Forward dynamics simulations can significantly reduce the development costs associated with new wearable assistive devices by minimizing the need for prototyping and experimentation. However, current model-based methods rely on experimental data to define the model posture for the simulation, making it challenging to design the wearer's posture suitable for reducing physical load with passive lower-limb assistive devices. To address this challenge, this study proposes a forward dynamics simulation method that focuses on optimizing physical posture. This simulation approach calculates human-device interactions, including reaction forces, physical posture, and physical load, based on the physical posture optimized by a cost function that evaluates both the physical load and the suitability of the posture for work, which contributes to estimating the impact of the device on the physical load of the wearer. To investigate the validation and advantage of the proposed simulation, this study compared the simulation and experimental results for existing and new passive lower-limb assistive devices. The results show that although the proposed method did not accurately simulate the individual human-device interactions for a given participant using the passive lower-limb assistive device, it accurately estimated the average reaction forces and lower limb posture across all participants. Additionally, the proposed method correctly represented the differences in reaction forces and lower limb posture resulting from changes in device structure. Consequently, the proposed simulation has advantages in computationally evaluating the device’s performance in reducing the lower limb loads and contributes to the development of effective assistive devices for preventing musculoskeletal disorders.

Epithelial folding is a fundamental process governing the transformation of flat epithelial sheets into intricate three-dimensional structures during morphogenesis. This phenomenon plays a pivotal role in the development of various organs across biological systems. Despite its importance, the underlying mechanisms of epithelial folding remain incompletely understood due to its dynamic and complex nature. In recent years, computational simulations have emerged as powerful tools to study epithelial folding, providing a means to test theories, generate predictions, and integrate data from various sources. The basic workflow of simulation-based research involves formulating hypotheses grounded in insights derived from experimental observations, constructing mechanical models based on these hypotheses, conducting simulations, and subsequently comparing simulation results with experimental observations. This review encompasses studies exploring how spatial distributions of contractile cells and temporal histories of growth and contraction contribute to the three-dimensionalization of epithelial sheets by modeling the mechanics of tissue growth and cell contractile forces. Additionally, it addresses the studies examining the impact of asymmetry in physical constraints imposed by the surrounding structures of epithelial sheets and the non-uniformity of growth on the undulation pattern formation of epithelial sheets by modeling the mechanical interaction between the growing tissue and the surrounding structures. Furthermore, a recent advancement proposes a new framework where computations are employed for initial stages of hypothesis formation by inferring the causality. In this context, we also discuss a recent study that quantitatively infers differential growth, causing the morphogenesis, solely from pre- and post-growth shape data. Through this comprehensive review, we demonstrate the utility of simulations in studying epithelial folding, emphasizing their potential for synergistic integration with various perspectives and exploring synergistic opportunities.

In sports, concussion prevention measures require the development of concussion evaluation criteria for improved head protective gear or early intervention through impact measurement in the field. The peak value of the brain strain has been used as a brain strain metric to evaluate the risk of brain injury. However, it extracts the instantaneous moment of strain history experienced by the brain tissue; therefore, it lacks the characteristics of the entire strain waveform experienced by the brain tissue during a head impact. This study developed a new method for classifying concussion cases based on the overall characteristics of the brain strain waveform. First, 53 head collision cases tagged with the concussion status in American football were simulated using a finite element head model, and the brain strain waveforms in four regions (right brain, left brain, brainstem, and cerebellum) were obtained. By applying the dynamic time-warping distance and clustering method to the brain strain waveforms in each case, a concussion classification method that considers the overall characteristics of the waveforms was constructed. The classification evaluation results showed that the concussion classification method had a higher performance than the conventional method using the peak value of brain strain. Brain strain waveforms in concussion cases have multiple high peaks, and it is important to understand the characteristics of the entire brain strain waveform, not just the instantaneous peak value, to classify concussion cases.

Analyzing the biomechanics of the thumb carpometacarpal (CMC) joint is essential for elucidating the etiology of osteoarthritis (OA) and for developing a mechanics-based treatment. This study aimed to identify the areas where the peak stress in the cortical bone is likely to occur during thumb motion. We also investigated whether the stress in the first metacarpal and trapezium differ. CT scan was performed on 11 healthy adult men during flexion and abduction. 3D CMC joint models were created from CT images and then finite element (FE) models under the static compressive force in the bone axial direction of the first metacarpal were constructed. As a result, the peak stress in the cortical bone of the first metacarpal tended to be concentrated in the volar–central region, and that of the trapezium was uniformly distributed across the entire articular surface. Furthermore, the trapezium had higher stress in the cortical bone than the first metacarpal. These results suggest that the volar–central region of the first metacarpal is easily worn, and that the trapezium is evenly worn. These results also suggest that wear is likely to progress from the trapezium.

The pulsed laser used in URS (ureteroscopy) is used effectively in the treatment of urologic diseases such as lithotripsy and benign prostatic hyperplasia. In the case of lithotripsy in a relatively narrow area or prostatectomy, since it is necessary to irradiate the laser near or directly into the tissue through an optical fiber, it is pointed out that thermal damage may be caused to areas other than the affected area. The authors have measured the temperature near the fiber tip and attempted to evaluate the damage to biological tissues using an evaluation method called CEM43℃ (cumulative equivalent minutes at 43℃). In this report, we measured the time-averaged temperature distribution on the wall surface around the bubbles using thermocouples flush-mounted on the wall, and examined the range where the tissue wall is expected to be damaged using CEM43℃. As a result, we found that the possibility of thermal damage could occur in the area in front of the fiber tip. In addition, the thermal damage area is closely related to the contact between the bubbles and the wall surface associated with the characteristic collapse behavior of the bubbles formed near the wall surface.