Flexible EMG arrays with integrated electronics for scalable electrode density

Abstract

AbstractRecent developments in electrode technology have demonstrated the power of flexible microelectrode arrays (FMEAs) for measuring muscle activity at high resolution. We recently introduced the Myomatrix array, a FMEA optimized for measuring the activity of individual motor units (the collection of muscle fibers innervated by a single motor neuron) [1] in freely behaving animals. Although FMEAs are fundamentally changing the way EMG is acquired, the number of recording channels is limited by the size of the plug that interfaces with the digital amplifier hardware and the density of electrode connections on the array. Increasing EMG channel count and supporting electrophysiological studies in smaller animals depends on two seemingly incompatible goals: reducing device size while increasing the number of recording channels. The solution to this is to increase channel density, which is currently limited by requiring that separate headstage and FMEA components be used simultaneously. In our prior devices [1], each FMEA had a dedicated wire output for every electrode input, creating a channel density is 1 : 1. To improve this channel density, we have developed a novel device integrating a digital amplifier (bare-die RHD2216 chip, Intan, Inc. [6]) directly onto an FMEA. This new design reduces the device’s backend footprint by 74% and relocates the intan bare die from the headstage to the FMEA itself, creating a channel density of 1 : 3.2. Our methodology combines standard FMEA microfabrication with wire-bonding and surface-mounted components, enabling direct integration into a Serial Peripheral Interface (SPI) connection into the device itself, without any separate headstage. With this initial device we see a 1 : 3.2 channel density, but our method allows for using other bare die amplifiers (Intan, Inc., USA) for a channel density of 1 : 12.8. Our findings present a robust technique for chip embedding in custom FMEAs, applicable to in-vivo electrophysiology