This study presents a new method for evaluating the natural frequencies of bone-conducted sounds using spectrograms obtained by short-time Fourier transform (STFT) and machine learning (ML) and examines its validity for practical applications. The natural frequencies of bone-conducted sounds is conventionally evaluated using fast Fourier transform (FFT) analysis. Spectrograms obtained by STFT are used to visualize bone-conducted sounds as a two-dimensional time-frequency representation. Another advantage of spectrograms is that they facilitate the development of a convolutional neural network based ML model for predicting natural frequency. Forty-five healthy college students (20.36 ± 1.53 years) participated in this study, and five hammer impacts were applied to the right medial malleolus to record bone-conducted sounds generated at the right medial tibial condyle. Spectrograms were obtained from the recorded waveforms using STFT and input into a ML model trained with natural frequencies evaluated by FFT as a ground truth. The natural frequencies predicted by the ML model were compared with the natural frequencies evaluated by the FFT analysis. The mean absolute error was 12.92 ± 4.05 Hz, and the mean coefficient of determination (R2) was 0.845 ± 0.163, demonstrating the high evaluation accuracy of the proposed method. Feature analysis conducted using gradient-weighted class activation mapping revealed that the developed model focused on the peak sound pressure of the spectrogram when predicting the natural frequency. Further, it was found that the predicted values were large discrepancies from those evaluated by FFT analysis when the ML model failed to capture the peak sound pressure.
Traditional stopwatch-based assessments such as the Timed Up and Go (TUG) test may lack sensitivity for high-functioning older adults because of ceiling effects. This study evaluated the potential of a markerless motion capture (MMC) framework using a single monocular camera to quantify subtle trunk kinematics during TUG and to explore motor control deficits that may be imperceptible to human observation. Thirty-four community-dwelling older adults (17 fallers and 17 non-fallers) performed TUG under a maximal-effort condition to impose biomechanical stress. MediaPipe-based pose estimation was used to extract the trunk center-of-mass (COM) trajectory, and a systematic screening of 18 metrics spanning temporal, variability, and smoothness domains was conducted to identify candidate biomarkers. Total time did not distinguish between groups, whereas the Log Cumulative Jerk (LCJ) in the return walk phase showed the largest effect size (Cohen's d = 0.68), although the between-group difference was not statistically significant under non-parametric testing (Mann-Whitney U, p = 0.130). In this context, lower LCJ may reflect a more constrained movement pattern consistent with a possible “stiffening strategy,” rather than improved coordination. LCJ yielded the highest classification performance among the tested parameters (AUC = 0.65), indicating modest relative discrimination in this sample. These exploratory findings suggest that markerless assessment of movement smoothness may provide complementary information beyond conventional time-based measures and may support hypothesis-generating, non-contact fall-risk screening in community settings.
Bone material properties in the femur exhibit marked spatial heterogeneity, which may influence stress distribution after total hip arthroplasty (THA). However, many finite element (FE) studies have relied on homogeneous material assumptions, potentially overlooking patient-specific femoral mechanical behavior. The objectives of this study were to investigate the influence of heterogeneous bone material properties on stress distribution in THA femurs and to clarify the relationship between local bone stiffness and stress distribution across Gruen zones. Subject-specific FE models of three femurs with different Dorr classifications (A-C) were constructed using computed tomography (CT) images. Heterogeneous material properties were assigned based on Hounsfield unit-derived density and elastic modulus, and two cementless stem designs (short and long stems) were analyzed under physiological walking loads. Average von Mises stress was evaluated in each Gruen zone and compared with composite elastic modulus calculated using a rule-of-mixtures approach. The results showed that overall stress distribution patterns were qualitatively similar to those obtained using homogeneous material models, exhibiting stress shielding and distal stress concentration regardless of stem type or femoral morphology. However, within the same Gruen zones, an inverse relationship was observed between composite elastic modulus and average von Mises stress, particularly in mid-to-distal regions. Compared with homogeneous models, heterogeneous models exhibited lower stress magnitudes due to reduced bending deformation. These findings indicate that while homogeneous models may be sufficient for comparative parametric analyses, heterogeneous material modeling provides important insights into local stress-stiffness relationships and patient-specific bone quality. Incorporating material heterogeneity is considered essential for accurate prediction of local mechanical behavior and for future simulations of bone remodeling and fracture risk after THA.
