Bionic legs – direct nerve stimulation restores natural limb touch and motion sensations
Commercially available prostheses do not elicit any sensory feedback, risking falls and loss of confidence in the prosthesis. Amputees rely mostly on the intact limb, producing asymmetrical walking which causes long-term arthritis, osteoporosis and back pain alongside reduced mobility and increased fatigue. Moreover, the lack of any physiological connection between the prosthesis and the nervous system of the patient causes phantom limb pain.
A prosthesis that restores the feeling of touch and motion
To address this issue, the EU-funded SensAgain project designed an innovative neuroprosthesis that brings back the feeling of the lost limb. The project was coordinated by SensArs Neuroprosthetics and relied on the SENSY technology developed during the NEBIAS project. Originally designed for hand amputees to give the user back sensations of a lost hand, the SENSY technology was further developed and adapted for lower limb prosthetics. As co-founder and CEO of SensArs Neuroprosthetics, Francesco Petrini explains: “The solution to more natural, controllable prostheses is interfacing the device with peripheral nerves which remain anatomically and functionally intact after amputation.″ The neuroprosthesis comprises an insole placed under the foot of the leg prosthesis used by the patient and an external controller which receives the pressure information from the insole and the movement information from the prosthetic leg. This information is then transduced through an implantable stimulating system, interfaced to the patient nerves. The signals are transmitted to the nerves through small impulses of current. As Petrini puts it, “SENSY communicates in the language of the nervous system″. Then nature does the rest: the signals from the nerves are conveyed to the brain of the subjects which are able to perceive the touch and movement from the lower limb prosthesis. “The prototype was clinically validated in three lower-limb amputees with very encouraging results with a consortium of European experts in neurology, neuroscience, neuroengineering, surgery and technology,″ continues Petrini. The results of this pilot trial were featured in Science Translation Medicine and Nature Medicine in 2019. Patients felt sensations of touch from more than 20 locations of the foot sole, and contraction from four muscles of the leg. These sensations, triggered by the sensors added to the prosthesis, allowed patients to reduce the risk of falls and increase mobility. The prosthesis was perceived as a continuation of the body and not as an external device as usually happens with commercial solutions. This increased the confidence in using the device and reduced the cognitive burden in controlling the prosthesis.
Future prospects
Collectively, the SensAgain team worked to solve the limitations of presently available lower limb prosthetic devices by interfacing the nervous system with the machines themselves and restoring sensations from the missing leg. This will not only provide disabled persons with a unique device for rehabilitation, but will also boost prosthetic adoption. Considering that limb amputees suffer from additional co-morbidities including arthritis, osteoporosis and back pain, the SENSY prosthesis that restores limb functionality is expected to improve overall patient health. SensArs has received additional funds from the European Commission through the GoSafe project that started in November 2019. Following finalisation of the industrial prototype, SENSY will be validated in animals and a larger clinical trial will be conducted. Clinical results are expected by the end 2022 and will be used to certify the device for commercialisation.
Keywords
SensAgain, limb, prosthesis, amputee, SENSY, electrode, sensory feedback