogenic differentiation compared to a flat substrate. Changes of cell adhesion and shape were observed at microgroove substrates by immunofluorescence staining of focal adhesion and actin filaments. We showed that to apply the stretching force promoted differentiation at microgroove substrates but inhibited differentiation at the flat surface. Through this study, a more efficient method to control cellular fate is expected to be established for tissue regeneration in vitro.

A numerical simulation model for the evaluation of the effectiveness of lifejackets against drowning in tsunamis considering both unsteady water currents and human movement was developed. The Constrained Interpolation Profile-Combined Unified Procedure scheme was combined with the link segment model to simulate interactions between the fluid and subjects in the developed model. The developed model was experimentally validated using a large flume. A manikin laid on blocks was swept down by a tsunami-like water current and caught by a vortex behind the blocks. The developed model accurately reproduced both water currents and the movement of the manikin and was thus considered adequate to analyze the movement of human bodies in tsunamis. The model was then used to analyze the movement of a human body in the same currents but with higher buoyancy, assumed to represent a lifejacket. Consequently, buoyancy greater than a human’s body weight was required to keep the subject afloat; a buoyancy corresponding to the body weight caused the total submergence of the entire subject. Through comparison of forces applied to the body with its movement, it is revealed that a human body receives strong downward force while and immediately after passing over the vortex. These forces are caused due to the attractive pressure at the center of the vortex and downward currents in the downstream side of the vortex. These forces are considered to be remarkable in the evaluation of lifejackets in actual tsunamis.

Formation of vascular anastomoses is critical for the development of transplantable tissue-engineered grafts, because rapid blood perfusion is required for the maintenance of implanted tissue grafts. However, the process of vascular anastomosis remains unclear due to difficulties in observing vascular anastomosis after transplantation. Although several groups have developed in vitro models of vascular anastomosis, there is a lack of a suitable in vitro anastomosis model that includes perivascular cells. Therefore, we aimed to establish an in vitro vascular anastomosis model containing perivascular cells by a combination of human umbilical vein endothelial cell (HUVEC) monoculture and HUVEC-mesenchymal stem cell (MSC) coculture in a microfluidic device. We found that vascular formation was inhibited when HUVECs were seeded on both sides of gel scaffolds, but HUVECs formed vascular networks when they were seeded on one side only. Next, we tested a series of HUVEC:MSC ratios to induce vascular anastomoses. The results demonstrated that addition of MSCs induced vascular anastomosis. In particular, the number of vascular anastomoses was significantly increased at a HUVEC:MSC ratio of 2:8. The process of vascular anastomosis was further investigated by live-cell imaging of green fluorescent protein-expressing HUVECs, which revealed that vascular anastomoses with continuous lumens were constructed during days 8–10. Computational simulation of VEGF concentrations suggested that local VEGF gradients play important roles in vascular formation while the addition of MSCs was critical for anastomosis. This anastomosis model will provide insights for both the development of tissue-engineered grafts and for the construction of large tissues by assembling multiple tissue-engineered constructs.

Vascular smooth muscle cells (VSMCs) actively remodel the arterial walls through biomechanical signals and dedifferentiate from the contractile to the synthetic phenotype under pathological conditions. It is important to elucidate the mechanism underlying phenotypic transition of VSMCs for understanding their role in the pathophysiology of disease and for developing engineered tissues. Although numerous studies have reported various biochemical or biomechanical factors that stimulate the phenotypic transition of VSMCs, very little is known about the changes in the mechanical environment of intracellular nucleus that are involved in various cellular functions. This study investigated the changes in the force exerted on the intracellular nucleus, and their morphology and mechanical properties during serum starvation-induced VSMC differentiation. Fluorescent microscopy image analysis and atomic force microscopy nano-indentation live cell imaging revealed that the serum-starvation culture conditions markedly promote the contractile differentiation of VSMCs with F-actin stabilization and reduces the internal force exerted on the nucleus. The nuclei in these contractile VSMCs exhibited surface stiffening and matured nuclear lamina. Additionally, the nuclei exhibited distinct surface dimples along the actin stress fibers even though these nuclei were exposed to lower internal forces. These results indicate that the distinct dimples on the nuclear surfaces represent a plastic remodeling of the nucleus under the serum-starvation culture conditions. The nuclear stiffening, local deformation, and plastic remodeling observed in this study may be important factors in contractile differentiation of VSMCs.

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.

Deformability of epithelial tissues plays a crucial role in embryogenesis, homeostasis, wound healing, and disease. The deformability is determined by the mechanical balance between active force generation and passive response of cells. However, little is known about how multiple cells in epithelial tissues passively respond to external forces. Using a 3D vertex model, we performed computational simulations of longitudinal tension and compression tests of an epithelial tube. Under tension, the tube extended with necking as exhibiting cell rearrangements that play a role in reducing local stiffness of the tube. On the other hand, under compression, the tube buckled with kinking without cell rearrangements. The cell rearrangements occurred when apical and basal cell surfaces stored elastic deformation energies. These results illustrate the variance of deformation modes of epithelial tissues in the single cell level as well as the importance of cell rearrangements in regulating epithelial deformability.

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.

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.

The endoscopic optical coherence tomography (OCT) has been developed for early detection of digestive system cancer. However, it is difficult to detect cancerous tissue due to complicated speckle patterns contributed by optical properties of scattering and absorption in the morphological images of OCT. In our previous papers, 2-color optical coherence dosigraphy (2C-OCD) was proposed, which quantified OCT signal as scattering and absorption coefficients and could provide drug distribution at the micro-scale spatial resolution. In this study, an in vivo tomographically diagnosing technique of early cancer is presented, in which 2C-OCD is applied to cancerous tissue with selective uptake of photosensitizer. The feasibility study was demonstrated and investigated, based on 2C-OCD visualization of the subcutaneous tumor-implanted nude mice with photosensitizer AlPcS administered. Consequently, it was confirmed that drug absorption coefficient obtained by 2C-OCD was correlated with fluorescence intensity from accumulated AlPcS (r = 0.918), comparing with their histological images. Additionally, 2C-OCD could diagnose tumor tissue significantly with sensitivity of 82.5% and specificity of 78.3%, respectively. Therefore, 2C-OCD can detect photosensitizer infiltration into cancerous tissue, and thus has a promising modality for in vivo tomographically diagnosing technique of early cancer.