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.

Keywords

Neuron, Stretch stimulation, Strain, Three dimensional cell culture system, Axonal extension, Enhancement

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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.

Keywords

Ankle contracture, Stretching, Ankle stretching machine, Rotation axis, At-home rehabilitation

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[Advance Publication] (Proper information for citation will be announced after formal publication)

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.

Keywords

Bathtub, Soaking posture, Biomechanical load, Joint torque, Biomechanics, Ergonomics

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[Advance Publication] (Proper information for citation will be announced after formal publication)