Micro/nanoplastics (MPs/NPs) in the environment exhibit various effects on ecosystems as well as living organisms, such as immune system toxicity. To understand the effects of MPs/NPs experimentally, preparing synthetic MPs/NPs with their geometrical morphology closely similar to the MPs/NPs present in natural environments and with specific material composition is necessary. A pin-on-disc method with plastic pins and micro-textured glass discs has been employed to generate MPs/NPs with defined composition for biological tests. However, these previous studies did not clarify the repeated elastic deformation and stress distribution inside the pin causing the fatigue of degraded areas. Accordingly, in this study, MPs/NPs were generated using a pin-on-disc method, and the interfacial pressure of the pin and disc and the micro-texture pattern were assessed as factors that could change the elastic deformation and the stress distribution inside the pin; additionally, how these factors affect the MP/NP geometrical morphology were investigated. Polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyethylene terephthalate were used as test materials. Almost all the MPs/NPs of these materials had a fragmented morphology. Further, these MPs/NPs were compared to those identified and they showed almost the same geometrical morphology as the fragmented MPs/NPs in the environment. The equivalent circle diameters of the generated MPs/NPs were suggested to be affected by micro-textures on the discs, which promoted fatigue failure. Additionally, by increasing the interfacial pressure, the stress was distributed deeper inside the pin depending on the plastic materials, which accelerated the crack propagation and generated a large amount of MPs/NPs. From these results, the fragmented morphology of MP/NP which is similar to those present in environments is expected to be generated with defined morphology and material composition for application to biological tests.

Recent advancements in motion measurement systems have facilitated the analysis of kinematic techniques in sports, emphasizing the importance of motion control for performance enhancement. Ground reaction forces and moments are crucial in biomechanical analysis, and are typically measured using force plates. However, conventional force plates pose limitations in winter sports due to their impracticality on ice. To address this, various methods have been explored, including skates equipped with strain gauges and pressure-sensitive insoles. Despite advancements, simultaneous measurement of forces and moments in three axes remains a challenge. In this study, we developed a new wearable system capable of comprehensively measuring the forces and moments during skating by attaching three wearable force plates between the boot and the blade. The precision of this measurement system was validated through an experiment employing a conventional force plate, demonstrating its high accuracy. On-ice trials confirmed the system's efficacy in capturing dynamic movements like forward sliding and half-turn jumps. The six-component force was successfully measured during skating motions, a task that is challenging with conventional systems. This system offers a promising avenue for nuanced biomechanical analysis in figure skating, facilitating insights into performance optimization and injury prevention.

This study presents a computational model that simulates the responses of tactile afferents, which are essential for designing tactile devices in addition to understanding the mechanism of tactile perception of vibrotactile stimuli. We employed finite element method analysis to simulate skin deformation accurately, and the leaky integrate-and-fire model to simulate the neural dynamics of tactile afferents. Previous studies using these models have failed to model the responses of tactile afferents to vibrotactile stimuli; therefore, we developed a computational model that can better reproduce the neural responses to vibrotactile stimuli, considering the appropriate filters. We subsequently validated this model by calculating the firing rates of tactile afferents in response to several vibrotactile stimuli. Our proposed computational model outperformed conventional models when evaluated using the averaged root mean square error. Overall, our results demonstrate the potential of our method to model the activities of tactile afferents and will provide insights into the development of not only computational neural models but also tactile devices.

The global demand for assistive devices to support individuals with disabilities is increasing, yet their accessibility remains limited. Self-help devices (SHDs), particularly for handwriting tasks, play a pivotal role in enhancing independence. This study presents a semi-automated method for producing personalized handwriting SHDs, thereby reducing the need for occupational therapists (OTs) to possess advanced technical skills and enabling them to concentrate on patient care. Ten healthy participants, simulating upper limb dysfunctions by restricting their finger joint mobility with bandages, are recruited for the study. OTs assess measurements that encompass manual measurements, automatic joint recognition, and 3D scanning for digital representation. This process facilitates the development of a personalized SHD 3D model, utilizing 3D CAD software. The SHD model is designed to be adaptable, allowing adjustments based on the individual's unique hand measurements. The 3D model, composed of six primary components, is then fabricated using 3D printing technology. The streamlined process, from measurement to production, reduces design and printing time to approximately two hours. Testing focuses on handwriting speed and letter legibility, with participants reporting enhanced comfort and a significant increase in handwriting speed using our SHD compared to conventional SHDs. Furthermore, users experienced improved letter legibility in addition to a significant increase in handwriting speed with our SHD. The study's innovation promises to broaden the reach of personalized assistive devices and allows OTs to better focus on patient care, improving therapy outcomes.

