Each year, thousands of people worldwide experience full or partial paralysis as a result of spinal cord injury. Though there’s currently no medical cure for such injuries, new EU-funded research poses the potential to give patients the ability to walk again, with the aid of a mind-controlled robotic exoskeleton dubbed “Mindwalker.”
The Mindwalker (or Mind-controlled orthosis and VR-training environment for walk empowering) project proposes that the damaged spinal cord be bypassed altogether, instead routing brain signals directly to a robotic exoskeleton in a bid to get patients back on their feet. Its development involved researchers collaborating across several European countries.
“Mindwalker was proposed as a very ambitious project intended to investigate promising approaches to exploit brain signals for the purpose of controlling advanced orthosis, and to design and implement a prototype system demonstrating the potential of related technologies,” explained Michel Ilzkovitz, project coordinator at Space Applications Services in Belgium.
The system implements BNCI (brain-neural-computer interface) technology, which can be used to convert either EEG (electroencephalography) signals from the brain, or EMG (electromyography) signals from patient’s shoulder muscles, into electronic commands. The electronic commands are then used to control an exoskeleton attached to the user’s legs.
Researchers based in the Laboratory of Neurophysiology and Movement Biomechanics at the Université Libre de Bruxelles, and the Foundation Santa Lucia in Italy, researched ways of controlling the exoskeleton, and came up with two practicable methods.
The first is based on a technique referred to as “steady-state visually evoked potential,” which essentially involves the use of flickering visual stimuli to induce correlated EEG signals. These EEG signals are then used to trigger exoskeleton movement commands such as “stand,” “walk,” “faster,” or “slower.”
The second approach involves processing EMG signals generated by the user’s shoulders in order to exploit the natural arm-leg coordination of human walking to convert arm-swing patterns into control signals for the exoskeleton.
The Mindwalker system also utilizes an innovative “dry” technology developed by Berlin-based company eemagine Medical Imaging Solutions, to read the EEG signals. This forgoes the need for invasive electrodes placed into brain tissue, or an awkward “wet” cap, in favor of a cap which is covered in electrodes. The cap can be fitted and worn without discomfort.
Power and poise
Researchers based at the universities of Delft and Twente in the Netherlands were tasked with working on the exoskeleton itself. Required to bear the weight of a 100-kg (220-pound) adult, it’s also designed to have enough poise to recover balance from external causes of instability, such as a gentle push from the back or side. Compared to other exoskeletons developed to date, the Mindwalker exoskeleton is said to be relatively light, weighing under 30 kg (66 pounds) without batteries.
Energy efficiency was maximized with the use of springs inserted in several joints, and these are capable of absorbing and recovering some of the energy otherwise dissipated during walking. The Dutch teams also utilized an efficient strategy for controlling the exoskeleton, known as “limit-cycle walking,” which is said to provide a more natural and balanced gait.
In order to better train users to control the exoskeleton, researchers from Space Applications Services, Belgium, developed a virtual reality training platform, which offers an environment in which new users can safely become accustomed to walking with the exoskeleton.
Looking to the future
Once tests with able-bodied trial users have been completed, the Mindwalker system will then be transferred to the Foundation Santa Lucia for a clinical evaluation until May 31, 2013. These trials are expected to highlight shortcomings and potential areas for improvement.
In addition to people who suffer from spinal cord injuries, the research could also eventually be used to assist the rehabilitation of stroke victims, and to help astronauts rebuild muscle mass after prolonged periods in space. The Mindwalker project is slated to run for three years in total, and has received a grant of EUR 2.75 million (roughly US$3.5 million) under the European Union's Seventh Framework Program (FP7.)