Continuous use of wearable robots can cause skin injuries beneath the cuffs of robots. To prevent such injuries, understanding the contact behavior of the cuff is important. Thus far, this contact behavior has not been studied because of the difficulty involved in measuring the slippage under the cuff. In this study, for the first time, the relative displacement, slippage, and interaction force and moment at the thigh cuff of a robot during sit-to-stand motion were measured using an instrumented cuff, which was developed for this purpose. The results indicated that the slippage and relative displacement under the cuff was uneven because of the rotation of the cuff, which suggests that the risk of skin injuries is different at different positions. Especially, the skin closer to the hip showed larger dynamism, with a maximum slippage of approximately 10 mm and a displacement of 20 mm during motion. Another important phenomenon was the individual difference among subjects. During motion, the interaction force, moment, and slippage of some subjects suddenly increased. Such behavior results in stress concentration, which increases the risk of skin injuries. These analyses are intended to understand how skin injuries are caused and to design measures to prevent such injuries.

Most lower-limb physical assistant robots are fixed to wearers using cuffs. Hence, skin injuries beneath the cuffs are one of the major concerns of the users. A model that describes the relationship between the body posture and the interaction forces at the cuff was developed for use in assessing the risk of injury and improving user comfort. We measured the motion and interaction force beneath cuffs during the sitting and standing motions of subjects and a physical assistant robot which has been hardly reported thus far. Because of slippage and biomechanical motion, a traditional spring-damper model was found to be insufficient to describe the interaction forces associated with the measured motion of the cuffs. A parameter representing the motion or the knee joint angle was added to take into account these factors. Our model for estimation of the interaction forces using a spring, a damper, and the attitude of the lower leg fits the measured data especially well for the thigh cuff and is better than the traditional model. The applicability of this model was verified for several assist modes and wearers. The model was found to describe approximately 90% of the burden on the wearer, which reached a peak of approximately 60 N, the most hazardous condition. Having been validated for a commercial assistant robot, the model can be used to estimate the skin burdens beneath the cuffs without any force-sensitive elements. Graphical Abstract

This study aimed to elucidate the ultrastructural role of Gla proteins in bone mineralization by means of a warfarin-administration model. Thirty-six 4-week-old male F344 rats received warfarin (warfarin group) or distilled water (control group), and were fixed after 4, 8 and 12 weeks with an aldehyde solution. Tibiae and femora were employed for histochemical analyses of alkaline phosphatase, osteocalcin and tartrate-resistant acid phosphatase, and for bone histomorphometry and electron microscopy. After 4, 8 and 12 weeks, there were no marked histochemical and histomorphometrical differences between control and warfarin groups. However, osteocalcin immunoreactivity was markedly reduced in the warfarin-administered bone. Mineralized nodules and globular assembly of crystalline particles were seen in the control osteoid. Alternatively, warfarin administration resulted in crystalline particles being dispersed throughout the osteoid without forming mineralized nodules. Immunoelectron microscopy unveiled lower osteocalcin content in the warfarin-administered osteoid, which featured scattered crystalline particles, whereas osteocalcin was abundant on the normally mineralized nodules in the control osteoid. In summary, Gla proteins appear to play a pivotal role in the assembly of mineralized nodules.

Interaction forces between a robotic cuff and the skin during assisted walking with a lower limb exoskeleton may cause skin injuries over time, such as blisters and ulcers. This study proposes a sensing cuff that can monitor the contact behavior between the exoskeleton and skin during assisted walking, and a functional test and assisted walking experiments were conducted to evaluate the performance of the proposed device. The functional test of the sensing cuff showed good performance of capturing the contact behavior for safety evaluation. The walking experiment involved subjects walking on a treadmill with a lower limb exoskeleton under different conditions (i.e., walking speed and clothing), and the sensing cuff attached to the exoskeleton measured the interaction forces and slip velocity. The magnitude of shear force in the movement direction peaked near the beginning and within 40 – 50% of the gait cycle. The contact safety of the lower limb exoskeleton during assisted walking was then evaluated based on the calculated shear stress. The designed sensing cuff could provide sufficient information regarding contact behavior and contact safety during assisted walking.

Understanding the tribological phenomena when fingers slide over soft surfaces such as skin is important for many practical applications. Therefore, this article analyzed the coefficients of friction for a bare finger sliding over artificial skin with different hardness under dry and lubricated surface conditions. This article contrasts with previous research that predominantly analyzed the contact between skin and hard surfaces or probes. Under dry conditions, the coefficient of friction was constant for artificial skins that were harder than the finger pad, irrespective of the normal force of the finger. However, the coefficient of friction decreased with increasing normal force for softer artificial skins. When the surface of the artificial skin model was lubricated with mica, the coefficient of friction exhibited normal-force dependence only for soft artificial skins, similar to the observations under dry conditions. This effect was due to the deformation friction; thus, the coefficient of friction increased as the normal force increased. Conversely, when the model was lubricated with ${\mathrm{ TiO}}_2$, the coefficient of friction depended on the normal force for all hardness levels. These findings provide insights into the friction experienced during skin-skin or skin-soft material contact under dry and lubricated conditions that can easily occur in daily life. Thus, the results of this study can be useful for the development of skin care products or assistive robots involving human-robot contact.

The elderly gait encompasses several disorders, including a lower minimum toe clearance (MTC) to the ground, which is a potential cause of tripping and falling while walking. Devices that assist in the MTC could reduce such risks. However, the development of effective assistive methods and their evaluation in the elderly might jeopardize their safety. To address this, young adults could take the place of the elderly. We present Muscle Activity Restriction Taping Technique (MARTT) that was devised to simulate the healthy-elderly gait characteristics in the young adults, particularly the lower MTC, by restricting the activity of lower-limb muscles. Two different restriction approaches, one that restricts muscles at the shank and the other at the shank and thigh, simultaneously, were tested at different walking speeds. Both approaches achieved a reduction in the MTC, regardless of the walking speed. The MTC was reduced to a median value lower than 10.1 mm, which is within the range of the MTC values reported for the elderly. The reduction of the MTC significantly increased toe contact to the ground. With the restriction of the shank muscles, the toe-contact frequency was more than twice as that in normal walking, and with the restriction of both the shank and thigh muscles, more than five times. In addition, MARTT reproduced the lower step length, the lower single support phase, and the joint motion compensation characteristic of the elderly gait, in the youth.