Polyimide cuff electrodes for peripheral nerve stimulation

This paper describes a new tripolar spiral cuff electrode, composed of a th in (10 mu m) and flexible polyimide insulating carrier and three circumneur al platinum electrodes, suitable for stimulation of peripheral nerves. The cuffs were implanted around the sciatic nerve of two groups of ten rats eac h, one in which the polyimide ribbon was attached to a plastic connector to characterize the in vivo stimulating properties of the electrode, and one without a connector for testing possible mechanical nerve damage by means o f functional and histological methods. The polyimide cuff electrodes induce d only a very mild foreign body reaction and did not change the nerve shape over a 2-6 month implantation period. There were no changes in the motor a nd sensory nerve conduction tests, nociceptive responses and walking track pattern over follow-up, and no morphological evidence of axonal loss or dem yelination, except in one case with partial demyelination of some large fib ers after 6 months. By delivering single electrical pulses through the cuff electrodes graded recruitment curves of alpha-motor nerve fibers were obta ined. Recruitment of all motor units was achieved with a mean charge densit y lower than 4 mu C/cm(2) for a pulse width of 50 mu s at the time of impla ntation as well as 45 days thereafter. These data indicate that the polyimi de cuff electrode is a stable stimulating device, with physical properties and dimensions that avoid nerve compression or activity-induced axonal dama ge. (C) 2000 Elsevier Science B.V. All rights reserved.