Regenerative electrodes for interfacing injured peripheral nerves: neurobiological assessment

Regenerative electrodes are designed to interface regenerated axons from a sectioned peripheral nerve that grow through an array of holes with metal electrodes. Applicability of regenerative electrodes is dependent on its biocompatibility, the success of axonal regeneration through the sieve electrode, the possible secondary nerve damage, and the adequacy of electronic component to interface regenerated axons. Polyimide-based regenerative electrodes have been fabricated that are highly flexible, do not cause substantial nerve damage, and provide a high number of holes. A first design of polyimide sieve electrodes were chronically implanted between the severed ends of the sciatic nerve in 30 rats. Regeneration was successful in all the animals implanted. The number of regenerated myelinated fibers increased from 2 to 6 months, when it was similar to control values. However, in a few cases decline of target reinnervation and loss of regenerated fibers was found from 6 to 12 months postimplantation. Large motor and sensory axons regenerate through the sieve with more difficulties than small axons. A second design of the electrode with 27 ring electrodes coated with Pt black was also implanted to assess the capabilities for nerve signal recordings. Recordings were obtained from a low proportion of electrodes on the sieve in response to functional stimulation of the paw. Difficulties inherent to recording impulses with regenerative electrodes are discussed, considering that regenerated axons have for long time smaller size than normal, and show notable changes in membrane excitability properties and in target reconnection