The three-dimensional morphogenesis of epithelial tissues is governed by robust physical mechanisms. Examples of this process include the folding of insect imaginal discs and cerebral convolutions. Reaction-diffusion theories have historically focused on chemical aspects to explain these structures. However, recent mechanobiological studies indicate that geometric constraints are equally pivotal. In this study, we investigate how the intrinsic curvature of a tissue substrate directs the buckling morphogenesis driven by cell division. Using a three-dimensional cell-center model, we simulated epithelial proliferation on spherical and ellipsoidal surfaces. Our results reveal a curvature-dependent mode transition on spherical surfaces. Specifically, the buckling pattern shifts from a dot-like state to a labyrinthine state as the radius increases. Crucially, we observed that tissue geometry regulates the spatial orientation of the buckling patterns. On prolate ellipsoids, the tissue spontaneously generates "Yoshimura pattern-like folds" (zig-zag patterns). This topological structure is similar to the folding of beetle horns. Conversely, on oblate ellipsoids, the tissue robustly forms concentric ring patterns. This morphology resembles the folding of Drosophila leg discs. We propose that this physical pattern selection arises from geometric confinement rather than solely from molecular pre-patterning. Specifically, the high-curvature poles of prolate ellipsoids generate effective axial compression. In contrast, the high-curvature equator of oblate ellipsoids induces radial compression. These findings suggest that morphogenetic outcomes are robustly "encoded" in the macroscopic geometry of the developing primordium. Therefore, this macroscopic geometry serves as a geometric bifurcation parameter to regulate the transition between ordered and disordered patterns.
Wear particles generated from ultra-high-molecular-weight polyethylene (UHMWPE) joint components play a central role in macrophage-mediated inflammatory responses associated with periprosthetic osteolysis. Although particle size, material modification, and particle load are known to influence biological reactivity, the temporal dynamics of macrophage responses under continuous exposure remain insufficiently understood. In this study, a microchamber-based platform was employed to enable controlled, cumulative, and time-resolved exposure of human monocyte-derived macrophages to clinically relevant UHMWPE wear particles. Wear particles were generated under four material conditions (virgin, 'y-irradiated, vitamin-E-blended, and vitamin-E-blended with 'y-irradiation) and classified into two size groups enriched in particles smaller or larger than approximately 1 & micro;m. Macrophages were continuously exposed for 24 h under two cumulative particle load conditions corresponding to approximately 5 & times; and 40 & times; the seeded cell number. Culture medium was collected at regular intervals and analyzed for tumor necrosis factor alpha (TNF-alpha) using an enzyme-linked immunosorbent assay. TNF-alpha production showed time-dependent changes, including transient early-phase increases followed by declines in some donor-derived macrophages. Higher cumulative particle loading generally resulted in greater TNF-alpha production than lower loading, indicating that cumulative particle burden influences the inflammatory response profile. In contrast, the effects of particle size and UHMWPE material modification were less distinct under the present conditions, while donor-dependent variation was evident. These findings indicate that cumulative particle load is an important determinant of macrophage inflammatory responses to UHMWPE wear particles. The microchamber-based system provides a useful experimental framework for time-resolved analysis of wear particle-cell interactions and contributes to a better understanding of the mechanisms underlying implant-related inflammation.
