Flexible thread-like electrical stimulation implants based on rectification of epidermically applied currents which perform charge balance

Abstract

Miniaturization of implantable medical electronic devices is currently compromised by the available means for powering them. Most common energy supply techniques for implants - batteries and inductive links - comprise bulky parts which, in most cases, are larger than the circuitry they feed. For overcoming such miniaturization bottleneck in the case of implants for electrical stimulation, we recently proposed and demonstrated a method in which the implants operate as rectifiers of bursts of high frequency current supplied by skin electrodes. In this way, low frequency currents capable of performing stimulation of excitable tissues are generated locally through the implants whereas the auxiliary high frequency currents only cause innocuous heating. The electronics of the prototype we demonstrated previously consisted of a single diode. As a consequence, it caused dc currents through it which made it impractical for clinical applications. Here we present an implantable prototype which performs charge balance for preventing electrochemical damage. It consists of a tubular silicone body with a diameter of 1 mm, two peripheral electrodes and a central electronic circuit made up of a diode, two capacitors and a resistor. We also report that this circuitry works even when water immersed, which may avoid the need for hermetic packaging.