Vocal fold paralysis is characterized by impairment of the nerve signals to one or both of the vocal folds. Signal propagation is most often compromised by surgery, trauma, disease, neuritis, and neck tumors. The location of the recurrent laryngeal nerve leaves it especially susceptible to injury during common neck and chest surgical procedures in which the nerves may be severed, crushed, or stretched. If the damage to the nerve during surgery is immediately recognized and repaired, the neurons usually regrow, but the regrowth is often random. This may lead to simultaneous activation of adductor and abductor muscles, which results in synkinesis.

In this study, unilateral vocal fold paralysis was induced in a cat model by transecting the recurrent laryngeal nerve and either reattaching the severed ends of the nerve to itself or to a branch of the ansa cervicalis. The nerves were allowed to regrow for 6 months after which a selective neural stimulating device, the Slanted Utah Electrode Array, was inserted into the nerve and immobilized with a silicone containment system. Selective stimulation of the nerve was attempted at the time of implantation and 30, 60, and 90 days postimplantation. Selective stimulation was only achieved at the time of implantation and in one animal at 30 days. Gross stimulation of the nerves and histological analysis suggest some nerve regrowth occured, but the device did not retain its functionality during chronic implantation. Failure analysis of the implant revealed several potential modes of implant failure including delamination of the electrode insulating layer, overetching of the electrodes during fabrication, and degradation of the insulation on the wires that connect the implant to the external electrical connector.

In order to better assure success in a chronic model, a more robust deposition of the electrode insulation or a different insulating material should be employed. Likewise, an alternative insulation or an additional protective layer, such as silicone, should be used on the wires that connect the device to the external connector. Additionally, a stricter quality control process for the electrode arrays during manufacture would ensure only devices that meet specification are released for implantation.