With the increase in the elderly, stroke has become a common disease, often leading to motor dysfunction and even permanent disability. Lower-limb rehabilitation robots can help patients to carry out reasonable and effective training to improve the motor function of paralyzed extremity. In this paper, the developments of lower-limb rehabilitation robots in the past decades are reviewed. Specifically, we provide a classification, a comparison, and a design overview of the driving modes, training paradigm, and control strategy of the lower-limb rehabilitation robots in the reviewed literature. A brief review on the gait detection technology of lower-limb rehabilitation robots is also presented. Finally, we discuss the future directions of the lower-limb rehabilitation robots.

/pdf/robotics-in-lower-limb-rehabilitation-after-stroke-6wlou3sse3.pdf

Robotics in Lower-Limb Rehabilitation after Stroke

The delivery of brain-controlled neuromodulation therapies during motor rehabilitation may augment recovery from neurological disorders. To test this hypothesis, we conceived a brain-controlled neuromodulation therapy that combines the technical and practical features necessary to be deployed daily during gait rehabilitation. Rats received a severe spinal cord contusion that led to leg paralysis. We engineered a proportional brain–spine interface whereby cortical ensemble activity constantly determines the amplitude of spinal cord stimulation protocols promoting leg flexion during swing. After minimal calibration time and without prior training, this neural bypass enables paralyzed rats to walk overground and adjust foot clearance in order to climb a staircase. Compared to continuous spinal cord stimulation, brain-controlled stimulation accelerates and enhances the long-term recovery of locomotion. These results demonstrate the relevance of brain-controlled neuromodulation therapies to augment recovery from motor disorders, establishing important proofs-of-concept that warrant clinical studies. Brain–spine interfaces have been used to enable leg movement following spinal cord injury, but movement is either involuntary or not adjustable. Here, the authors show in rats that a proportional stimulation interface permits voluntary movement and augments recovery in conjunction with rehabilitation.

/pdf/brain-controlled-modulation-of-spinal-circuits-improves-1d3edftery.pdf

Brain-controlled modulation of spinal circuits improves recovery from spinal cord injury

The closed-loop control of rehabilitative technologies by neural commands has shown a great potential to improve motor recovery in patients suffering from paralysis. Brain-machine interfaces (BMI) can be used as a natural control method for such technologies. BMI provide a continuous association between the brain activity and peripheral stimulation, with the potential to induce plastic changes in the nervous system. Paraplegic patients, and especially the ones with incomplete injuries, constitute a potential target population to be rehabilitated with brain-controlled robotic systems, as they may improve their gait function after the reinforcement of their spared intact neural pathways. This paper proposes a closed-loop BMI system to control an ambulatory exoskeleton–without any weight or balance support–for gait rehabilitation of incomplete spinal cord injury (SCI) patients. The integrated system was validated with three healthy subjects, and its viability in a clinical scenario was tested with four SCI patients. Using a cue-guided paradigm, the electroencephalographic signals of the subjects were used to decode their gait intention, and to trigger the movements of the exoskeleton. We designed a protocol with a special emphasis on safety, since patients with poor balance were required to stand and walk. We continuously monitored their fatigue and exertion levels, and conducted usability and user-satisfaction tests after the experiments. The results show that, for the three healthy subjects, 84.44□14.56% of the trials were correctly decoded. Three out of the four patients performed at least one successful BMI session, with an average performance of 77.61□14.72%. The shared control strategy implemented (i.e., the exoskeleton could only move during specific periods of time) was effective in preventing unexpected movements during periods in which patients were asked to relax. On average, 55.22□16.69% and 40.45□16.98% of the trials (for healthy subjects and patients, respectively) would have suffered from unexpected activations (i.e., false positives) without the proposed control strategy. All the patients showed low exertion and fatigue levels during the performance of the experiments. This paper constitutes a proof-of-concept study to validate the feasibility of a BMI to control an ambulatory exoskeleton by patients with incomplete paraplegia (i.e., patients with good prognosis for gait rehabilitation).

/pdf/control-of-an-ambulatory-exoskeleton-with-a-brain-machine-hbt6vsiqmm.pdf

Control of an Ambulatory Exoskeleton with a Brain–Machine Interface for Spinal Cord Injury Gait Rehabilitation

Smart implants are envisioned to revolutionize personal health care by assessing physiological processes, for example, upon wound healing, and communicating these data to a patient or medical doctor. The compactness of the implants is crucial to minimize discomfort during and after implantation. The key challenge in realizing small-sized smart implants is high-volume cost- and time-efficient fabrication of a compact but efficient antenna, which is impedance matched to 50 Ω, as imposed by the requirements of modern electronics. Here, we propose a novel route to realize arrays of 5.5-mm-long normal mode helical antennas operating in the industry-scientific-medical radio bands at 5.8 and 2.4 GHz, relying on a self-assembly process that enables large-scale high-yield fabrication of devices. We demonstrate the transmission and receiving signals between helical antennas and the communication between an antenna and a smartphone. Furthermore, we successfully access the response of an antenna embedded in a tooth, mimicking a dental implant. With a diameter of ~0.2 mm, these antennas are readily implantable using standard medical syringes, highlighting their suitability for in-body implant applications. Helical antennas that are just 5.5 millimetres long have been developed for use in smart medical implants by scientists in Germany. Smart implants are set to transform personal health care by monitoring physiological processes and relaying data to medical workers. It is critical for such implants to be compact, but miniaturizing antenna has proved challenging. Now, researchers based in Dresden have applied strain engineering to polymer–metal heterostructures to achieve large scale high yield fabrication of compact helical antennas that are about five times smaller than conventional two-dimensional dipole antennas. They demonstrate transmission and reception of signals between a pair of antennas as well as between an antenna and smartphone. They also show that the antenna can be addressed when embedded in a tooth model. The small size of the antennas permits them to be implanted using standard medical syringes. We fabricated compact helical antenna operating in the industry-scientific-medical radio band. With a total length of only 5.5 mm, it is about five times smaller compared with the conventional dipole antenna. The transmission and receiving signals between helical antennas and the communication between a helical antenna and a smartphone is reported. Owing to the shape and dimensions, we successfully demonstrate the possibility to address the antenna, when embedded in a tooth, as well as to implant the antenna using standard medical syringes. These demonstrations highlight the potential of helical antennas for medical applications as components of smart system implants.