This study proposes a motion analysis method for human-machine systems involving contact phenomena. When human skin comes into surface contact with objects, the flexibility of the skin and the friction between the epidermis and the object can result in different state distributions on the skin surface, such as stick/slip and contact/floating. We introduce a discretized model for motion analysis to express the state distributions and internal deformations. In the proposed method, contact phenomena, including friction, are formulated as a mathematical problem called the linear complementarity problem (LCP), and the flexibility of the skin is modeled using a mass-spring-damper model. We propose a hybrid integration method (Moreau’s midpoint method for epidermis motion analysis and the Runge-Kutta method for subcutaneous tissue motion analysis) to simultaneously address non-smooth phenomena such as friction and large deformations. In this method, the motion of the epidermis and subcutaneous tissue affect each other via virtual springs and dampers. As a preliminary investigation, real motion measurements are conducted for a fingertip sliding on a plane surface to verify the phenomena occurring on the skin. Subsequently, the analysis using the proposed method revealed trends similar to those observed in the motion measurements, demonstrating the effectiveness of the proposed method for analyzing the motion of skin in contact with objects.

Osteoarthritis (OA) of the thumb carpometacarpal (CMC) joint is a common disease in hand OA. Low joint congruity could increase articular stress in the CMC joint and is thus considered among the risk factors for CMC OA. However, this relationship has not been clarified. This study aimed to examine whether low joint congruity correlated with high stress on the articular surface of the CMC joint. CT images were obtained for 14 healthy subjects in eight static limb positions during flexion and extension, and 3D CMC joint models were created. First, cross-sectional images of the CMC joint in the dorsal–volar and radial–ulnar directions were acquired, and the curvature radius ratio between the trapezium and the first metacarpal was then calculated as the joint congruity from these images using image processing and curve fitting. Subsequently, a finite element (FE) model was created, and the maximum value of compressive stress was evaluated. Finally, the correlation coefficients between joint congruity and compressive stress were assessed. As a result, a negative correlation was found between the joint congruity in the volar–dorsal direction and the compressive stress in the trapezium (R = -0.648, p<0.001), showing that low congruity increases the compressive stress on the articular surface of the trapezium. This finding suggests that a low joint congruity contributes to the onset of CMC OA. This could help predict the risk of OA and improve treatments and prevention measures for CMC OA.

According to medical statistics, sacroiliac joints (SIJs) appear to be the source of low back pain in 15 - 30% of cases. The SIJs are located at the junction between the sacrum and the ilium, supported by strong ligaments and with low mobility. Due to unexpected external force or repeated impact, pain may arise from the SIJ region (SIJ dysfunction). The treatment to cure SIJ dysfunction includes nonsurgical approaches as well as surgery with implants (SIJ fixation). Previous studies have assessed the consequences of SIJ fixation, but no simulation study so far has been performed during walking. The SIJ is burdened with variant loads during walking. In this given study, walking conditions were replicated in a finite element model of the pelvis combined with 3D walking analysis data. The simulation mimicked two types of unilateral SIJ fixation: anterior fixation with a plate implant and screws (model A) and posterior fixation with a rod, a cage and screws (model P). Equivalent stress of the SIJ and the loading of the SIJ ligaments decreased in the fixed models. In these fixed pelves, the slight motion on the SIJ decreased. The reduction rates on equivalent stress, ligament loads and equivalent stress were low during the swing phase. In addition, the efficiency of fixations was mostly same on anterior and posterior fixations. It can be concluded that the stronger fixation reduces the loading but also may have a greater impairment effects on walking.