Wireless Microstimulators Based on Electronic Rectification of Epidermically Applied Currents : Safety and Portability Analysis

Miniaturization of implantable medical electronic devices is currently compromised by the available means for electrically powering them. Most common energy supply techniques for implants – batteries and inductive couplers – comprise bulky parts which, in most cases, are significantly 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 (HF) current supplied by remote electrodes. In this way, low frequency currents capable of performing stimulation of excitable tissues are generated locally around the implants whereas the auxiliary high frequency currents only cause innocuous heating. This approach has the potential to reduce the diameter of the implants to one-tenth the diameter of current microstimulators and, more importantly, to allow that most of the implants’ volume consists of flexible materials. Implants based on the proposed method may look like short pieces of flexible thread. With currently available microelectronic techniques, diameters down to 200 μm are easily conceivable. The numerical study presented here, in which a hypothetical but plausible clinical scenario for paralysis is analyzed, shows that the auxiliary high frequency (1 MHz) currents will be indeed safe according to safety standards and that portable systems based on portable batteries will be feasible.