Sound reaches the auditory system through air conduction (AC) via the ear canal or bone conduction (BC) via vibrations of the temporal bone, and both pathways are often activated simultaneously in real environments such as trains and vehicles; environmental sounds are transmitted via AC, while mechanical vibrations may be perceived not only as tactile stimuli but also as BC-like vibrational stimuli. Previous studies have demonstrated AC-BC interference for identical pure tones, but directly measuring cochlear vibrations during simultaneous acoustic and vibrational stimulation remains challenging. Computational simulation can therefore help clarify intracochlear mechanics under such combined stimulation. However, intracochlear mechanical responses under simultaneous AC and vibrational stimulation at different frequencies, which more closely reflect real-world environments, remain insufficiently characterized. In this study, cochlear vibrations under simultaneous AC and vibrational stimulation were simulated using a computational model of human cochlea. Displacement-driven BC stimulation consistently generated basilar-membrane (BM) traveling waves comparable in overall pattern to those induced by AC stimulation. Under same-frequency stimulation, the BM response at the AC-defined CF location varied systematically with AC-BC relative phase and relative magnitude, including marked reductions consistent with destructive interference. Under different-frequency stimulation, the traveling-wave envelope departed from a single spindle-shaped profile and could become bimodal or otherwise non-spindle-shaped, indicating superposition of concurrent response components. These results show that AC-BC interference depends on stimulus magnitude, phase, and frequency, and provide a basis for quantitatively assessing vibroacoustic interactions in the cochlea.
This study investigated the low-dimensional spatiotemporal structure of overground walking using displacement-based principal component analysis (PCA). Four healthy young male subjects participated in the walking measurement experiment. Three-dimensional marker trajectories were collected during overground walking at three different walking rates, and marker displacements were analyzed to reduce the influence of translational components. Cumulative variance of the first two principal components (PC1 and PC2) consistently accounted for more than 85% of the total variance across all walking rates. Temporal analysis showed that PC1 exhibited a regular sinusoidal waveform corresponding to the fundamental gait frequency, whereas PC2 showed a periodic structure at approximately twice that frequency. In contrast, higher-order components displayed complex composite waveforms. Principal component loadings indicated that PC1 primarily represented alternating anterior-posterior displacements of the left and right lower limbs, while PC2 reflected coordinated in-phase displacements associated with the double-support phase. The variance explained by PC1 slightly increased with walking rate, likely due to increased step length. Sinusoidal models of PC1 and PC2 were used to successfully reconstruct walking movements with high temporal fidelity. The temporal and spatial characteristics of these components were preserved across all walking rates. Within this preliminary dataset of four healthy young males, overground walking was characterized by low-dimensional periodic coordination patterns that were relatively consistent across individuals. These findings highlight the effectiveness of displacement-based PCA for revealing fundamental walking movement organization.
Mammalian spermatozoa navigating through the female reproductive tract to reach the egg comprises a fundamental step in achieving successful fertilization. Within the oviduct, sperms encounter oviductal mucus, which is a highly viscous and shear-thinning non-Newtonian fluid whose rheological characteristics strongly influence sperm motility and guidance. During their journey, sperms are subjected to fluid flow generated by the peristaltic motion of the oviductal wall, prompting them to employ behavioral mechanisms such as thigmotaxis and rheotaxis to efficiently migrate toward the oocyte. In the present study, we experimentally examined the interplay between rheotactic behavior and collective swimming of sperm in shear-thinning fluids. To reproduce the physiological flow conditions in the oviduct, we designed and fabricated microchannels. These microchannels mimic the geometry and flow environment of the oviduct using a combination of high-resolution 3D printing and soft lithography techniques. These microfluidic systems allow precise control of the flow field and viscosity distribution, thereby enabling quantitative analysis of sperm motility under conditions relevant to in vivo reproduction. Our results demonstrate that spermatozoa exhibit pronounced rheotaxis within regions near the channel wall, where strong velocity gradients are present. The shear-thinning nature of the medium enhances this orientation response, which results in improved alignment of swimming directions and spontaneous formation of sperm clusters. Furthermore, sperms engaged in collective motion exhibit significantly higher swimming velocities than those swimming individually, suggesting hydrodynamic cooperation among neighboring cells. These findings provide new insights into the physical and biological mechanisms underlying sperm transport in complex reproductive environments. The enhanced rheotactic alignment and collective behavior observed in shear-thinning fluids may confer evolutionary advantages by increasing the probability of successful fertilization under physiological flow conditions.