/pdf/compact-helical-antenna-for-smart-implant-applications-4spa2h428c.pdf

Compact helical antenna for smart implant applications

Contrary to cats and primates, cortical contribution to hindlimb locomotor movements is not critical in rats. However, the importance of the motor cortex to regain locomotion after neurological disorders in rats suggests that cortical engagement in hindlimb motor control may depend on the behavioral context. To investigate this possibility, we recorded whole-body kinematics, muscle synergies, and hindlimb motor cortex modulation in freely moving rats performing a range of natural locomotor procedures. We found that the activation of hindlimb motor cortex preceded gait initiation. During overground locomotion, the motor cortex exhibited consistent neuronal population responses that were synchronized with the spatiotemporal activation of hindlimb motoneurons. Behaviors requiring enhanced muscle activity or skilled paw placement correlated with substantial adjustment in neuronal population responses. In contrast, all rats exhibited a reduction of cortical activity during more automated behavior, such as stepping on a treadmill. Despite the facultative role of the motor cortex in the production of locomotion in rats, these results show that the encoding of hindlimb features in motor cortex dynamics is comparable in rats and cats. However, the extent of motor cortex modulations appears linked to the degree of volitional engagement and complexity of the task, reemphasizing the importance of goal-directed behaviors for motor control studies, rehabilitation, and neuroprosthetics.

https://www.jneurosci.org/content/jneuro/36/40/10440.full.pdf

Engagement of the Rat Hindlimb Motor Cortex across Natural Locomotor Behaviors.

A brain-machine interface (BMI) is a neuroprosthetic device that can restore motor function of individuals with paralysis. Although the feasibility of BMI control of upper-limb neuroprostheses has been demonstrated, a BMI for the restoration of lower-limb motor functions has not yet been developed. The objective of this study was to determine if gait-related information can be captured from neural activity recorded from the primary motor cortex of rats, and if this neural information can be used to stimulate paralysed hindlimb muscles after complete spinal cord transection. Neural activity was recorded from the hindlimb area of the primary motor cortex of six female Sprague Dawley rats during treadmill locomotion before and after mid-thoracic transection. Before spinal transection there was a strong association between neural activity and the step cycle. This association decreased after spinal transection. However, the locomotive state (standing vs. walking) could still be successfully decoded from neural recordings made after spinal transection. A novel BMI device was developed that processed this neural information in real-time and used it to control electrical stimulation of paralysed hindlimb muscles. This system was able to elicit hindlimb muscle contractions that mimicked forelimb stepping. We propose this lower-limb BMI as a future neuroprosthesis for human paraplegics.

/pdf/a-brain-machine-muscle-interface-for-restoring-hindlimb-3o7sjk2iom.pdf

A Brain-Machine-Muscle Interface for Restoring Hindlimb Locomotion after Complete Spinal Transection in Rats

Background: Lower motor neurons in the spinal cord lose supraspinal inputs after complete spinal cord injury, leading to a loss of volitional control below the injury site. Extensive locomotor training with spinal cord stimulation can restore locomotion function after spinal cord injury in humans and animals. However, this locomotion is non-voluntary, meaning that subjects cannot control stimulation via their natural “intent”. A recent study demonstrated an advanced system that triggers a stimulator using forelimb stepping electromyographic patterns to restore quadrupedal walking in rats with spinal cord transection. However, this indirect source of “intent” may mean that other non-stepping forelimb activities may false-trigger the spinal stimulator and thus produce unwanted hindlimb movements. Methods: We hypothesized that there are distinguishable neural activities in the primary motor cortex during treadmill walking, even after low-thoracic spinal transection in adult guinea pigs. We developed an electronic spinal bridge, called “Motolink”, which detects these neural patterns and triggers a “spinal” stimulator for hindlimb movement. This hardware can be head-mounted or carried in a backpack. Neural data were processed in real-time and transmitted to ac omputer for analysis by an embedded processor. Off-line neural spike analysis was conducted to calculate and preset the spike threshold for “Motolink” hardware. Results: We identified correlated activities of primary motor cortex neurons during treadmill walking of guinea pigs with spinal cord transection. These neural activities were used to predict the kinematic states of the animals. The appropriate selection of spike threshold value enabled the “Motolink” system to detect the neural “intent” of walking, which triggered electrical stimulation of the spinal cord and induced stepping-like hindlimb movements. Conclusion: We present a direct cortical “intent”-driven electronic spinal bridge to restore hindlimb locomotion after complete spinal cord injury.

/pdf/electronic-bypass-of-spinal-lesions-activation-of-lower-3m7vawkia4.pdf

Electronic bypass of spinal lesions: activation of lower motor neurons directly driven by cortical neural signals.

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A Brain-Machine-Muscle Interface for Restoring Hindlimb Locomotion after Complete Spinal Transection in Rats

Electronic bypass of spinal lesions: activation of lower motor neurons directly driven by cortical neural signals.