The evaluation of tactile sensitivity involving frictional behavior via computational models can further accelerate the development of industrial products in terms of usability. This study aimed to confirm the capability of a previously proposed mechano-neurophysiological model, representing the basic mechanical (i.e., finger skin deformation) and neurophysiological (i.e., neural activities of slowly adapting type-1 (SA1) afferents) functions in the tactile sensation process, for simulating tactile responses during Braille reading under multiple frictional conditions. A previous psychophysical experiment on tactile recognition during Braille reading reported that the misread rate was significantly higher at frictional coefficient (μ) = 2.62 than at μ = 0.56, whereas no significant differences were observed between the misread rates at μ = 0.25 and 0.77. The Braille reading experiment was simulated using the mechano-neurophysiological model to achieve the present aim. The simulation results revealed marginal differences in the SA1 responses between μ = 0.25 and 0.77, and the correlation coefficients between the SA1 responses and Braille patterns were 0.98 at μ = 0.25 and 0.96 at μ = 0.77, suggesting a limited influence of friction on Braille recognition. However, the SA1 responses varied considerably between μ = 0.56 and 2.62, and the correlation coefficients were 0.97 at μ = 0.56 and 0.49 at μ = 2.62, implying a relatively strong influence of friction. The simulation results supported the above-mentioned findings of the previous psychophysical experiment, thereby demonstrating that the mechano-neurophysiological model qualitatively determined the tendency of influence of friction on Braille recognition.

The thrombus formation process has yet to be fully simulated, which necessitates the design of a novel method for the quantitative assessment of device thrombogenicity that complements animal experiments/ex vivo experiments using animal blood and computational fluid dynamics analysis. This study aimed to develop a model blood capable of simulating the formation of red thrombus owing to stagnation of blood flow by applying the phenomenon of milk clot formation. To render the rheological properties of skim milk solution used as a model blood closer to those of human blood, the ratio of the amounts of casein in skim milk, calcium chloride, and rennet (constituents of the solution of the model blood) was varied and the rheological properties of the clot formation process of human blood and skim milk solution were measured using a cone-plate viscometer. Comparisons of the rheological properties of human blood and skim milk solutions during clotting revealed that during clot formation of human blood, four characteristic quantities of the time-series change in rheological properties were observed: the viscosity before clotting, coagulation start time, viscosity increase rate, and first yield viscosity. Further, hypercoagulable skim milk solutions with rheological properties similar to those of human blood were prepared by adjusting the solution composition ratio. When this model blood was circulated in a closed-loop circuit with a saccular aneurysm model, the growth rate of skim milk clot formation in the aneurysm model was significantly different in a flow diverter stent model and a micro-porous covered stent. The variation in porosity between these two stent models has a direct impact on the rate of embolisation. The proposed blood model can effectively replicate the formation of red thrombus, providing a valuable means to accurately and quantitatively assess the therapeutic efficacy of embolisation devices.

Herein, an implantable energy-harvesting system utilizing the contraction of electrically stimulated skeletal muscle is proposed for self-sustainable batteries of implantable medical devices (IMDs) and health-monitoring devices. To achieve high energy conversion efficiency, a resonance generator utilizing the vibration of the skeletal muscle, called as incomplete tetanus, is proposed. Considering the multi-dynamics of muscle contraction, oscillator, and electrostatic induction, design parameters, such as the stimulation condition of the muscle and the mechanical characteristics of the resonance generator, are optimized. In the benchtop experiment, the power generated by the prototype is 20.48 μW. Moreover, a positive net power of 13.1 μW is generated in the ex vivo experiments using the skeletal muscles of toads; this power is sufficient to operate IMDs, thus demonstrating the feasibility of the proposed energy harvesting system using incomplete tetanus of the skeletal muscle.

