S.J. Hwang

Human Mesenchymal Stromal Cells are Mechanosensitive to Vibration Stimuli

Low-magnitude high-frequency (LMHF) vibrations have the ability to stimulate bone formation and reduce bone loss. However, the anabolic mechanisms that are mediated by vibration in human bone cells at the cellular level remain unclear. We hypothesized that human mesenchymal stromal cells (hMSCs) display direct osteoblastic responses to LMHF vibration signals. Daily exposure to vibrations increased the proliferation of hMSCs, with the highest efficiency occurring at a peak acceleration of 0.3 g and vibrations at 30 to 40 Hz. Specifically, these conditions promoted osteoblast differentiation through an increase in alkaline phosphatase activity and in vitro matrix mineralization. The effect of vibration on the expression of osteogenesis-related factors differed depending on culture method. hMSCs that underwent vibration in a monolayer culture did not exhibit any changes in the expressions of these genes, while cells in three-dimensional culture showed increased expression of type I collagen, osteoprotegerin, or VEGF, and VEGF induction appeared in 2 different hMSC lines. These results are among the first to demonstrate a dose-response effect upon LMHF stimulation, thereby demonstrating that hMSCs are mechanosensitive to LMHF vibration signals such that they could facilitate the osteogenic process.

Osteogenic Responses of Human Mesenchymal Stromal Cells to Static Stretch

Molecular signals driving the regenerative process in distraction osteogenesis (DO) involve a complex system of cellular behavior triggered by mechanical strain. However, it remains unclear how mesenchymal stromal cells (MSCs) adapt to osteogenic demands during DO. We hypothesized that human MSCs (hMSCs) modulate early osteogenic metabolism during exposure to static stretch. The proliferation of hMSCs was increased by static stretch, which, in turn, suppressed TGF-β1-mediated decreases in cell proliferation. The amount of stretching force applied had little effect on osteoblast differentiation of hMSCs induced by dexamethasone treatment. However, this strain induced sustained production of nitric oxide and vascular endothelial growth factor (VEGF), which are critical factors in angiogenesis, from differentiated hMSCs. Mechanical stretch involved ERK and p38 mitogen-activated protein kinase pathways, the selective inhibitors of which decreased static-stretch-induced VEGF production. These findings provide evidence that hMSCs act to facilitate early osteogenic metabolism during exposure to static stretch.

Efficacy of rhBMP-2/Hydroxyapatite on Sinus Floor Augmentation A Multicenter, Randomized Controlled Clinical Trial

The aim of this randomized single-blinded active-controlled clinical study was to evaluate the early efficacy of low-dose Escherichia coli–derived recombinant human bone morphogenetic protein 2 (rhBMP-2) soaked with hydroxyapatite granules (BMP-2/H) as compared with an inorganic bovine bone xenograft (ABX) in maxillary sinus floor augmentation. In a total of 127 subjects who were enrolled at 6 centers, maxillary sinus floors were augmented with 1 mg/mL of rhBMP-2 (0.5 to 2.0 mg per sinus) and BMP-2/H (0.5 to 2.0 g; n = 65) or with ABX alone (0.5 to 2.0 g; n = 62). Core biopsies were obtained 3 mo after the augmentation surgery and were analyzed histomorphometrically. The mean new bone formation with BMP-2/H and ABX augmentation was 16.10% ± 10.52% and 8.25% ± 9.47%, respectively. The BMP-2/H group was noninferior to the ABX group; the lower limit of the 1-sided 97.5% confidence interval for the difference between the 2 groups was calculated as 4.33%, which was greater than the prespecified noninferiority margin of −3.75%. An additional test with the Wilcoxon rank-sum test with a 2-sided 5% significance level showed that bone formation between the 2 groups was significantly different (P < 0.0001). The soft tissue and residual graft areas showed no significant differences between the groups. With regard to safety, no significant difference between the 2 groups was observed; there was no significant increase in the amount of rhBMP-2 antibody in the serum after BMP-2/H grafting. Our study suggested that low-dose Escherichia coli–derived rhBMP-2 with hydroxyapatite was effective in early stages for enhanced bone formation after maxillary sinus floor augmentation without harmful adverse events (Clinicaltrials.gov NCT01634308).

Balancing of humanoid robot using contact force/moment control by task-oriented whole body control framework

Balancing control of humanoid robots is of great importance since it is a necessary functionality not only for maintaining a certain position without falling, but also for walking and running. For position controlled robots, the for-ce/torque sensors at each foot are utilized to measure the contact forces and moments, and these values are used to compute the joint angles to be commanded for balancing. The proposed approach in this paper is to maintain balance of torque-controlled robots by controlling contact force and moment using whole-body control framework with hierarchical structure. The control of contact force and moment is achieved by exploiting the full dynamics of the robot and the null-space motion in this control framework. This control approach enables compliant balancing behavior. In addition, in the case of double support phase, required contact force and moment are controlled using the redundancy in the contact force and moment space. These algorithms are implemented on a humanoid legged robot and the experimental results demonstrate the effectiveness of them.

Approach of Team SNU to the DARPA Robotics Challenge finals

This paper presents the technical approaches including the system architecture and the controllers that have been used by Team SNU at the DARPA Robotics Challenge (DRC) Finals 2015. The platform THORMANG we used is a modular humanoid robot developed by ROBOTIS. On top of this platform, Team SNU developed the iris camera module and the end effector with passive palm in order to increase success rate of the tasks at the DRC Finals. Also, we developed the software architecture to operate the robot intuitively, in spite of degraded communication. The interface enables operator to select sensor data to be communicated during each task. These efforts on the hardware and the software reduce operation time of the tasks, and increase reliability of the robot. Finally, the controllers for THORMANG were developed to consider stability as the first priority, because the humanoid robot for rescue should perform complex tasks in unexpected environments. The proposed approaches were verified at the DRC Finals 2015, where Team SNU ranked 12th place out of 23 teams.

