Scientists develop wearable robotic system to restore hand function

Researchers at the Medical University of Vienna, in collaboration with ETH Zurich, the Technical University of Munich and Medical Faculty Belgrade, have developed a wearable neurorobotic system that combines electrical neurostimulation with hand exoskeletons. In a clinical trial involving 14 patients with hand impairments caused by neurological injury, the technology supported finger mobility, tactile perception and grip control. The results demonstrate the potential of personalised assistive systems for people living with the consequences of spinal cord or brain injury. The study has recently been 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 sufficient 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 has developed the "SensoExo" system for assisting people with hand sensorimotor impairements. It combines a wearable hand exoskeleton with a custom-fitted neurostimulation sleeve. The sleeve stimulates specific nerves and muscles in the forearm through the skin. Sensors on the fingers detect touch and gripping forces and translate this information into electrical stimulation, providing users with tactile feedback. In addition, functional electrical stimulation can assist users open and close their fingers more easily.

Our aim was not only to provide mechanical support for movement, but also to restore their sense of touch. The interplay of strength, movement and the sense of touch is crucial, particularly when gripping. 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

Individualized support depending on the impairment

The system was tested on 14 patients with neurological hand impairments. All study participants exhibited sensory deficits and therefore received tactile feedback via transcutaneous electrical nerve stimulation. In seven individuals with particularly severe motor impairments, functional electrical muscle stimulation was also used to support hand opening and grip strength.

The study compared three conditions: no support, support from an exoskeleton alone, and the combined use of an exoskeleton and neurostimulation. Eight of the 14 participants also completed functional grasping and releasing tasks with bulky and fragile objects. This investigation revealed that the combination of exoskeleton and neurostimulation provided additional benefits compared to an exoskeleton alone. In patients with severe motor impairment, SensoExo improved finger mobility to a greater extent than the exoskeleton alone. The artificially mediated tactile feedback also increased the areas of the hand where touch 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 depending on the individual's impairment profile. People with more severe motor impairments benefited particularly from additional motor support, while those with pronounced sensory loss used the sensory feedback to grasp fragile objects more precisely."

Improved grasping of everyday objects

In the functional tests, participants using SensoExo achieved the highest success rates when grasping and carrying objects. With bulky objects, muscle stimulation supported grip strength. With fragile objects, sensory feedback helped to avoid applying too much pressure.

"The technology is currently a prototype and not a fully developed medical device for everyday use," emphasises Raspopovic. "However, the study provides early clinical evidence that non-invasive neurostimulation combined with wearable robotics can form a realistic basis for future personalised assistance systems."

In addition to MedUni Vienna, research teams of Lorenzo Masia at Technical University of Munich and Olivier Lambercy from ETH Zurich developed exoskeletons, while the team of Ljubica Kostadinovic from Medical Faculty Belgrade supported the clinical assessments. Future investigations involving larger patient groups, 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 everyday life over the long term.