Irreversible electroporation (IRE) is a less-invasive therapy to treat tumors by delivering short and intensive electric pulses to the tissue. The pulse settings are important factors that affect IRE outcome. In this study, we proposed a three-dimensional (3-D) cell culture model to determine the critical electric field for IRE depending on the effect of pulse parameters, particularly pulse repetition and interval, and adjuvants. Agarose gel containing fibroblasts was used as a tissue phantom. After application of electric pulses, the area that contained full of necrotized cells was quantified and compared with the distribution of the electric field estimated from a numerical analysis, so that the critical electric field strength to cause cell necrosis was determined. Ablated area increased as a function of pulse repetition, and reached a plateau at 120 pulses. When the pulse interval was extended from 100 ms to 1 s, the ablated area increased by approximately 30%. Addition of 10% DMSO and 5% ethanol also significantly increased the ablated area by 15% and 55%, respectively, indicating a reduction of the critical electric field strength. The critical electric field strength was independent of the magnitude of the applied voltage when the pulse length, interval, and the number of pulses were fixed. A longer interval and adjuvants increased the ablated area, and therefore decreased the critical electric field strength. The 3-D tissue phantom composed of agarose gel and cells was useful for examination of the IRE effect by comparing the experimentally determined necrotized region with a numerical analysis.

In addition to the characteristics of soft actuators, such as flexibility and elasticity, biohybrid actuators also exhibit few distinctive functions, such as self-growth and self-healing. The previous research on biohybrid actuators has focused on culturing muscle cells and assembling them into micro-robots. These technologies are well-developed, however they lack the design and control methods found in the existing actuators that enable an appropriate performance. Therefore, we propose a simple muscle contraction model against external electrical stimulation, applying the model-based design and realizing the control of biohybrid actuators. The model comprises three sub-models—the electrical dynamic, physiological, and mechanical dynamic characteristics. The input of the model is the time-series stimulation voltage, and therefore, it can be applied to any complex stimulation waveform. The model parameters were identified with multiple square waves with different frequencies and amplitudes, based on the actual skeletal muscle of a toad. Subsequently, in the validation test, the actual muscle contraction was compared with the simulated force that was calculated using the identified parameters. Although the stimulations for the validation were different from those for the identification, the results obtained based on the model showed a good agreement with the experimental results. In addition, the optimal stimulation signal could be also calculated based on the model, to obtain the maximum net work. The findings of this study facilitate the development of model-based design and control methods for biohybrid actuators in the future, that will lead to significant development in this field.

Flying insects are capable of hovering and rapid maneuver under unpredictable environments. The principal wing-beat is generated by transmitting the rhythmical contractions of power muscles to the exoskeleton and wing-base articulation. Fine-tuning of the flapping wing kinematics is achieved by deforming the articulation with tiny steering muscles. This flapping mechanism of insect flight is distinct from that of conventional man-made aerial vehicles, enabling superior flight. In this study, we propose an insect-inspired flapping mechanism, which is comprised of two different types of actuators and a flexible wing-base structure. The flapping mechanism is driven by electric motors, which modulate wing kinematics by adjusting the flexible wing-base structure using electromagnetic actuators (EMAs). First, the EMA design was optimized based on analysis of the dynamic forces and displacements to enable deformations of the wing-base structure. A prototype flapping mechanism was then constructed, and its performance was evaluated experimentally by adjusting the actuation phase of the EMAs being synchronized with flapping motions of the wing. The results indicate that the wingbeat kinematics and aerodynamic performance are noticeably sensitive to the actuation timing of EMAs and can thus be controlled by tuning the EMA actuating timing and direction. The flapping mechanism can potentially be applied as a novel means for controlling body posture of flapping-wing micro air vehicles to achieve insect-inspired stable flights in natural environments.

Mechanosensing-based cell orientation and migration in microenvironments, such as microgrooved surfaces, are essential in biological tissue growth and repair. These responses might be cell type-dependent as they are deeply involved in cellular functions. Despite their orientation and migration responses are depended on cell-substrate adhesion, which is deeply involved with focal adhesions (FAs) of cells, we have limited information on the cell behavior on FA-sized microgrooved surfaces. Here, we systematically investigated the cell orientation and migration behavior of primary porcine aortic smooth muscle cells (PASMs), embryonic rat aortic smooth muscle cells with fibroblast-like phenotype (A7r5), and human cervical cancer cells (HeLa) on a substrate comprised of superficial grooves with three widths (1 μm, 5 μm, and 10 μm) and 150-nm depth, which are the same order of magnitude of the three-dimensional size of FAs. PASM and A7r5 cells including thick bundles of actin fibers with elongated FAs showed pronounced cell polarization and directional migration on the 1 and 5 μm wide grooves. PASMs were more sensitive to the superficial grooves than A7r5 cells. HeLa cells adhering to the grooves had non-oriented actin fibers with smaller FAs, and they did not show specific orientation nor directional migration in any groove type. Atomic force microscopy elucidated that the mechanical tension of the actin fibers in live cells had a significant positive correlation with the length/width ratio of FAs, reflecting the cell alignment and directional migration on the grooves. The increase or decrease in the mechanical tension of the actin fibers improved or diminished the mechanosensing for the grooves, respectively. The results strongly suggested that the differences in cell type-specific alignment and migration become much more pronounced on the microgrooves which are similar in three-dimensional size of FA, and that is useful for clarifying slight differences in force-dependent cellular mechanosensing.

