A non-invasive wearable sensory leg neuroprosthesis: mechanical, electrical and functional validation.

Objective . Lower limb amputees suffer from a variety of functional deficits related to the absence of sensory communication between the central nervous system and the lost extremity. Indeed, they experience high risk of falls, asymmetric walking and balance, and low prosthesis embodiment, that significantly decrease their quality of life. Presently, there are no commercially available devices able to provide sensory feedback to leg amputees but recently some invasive solutions (i.e. requiring surgery) have been proposed by different research groups. However, a non-invasive effective alternative exploitable in everyday life is still missing. Approach . To address this need we developed and tested a lightweight, non-invasive, wearable technology (NeuroLegs) providing sensory (i.e. knee angle joint and tactile) feedback to the users through electro-cutaneous stimulation. Standard mechanical and electrical tests were performed to assess the safety and reliability of the technology. The NeuroLegs system was verified in terms of accuracy in measuring relevant gait parameters in healthy participants. The effectiveness of the NeuroLegs system at improving walking of three transfemoral amputees was then verified in movement laboratory tests. Main results . No mechanical failures, stable communication among system's parts and a long-lasting battery were demonstrated. A high temporal reliability was found when detecting stride features (important for the real-time configuration) with a correct match to the walking cadence in all assessed walking conditions. Finally, transfemoral amputees showed increased temporal gait symmetry and augmented confidence when walking with the sensory feedback compared to no feedback condition. Stepping outside from the lab, NeuroLegs was successfully exploited by a transfemoral amputee in CYBATHLON Global Edition 2020 in several challenging situations related to daily-living activities. Significance . Our results demonstrate that the NeuroLegs system provides the user with useful sensory information that can be successfully exploited in different walking conditions of daily life.