Significant progress has recently been made in the development of extracellular stimulation technology for the enhancement of nerve axonal extension and network generation and regeneration in three-dimensional (3D) bioreactors for neural tissue engineering. In this study, a 3D cell culture cell culture system was developed to accelerate the regeneration of axons using cyclic stretch stimulation. A modified collagen gel was used as a scaffold to mimic the extracellular matrices of the central nervous system in the human brain. First, a cyclic stretch stimulation cell culture system was designed and fabricated in order to load uniform strain onto a 3D culture. Pheochromocytoma (PC12) cells were then mixed with the collagen gel and poured into the stretch chamber of the cell culture system. The stretch stimulation cell culture system was then used to load the cyclic tensile strain against the PC12 cells embedded in the collagen gel, where an in-situ microscopic observation was performed. Second, cyclic stretch stimulations of the PC12 cells were performed, and the 3D morphologies of the cell bodies, neurites, and axons within the PC12 cells were observed using a multi photon microscope (MPM) system. We evaluated the effectiveness of the cyclic stretch stimulation on the axonal extension of nerves in a 3D cell culture system. Finally, we confirmed the enhancement of the axonal extension and determined the optimum tensile strain and the number of cyclic stimulations required to achieve the maximum axonal extension of the PC12 cells. Using these optimum conditions—2.3% strain, 1 Hz cycles, and 1.7×10⁵ times—the cyclic stretch stimulation was performed on rat cerebral cortex cells, and the effectiveness of the enhancement was also confirmed in these cells.

The mechanical rotation axes of joint exercisers are believed to operate better when they match the biomechanical axes of human joints. However, there are few studies regarding ankle stretching machines. Further, the maleffects of rotation axis misalignments are not well known. Hence, we investigate the effective positions of rotation axes for ankle stretching machines and the effects of misalignments using a pneumatic-driven stretching machine developed in our previous study (Shiraishi et al., 2020). Eight healthy young males (ages 23.3 ± 1.4 years) participated in stretching exercises while the relative positions of the rotation axes between the machine and ankle were changed via plates installed under the heel. The stretching machine dorsiflexed the feet of the participants, and the dorsiflexion angles and three-axial forces applied to the forefeet were recorded. The measured values at the maximum dorsiflexion angle were evaluated by two-way analysis of variance and/or regression analysis. We determined that the rotation axis of the machine must be placed 7 mm above the lateral ankle because the normal force applied to the forefoot and maximum dorsiflexion angle were large, whereas the friction force was moderate. Further, the relationships among the dorsiflexion angle and contact forces were investigated via covariance selection. The three-axial forces significantly decreased as the axis of the machine was lowered below the ankle. Additionally, the force normal to the sole had large positive effects on the dorsiflexion angle and friction force of the sole, which could damage the skin. The misalignment of the rotation axis increased the contact force at the sole when the axis of the machine was above the ankle or decreased the efficiency of force transmission from the stretching machine to the user’s foot when the machine’s axis was below the ankle.

Comfort is required for soaking in bathwater. Although several studies investigated comfort during soaking from a biomechanical viewpoint, these previous studies employed two-dimensional models in the sagittal plane of a bather. The objectives of this study were to take three-dimensional postures of the bather into account and to evaluate the biomechanical loads for three-dimensional soaking postures. A three-dimensional biomechanical model was constructed, and an experiment to measure the soaking postures and reaction forces from the bathtub was conducted for eight participants. In addition, a supplementary experiment to measure the passive elastic joint torques was conducted for the same participants as well. Using the experimental results, the joint torques during soaking were calculated. In addition, the biomechanical load during soaking was defined as the sum of weighted joint torques, and the weighting coefficients were determined so that the tendencies of the biomechanical load were consistent with those of sensory evaluation of comfort. Finally, the biomechanical loads were calculated for various bathtub conditions and evaluated. It was found that the contributions of joint torques at the hip and neck to the comfort were dominant. It was also found that hip joint torques not only in the flexion/extension direction but also in the abduction/adduction direction were affected by the difference in bathtub length. It was suggested that the biomechanical load in the convex foot wall was smaller than those in the flat and concave ones for male bathers.

