Toshihiko Shiraishi

For the regeneration of the central nervous system, neural stem cells have been proposed as graft donors. Conventional studies have used biochemical factors to induce their differentiation into neurons and to enhance axon elongation. However, few studies have been reported on the effects of mechanical factors on neural stem cells. In this study, we show that mechanical vibration directs the differentiation of neural stem cells into neuronal cells, elongates their axons, and increases the number of differentiated cells. We found that the 25 Hz and 0.5 G vibration promoted the differentiation of neural stem cells into neuronal-marker-positive cells expressing neurofilament heavy polypeptide by 2.5-fold compared to the control conditions and increased the number of differentiated cells with axons longer than 10 μm by 1.5-fold at 7 days of culture. Furthermore, we found that the total number of differentiated and undifferentiated cells in the vibration condition reached 2.9-fold more than the control condition and that this effect depended on the frequency and acceleration. We anticipate our system to facilitate further studies using mechanical vibration such as regenerative therapy using neural stem cells and the elucidation of differentiation mechanisms in neural stem cells.

Introduction: Traditional speech separation algorithms used time–frequency (T-F) masks. Recently, deep neural networks, which are generally called deep learning, have been used to estimate T-F masks, and the separation performance has been improved owing to it. However, a conventional deep learning approach that achieved the high separation performance requires a large number of parameters because its network is composed of recurrent neural networks (RNNs) which have recurrent and full connections. This is a disadvantage because the low memory consumption is desired in the case of using speech separation algorithms for actual applications. Because of this shortcoming, we proposed a novel network architecture that balances both the high separation performance and the low memory cost. Methods: The proposed network is composed of convolutional neural networks (CNNs) which have a sparse connection instead of RNNs to reduce the number of parameters. Additionally, aiming to achieve the high separation performance, we designed the proposed network for speech separation to make it possible to learn the feature of speech. We evaluated the separation performance for each network on the task of separating two-speaker mixture. Results: In the simulation results, the separation performance of the proposed network was competitive with one of conventional ones with the highest separation performance regardless of realizing the more than 80% reduction of the number of parameters. Conclusion: The results indicated that the proposed network is superior to a conventional one considering the cost-performances of both the speech separation performance and the memory cost.

We present an intelligent foot orthosis (IFO) designed to prevent lateral falls during walking by employing a magnetorheological (MR) fluid brake. This study aims to demonstrate the feasibility of evaluating effectiveness of the proposed orthosis in fall prevention. Seventeen healthy adults underwent four conditions: (1) without IFO, (2) with IFO and current-OFF, (3) with IFO current-ON, and (4) with IFO and control-ON. Gait was assessed by three-dimensional motion capture and with ground reaction force. Postural changes on the frontal plane were measured, and the mediolateral center of gravity and center of pressure inclination angle (ML COG-COP IA) was calculated. Additionally, tibialis anterior (TA) and peroneus longus (PL) muscle activity during walking were measured using surface electromyography. Results indicate a significant increase in ML COG-COP IA in (3). No significant differences were found in muscle activity between conditions. The study suggests that the posture's deviation from the lateral fall direction in (3) is primarily due to wearing the IFO, emphasizing human postural control over muscle activity. A negative correlation between ML COG-COP IA and TA muscle activity under (4), implies that individuals with lower TA muscle activity may benefit more from IFO fall prevention. In conclusion, the study demonstrates the feasibility of preventing lateral falls in human walking using the proposed orthosis with an MR fluid brake. The general efficacy of the orthosis in lateral fall prevention is suggested, emphasizing the need for further development.

