The electrodes: the communication hardware between the nerve fibres and computer

Known as TIME (Transverse Intrafascicular Multichannel Electrodes), the intraneural electrodes placed in the patient’s nerves for the LifeHand 2 experimentation were designed and developed at
the laboratory for Biomedical Microtechnology at the iMTeK (Institut für Mikrosystemtechnik) of the University of Freiburg, supervised by Prof. Thomas Stieglitz. 

Completely biocompatible, these TIME electrodes were designed, made and tested to be placed transversally to the nerve fascicles constituting a nerve (with a minimum diameter of 220 micrometres, about 3 human hairs). The transversal implant onto the nerves is aimed at establishing the largest amount possible of contact points between the communication channels of the electrodes and the nervous fibres, so as to amplify the possibility of communicating with the central nervous system. The width of the TIME electrodes is variable. The widest part inserted into the nerve is approximately 350 micrometres. Their overall thickness is approximately 22 micrometres. 

The 16 electrical contacts (or active sites) that are incorporated in the electrodes, are made from platinum and iridium oxide on a sub-layer of polyimide, guaranteeing their isolation and flexibility. each has a diameter of 80 micrometres (a human hair is equivalent to 70 micrometres). The electrodes are capable of supporting an electric charge of 120 nanoColumb. in the laboratory tests they were found to be functionally stable after receiving over 25 million electric impulses.

During experimentation, the electrodes proved to have an extremely high level – never before reached – of selective activation of the nerve fibre distributed across the length of the nerve. This helped generate sensations in the patient’s nervous system using much lower intensity level impulses than with LifeHand 2008 experimentation. lowering intensity of the impulses is important as it coincides with a reduction in pressure on the nerves during the experimentation stage and consequently of the risk of inflammation.

Up until the thirtieth day of experimenting, the four electrodes did not cause any type of discomfort or irritation to the patient. even after their removal, the TIME implants were fully functional and performing soundly.

The prosthesis: a sensorized artificial hand

The biomechatronic prosthesis prototype used for the experimentation was developed and produced at the ArtsLab of The BioRobotics Institute of Scuola Superiore Sant’Anna of Pisa. Known as OpenHand, it represents the evolution of the Cyberhand and smarthand prototypes used in previous projects, also including the 2008 research project LifeHand. The structure of the prototype was made in order to guarantee, at a mechanical level, greater freedom degrees. OpenHand is the outcome of a biennial research programme (OPEN neuro-prosthetic HAND platform for clinical trials) promoted by the italian Ministry of education, University and Research (MUiR). size, ability to move fingers and weight (just over 600 grammes) are equivalent to that of a human hand. For this experimentation, the index and small finger, out of the tactile sensors on the five OpenHand fingers, were activated at the same time. The tactile sensors were able, thanks to a special conversion and decoding algorithm in the computer connected to the OpenHand, to send back an electric charge proportional to the amount of pressure used in touching objects or other external elements.