Researchers at the Medical University of Vienna, in collaboration with ETH Zurich, the Technical University of Munich and the Medical School of Belgrade, have developed a wearable neurorobotic system that combines electrical neurostimulation with hand exoskeletons. In a clinical trial involving 14 patients with hand disabilities caused by neurological injury, the technology supported finger mobility, tactile perception and grip control. The results demonstrate the potential of personalized support systems for people living with the consequences of a spinal cord or brain injury. The study was recently published in the journal Science Advances.
Hand movements and the sense of touch are essential for everyday activities such as grasping, eating, dressing or personal hygiene. However, after damage to the central nervous system, motor and sensory impairments of the hand often persist. Conventional rehabilitation can achieve improvements, but does not always lead to adequate restoration of hand function. There is therefore a great need for assistive technologies suitable for everyday use.
A research team led by study director Stanisa Raspopovic from the Center for Medical Physics and Biomedical Engineering at MedUni Vienna developed the ‘SensoExo’ system to assist people with sensorimotor hand disabilities. It combines a wearable hand exoskeleton with a custom neurostimulation sleeve. The sleeve stimulates specific nerves and muscles in the forearm through the skin. Sensors on the fingers detect touch and grip forces and translate this information into electrical stimulation, providing users with tactile feedback. In addition, functional electrical stimulation can help users open and close their fingers more easily.
Our goal was not only to provide mechanical support for movement, but also to restore their sense of touch. The interplay of force, movement and the sense of touch is vital, particularly when grasping. Without feedback on how firmly an object is being held, hand function remains significantly limited in everyday life.”
Stanisa Raspopovic, Center for Medical Physics and Biomedical Engineering, MedUni Vienna
Personalized support according to impairment
The system was tested on 14 patients with neurological damage to the hands. All study participants had sensory deficits and therefore received tactile feedback via transcutaneous electrical nerve stimulation. In seven subjects with particularly severe motor disabilities, functional electrical muscle stimulation was also used to support hand opening and grip strength.
The study compared three conditions: no support, support from only an exoskeleton, and combined use of an exoskeleton and neurostimulation. Eight of the 14 participants also completed operant catch-and-release tasks with bulky and fragile objects. This research revealed that the combination of an exoskeleton and neurostimulation provided additional benefits compared to an exoskeleton alone. In patients with severe motor dysfunction, the SensoExo improved finger mobility to a greater extent than the exoskeleton alone. Artificially mediated tactile feedback also increased the areas of the hand where tactile sensations could be perceived.
“The results show that motor assistance and sensory feedback must be considered together,” explains lead author Andrea Cimolato from the Center for Medical Physics and Biomedical Engineering at MedUni Vienna. “The system can be adapted to the person’s impairment profile. People with more severe motor impairments particularly benefited from the additional motor support, while those with severe sensory loss used the sensory feedback to more accurately grasp fragile objects.”
Improved perception of everyday objects
In functional tests, participants using SensoExo achieved the highest success rates when grasping and carrying objects. With bulky objects, muscle stimulation supported grip strength. With the fragile objects, the sensory feedback helped to avoid excessive pressure.
“The technology is currently a prototype and not a fully developed medical device for everyday use,” emphasizes Raspopovic. “However, the study provides early clinical evidence that non-invasive neurostimulation combined with wearable robotics may provide a realistic basis for future personalized assistance systems.”
In addition to MedUni Vienna, research groups of Lorenzo Masia at the Technical University of Munich and Olivier Lambercy from ETH Zurich developed exoskeletons, while Ljubica Kostadinovic’s group from the Medical School of Belgrade supported the clinical evaluations. Future research involving larger groups of patients, grouped more specifically according to the type and severity of their symptoms, will help determine the robustness of these effects and assess the extent to which such systems can be integrated into rehabilitation and daily life in the long term.
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