Unique electrophysiological and impedance signatures between encapsulation types: An analysis of biological Utah array failure and benefit of a biomimetic coating in a rat model

Abstract

Intracortical microelectrode arrays, especially the Utah array, remain the most common choice for obtaining high dimensional recordings of spiking neural activity for brain computer interface and basic neuroscience research. Despite the widespread use and established design, mechanical, material and biological challenges persist that contribute to a steady decline in recording performance (as evidenced by both diminished signal amplitude and recorded cell population over time) or outright array failure. Device implantation injury causes acute cell death and activation of inflammatory microglia and astrocytes that leads to a chronic neurodegeneration and inflammatory glial aggregation around the electrode shanks and often times fibrous tissue growth above the pia along the bed of the array within the meninges. This multifaceted deleterious cascade can result in substantial variability in performance even under the same experimental conditions. We track both impedance signatures and electrophysiological performance of 4 × 4 floating microelectrode Utah arrays implanted in the primary monocular visual cortex (V1m) of Long-Evans rats over a 12-week period. We employ a repeatable visual stimulation method to compare signal-to-noise ratio as well as single- and multi-unit yield from weekly recordings. To explain signal variability with biological response, we compare arrays categorized as either Type 1, partial fibrous encapsulation, or Type 2, complete fibrous encapsulation and demonstrate performance and impedance signatures unique to encapsulation type. We additionally assess benefits of a biomolecule coating intended to minimize distance to recordable units and observe a temporary improvement on multi-unit recording yield and single-unit amplitude.

Chronically Implanted Intracranial Electrodes: Tissue Reaction and Electrical Changes

“…At this point, the glial sheath has effectively walled the implant off from the rest of the brain tissue with minimal extension of the inflammatory response into the surrounding area. It should be noted that at these later time points, there is significant variability in the degree of these immunohistochemically visualized cellular responses, which tend to coincide with similar variability in the changes occurring in individual electrodes [ 5 , 46 , 47 ].…”

Injectable Biomedical Devices for Sensing and Stimulating Internal Body Organs

“…Other forms of large array probes consisted of microwires39 or metalized microdisks 130. However, long‐term implantation suffered from astroglial response and fibrous encapsulation of the probes, leading to limitations in chronic applications, such as the impedance rise of microelectrodes 113,114,131. With the advent of microelectronics, lithography techniques were applied on silicon‐based probes, which allowed multiple electrode sites within a single probe 40,41,132.…”

The History and Horizons of Microscale Neural Interfaces

“…For example, the standard Blackrock arrays have 400 μm shank pitch [ 97 ]. This is not because 400 μm is the optimal pitch to maximize signal detection or the optimal pitch to record from neighboring cortical columns.…”

“…and commercial Bioelectronic Medicine (Galvani Bioelectronics (GSK and Verily), NeuraLink, Kernel, etc.) is to understand brain function and treat neurological and physiological disease via the nervous system, the critical hurdle is placed on unreliable neuroelectronic interfaces over relevant time scales and the limited understanding in the neural interfacing field [ 36 , 67 , 68 , 97 , 106 , 107 , 108 , 109 ]. Just as a diversity of expertise is necessary to develop the next-generation microscale neural interfaces, it is necessary to have a diversity of perspectives and problem-solving approaches.…”