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The IMES1 Implantable MyoElectric Sensor device is currently in human clinical trials led by the Alfred Mann Foundation. The IMES is implanted in a residual limb and is powered wirelessly using a magnetic field. EMG signals resulting from the amputee's voluntary movement are amplified and transmitted wirelessly by the IMES to an external controller which controls movement of an external motorized prosthesis. Development of the IMES technology is on-going, producing the next-generation IMES2. Among various improvements, a new feature of the IMES2 is a low-power polling mode. In this low-power mode, the IMES2 power consumption can be dramatically reduced when the limb is inactive through the use of a polled sampling. With the onset of EMG activity, the IMES2 system can switch to the normal higher sample rate to allow the acquisition of high-fidelity EMG data for prosthesis control.

The stability of thin-film multielectrode devices fabricated on flexible polyimide substrates was evaluated for wireless subdural recording and stimulation in intracranial electrocorticogram (ECoG) monitoring prior to epilepsy surgery. Devices were fabricated with either 48 or 64 sputtered iridium oxide (SIROF) electrodes. Power and bidirectional data transfer were provided via 121 kHz and 13.56 MHz RF links, respectively. A 64-channel application specific integrated circuit (ASIC) was developed for the devices and provided both the recording and stimulation capability. The ASIC, supporting discrete electronic components, and data/power coils were incorporated on a polyimide substrate and protected from the saline environment by a combination of amorphous silicon carbide (a-SiC) and silicone encapsulants. Soak testing at 37°C in saline under continuous power, and unpowered soak testing at 87°C, were conducted for 29 days and 12 days, respectively. Normal function of the ASIC and device, as measured by the consistency in RMS signal strength and stimulation driving voltage, was observed over the test periods. The charge capacity measured by cyclic voltammetry and the impedance of the SIROF electrodes remained stable over 20 days at 87°C. The results suggest that a-SiC and silicone encapsulants can protect active electronics for implantation periods up to 29 days, the maximum length anticipated for ECoG monitoring in epilepsy patients.

Activated Iridium Oxide Film (AIROF) microelectrodes are regarded as advantage for stimulation of neural tissue owing to their superior charge injection capabilities, as compared to other noble-metal based electrodes. Including AIROF electrodes within an implantable neural stimulator can be challenging since the stimulator fabrication steps often involve elevated temperatures at which the AIROF can be damaged. In this work, a wireless neural stimulator application-specific-integrated-circuit (ASIC) was used to intrinsically activate iridium microelectrodes. This intrinsic activation allows for the growth of the AIROF as the final assembly step after the entire device is assembled, thus avoiding stress on the AIROF. Since a typical neural stimulator is essentially a current-controlled driver with voltage compliance limits, its output waveform can be tuned to match the traditional voltage pulsing/ramp activation waveform. Here the feasibility of the current driven activation of iridium electrodes, over a wireless link, is demonstrated.

As a component of the RP2009 project, the IMES system has emerged as a strong candidate for extracting naturally-occurring control signals to be used for providing functional control of an upper body artificial limb. In earlier publications, we described various elements of this system as they were being researched and developed. Presently, the system has matured to a level for which it is now appropriate to consider application-specific-integrated circuits (ASIC) that are of a standardized form, and are suitable for clinical deployment of the IMES system. Here we describe one of our emerging ASIC designs that addresses the design challenges of the extracoporal transmitter controller. Although this ASIC is used in the IMES system, it may also be used for any command protocol that requires FSK modulation of a Class E converter.

We present updated progress on the design, construction and testing of an upper-extremity prosthesis control system based on implantable myoelectric sensors. The miniature injectable implant consists of a single silicon chip packaged with transmit and receive coils. Preparation for human implantation of the IMES system is underway. As part of this process, critical design improvements in the IMES implant were required. Here we report improved functionality of the IMES implant, hardened protection against electrical malfunction and tissue damage.

The limitation of current prostheses is not the devices themselves but rather the lack of sufficient independent control sources. A system capable of reading intra muscular EMG signals would greatly increase the number control sources available for prosthesis control. We are developing a multichannel/multifunction prosthetic hand/arm controller system capable of receiving and processing signals from up to sixteen implanted bipolar differential electromyographic (EMG) electrodes. An external prosthesis controller will decipher user intent from telemetry sent over a transcutaneous magnetic link by the implanted electrodes. The same link will provide power for the implanted electrodes. This paper describes some of the technical aspects of the implant and telemetry design.

We are developing a multichannel/multifunction prosthetic hand/arm controller system capable of receiving and processing signals from up to sixteen Implanted MyoElectric Sensors (IMES). A BION/spl reg/ II package will house the implantable electrode electronics and associated circuitry. An external prosthesis controller will decipher user intent from telemetry sent over a transcutaneous magnetic link by the implanted electrodes. The same link will provide power for the implanted electrodes. Development of such a system will greatly increase the number of control sources available to amputees for control of their prostheses. This will encourage the design and fitting of more functional prostheses than are currently available.