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(z₁) and fiber orientation function D(z₁), 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 ~ 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 Euglena-like 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.

The 100-meter sprint is a central focus in sports biomechanics due to its relevance to performance enhancement. In this study, we reviewed electromyographic (EMG) data from ground sprinting and analyzed stride and joint kinematics from treadmill sprinting to examine and propose the coactive roles of femoral biarticular muscles alongside femoral monoarticular and lower leg muscles during sprint gait. The EMG data were interpreted using the static two-joint link model, which characterizes the functional coordination of human femoral muscles. According to the model, activity switches occur among three antagonistic pairs of femoral muscles at distinct phases of the sprint cycle. Concurrently, six muscle pairs generate sequential combined force outputs, applied to specific sectors of the ankle joint, contributing to coordinated movement at the hip, knee and ankle joints. During the stance phase, the coactivity of the gluteus maximus and/or biceps femoris long head facilitates hip extension and forward propulsion, while the gastrocnemius and soleus support plantar flexion and ground reaction force modulation. We conclude that femoral biarticular muscles play significant coactive roles with femoral monoarticular and lower leg muscles during sprinting. The EMG and treadmill kinematic analyses provide valuable insights into the biomechanics of sprint gait.

Interstitial flow (IF) across the aortic walls induces mechanical stress on smooth muscle cells, altering their function in response to the flow. Due to the heterogeneous structure of the aorta, IF velocity varies locally. We previously developed a method for measuring local IF velocity by directly visualizing the movement of a fluorescence dye driven by the fluid flow using fluorescence microscopy and quantifying the velocity based on a one-dimensional convection-diffusion equation (Fukui et al., Sci. Rep. 2022:12(1), 5381). However, the original method had low measurement reliability due to the widely scattered data points in kymograph-based analyses, leading to low correlation coefficients. This study aimed to refine the method for improved reliability. Several modifications were introduced, including replacing the forward difference scheme with a central difference scheme in the convection-diffusion equation, minimizing image drift, compressing the image size of kymograph, and optimizing the image analysis region. These modifications enhanced data fitting to a linear trend, leading to more accurate interstitial flow velocity measurements. When applied to the dataset from Fukui et al., the modified method significantly improved measurement reliability, yielding correlation coefficients above 0.90 and velocity values several times higher than those obtained before modification. The proposed approach provides a more reliable technique for quantifying IF velocity in the aortic wall for future biomechanical studies.