Despite enormous progress in the past two decades, the intentional control of bionic prostheses remains a challenge and the subject of intensive research. Now, scientists at the Medical University of Vienna and Imperial College London have developed a new method for precisely detecting the nerve signals remaining after an arm amputation and utilising them to control an artificial arm. The study results, published in the journal Nature Biomedical Engineering, could form the basis for the development of the next generation of prostheses.
As part of the Natural BionicS project funded by the European Research Council, novel (40-channel) microelectrodes were implanted in the muscles of three arm amputee study participants, which had previously been reconnected to nerves through a process known as targeted muscle reinnervation (TMR). This surgical procedure redirects nerve pathways remaining after amputation to muscles that are still present, thus creating new interfaces through which neural signals can be retrieved.
By combining surgical reinnervation with implantable microelectrodes, scientists at MedUni Vienna and Imperial College London succeeded for the first time in directly measuring the activity of individual motor neurons – the nerve cells in the spinal cord that transmit movement commands to the muscles – and linking their signal patterns to specific movement intentions. To achieve this result, the participants mentally performed various movements with their phantom arm. "Using our method, we were able to precisely identify the nerve signals that underlie, for example, the stretching of a finger or the bending of the wrist," reports study author Oskar Aszmann, head of the Clinical Laboratory for Bionic Limb Reconstruction at the Department of Plastic, Reconstructive and Aesthetic Surgery at MedUni Vienna.
Foundation for the development of wireless implants
Analysis of the recorded, highly differentiated nerve signals also showed that complex movement intentions remain intact in the nervous system even after amputation and can be mathematically reconstructed. This means that this information can be used in future for the precise control of bionic prostheses. "This is a crucial step towards making the control of bionic limbs more natural and intuitive," says Oskar Aszmann, emphasising the relevance of the study results.
In the long term, these findings will lead to the development of a so-called bioscreen – a system that visualises the complex neural patterns of human movements and thus forms the basis for new generations of prostheses. Current research is thus laying the foundation for the development of wireless implants that can transmit nerve signals directly and in real time to bionic hands or other assistance systems.