Grinding methods have been widely used in orthopedic surgery, which has high requirements for surface quality, grinding force and temperature control. It is necessary to explore the influence of micro-grinding parameters on the grinding force temperature from a microscopic perspective. This paper describes the micro structure, composition and thermodynamic properties of bone. From the perspective of the single abrasive grain, the single abrasive grain cutting model is established, and the single abrasive grain cutting force equation is derived. ABAQUS is used to establish a 2D cutting simulation model of abrasive grains, and the internal structure of the bone material is considered, and the bone micro structure model (including osteon orientation , matrix, cement line ) is established. The simulation study is carried out on the cutting direction of the abrasive grains in parallel, vertical and cross with the axial unit axis. The study of the relationship between force and temperature and cutting parameters shows that the abrasive cutting force increases with the increase of grinding speed and grinding depth. The cutting force is the largest in the vertical cutting mode, the cutting force is the second in the cross cutting mode, and the cutting force is the smallest in the parallel cutting mode. Finally, the comparison between theory and simulation shows that the theoretical analysis results are consistent with the finite element simulation results, which verifies the correctness of the theoretical model of single abrasive grain cutting force.

This study is based on an analysis of visual-motor coordination as a ball is caught. Humans obtain most of their information about the external environment from their sense of sight during daily life and sports activities. Sight enables us to judge the distance to objects and is important for controlling the musculoskeletal system and maintaining posture. Therefore, analyzing visual-motor coordination is essential for clarifying how humans relay visual information to their motor control system. This study analyzed the coordination between the lines of sight and upper limbs of receivers as they caught a ball with both hands, as a first step in the quantitative evaluation of visual-motor coordination. Singular value decomposition was applied to an observation matrix consisting of the upper limb joint angles and the pixel coordinates of the line-of-sight positions obtained in the experiment. We evaluated the cooperative relation between the lines of sight and the upper limbs by using the space basis vectors in the first and second modes, which had the highest contribution ratios. We compared the results for the condition in which a thrower tossed the ball after stating the direction in which the ball would be tossed. Furthermore, we also compared the results for the condition in which the thrower tossed the ball without stating the intended direction. The results demonstrated that the movements of specific joints were coordinated with changes in the lines of sight when the throwing direction was announced in advance. We therefore conclude that visual-motor coordination during daily life and sports activities can be clarified using the proposed method.

In vivo aortic wall thickening is a mechanical adaptation to the prolonged increase in intravascular pressure resulting from hypertension, which is mainly regulated by primary components of the aortic media, the elastic lamina (EL) and the smooth muscle-rich layer (SML). This study built a simplified finite element (FE) model of the aortic medial wall comprising the EL and SML, and simulated EL undulation or buckling at a no-load condition, i.e., (in the in vitro) unloaded state, by releasing a set of compressive prestresses initially given to the EL. Using the design of experiments approach (Graeco–Latin square method), we identified specific mechanical boundary conditions to computationally reconstruct EL buckling in the circumferential direction of the aorta. Additionally, it was shown that EL waviness almost vanished when ~20% strain (mimicking a circumferential stretch due to intravascular pressure) was applied to the buckled FE model obtained in the in vitro unloaded state. This feature is beneficial for numerical modeling of the detailed aortic wall structure, because the entire process is computationally efficient and can be readily implemented in a commercially available FE solver. Although further study is required, our findings will help clarify the roles of the EL and SML in the aortic wall and promote the understanding of the mechanisms of the medial tissue stress response. In addition, we expect this modeling technique to serve as a useful tool in the future for interpreting stress distribution relevant to vascular physiology at normal and pathological states.