Analysis of experimental data of the project LifeHand 2 provided researchers with scientific feedback that confirmed the possibility of restoring, to a patient whose upper limb had been amputated, tactile sensations and the ability to handle objects near to a natural way. The patient, in particular, was quickly able to: 

  • combine the sensory areas so to manipulate robustly the overall palm force

  • distinguish the different consistencies of hard, medium and soft objects (with more than 78.7% accuracy)

  • recognise the basic shape and size of objects, such as the cylinder of a bottle, the sphere of a baseball ball and the oval of a mandarin (88% accuracy)

  • understand the location of an object in relation to the hand, therefore sending to the prosthesis the most appropriate command in order to shape the best grasp (97% accuracy)

  • self-rectify when applying the wrong amount of pressure on an object during the movement itself, thanks to a communication flow between the prosthesis and the brain in a reaction time of less than 100 milliseconds;

  • manage in real time the different levels of exerted force for the two different nerve sensory areas (index finger-thumb, small finger) while holding an object in palm of hand (with 93% accuracy)

The pointers from experimentation also highlighted the importance of reactivating tactile feedback in order to enable the patient to use the robotic prosthesis with dexterity. When, in fact, the artificial circuit taking sensory information from the prosthesis to the brain was deactivated, the patient’s dexterity markedly diminished despite being able to see (holding exercises with active sensory feedback were on the other hand undertaken blindfolded and in acoustic isolation).ù

A Problem to Solve

in the first LifeHand experiment in 2008, the biomechatronic prosthesis connected to the patient’s nervous system was placed on a surface, about two metres away from the arm fitted with electrode implants. in the case of LifeHand 2, on the other hand, the prosthesis was fitted onto the arm, at a distance therefore of a few centimetres from the electrodes implanted in the patient’s median and ulnar
nerves.

The vicinity of the biomechatronic prosthesis’ electronic circuits to the electrodes implanted in the nerves triggered an electronic interference – so-called ‘background noise’ – impairing the clarity of the intraneural communication signals between the prosthesis and nervous system. 

For this reason, during the course of the experimental sessions, researchers decided to forsake sending the movement intentions from the brain to the prosthesis via intraneural electrodes, creating an alternative path through myoelectric electrodes applied to the surface of the arm in proximity to the amputation. Communication via intraneural electrodes was instead used so as to send sensory information from the prosthesis to the patient’s nervous system. in LifeHand 2 it was therefore a matter of prioritising assessment of the working, through the intraneural electrodes, of the communication flows in the opposite direction (from the prosthesis to the brain). Through improved shielding of the biomechatronic prosthesis, in future experimentation a successful completely intraneural bidirectional communication may be expected.