A number of studies have been conducted on the relationship between plant growth and external stimuli. There has been, however, little research on the effects of wind stimuli that are one of the major stress factors acting on plants in natural environments. Understanding how mechanical properties and morphologies of plants respond to external stimuli is essential for elucidating plant growth mechanisms. This study, therefore, focused on wind-induced changes in mechanical, histological and cellular properties of plants. Mini sunflowers ( Helianthus annuus L. ) were grown in a wind tunnel with wind speeds of 3.0 m/s and no-wind (control), while room temperature and light-dark conditions were kept consistent between the two groups. After approximately one month of growth under each condition, measurements of the length of stem, the Young's modulus of stem, the length of cells, the lignified cell area ratio and the cell cycle were conducted. Compared with the control group, the wind-stimulated group exhibited a 67% decrease in the Young's modulus, a 38% reduction in the stem length, and a 64% reduction in the lignified area ratio, whereas no significant difference in the cell length was observed. In addition, cell cycle progression was inhibited under the wind-stimulated condition. The results indicate that a reduction in cell number contributes to decreased stem length, while a lower ratio of lignified cell area contributes to decreased Young's modulus. These findings suggest that plants adapt to wind stimuli by maintaining shorter and more flexible stems, thereby reducing the risk of mechanical failure.
The periodic motion of the lower trunk region during human locomotion is analyzed from a kinematic perspective for different gaits using inertial measurement units (IMUs). Experiments are performed on subjects who walked or ran on a treadmill, each equipped with an IMU attached to their lower trunk. The treadmill speed was externally controlled according to a fixed protocol consisting of speed-up and speed-down phases. Time-series data of acceleration and angular velocity were collected and analyzed. We propose a method to estimate the initial elevation angle and velocity associated with the periodic motion, and we focus on the three dynamical aspects of the subject's movements: the trajectory of the lower trunk in the sagittal plane, the excess kinetic energy ratio, and the position of the least acceleration fluctuation point. The results revealed that the rotation direction of the trajectory in the sagittal plane in the moving frame differed between walking and running for almost all subjects. This difference is interpreted kinematically in terms of the direction and timing of the ground reaction force. The excess kinetic energy ratio as a function of Froude number also well characterizes the gait differences. Furthermore, it is found that the point of least acceleration fluctuation is located consistently behind the body during running.
In both engineered and living systems composed of mechanically interacting elastic bodies, variational modeling, which assigns an energy function to a system, has effectively captured the shape evolution in the elastic body system in response to the mechanical interactions. However, to make an energy function represent componentlevel shape evolution, the energy function should account for the evolution of mechanical interactions along with the shape evolution of the individual elastic bodies. In this study, we develop an energy function-based model that assigns an energy function with landscape evolution to each elastic body in a system. This model formulates the shape evolution of individual elastic bodies and the evolution of their contact forces, based on the shape gradients of the assigned energy functions and the landscape evolution, respectively. To clarify a characteristic of the system dynamics, we implement this formulation on finite element simulations for a simple twodimensional system with concave-convex joint-like geometry under axial and oblique loading conditions. Under axial loading, the contact force distribution remains substantially constant, and the energy values decrease as expected from the shape gradients. Under oblique loading, localized increases in the contact force at specific corners generate landscape evolution that increases the energy. Consequently, our formulation has clarified that the energy increase of the components emerges as a characteristic of system dynamics associated with the landscape evolution of the energy functions.
