MUNDUS project: MUltimodal neuroprosthesis for daily upper limb support

Abstract

Background: MUNDUS is an assistive framework for recovering direct interaction capability of severely motor impaired people based on arm reaching and hand functions. It aims at achieving personalization, modularity and maximization of the user's direct involvement in assistive systems. To this, MUNDUS exploits any residual control of the end-user and can be adapted to the level of severity or to the progression of the disease allowing the user to voluntarily interact with the environment. MUNDUS target pathologies are high-level spinal cord injury (SCI) and neurodegenerative and genetic neuromuscular diseases, such as amyotrophic lateral sclerosis, Friedreich ataxia, and multiple sclerosis (MS). The system can be alternatively driven by residual voluntary muscular activation, head/eye motion, and brain signals. MUNDUS modularly combines an antigravity lightweight and non-cumbersome exoskeleton, closed-loop controlled Neuromuscular Electrical Stimulation for arm and hand motion, and potentially a motorized hand orthosis, for grasping interactive objects.

Methods: The definition of the requirements and of the interaction tasks were designed by a focus group with experts and a questionnaire with 36 potential end-users.

Results: The functionality of all modules has been successfully demonstrated. User's intention was detected with a 100% success. Averaging all subjects and tasks, the minimum evaluation score obtained was 1.13 ± 0.99 for the release of the handle during the drinking task, whilst all the other sub-actions achieved a mean value above 1.6. All users, but one, subjectively perceived the usefulness of the assistance and could easily control the system. Donning time ranged from 6 to 65 minutes, scaled on the configuration complexity.

Conclusions: The MUNDUS platform provides functional assistance to daily life activities; the modules integration depends on the user's need, the functionality of the system have been demonstrated for all the possible configurations, and preliminary assessment of usability and acceptance is promising.

Figure 1

MUNDUS concept.

Figure 2

The exoskeleton. a) Digital mock-up of the exo-Version 2; b) The exo worn by a test participant in a wheelchair.

Figure 3

The hand module. a) The stimulation arrays embedded in the garment: MD, medial distal, and MP, medial proximal for finger flexion (indifferent electrode A); LD, lateral distal, and LP, lateral proximal for finger extension (indifferent electrode B); T, thenars, and P, palmar (indifferent electrode C). b) The robotic hand orthosis.

Figure 4

Modules integration in the three scenarios. Two examples of modules integration are depicted in the flowcharts corresponding to the different user scenarios. In all the flowcharts the subject block shows the condition of the user: red body districts are impaired, while green ones have still residual functional ability. The upper flowchart is referred to scenario 1. The lower flowchart is representative of both scenario 2 and 3.

Figure 5

Tests on subject FS001. Subject FS001 movement phases during the drinking task (Additional file 2). From left to right: initial position (a), reaching of the cup (b), grasping of the cup (c), cup to mouth (d), releasing of the cup (e) and return to initial position (f).

Figure 6

Tests on subject RF002. Subject RF002 angles and EMG signals measured during the drinking task (panels a-c) and the touching the left shoulder task (panels d-f), with the support of the exo. In panels a) and d) the angles profiles are reported, the vertical lines limit the phase of the brakes activation. The correspondent EMG signals of the biceps and anterior deltoid (panels b) and e)) and of the medial and posterior deltoid (panels c) and f))are reported.

Figure 7

Tests on subject RF002. Subject RF002 EMG signals performing the drinking task (panels a-b) and the touching the left shoulder task (panels c-d) without any support. EMG signals of the biceps and anterior deltoid (panels a) and c)) and of the medial and posterior deltoid (panels b) and d)) are reported.

Figure 8

Tests of the arm NMES on subject ND004. Subject ND004 movement phases, stimulation and breaks activation. A complete drinking task is reported. Panels (a-c) report pictures of the subject in the initial position, at the mouth and back to rest position, respectively. In panel d) the angles are reported in solid lines, target angles for each phase of the task are as shadows of the same color of the correspondent angle. In panel e) the levels of stimulation are reported as percentage of the maximal stimulation intensity as set during the identification of the parameters on the subject. Panel f) reports the activation of the brakes; the indicated sentences indicate the ongoing sub-actions.

Figure 9

Tests of the hand module on subject ND004. In panel (a), the force measured at the finger tips (FSR) are shown in terms of raw data having values ranging from 0 to 1023; the stimulation intensities provided to the electrodes arrays inducing the grasping and the opening of the hand are depicted in panels b) and c), respectively.

Figure 10

Tests on subject GD007. An example of the results obtained by patient GD007 during the drinking task supported by the exo, the EMG-based NMES arm module and the hand NMES module (Additional file 8) Panel a) shows the angles of the exoskeleton: shoulder elevation (in blue), shoulder rotation (in red), elbow angle (in green); the dashed black line shows the activation of the brakes; panels b) and c) report the root mean square of the voluntary EMG and the pulse width delivered to the muscles (the biceps and the medial deltoid are reported in panel b) and c) respectively). The activation and deactivation thresholds of the NMES controller are shown in dashed and solid horizontal line respectively. In panels (a-c) the vertical lines indicate the instants in which the subject interacted with the system and delimitate 8 different phases of the movement: 1. approach the object; 2. interaction with MUNDUS CC; 3. open hand and reach the object; 4. grasp object and move to mouth; 5. drink; 6. move back to table; 7. release object and back to rest; 8. relax hand. Data coming from the hand module are reported in the panels on the right: panel d) shows the kinematic raw data (range 0–1023) measured by the instrumented glove at the PIP joints, panel e) reports the raw data (range 0–1023) of the force sensors; the stimulation currents for the muscles involved in the grasping and hand opening are reported in panels f) and g), respectively. In panels d-g the vertical lines indicates the different phases in terms of hand functions.

Figure 11

Tests on subject GC008. An example of the results obtained by subject GC008 while testing the robotic hand orthosis. MetaCarpoPhalangeal (MCP) and the Proximal InterPhalangeal (PIP) joint angles during the GUI-guided calibration and the subsequent testing phase are shown. The MCP joint reference is the only reference signal controlling the two coupled degrees of freedom.