The goal of the MoreGrasp project was to develop a sensoric grasp neuroprosthesis to support the daily life activities of people living with severe to completely impaired hand function due to spinal cord injuries. The motor function of a neuroprosthesis was to be intuitively controlled by means of a brain-computer interface with emphasis on natural motor patterns. After three years, the breakthrough was reported by the members of the project consortium led by Gernot Müller-Putz, head of the Institute of Neural Engineering at TU Graz, which include the University of Heidelberg, the University of Glasgow, the two companies Medel Medizinische Elektronik and Bitbrain as well as the Know Center.
Gernot Müller-Putz says, “In tetraplegia, all the circuits in the brain and muscles in the body parts concerned are still intact, but the neurological connection between the brain and limbs is interrupted. We bypass this by communicating via a computer, which in turn, passes on the command to the muscles.” The muscles are controlled and encouraged to move by electrodes that are attached to the outside of the arm and can, for example, trigger the closing and opening of the fingers. The key was the sufficient distinguishability of the brainwaves to control the neuroprosthesis. For instance, if the participant thought about raising and lowering their foot and the signal measured by the EEG opened the right hand, the subject then—for instance—would think of a movement of the left hand and the right hand would close again.
The MoreGrasp consortium developed this technique further. This mental ‘detour’ of any distinguishable movement pattern is no longer necessary, as Müller-Putz explains: “We now use so-called ‘attempted movement.'” In doing so, the test subject attempts to carry out a movement like grasping a glass of water. Due to the tetraplegia, the brain signal is not passed on, but can be measured by means of an EEG and processed by the computer system. Müller-Putz is extremely pleased with the success of the research. He says, “We are now working with signals that only differ from each other very slightly. Nevertheless, we have managed to control the neuroprosthesis successfully. For users, this results in a completely new possibility of making movement sequences easier—especially during training. A variety of grips were investigated in the project: the palmar grasp (cylinder grasp, as for grasping a glass), the lateral grasp (key grasp, as for picking up a spoon), and opening the hand and turning it inwards and outwards.
End users can register on the special online platform to enter a large-scale feasibility study intended to check compatibility of the technique in everyday life. Participants eligible for the study will be tested according to a complex procedure. Afterward, each subject will be provided with a tailor-made BCI training course which must be completed independently in sessions lasting several hours each week. In this way, brain signals will be gathered and the system itself will learn during each experiment.
Hybrid rehabilitation robotics combine neuro-prosthetic devices (close-loop functional electrical stimulation systems) and traditional robotic structures and actuators to explore better therapies and promote a more efficient motor function recovery or compensation. Although hybrid robotics and ankle neuroprostheses (NPs) have been widely developed over the last years, there are just few studies on the use of NPs to electrically control both ankle flexion and extension to promote ankle recovery and improved gait patterns in paretic limbs. The aim of this work is to develop an ankle NP specifically designed to work in the field of hybrid robotics. This article presents early steps towards this goal and makes a brief review about motor NPs and Functional Electrical Stimulation (FES) principles and most common devices used to aid the ankle functioning during the gait cycle. It also shows a current sources analysis done in this framework, in order to choose the best one for this intended application.
Non-invasive neuroprosthetic (NP) technologies for movement compensation and rehabilitation remain with challenges for their clinical application. Two of those major challenges are selective activation of muscles and fatigue management. This review discusses how electrode arrays improve the efficiency and selectivity of functional electrical stimulation (FES) applied via transcutaneous electrodes. In this paper we review the principles and achievements during the last decade on techniques for artificial motor unit recruitment to improve the selective activation of muscles. We review the key factors affecting the outcome of muscle force production via multi-pad transcutaneous electrical stimulation and discuss how stimulation parameters can be set to optimize external activation of body segments. A detailed review of existing electrode array systems proposed by different research teams is also provided. Furthermore, a review of the targeted applications of existing electrode arrays for control of upper and lower limb NPs is provided. Eventually, last section demonstrates the potential of electrode arrays to overcome the major challenges of NPs for compensation and rehabilitation of patient-specific impairments.
Fig. 2 Two versions of SMARTEX electrode. Single electrode array version right corner and 4-electrode array garment for full upper limb sFES applications
A new generation of orthotic and prosthetic devices has started to include active elements capable of providing (or removing) energy to compensate and enhance human function. In this regard, the application of human muscles as actuators of orthotic systems by surface Functional Electrical Stimulation (sFES) is a promising technology . FES systems were introduced as a method to externally activate the sensory-motor system in case of central nervous system (CNS) lesion [2, 3]. FES systems can be applied as motor neuroprostheses of motor functions for recovery in stroke patients [4, 5] or as means for compensation in assistive technologies, for example for control of walking and grasping after spinal cord injury (SCI)  or tremor suppression . In general, available sFES systems for motor neuroprostheses face two major limitations, in addition to skin irritation and pain: a) insufficient selective activation of muscles and b) muscle fatigue as a reaction to muscle stimulation . These two challenges remain open and the goal of this review is to assess the recent progress of research groups to overcome these limitations.
Consequently, the following question arises: How can selective and less fatiguing muscle activation be achieved with surface electrode arrays The review of the literature in this article is aimed to answer this question, providing a detailed revision of the state-of-the-art on selective sFES technology, their benefits, advantages and challenges. This work aims to revise both the available surface electrode arrays and the applied control strategies on this kind of sFES applications. The structure of this article is the following. Functional electrical stimulation and selectivity section provides an overview of the theoretical basis of sFES activation; feasibility of selective muscle activation through sFES is discussed. In Electrodes for muscle activation selectivity section novel solutions to design surface electrodes to improve muscle selectivity are revised. Selective control of muscle activation section presents a list of candidate applications of surface array electrodes in motor rehabilitation while Discussion section discusses in detail the current technology applied in most relevant available systems that address selective activation of muscles. Finally, conclusions are presented in Conclusions section.