Missing a limb leads to dramatic impairments in the capacity to move and interact with the environment and to a substantial worsening in quality of life. This deficiency is also associated with a large portion of the sensory-motor cortex facing neural deafness. Missing or damaged limbs can be substituted by robotic limbs, connected to humans with neural interfacing.
The project NaturalBionicS aims at creating bio-connectors (compacted in a bio-hub) to access the spinal cord circuitries of patients with amputations so that bionic limbs can be controlled and sensed by the patient in a similar way as natural limbs. The core approach consists of utilising biological pathways of encoding and decoding neural information. This corresponds to the use of biological structures still present after the amputation and through which it is easier to communicate with the nervous system of the patient.
At this stage of the project, the progress towards the final goals has been substantial in each of the three main disciplines – neurosurgery, neural interfacing, robotics – as well as in the synergies between disciplines. The surgical research has demonstrated in pre-clinical models that it is possible to transfer multiple nerves previously controlling the missing limb in muscle tissue above the amputation. The muscle tissue is reinnervated and becomes electrically active so that the nerve activity can be measured from it. In this way, the reinnervated muscle becomes a “screen” of the activity of the nerves that were controlling the missing limb. With respect to other approaches, in which different nerves are transferred in different muscles, we demonstrated the possibility to hyper-reinnervate a single muscle, so that the muscle becomes a compact “neural image” of the control of the missing limb by the patient. Moreover, we demonstrated surgically that skin sensors can be reinnervated by the sensory nerves previously sensing the missing limb. For this purpose, a small skin flap is surgically located on top of the reinnervated muscle and the sensory fibers previously sensing the missing limb are transferred to this newly transplanted skin. In this way, mechanical or electrical elicitation of the reinnervated skin will be sensed as sensation coming from the missing limb.
The two reinnervation procedures (motor and sensory) establish the biological structures that allow us to extract information (motor) and to provide information (sensory) from and to the nervous system. We have then interfaced these structures with novel implantable arrays of electrodes to establish a bidirectional interface (from and to the nervous system). In doing so, we have demonstrated that the activity recorded from the reinnervated muscles with the novel implants can be decoded to infer the motor intent of the patient. Moreover, the activity of the multiple nerves can be separated into the individual sources (that is, into the individual nerve activity underlying specific motor tasks) by processing methods based on machine learning and artificial intelligence. This achievement (separation of nerve activity from the hyper-reinnervated muscle) confirms one of the highest-risk hypotheses we made at the beginning of the project.
Finally, the decoded neural activity has been mapped into robotic movements. A novel soft robotic hand controlled by commands that can be synergistically combined has been actuated by the neural information extracted from the bio hub. Interestingly, we were able to show that it is possible to match the neural activity corresponding to specific hand motions to the commands provided to the motors of the robotic hand. This matching has been possible by mapping the neural representation of a motor task to the kinematic posture of the hand. This allowed us to progress towards the very ambitious goal of matching the sensory-motor image of the missing limb emerging from the neural interfacing to the soft robotic arms/legs that will embed kinematic synergies and tactile-proprioceptive functions, intimately matched with the neural sensory-motor synergies extracted from the bio-hub.
The project has therefore achieved a full proof-of-concept of all its main foundational assumptions. The next phase will be dedicated to the clinical integration of the developed technologies for a full real-life demonstration of the achieved scientific results.
