Mechanosensing-based cell orientation and migration in microenvironments, such as microgrooved surfaces, are essential in biological tissue growth and repair. These responses might be cell type-dependent as they are deeply involved in cellular functions. Despite their orientation and migration responses are depended on cell-substrate adhesion, which is deeply involved with focal adhesions (FAs) of cells, we have limited information on the cell behavior on FA-sized microgrooved surfaces. Here, we systematically investigated the cell orientation and migration behavior of primary porcine aortic smooth muscle cells (PASMs), embryonic rat aortic smooth muscle cells with fibroblast-like phenotype (A7r5), and human cervical cancer cells (HeLa) on a substrate comprised of superficial grooves with three widths (1 μm, 5 μm, and 10 μm) and 150-nm depth, which are the same order of magnitude of the three-dimensional size of FAs. PASM and A7r5 cells including thick bundles of actin fibers with elongated FAs showed pronounced cell polarization and directional migration on the 1 and 5 μm wide grooves. PASMs were more sensitive to the superficial grooves than A7r5 cells. HeLa cells adhering to the grooves had non-oriented actin fibers with smaller FAs, and they did not show specific orientation nor directional migration in any groove type. Atomic force microscopy elucidated that the mechanical tension of the actin fibers in live cells had a significant positive correlation with the length/width ratio of FAs, reflecting the cell alignment and directional migration on the grooves. The increase or decrease in the mechanical tension of the actin fibers improved or diminished the mechanosensing for the grooves, respectively. The results strongly suggested that the differences in cell type-specific alignment and migration become much more pronounced on the microgrooves which are similar in three-dimensional size of FA, and that is useful for clarifying slight differences in force-dependent cellular mechanosensing.
The capillary refill time (CRT) is the time that elapses before the fingernail color returns to red from white after releasing a load applied to the nail. We aimed to estimate hypovolemic status using the CRT. However, the precision of CRT is low. The first step toward improving precision was estimation of the coefficient of variance (CV) via repeated measurements. The best and next-best indices of the CRT change rates in the hypovolemic state were 0.19 and 0.48 respectively, and the corresponding target CVs were ≤ 0.10 and 0.24. The CRTs of subjects were measured by imaging nails during loading and unloading and fitting of an exponential function to the curve of intensity changes. The CRT was 0.77 ± 0.35 s (n = 108), which is comparable to previous studies. However, the CV was 0.37 ± 0.13, which is higher than even the second-best index. Thus, we used only the green color channels of nail images to generate algorithms to define the optimal start time of the CRT calculations; this provided a lower CV (0.31 ± 0.12). Finally, we investigated the effects of fingertip temperature and load release timing on CRT during a cardiac cycle. Correction of the temperature effect with a care on a phase during the cardiac cycle to trigger data collection reduced CV to 0.15 ± 0.11, which cleared the second-best index. Thus, our protocol improves CRT precision; it may be possible to estimate hypovolemic status using the CRT.
This study proposes a squatting model that describes the relation between the center of gravity velocity and lower limb muscle forces that contribute to hip and knee flexion-extension and ankle dorsi-plantar flexion during squatting. Squatting exercises are experimentally monitored using a 3D motion analysis system and two force plates. Participants perform a squatting exercise with their feet shoulder-width apart without using a weight such as a barbell. Simulations using the musculoskeletal model calculate the lower limb muscle forces based on measured marker positions and floor reaction forces. The squatting model parameters are determined by a Kalman filter using the experimentally obtained center of gravity velocity, and lower limb muscle forces estimated by the simulations. The analysis results quantitatively demonstrate the contribution of each muscle to the center of gravity velocity during squatting. To verify the model accuracy, the root mean squared errors are calculated by using the center of gravity velocity that is obtained by the squatting model and the 3D motion analysis system. The root mean squared errors indicate that the contribution of each muscle to the center of gravity velocity may have differed between participants and between trials. The proposed method is expected to be utilized to evaluate the relation between the exercise velocity and muscle forces that is different among individual.
Tremolo is a technique to produce the same note continuously in short spans, and is an important technique for musical performance on a mandolin. However, it is not easy for beginners to master this technique, nor is it easy for even expert players to perform a wide range of expressions. There is no unified view on the proper behavior of tremolo playing, and there are no examples of measured tremolo behavior. In this study, we measured the hand movements during tremolo playing on a mandolin. One test subject was included in this study. An inertial sensor was attached to the back of the hand, and the movement was evaluated by the angles which were the time integrated angular velocity on each axis. Tremolo playing is a combination of elbow and wrist motion. We examined how those motions were used for playing strong/weak tones or fast/slow tremolos. The results showed that there was a clear difference in motion between tremolo using the wrist and tremolo using the elbow. The results also suggested that the combination of each joint motion was changed when adjusting the volume and tremolo speed. It indicated that the measurement of hand movements by inertial sensors could be used to evaluate tremolo playing. Our future plan includes a more detailed analysis of the relationship between musical expression and tremolo movement, and an examination of how movement changes with practice.
A passive lower-limb assistive device that supports standing work has been developed to reduce lower limb loads in workers. The device effectively prevents lower limb musculoskeletal disorders such as osteoarthritis and contributes to the improvement of occupational health. However, previous studies have not clarified lumbar load when wearing the device. The present study investigated the effect of a passive lower-limb assistive device on lumbar load and verified the effectiveness of biomechanical analysis for evaluating the physical load while wearing the device. Twelve healthy male participants performed an assembly task under three conditions: standing and high and low sitting while wearing the device. We mainly analyzed the joint torque and joint compression force (JCF) computed using a full-body musculoskeletal model based on measurements obtained from a motion capture system and force platform. The present study concluded that the lumbar load increased when wearing the device because the lumbar joint torque was significantly larger than that for standing. In addition, the biomechanical analysis has the advantage of evaluating the lumbar load when wearing the device because the current method of analyzing muscular activity is not able to evaluate the lumbar load including the effects of passive resistance, such as those generated by ligament force and abdominal pressure. Furthermore, the present method is able to simultaneously investigate physical loads in the lower limb and neck joint based on the analysis of the JCFs in the lower limb and the neck joint torque, which is effective as an analytical method for the effect of the passive lower-limb assistive device on the risk of musculoskeletal disorders.