This study reports the development of a compact tabletop onsite device designed to facilitate non-invasive, rapid, low-cost, and user-friendly health evaluation by quantifying amino acids in sweat through enzymatic reactions. The system employs freeze-dried reagents coated onto a multilayer PET film-based microfluidic channel. As sweat extract flows through the channel, each target amino acid reacts selectively with its corresponding enzyme, and the resulting color change is quantified within a short onsite analysis time. Sweat was collected using a pre-wetted non-woven patch, automatically extracted into liquid form with a dedicated cassette, and applied to the analytical film device. The extract contained multiple amino acids, including glycine, aspartic acid, leucine, histidine, and serine, which were detected by their respective enzymes. Although further optimization of the enzymatic reaction conditions is required to reduce variability among amino acids, the present device demonstrates a practical platform for convenient onsite multi-amino acid analysis in sweat, with potential applications in beauty, sports, health screening, agriculture, environmental monitoring, and space exploration.
Physics-informed neural networks (PINNs) offer a promising framework by embedding partial differential equations (PDEs) into the loss function together with measurement data, making them well-suited for inverse problems. However, plain PINNs face challenges with time-dependent PDEs due to the high computational cost of space-time training and the risk of convergence to local minima. These limitations are particularly pronounced in hemodynamic analysis, where 4D-flow magnetic resonance imaging (4D-flow MRI) yields temporally sparse velocity snapshots over the cardiac cycle. To address this challenge, we propose a PINN framework that reconstructs instantaneous flow fields from transient velocity snapshots by inferring the acceleration term in the incompressible Navier-Stokes equations. By designing the network without explicit time as an input, the proposed approach enables physics enforcement using spatial evaluations alone, improving training efficiency while maintaining physical consistency with transient flow characteristics. In addition, we introduce an acceleration-mismatch loss that penalizes discrepancies between predicted and measured accelerations, which improves prediction accuracy through regularization. Numerical examples on pulsatile flow behind a stenosis using temporally and spatially downsampled synthetic data generated from time-resolved CFD demonstrate that the proposed framework reliably reconstructs velocity fields even under sparse temporal sampling, and appropriate regularization for acceleration improves predictions of pressure-gradient and acceleration fields.
The aortic valve plays a crucial role in cardiac function by opening synchronously with left ventricular contraction to pump blood into the aorta and closing during left ventricular relaxation to prevent blood regurgitation. Aortic valve stenosis (AS), resulting from congenital bicuspid valves or age-related calcification, can cause symptoms of heart failure (HF) or angina. In severe cases, angina may develop even in the absence of coronary artery stenosis, potentially leading to impaired cardiac function or worsening HF. In this study, we developed a patient-specific hemodynamic computational fluid dynamics model by adjusting internal parameters such as vessel length, cardiac resistance, and cardiac elastance, based on previously established 0D-1D multiscale cardiovascular hemodynamic models developed by our research team. Seven patients with both diastolic and systolic HF were included, and their hemodynamic parameters were used to construct patientspecific models. This study aims to predict coronary hemodynamics and cardiac function under conditions of AS using patient-specific models of individuals with HF. Hemodynamics and coronary circulation were evaluated under various conditions by imposing AS on the HF models. As a result, coronary blood flow was decreased by approximately 20% in HF patients under AS, compared to a 7% reduction observed in healthy individuals. These simulation results suggest that AS in HF patients leads to a reduction in coronary blood flow and may contribute to myocardial ischemia, even in the absence of coronary artery stenosis. Furthermore, patient-specific hemodynamic models may offer a valuable non-invasive approach for evaluating cardiovascular risk and guiding individualized treatment strategies.
