Introduction to robotics for medical professionals

The course “Introduction to robotics for medical professionals” aims to present a common ground for students of medical and engineering disciplines alike. This will pave the way for further disciplinary integration of medical professionals in theresearch, development, and effective use of medical robotics. Medical professionals and students will better understand the basic robotics principles and can more efficiently contribute to interdisciplinary teams working on the development andimplementation of healthcare robotics. The underlying objective of this chapter is to facilitate further adoption of robotics in healthcare environments. As medical professionals will be able to better understand the potential and limitations of robotics, they may provide complementary insights to engineers and roboticists, and actively collaborate in robotic projects

Center of mass velocity-based predictions in balance recovery following pelvis perturbations during human walking

In many simple walking models foot placement dictates the center of pressure location and ground reaction force components, whereas humans can modulate these aspects after foot contact. Because of the differences, it is unclear to what extend predictions made by models are valid for human walking. Yet, both model simulations and human experimental data have previously indicated that the center of mass (COM) velocity plays an important role in regulating stable walking.\ud \ud Here, perturbed human walking was studied for the relation of the horizontal COM velocity at heel strike and toe-off with the foot placement location relative to the COM, the forthcoming center of pressure location relative to the COM, and the ground reaction forces. Ten healthy subjects received various magnitude mediolateral and anteroposterior pelvis perturbations at toe-off, during 0.63 and 1.25 m s−1 treadmill walking.\ud \ud At heel strike after the perturbation, recovery from mediolateral perturbations involved mediolateral foot placement adjustments proportional to the mediolateral COM velocity. In contrast, for anteroposterior perturbations no significant anteroposterior foot placement adjustment occurred at this heel strike. However, in both directions the COM velocity at heel strike related linearly to the center of pressure location at the subsequent toe-off. This relation was affected by the walking speed and was, for the slow speed, in line with a COM velocity based control strategy previously applied by others in a linear inverted pendulum model. Finally, changes in gait phase durations suggest that the timing of actions could play an important role during the perturbation recovery

Vestibular contributions to lateral stabilization are bilaterally dependent during split belt walking

Vestibular information is critical for maintaining balance during locomotion, and is known to be attenuated with increasing locomotor velocity and cadence. This attenuation is muscle and phase dependent, and is thought to reflect the functional contribution of each muscle to balance control during each stride of the gait cycle. Bilaterally, the vestibular coupling is mirrored relative to the gait cycle as each leg undergoes similar modulation with variation in phase, velocity and cadence. Here, we asked whether the modulation of the vestibular contribution to each limb is bilaterally dependent. By using a split-belt treadmill with asymmetric belt speeds, we can control the locomotion properties of each leg and compare the vestibular modulation to symmetric conditions. We hypothesized that bilaterally symmetric vestibular modulation would indicate leg independent vestibular influence while bilaterally asymmetric vestibular modulation would indicate leg dependent vestibular influence. Subjects were exposed to binaural bipolar stochastic vestibular stimulation (0-25 Hz) during symmetric and asymmetric walking conditions. Symmetric trials were performed at belt speeds of 0.4 and 0.8 m/s and for 10 min. The asymmetric trial was performed at belt speeds of 0.4 and 0.8 m/s for 16 min. Subjects walked with a cadence of 78 steps/min which was easily maintained in both limbs. EMG of the bilateral medial gastrocnemii and three-dimensional ground reaction force and torques were collected. Only the last 340 strides (~ 9 min of data) were used in the analysis to avoid the adaptation that typically occurs within the first 250 strides (~ 6 min) of asymmetric walking. Significant muscle activity and lateral ground reaction forces (P < 0.01) were correlated to the input stimuli in all trials. Stimulus-EMG and -lateral ground reaction force correlations decreased at higher belt speeds during symmetric walking, as previously reported. During the split belt condition, the magnitude of correlations stimulus-EMG and -force were bilaterally asymmetric and different from their symmetric counterparts. During the asymmetric condition correlations decreased for the slow leg, but more closely resembled the responses observed during slow symmetric walking, and increased for the fast leg, but more closely resembled the responses observed during fast symmetric walking. These results indicate that the modulation of vestibular reflexes is dependent upon the specific kinematics of each leg but bilaterally linked to respond to the properties of the locomotion pattern

Assisting Human Balance in Standing With a Robotic Exoskeleton

This letter presents an experimental study on balance recovery control with a lower limb exoskeleton robot. Four participants were subjected to a perturbation during standing, a forward force impulse applied to their pelvis that forced them to step forward with the right leg for balance recovery. Trials with and without exoskeleton assistance to move the stepping legs thigh were conducted to investigate the influence of the exoskeletons control assistance on balancing performance and a potential adaptation. Analysis of the body kinematics and muscle activation demonstrates that robotic assistance: first, was easy to use and did not require learning, nor inhibited the healthy stepping behavior; second, it modified the stepping leg trajectories by increasing hip and knee movement; third, increased reaction speed and decreased the step duration; and finally, generally increased biceps femoris and rectus femoris muscle activity

