Implanted neuroprosthetic systems have been successfully used to provide upper-limb function for over 16 years. A critical aspect of these implanted systems is the safety, stability, and reliability of the stimulating electrodes and leads. These components are (1) the stimulating electrode itself, (2) the electrode lead, and (3) the lead-to-device connector. A failure in any of these components causes the direct loss of the capability to activate a muscle consistently, usually resulting in a decrement in the function provided by the neuroprosthesis. Our results indicate that the electrode, lead, and connector system are extremely durable. We analyzed 238 electrodes that have been implanted as part of an upper-limb neuroprosthesis. Each electrode had been implanted at least 3 years, with a maximum implantation time of over 16 years. Only three electrode-lead failures and one electrode infection occurred, for a survival rate of almost 99 percent. Electrode threshold measurements indicate that the electrode response is stable over time, with no evidence of electrode migration or continual encapsulation in any of the electrodes studied. These results have an impact on the design of implantable neuroprosthetic systems. The electrode-lead component of these systems should no longer be considered a weak technological link.

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An implantable stimulator-telemeter (IST-12) was developed for applications in neuroprosthetic restoration of limb function in paralyzed individuals. The IST-12 provides 12 stimulation channels and two myoelectric signal (MES) channels. The MES circuitry includes a two-channel multiplexer, preamplifier, variable gain amplifier/bandpass filter, full-wave rectifier, and bin integrator. Power and control signals are transmitted from an external control unit to the IST-12 through an inductive link. Recorded MES signals are telemetered back to the external control unit through the same inductive link. Following bench testing, one device was implanted chronically in a dog for 15 months and evaluated. Conditions were identified in which MES could be recorded with minimal stimulus artifact. The ability to record MES in the presence of stimulation was verified, confirming the potential of the IST-12 to be used as a myoelectric controlled neuroprosthesis.

The application of a train of cathodic-first/charge-balanced/biphasic pulses applied to a platinum electrode resulted in a positive creep of the anodic phase potential that increases with increasing charge injection but reaches a steady-state value before 1000 pulses have been delivered. The increase follows from the fact that charge going into irreversible reactions occurring during the anodic phase must equal the charge going into irreversible reactions during the cathodic phase for charge-balanced pulses. In an oxygenated electrolyte the drift of the measured positive potential moved into the platinum oxidation region of the i(V e) profile when the charge injection level exceeds k = 1.75. Platinum dissolution may occur in this region and k = 1.75 defines a boundary between damaging and non-damaging levels on the Shannon Plot. In a very low oxygen environment, the positive potential remained below the platinum oxidation region for the highest charge injection values studied, k = 2.3. The results support the hypothesis that platinum dissolution is the defining factor for the Shannon limit, k = 1.75. Numerous instrumentation issues were encountered in the course of making measurements. The solutions to these issues are provided.