Multielectrode spiral cuff for selective stimulation of nerve fibres.

In this paper we present the modelling, design, and initial experimental testing of a nerve cuff multielectrode system for selective stimulation of fibres in superficial peripheral nerve trunk regions which is capable of making a selective activation of multiple muscles. The developed multielectrode nerve cuff consists of 14 platinum stimulating electrodes embedded within a self-curling sheet of biocompatible insulation, exhibiting a spiral transverse cross-section. The spiral shape of the system is such that the number of stimulating electrodes which can be utilized depends on the diameter of the stimulated nerve. Nerves with a greater diameter automatically make use of more electrodes than thin ones. The development was based on results obtained by a histological examination of the peripheral nerves which were planned to be stimulated, and on models of excitation of myelinated nerve fibres. The modelling objectives were to determine the electric field that would be generated within a nerve trunk by a specific electrode. Moreover, the extent of initial excitation of the nerve fibres within the superficial region of the dog sciatic nerve elicited by a certain discrete stimulating electrode was predicted. For this purpose a calculation of activating function for six positions where the nerve fibres were supposed to lie within the longitudinally dissected sciatic nerve was performed. In two acute experiments on the sciatic nerve of the dog the objective was to characterize the effectiveness of the multielectrode system in monopolar selective stimulation of the superficial regions, innervating the gastrocnemius and tibialis anterior muscle. A selectivity preliminary tested by measuring the myoelectric activity of the gastrocnemius and tibialis anterior muscle after 2 months showed good results in both animals.