Miniaturization of a radio frequency powered implantable electrode for targeted muscle reinnervation

Emily M Cook, Purdue University

Abstract

Currently, the number of amputees in the United States is estimated between 1.6 and 1.9 million people, and of that number, approximately 100,000 are upper limb amputees. Despite these numbers until recently, upper limb prosthetics had changed little since World War II. Targeted muscle reinnervation, which launched the current revolution in upper limb prosthetics, is a new surgical procedure. During this procedure, the nerves that once innervated the amputated limb are redirected to new muscle and skin sites. The electromyogram (EMG) signals from the targeted muscle sites can then be recorded, decoded, and used to control an amputee's prosthetic device. However, these EMG signals are currently collected using surface electrodes which may shift on the skin during normal activity and need to be reapplied daily. To create a more stable system, implantable EMG electrodes must be developed. This study examines the miniaturization of a radio frequency powered, implantable electrode for this application. As such, a 11mm by 3mm by 1mm system prototype was fabricated on a liquid crystal polymer substrate. Testing of this prototype revealed a successful fabrication process but a need to redesign the receiving and transmitting antennas. Additionally, two custom integrated circuits were designed with the goal of reducing the necessary implant size by replacing the off-the-shelf crystal oscillator. The topologies for these application specific integrated circuits (ASICs) are a ring oscillator and a multivibrator circuit. Both circuits meet the system requirements: operate with a 1.5V supply and output a square wave with 1.5V amplitude, approximately 50 percent duty cycle, and minimum 24kHz frequency. The redesign of the system's antennas and the integration of a clock ASIC into the full system is still in progress, but testing indicates a working implantable electrode prototype is within reach.

Degree

M.S.B.M.E.

Advisors

Irazoqui, Purdue University.

Subject Area

Systematic|Biomedical engineering

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