Increasingly advanced tools are desired for understanding electrical activity in the brain, whether for basic neuroscience or clinically relevant brain-machine interfaces. Among the many classes of tools available, intracortical neural recording electrodes have the potential advantage of both high spatial and temporal resolution, and depending on the device can be suitable for either acute or chronic applications. To achieve the breadth of desirable characteristics for an acute neural recording array, including minimal adverse biological response, full-volume sampling, and scalability to a large number of recording electrodes, a new type of device must be developed. This dissertation presents significant steps toward such a device, demonstrating a high-density 32-channel carbon fiber microwire neural recording array capable of acutein vivo recording. Departing from the in-plane architectural paradigm of conventional microwire-style neural recording arrays, an array substrate is microfabricated in silicon and 5 μm diameter carbon fiber monofilaments are threaded through holes in that silicon substrate to create a two-dimensional array of carbon fiber recording electrodes that can, in principle, be scaled to an arbitrary number of recording electrodes. In addition to scalability, this device architecture affords electrode pitch four timesfiner than the state of the art among microwire recording arrays. The fine diameter of the carbon fibers affords both minimal cross-section and nearly three orders of magnitude greater lateral compliance compared to traditional tungsten microwires, with these features serving to minimize the adverse biological response of the implanted electrodes.
The substrate microfabrication and array assembly processes are robust and repeatable, and with the introduction of a robotic system to automate the insertion of carbon fibers into the through-silicon vias with submicron precision, the processes are fundamentally scalable to an array with a large number of electrodes. A specially formulated isotropically conductive adhesive mechanically and electrically bonds the carbon fiber recording electrodes to the silicon substrate, and post-processing of both the adhesive and the recording sites serves to further lower the impedancefor superior electrophysiological characteristics. Recording is demonstrated in the primary motorcortex of a rat, with single-unit action potentials being recorded on many channels. This carbonfiber microwire neural recording array is a promising technology for increasing information density while minimizing the adverse biological response in acute preparations, particularly in applications where microwire arrays are already commonplace.
June 20, 2018
Massey, T. L. (2018). A High-Density Carbon Fiber Neural Recording Array Technology: Design, Fabrication, Assembly, and Validation. United States: University of California, Berkeley.