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We have developed a multichannel electrogmyography sensor system capable of receiving and processing signals from up to 32 implanted myoelectric sensors (IMES). The appeal of implanted sensors for myoelectric control is that electromyography (EMG) signals can be measured at their source providing relatively cross-talk-free signals that can be treated as independent control sites. An external telemetry controller receives telemetry sent over a transcutaneous magnetic link by the implanted electrodes. The same link provides power and commands to the implanted electrodes. Wireless telemetry of EMG signals from sensors implanted in the residual musculature eliminates the problems associated with percutaneous wires, such as infection, breakage, and marsupialization. Each implantable sensor consists of a custom-designed application-specified integrated circuit that is packaged into a bio-compatible RF BION capsule from the Alfred E. Mann Foundation. Implants are designed for permanent long-term implantation with no servicing requirements. We have a fully operational system. The system has been tested in animals. Implants have been chronically implanted in the legs of three cats and are still completely operational four months after implantation.

In order to track the on-going changes and ultimate reliability of neural recording and stimulation arrays, it is beneficial to regularly characterize electrode arrays within the use environment. Microelectrodes used for neural stimulation or recording research can have different behaviors in-vivo vs. in- vitro, and once implanted the success of the experiment often hinges upon knowing the stability, changes, or deterioration of the electrodes. This paper describes a new instrument that is capable of batch characterizing 16 electrodes using cyclic voltammetry, electrochemical impedance spectroscopy and charge injection measurements. The latest web based technology was applied to the software design, which greatly facilitates electrode data sharing among researchers.

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.

Long-term reliability of an implanted system is an implicit requirement. The catastrophic failure of an implanted device is often the only indication that reliability expectations have not been met. In the design of a wireless EMG sensor, we have integrated three “Reliability Modules” specifically designed to monitor the state of the silicon integrated circuit and its environment.

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.

This paper reports on a wireless stimulator device for use in animal experiments as part of an ongoing investigation into intraspinal stimulation (ISMS) for restoration of walking in humans with spinal cord injury. The principle behind using ISMS is the activation of residual motor-control neural networks within the spinal cord ventral horn below the level of lesion following a spinal cord injury. The attractiveness to this technique is that a small number of electrodes can be used to induce bilateral walking patterns in the lower limbs. In combination with advanced feedback algorithms, ISMS has the potential to restore walking for distances that exceed that produced by other types of functional electrical stimulation. Recent acute animal experiments have demonstrated the feasibility of using ISMS to produce the coordinated walking patterns. Here we described a wireless implantable stimulation system to be used in chronic animal experiments and for providing the basis for a system suitable for use in humans. Electrical operation of the wireless system is described, including a demonstration of reverse telemetry for monitoring the stimulating electrode voltages.

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 trained a rhesus monkey to perform randomly cued, individuated finger flexions of the thumb, index, and middle finger. Nine Implantable MyoElectric Sensors (IMES) were then surgically implanted into the finger muscles of the monkey's forearm, without any observable adverse chronic effects. Using an inductive link, we wirelessly recorded EMG from the IMES as the monkey performed a finger flexion task. A principal components analysis (PCA) based algorithm was used to decode which finger switch was pressed based on the recorded EMG. This algorithm correctly decoded which finger was moved 89% of the time. These results demonstrate that IMES offer a safe and highly promising approach for providing intuitive, dexterous control of artificial limbs and hands after amputation.

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.

We present progress on the design and testing of an upper-extremity prosthesis control system based on implantable myoelectric sensors. The implant consists of a single silicon chip packaged with transmit and receive coils. Forward control telemetry to, and reverse EMG data telemetry from multiple implants has been demonstrated. I. INTRODUCTION NCREASING the number of mechanical degrees of freedom available from a hand prosthesis beyond the current state of the art will allow a more accurate duplication of the functionality of a human hand. In order to effectively utilize the additional degrees of freedom a complex mechanical design would offer, a larger number of control signals must be collected from the user. It has been proposed that intra- muscular EMG signals from multiple residual muscles could be used to provide simultaneous control of multiple degrees of freedom in the prosthesis (1,2). Wireless telemetry of EMG signals from sensors implanted in the residual musculature would eliminate the problems associated with percutaneous wires.

We present a monolithic microelectronic multichannel amplifier designed to facilitate measurements from multi-electrode arrays. A single silicon chip includes sixteen electrode amplifiers, along with interface and control circuitry to allow data collection through a compact 4-wire interface.

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.

Despite the success of implantable batteries as commonly used in pacemakers, implantable neural prosthetic devices typically have power requirements that exceed the capability of reasonably-sized implantable batteries. Therefore, transcutaneous magnetic coupling remains the method of choice for powering implanted neural prostheses. Using the same inductive link for transfer of power and bidirectional telemetry is an attractive solution to powering and communicating with implanted devices thus avoiding percutaneous plugs, wires, or conduits. The Class-E power oscillator has been identified as a highly-efficient transmitter circuit for use as a means of transferring power to an implant. Although the high-Q nature of this topology makes rapid modulation difficult, it is feasible to use synchronous frequency-shift-keyed (FSK) modulation of the Class-E circuit thereby combining an efficient power transmitter with a highspeed data link. Using this method, the transmitter can be modulated on a cycle-by-cycle basis with little to no additional power loss. Within an implanted device, demodulation of the FSK transmitted carrier can be accomplished using a novel demodulation circuit.

Design of circuitry for implantable neural prostheses requires the use of novel VLSI techniques that deviate from those commonly used for commercial mixed-signal application-specific integrated circuits (ASIC). Often implant designers are faced with competing requirements for low-power and high data-bandwidths with a growing need for increased functionality in smaller implantable packages. Combining transcutaneous powering of neural prostheses with bidirectional telemetry challenges conventional communication circuits commonly found in modern wireless devices. Using the consumer electronics industry as a model, a method of modular design for neural prostheses is discussed.