Demonstration of 2 mm Thick Microcontrolled Injectable Stimulators Based on Rectification of High Frequency Current Bursts

Abstract

Existing implantable stimulators use powering approaches that result in stiff and bulky systems or result in systems incapable of producing the current magnitudes required for neuromuscular stimulation. This hampers their use in neuroprostheses for paralysis. We previously demonstrated an electrical stimulation method based on electronic rectification of high frequency (HF) current bursts. The implants act as rectifiers of HF current that flows through the tissues by galvanic coupling, transforming this current into low frequency current capable of performing neuromuscular stimulation. Here we developed 2 mm thick, semi-rigid, injectable and addressable stimulators made of off-the-shelf components and based on this method. The devices were tested in vitro to illustrate how they are powered by galvanic coupling. In addition they were tried in an animal model to demonstrate their ability to perform controlled electrical stimulation. The implants were deployed by injection into two antagonist muscles of an anesthetized rabbit and were addressed resulting in independent isometric contractions. Low frequency currents of 2 mA were delivered by the implants. The HF currents are safe in terms of unwanted electrostimulation and tissue heating according to standards. This indicates that the proposed electrical stimulation method will allow unprecedented levels of miniaturization for neuroprostheses.

Powering Implants by Galvanic Coupling: A Validated Analytical Model Predicts Powers Above 1 mW in Injectable Implants

“…Peak powers in the order of tens or hundreds of mW are attainable when bursts are very short in comparison to their repetition period. This suggests that galvanic coupling may be particularly useful in applications requiring large amounts of power in short intervals, such as is the case of neuromuscular stimulation [1].…”

“…As we have recently shown in vivo [1], galvanic coupling can be an effective power transfer method which can lead to unprecedented implant miniaturization. Remarkably, although galvanic coupling for intrabody communications has been proposed lately by different research groups [2], its use for powering implants has remained almost non-existent.…”

First Steps Towards an Implantable Electromyography (EMG) Sensor Powered and Controlled by Galvanic Coupling

“…The core architecture of the microcontrolled injectable stimulators was described in [6]. Briefly, implant electrodes E1 and E2 pick up a portion the HF current delivered to the tissues by the external system (Fig.…”

“…1). We in vivo demonstrated microcontrolled injectable stimulators that could be galvanically powered and that could deliver low frequency (LF) currents capable of stimulating excitable tissues [6]. These implants (diameter = 2 mm), made of commercially available components, are the first step towards future ultrathin and flexible implants (diameter < 1 mm) based on an application-specific integrated circuit (ASIC).…”

Injectable Biomedical Devices for Sensing and Stimulating Internal Body Organs

“…In contrast, utilizing miniaturized needle‐like carriers to deliver tiny sensors and stimulation tools inside the body can overcome these challenges. Biomedical devices fabricated in high aspect ratio structures or integrated on catheter‐shaped carriers empowered accurate and minimally invasive insertion of high‐performance devices into soft, inhomogeneous tissues 27–29. As a result, tools with high aspect ratio forms are rapidly developing for minimally invasive targeted sensors and therapy systems within the field of bioelectronics.…”