The capillary refill time (CRT) is the time that elapses before the fingernail color returns to red from white after releasing a load applied to the nail. We aimed to estimate hypovolemic status using the CRT. However, the precision of CRT is low. The first step toward improving precision was estimation of the coefficient of variance (CV) via repeated measurements. The best and next-best indices of the CRT change rates in the hypovolemic state were 0.19 and 0.48 respectively, and the corresponding target CVs were ≤ 0.10 and 0.24. The CRTs of subjects were measured by imaging nails during loading and unloading and fitting of an exponential function to the curve of intensity changes. The CRT was 0.77 ± 0.35 s (n = 108), which is comparable to previous studies. However, the CV was 0.37 ± 0.13, which is higher than even the second-best index. Thus, we used only the green color channels of nail images to generate algorithms to define the optimal start time of the CRT calculations; this provided a lower CV (0.31 ± 0.12). Finally, we investigated the effects of fingertip temperature and load release timing on CRT during a cardiac cycle. Correction of the temperature effect with a care on a phase during the cardiac cycle to trigger data collection reduced CV to 0.15 ± 0.11, which cleared the second-best index. Thus, our protocol improves CRT precision; it may be possible to estimate hypovolemic status using the CRT.

Flying animals such as insects, bats, and birds have acquired the ability to achieve diverse and robust flight patterns in various natural environments. Their sophisticated morphologies, kinematics, and dynamics have motivated engineers to develop bioinspired flying robots. Particularly, the capabilities of morphing wing and tail controls in birds have received significant attention. Such controls are expected to introduce novel mechanisms to achieve flight stabilization while maintaining high maneuverability with a low energy cost. While the control of tail posture and motion is considered to exhibit a significant influence on flight performance, there have been few studies focusing on control with multiple degrees of freedom in small flying robots. In this study, we developed a bird-inspired morphing tail mechanism; a model was fabricated and investigated its aerodynamic performance through wind tunnel experiments. The results indicate that the tail attitude can be controlled effectively to enable the enhancement of aerodynamic performance in terms of mechanical efficiency and controllability. We also verified that controlling the tail attitude is redundant in the control of aerodynamic force and moment production, implying the potential capability to achieve stable flight control strategies in response to various disturbances. Therefore, our results indicate that tail-attitude-based aerodynamic control may be able to cope with the conflicting requirements of improving stability and maneuverability of flyers.

Optical coherence tomography (OCT) is a three-dimensional imaging technique based on low coherence interferometry of near-infrared broadband light and has been applied to medical diagnoses, such as structural diagnosis of the retina in ophthalmology. For several decades, functional variations of OCT have been also developed. OCT angiography (OCTA) is one of the functional variations of OCT and can visualize blood flows (microvasculature) in biological tissues by analyzing the time-series of OCT signals. Recently, several studies suggested the possibility that OCTA can not only visualize blood flows but also detect the blood flow velocity quantitatively, where the blood flow velocity is estimated by analyzing OCTA signals computed with multiple time separations from the time-series of OCT signals measured at a short time interval. OCTA signals computed with short time separations, however, reduce its contrast between dynamic tissues (blood flows) and other static tissues, resulting in the decrease of signal-to-noise (SN) ratio of the flow detection. This study proposed a novel method to enhance the SN ratio of the flow detection from such OCTA signals computed with short time separations, by means of mapping the gradient of OCTA signals against the time separations. In the experiments, a flow phantom and human skins were employed to compare SN ratios among OCTA with a long time separation (standard OCTA), OCTA with a short time separation, and the proposed method. The results showed that the proposed methods can detect flow signals with a high SN ratio equivalent to that of the standard OCTA and, therefore, suggested that quantitative detection of the flow velocity with OCTA will be possible with a high SN ratio of flow detection.

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.