Epithelial cell layers dynamically remodel their mechanical interactions with the substrate, but the quantitative evaluation of such interfacial behavior remains challenging. Here, we employed quartz crystal microbalance with dissipation (QCM-D) monitoring to investigate how the viscoelastic coupling between epithelial monolayers and their substrate responds to calcium chelation by ethylene glycol tetraacetic acid (EGTA), which disrupts cadherin-mediated cell-cell adhesion and mimics an epithelial-mesenchymal transition (EMT)-like condition. Time-resolved measurements of resonance frequency and energy dissipation were analyzed using a viscoelastic model to extract changes in apparent elastic modulus and damping ratio. EGTA treatment induced a gradual increase in apparent elasticity and a concurrent reduction in viscous damping, reflecting a transition from a strongly coupled viscoelastic state to a partially decoupled and effectively more elastic configuration. The magnitude of these responses increased with culture duration, indicating stronger collective mechanics in more mature cell layers. These findings demonstrate that QCM-D can sensitively detect dynamic alterations in the interfacial mechanical behavior of living cell layers, providing a simple and quantitative platform for investigating EMT-associated transitions and other processes involving collective mechanical remodeling.
The antenna of a male insect can capture pheromones generated by a female insect. In this study, the sensilla of an antenna are represented by a row of cylinders, and the mass of pheromones they capture along with the capture rate are calculated. The diameter of the real sensilla of a moth Bombyx mori is assumed in the calculation. Reynolds number and P & eacute;clet number, which are defined by the diameter of cylinders and the uniform flow, are 0.04 and 0.26, respectively. Calculation parameters are the gap between neighboring cylinders representing sensilla and their angle of attack. For a high angle of attack, the analytical exams show that the capture rate is maximized when the ratio of the gap between cylinders to their diameter is 10. In all the cases, the capture rate is maximum when the angle of attack is 90 degrees and the ratio of the gap between cylinders to their diameter is 10. This ratio is close to that observed in the sensilla of a moth Bombyx mori. When the ratio of the gap between cylinders to their diameter is smaller than 3, the capture rate is nearly independent of the ratio of the gap between cylinders to their diameter and the angle of attack.
Accurate, objective estimation of subjective workload is critical issue in occupational health and safety, yet existing methods largely rely on observational assessments rather than quantitative metrics. To address this gap, this paper presents a novel approach for objectively estimating subjective workload by combining the substantial muscle activity ratio, which accounts for fatigue-induced reductions in muscle strength, with a logistic function approximating individual sensitivity curves. The method was applied to three shoulder muscles during a repetitive upper-limb task performed by healthy participants. The results indicated that, for each participant, the estimated subjective workload closely approximated the perceived workload in at least one of the three muscles. This finding demonstrates that the proposed method can simulate temporal changes in perceived workload despite inter-individual variability. Incorporating the logistic function allowed the model to account for nonlinear perception of workload. Further analysis suggested that the dominant muscle contributing to perceived workload differed across participants, depending on individual movement strategies during the task. Motion analysis confirmed that differences in shoulder joint kinematics were associated with the muscles most closely tracking perceived workload. These findings highlight the necessity of accounting for both biomechanical and kinematical factors when estimating subjective workload. Overall, the study demonstrates a physiologically grounded framework for predicting perceived workload and provides a foundation for developing generalized models applicable to real-world tasks, supporting more informed strategies for worker load management.
Fibrosis is a condition resulting from tissue damage and inflammation that causes loss of function by hardening the tissue while accumulating collagen. Although there are drugs that inhibit the progression of fibrosis, there are few effective treatment options once fibrosis has developed. In response, we proposed a therapeutic technology that thermally denatures collagen in fibrotic tissues and restore flexibility to tissues stiffened by fibrosis. The purpose of this paper is to evaluate the above therapeutic technology using fractional laser as a heat source for collagen thermal denaturation. Using 450 nm semiconductor lasers with high absorption from surfaces, Fractional laser irradiation was applied to simulated fibrosis samples derived from bovine Achilles tendon. Laser irradiation was performed with irradiation patterns of 3, 6 and 12 dots/mm2 and irradiation energy conditions of 65, 84, 99, 110 and 116 mJ/dot. Fibrosis that originates from tissue damage should have as low tissue damage as possible because of the possibility of re-fibrosis due to laser damage. Therefore, we performed CHP staining to verify thermal denaturation at the laser irradiation point, and based on the staining results, determined the laser energy settings that could induce thermal denaturation of collagen while minimizing tissue ablation. To evaluate the mechanical properties of the laser-irradiated samples under set conditions, tensile tests were carried out to verify the rate of change in Young's modulus, which showed a 22.1, 23.0 and 32.0% increase in flexibility for irradiation patterns of 3, 6 and 12 dots/mm2, respectively. These results suggest that the thermal use of fractional laser can restore the flexibility of fibrotic tissue.