Power-Assisted Wheelchair With Gravity and Friction Compensation

In this paper, a gravity compensated power-assisted wheelchair (GCPAW) is proposed, which will climb a hill, and stop, and make as a delicate movement in the middle of the hill as it can do on a flat surface. To climb the hill, the proposed GCPAW compensates for the parallel component of the force of gravity (the force that causes acceleration or deceleration) on a hill. A tilt sensor measures the angle of the inclined plane and electric clutches automatically connect and disconnect drive mechanisms with the wheels. The GCPAW also compensates for friction in the drive mechanism that would cause additional resistance. The rider propels the GCPAW in the same way that he/she would propel a manual wheelchair, but the mechanism compensates for both gravity and the friction. Additionally, overcompensation for the friction helps the riders propulsion, so that with the same propulsion force the rider travels further than in a manual wheelchair, resulting in an easier movement for the rider.

Aesthetic design and development of humanoid legged robot

This paper presents a new full sized humanoid leg robot that combines aesthetics and design theory with practical research goals in robotics. The research goal of the robot is to create human-like and compliant motion in multiple contact situations through the use of torque controlled joints. Low gear ratio and direct connections are used at each joint for low-friction and back-drivability but without explicit joint torque sensors. On the other hand, in creating human-like motions, not only technical specifications but also aesthetic design is important as the same performance of the robot can be perceived very differently depending on the design. The aesthetic design is, in this paper, achieved by the robot design process using an integrated design and frame through multi-axis CNC machining. The unique integration of the frame and design also drastically reduces parts and complexity of assembly for easy maintenance. In this paper, the design process and features are presented with range of motion, weight, and key aesthetic decisions. Compliant motion capability is demonstrated by experimental results.

Team SNU's Control Strategies for Enhancing a Robot's Capability: Lessons from the 2015 DARPA Robotics Challenge Finals

This paper presents the technical approaches used and experimental results obtained by Team SNU Seoul National University at the 2015 DARPA Robotics Challenge DRC Finals. Team SNU is one of the newly qualified teams, unlike 12 teams who previously participated in the December 2013 DRC Trials. The hardware platform THORMANG, which we used, has been developed by ROBOTIS. THORMANG is one of the smallest robots at the DRC Finals. Based on this platform, we focused on developing software architecture and controllers in order to perform complex tasks in disaster response situations and modifying hardware modules to maximize manipulability. Ensuring stability and modularization are two main keywords in the technical approaches of the architecture. We designed our interface and controllers to achieve a higher robustness level against disaster situations. Moreover, we concentrated on developing our software architecture by integrating a number of modules to eliminate software system complexity and programming errors. With these efforts on the hardware and software, we successfully finished the competition without falling, and we ranked 12th out of 23 teams. This paper is concluded with a number of lessons learned by analyzing the 2015 DRC Finals.

Whole Body Vibration Reduces Inflammatory Bone Loss in a Lipopolysaccharide Murine Model

Whole body vibration (WBV) stimulation has a beneficial effect on the recovery of osteoporotic bone. We aimed to investigate the immediate effect of WBV on lipopolysaccharide (LPS)–mediated inflammatory bone loss by varying the exposure timing. Balb/C mice were divided into the following groups: control, LPS (L), and LPS with vibration (LV). The L and LV groups received LPS (5 mg/kg) by 2 intraperitoneal injections on days 0 and 4. The LV group was exposed to WBV (0.4 g, 45 Hz) either during LPS treatment (LV1) or after cessation of LPS injection (LV2) and then continued WBV treatment for 10 min/d for 3 d. Evaluation based on micro–computed tomography was performed 7 d after the first injection, when the L group showed a significant decrease in bone volume (−25.8%) and bone mineral density (−33.5%) compared with the control group. The LV2 group recovered bone volume (35%) and bone mineral density (19.9%) compared with the L group, whereas the LV1 group showed no improvement. This vibratory signal showed a suppressive effect on the LPS-mediated induction of inflammatory cytokines such as IL-1β or TNF-α in human mesenchymal stem cells in vitro. These findings suggest that immediate exposure to WBV after the conclusion of LPS treatment efficiently reduces trabecular bone loss, but WBV might be less effective during the course of treatment with inflammatory factor.

Terrain edge detection for biped walking robots using active sensing with vCoP-position hybrid control

Abstract Perception of terrain is one of the most important technical impediments for biped robots to locomote in human environments. Perception error exists due to imperfect exteroceptive devices causing issues such as limited viewing angles or occlusion of visual sensors. This error can cause unexpected contact between the robot and the environment. The reaction wrenches from unexpected contact negatively affect the control and balance of the biped robot. In this study, active sensing method is proposed to estimate the edges of the contact terrain using robot link geometry information. By generating proper active motion that maintains the contact, the geometric information of the contact link is collected to estimate the edge of the contact terrain. To recognize contact and calculate its geometry, a multi-modal sensory strategy with 6 degrees of freedom (DOF) force/torque sensors at robot ankles and joint encoders is proposed. The concept of virtual Center-of-Pressure (vCoP) is utilized to generate active motion of the foot while maintaining the contact. To prevent loss of balance during active motion, the normal force condition of the vCoP is taken into account and the contact moment of the supporting foot is controlled. The operational space control scheme for a floating-base robot is adopted to apply compliant motion and vCoP-position hybrid control framework. The proposed method is verified by experiments using a 12-DOF biped robot to estimate the edge line of a block that has contact with the robot foot.