Mechanical vibration has been shown to regulate cell proliferation and differentiation in vitro and in vivo. However, the mechanism of its cellular mechanotransduction remains unclear. Although the measurement of intracellular deformation dynamics under mechanical vibration could reveal more detailed mechanisms, corroborating experimental evidence is lacking due to technical difficulties. In this study, we aimed to propose a real‐time imaging method of intracellular structure deformation dynamics in vibrated adherent cell cultures and investigate whether organelles such as actin filaments connected to a nucleus and the nucleus itself show deformation under horizontal mechanical vibration. The proposed real‐time imaging was achieved by conducting vibration isolation and making design improvements to the experimental setup; using a high‐speed and high‐sensitivity camera with a global shutter; and reducing image blur using a stroboscope technique. Using our system, we successfully produced the first experimental report on the existence of the deformation of organelles connected to a nucleus and the nucleus itself under horizontal mechanical vibration. Furthermore, the intracellular deformation difference between HeLa and MC3T3‐E1 cells measured under horizontal mechanical vibration agrees with the prediction of their intracellular structure based on the mechanical vibration theory. These results provide new findings about the cellular mechanotransduction mechanism under mechanical vibration.

We investigated a damping switching control law with simplicity and high performance for semi-active suspension with time delay. The present law simply switches damping according to the sign of the condition function of ( + ₀) using target and base velocity and ₀, respectively, whereas a skyhook-based law does it by ( − ₀). We conducted the simulations and experiments of vibration suppression for a single degree-of-freedom system with a semi-active magnetorheological damper to compare both the law. The key findings of this study are as follows: (1) In the time delay of 10–100 ms, the ON–OFF control using the present law maintains the vibration suppression performance under sine excitations although that using a skyhook-based law degrades it increasing with time delay. At least, over the time delay of 50 ms, the present law has the vibration suppression performance higher than a skyhook-based law in the overall range of frequency ratio of 0–4. (2) The velocity-proportional damping control using the present law shows the vibration suppression performance higher than or equal to the ON–OFF control using the present law under sine excitations. (3) Under a road surface excitation, the velocity-proportional damping control using the present law shows the ideal vibration suppression performance that the response displacement in the control is equal to that in the ON state around the natural frequency and close to that in the OFF state over the frequency ratio of √2.

Cartilage regenerative medicine requires time and effort to regenerate thick hyaline cartilage. In this study, we investigated the effects of mechanical vibrations on chondrocyte proliferation and cartilage matrix production to simplify the regenerative medicine procedure. Chondrocytes were harvested from the metatarsophalangeal joints of pigs. Isolated chondrocytes were cultured in a monolayer without a scaffold for up to 26 days. Mechanical vibrations at 12.5, 25, and 50 Hz of 0.5 G were applied to a culture plate. Cell morphology, cell counting, tissue staining of proteoglycan and type II collagen, and real-time reverse transcription polymerase chain reaction were performed. The target genes were type II collagen, aggrecan, SOX9, type I collagen, and fibronectin. No significant difference in cell counts was observed at any of the measurement dates. Tissue staining showed that the cultured cartilage tissue contained hyaline cartilage matrices. The 25 Hz and 0.5 G mechanical vibration significantly increased the gene expression levels of type II collagen, aggrecan, fibronectin, and type I collagen by approximately 4.4, 3.4, 3.2, and 4.8 folds, respectively, compared to the static state. This suggests that the 25 Hz and 0.5 G mechanical vibration is beneficial for cultured cartilage transplantation in a simple procedure, providing the cultured cartilage with more hyaline cartilage characteristics, higher adhesion to cartilage defects, and greater strength than in the static state. Additionally, the gene expression levels of type I and II collagens at 25 Hz were significantly higher than those at 12.5 Hz and 50 Hz under the 0.5 G mechanical vibrations. This indicates that mechanical vibrations have a frequency-dependent effect on the gene expression of type I and II collagens.

Ultrasound therapy is advantageous because it is a noninvasive treatment for the body. Low-intensity pulsed ultrasound can aid fracture healing. We focus on phased array transducers (PATs) to render force fields and realize the improvement in medical equipment to enhance this therapy. This can both render an arbitrary acoustic field and quickly change it by controlling the output and phase of each transducer. There are some algorithms for controlling PATs; however, the effectiveness of these algorithms is limited at sparse control points. We propose a novel algorithm to control PATs at many and close control points in this research. We compare the proposed algorithm with previous ones and assess the avoidance of negative effects outside the target area. The findings show that the proposed algorithm achieves both excellent reconstruction performance and low computational cost, and it can render an acoustic field sufficient to prevent negative effects on the body.