Injectable rectifiers as microdevices for remote electrical stimulation: an alternative to inductive coupling

Abstract

Miniaturization of implantable medical elec-tronic devices is currently compromised by the available means for electrically powering them. Most common energy supply techniques for implants – batteries and inductive cou-plers – comprise bulky parts which, in most cases, are signifi-cantly 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 based on making the implants operate as rectifiers of bursts of high frequency current supplied by remote electrodes. In this way, low frequency current is generated locally around the implant and this low frequency current performs stimulation of excitable tissues whereas the high frequency current only causes innocuous heating. The present paper reports further progress in this technology. We first describe construction and functional test of an injectable stimulator consisting of a single miniature diode (300 μm × 300 μm × 600 μm) and two thin electrodes which is implanted trough a 19G needle into an anesthetized earthworm. We then propose a circuit architec-ture for implementing smart implants based on this technol-ogy. Both accomplishments are steps towards the implementa-tion of injectable addressable microsystems for neuroprosthetics. These systems based on the proposed tech-nology will look like short pieces of flexible thread rather than rigid capsules, as it was the case of previous miniature electri-cal stimulation implants. With currently available microelec-tronic techniques, very thin stimulation implants (diameter < 200 μm) are easily conceivable. This technology may be foun-dational to a broad range of new developments in the field of implantable medical devices with applications ranging from wound healing to nerve stimulation for pain relief. In addition, other non-medical devices could also emerge such as implant-able identification devices.