Vertical jump tests, including the squat jump and countermovement jump, are widely used to evaluate athletic performance or the muscular strength of the lower limbs. Biomechanical analysis using musculoskeletal models provides a valuable tool to clarify the mechanisms of body movement and muscular function in such physical tests because it is impractical to simultaneously measure the state of every muscle or joint in the body. Although the vertical jump is a multi-joint movement that requires coordinated activity of skeletal muscles throughout the body, few musculoskeletal models incorporating the muscles of the entire body have been proposed. The aim of this study was to conduct an exploratory investigation into the causal effects of individual muscle activities on the exertions in other muscles and resulting jump performances from the perspective of the coordinated motion or kinematic chain using a whole-body musculoskeletal model. A forward dynamics-based whole-body human musculoskeletal model with an appropriate range of articular motion was developed. The muscle dynamics are described using a biofidelic Hill-type muscle-tendon complex model, which includes concentric and eccentric contractions and the pennation angle with serial damping in the tendon. The moment arms of muscles in the model were validated against literature data. Using the developed musculoskeletal model, simulations of squat jumping were performed by inputting the activation level of each muscle. The results indicated that reducing the activity of the extensors in the shoulder, trunk, and neck indirectly decreased muscular forces in the lower extremities immediately before take-off, resulting in a lower jump height. These findings emphasize the importance of regarding the vertical jump as a coordinated motion driven by muscles throughout the body. Additionally, the developed musculoskeletal model is useful for investigating biologically plausible muscle control algorithms and enhancing human movement analysis.
Conventional screw-type propellers are widely used but have pose environmental concerns, including sediment disturbance and potential harm to aquatic ecosystems. These concerns have prompted interest in biologically inspired propulsion mechanisms. Previous studies have explored biomimetic motion strategies, such as body-caudal fin (BCF) movements for high Reynolds number (Re) regimes and ciliary or undulatory locomotion for low Re environments. This study focuses on the latter and advancing a propulsion mechanism inspired by the pellicular strip gliding motion of Euglena, aiming for low environmental impact and cross-environmental adaptability. While our previous work demonstrated only two-dimensional deformation, the present study achieves three-dimensional motion by introducing a three-dimensional sliding deformation mechanism using circumferentially arranged porous polytetrafluoroethylene (PTFE) sheets actuated by tensioned wires. Unlike conventional sharp memory alloy (SMA) coil actuators, mechanical wire traction allows for rapid and spatially variable deformation. Time-series analyses of localized expansion and bending motion were conducted, and a geometric model was developed to describe surface profiles and fiber orientations along the longitudinal axis. Experimental results revealed asymmetric displacement distributions during both localized expansion and bending motions. The deformation patterns observed in localized expansion resembled the non-uniform peristaltic motion characteristic of Euglenoid movement. The surface function E(z(1)) and fiber orientation function D(z(1)), extracted via marker-based image tracking, effectively captured the deformation behavior. Although discrepancies in shrinkage ratios arose-likely due to structural limitations near constrained regions-the deformation cycle was completed within 1.2 seconds, corresponding to an actuation frequency of similar to 0.5 Hz. This frequency surpasses that of microorganisms like Euglena and is comparable to the lower end of swimming frequencies observed in fish. These findings demonstrate that the proposed mechanism can reproduce Euglenalike three-dimensional deformation and serve as a foundational platform for multimodal, bioinspired propulsion. With future improvements in constraint design and control coordination, this system shows strong potential for adaptive robotic applications across a wide range of Re conditions.