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Maintaining sagittal plane balance compromises frontal plane balance during reactive stepping in people post-stroke

Background. Maintaining balance in response to perturbations during walking often requires the use of corrective responses to keep the center of mass within the base of support. The relationship between the center of mass and base of support is often quantified using the margin of stability. Although people post-stroke increase the margin of stability following perturbations, control deficits may lead to asymmetries in regulation of margins of stability, which may also cause maladaptive coupling between the sagittal and frontal planes during balance-correcting responses. Methods. We assessed how paretic and non-paretic margins of stability are controlled during recovery from forward perturbations and determined how stroke-related impairments influence the coupling between the anteroposterior and mediolateral margins of stability. Twenty-one participants with post-stroke hemiparesis walked on a treadmill while receiving slip-like perturbations on both limbs at foot-strike. We assessed anteroposterior and mediolateral margins of stability before perturbations and during perturbation recovery. Findings. Participants walked with smaller anteroposterior and larger mediolateral margins of stability on the paretic versus non-paretic sides. When responding to perturbations, participants increased the anteroposterior margin of stability bilaterally by extending the base of support and reducing the excursion of the extrapolated center of mass. The anteroposterior and mediolateral margins of stability in the paretic limb negatively covaried during reactive steps such that increases in anteroposterior were associated with reductions in mediolateral margins of stability. Interpretation. Balance training interventions to reduce fall risk post-stroke may benefit from incorporating strategies to reduce maladaptive coupling of frontal and sagittal plane stability

Direct measurement of the intrinsic ankle stiffness during standing

Ankle stiffness contributes to standing balance, counteracting the destabilizing effect of gravity. The ankle stiffness together with the compliance between the foot and the support surface make up the ankle-foot stiffness, which is relevant to quiet standing. The contribution of the intrinsic ankle-foot stiffness to balance, and the ankle-foot stiffness amplitude dependency remain a topic of debate in the literature. We therefore developed an experimental protocol to directly measure the bilateral intrinsic ankle-foot stiffness during standing balance, and determine its amplitude dependency. By applying fast (40 ms) ramp-and-hold support surface rotations (0.005–0.08 rad) during standing, reflexive contributions could be excluded, and the amplitude dependency of the intrinsic ankle-foot stiffness was investigated. Results showed that reflexive activity could not have biased the torque used for estimating the intrinsic stiffness. Furthermore, subjects required less recovery action to restore balance after bilateral rotations in opposite directions compared to rotations in the same direction. The intrinsic ankle-foot stiffness appears insufficient to ensure balance, ranging from 0.93±0.09 to 0.44±0.06 (normalized to critical stiffness ‘mgh’). This implies that changes in muscle activation are required to maintain balance. The non-linear stiffness decrease with increasing rotation amplitude supports the previous published research. With the proposed method reflexive effects can be ruled out from the measured torque without any model assumptions, allowing direct estimation of intrinsic stiffness during standing

Reduced center of pressure modulation elicits foot placement adjustments, but no additional trunk motion during anteroposterior-perturbed walking

Understanding balance during human gait is complicated by the abundance of recovery options. Among all possible recovery options, three main strategies are often considered for human balance control, being the ankle, hip, and foot placement strategies. All can be addressed when balance is threatened during walking, but their relative importance remains uncertain. We have previously shown that healthy human subjects did not significantly adjust their foot placement relative to the body's center of mass (COM) in the first recovery step following anteroposterior pelvis perturbations, as compared to unperturbed walking. An ankle strategy could have contributed to the recovery instead.Here the goal is to further elucidate balance strategy preferences by investigating the stepping and hip strategies following these anteroposterior perturbations, but with an ankle strategy made ineffective. This was achieved by physically blocking each ankle and minimizing the support area of each foot through a pair of modified ankle-foot orthoses. These "pin-shoes" enabled stilt-like walking and ensured that foot placement adjustment was the only way to modulate the center of pressure location, comparable to "footless" inverted pendulum models of walking.Despite the pin-shoes, subjects did not additionally address a hip strategy compared to normal walking, but relied on foot placement adjustments instead. The observed foot placement adjustments were furthermore in line with concepts derived from a linear inverted pendulum model of walking. These results suggest low hip strategy priority when a foot placement strategy is available, while the latter can be predicted with concepts derived from a simple walking model