Neurobiological evaluation of thin-film longitudinal intrafascicular electrodes as a peripheral nerve interface

Longitudinal intrafascicular electrodes (LIFEs) designed to be placed inside a peripheral nerve seem adequate devices for constituting a nerve-prosthesis interface. In this study we evaluated the functional and morphological effects of newly designed polyimide-based thin-film (tf-)LIFEs implanted in the rat sciatic nerve for 3 months. The tf-LIFEs used are highly flexible, and have 8 regularly spaced contacts, 4 at each side of the folded structure. Functional results at 1 month showed a mild decline in nerve conduction velocity and amplitude of muscle responses, which recovered during the following 2 months. Histological results showed a mild scar response around the intraneural electrode, but no signs of axonal loss and degeneration. Longitudinally implanted LIFEs behaved slightly better than transversally inserted LIFEs. Acute experiments proved that selective neural signal recording and nerve stimulation could be achieved from the different active sites in one tf-LIFE.