Explant Analysis of Utah Electrode Arrays Implanted in Human Cortex for Brain-Computer-Interfaces

Abstract

Brain-computer interfaces are being developed to restore movement for people living with paralysis due to injury or disease. Although the therapeutic potential is great, long-term stability of the interface is critical for widespread clinical implementation. While many factors can affect recording and stimulation performance including electrode material stability and host tissue reaction, these factors have not been investigated in human implants. In this clinical study, we sought to characterize the material integrity and biological tissue encapsulation via explant analysis in an effort to identify factors that influence electrophysiological performance. We examined a total of six Utah arrays explanted from two human participants involved in intracortical BCI studies. Two platinum (Pt) arrays were implanted for 980 days in one participant (P1) and two Pt and two iridium oxide (IrOx) arrays were implanted for 182 days in the second participant (P2). We observed that the recording quality followed a similar trend in all six arrays with an initial increase in peak-to-peak voltage during the first 30–40 days and gradual decline thereafter in P1. Using optical and two-photon microscopy we observed a higher degree of tissue encapsulation on both arrays implanted for longer durations in participant P1. We then used scanning electron microscopy and energy dispersive X-ray spectroscopy to assess material degradation. All measures of material degradation for the Pt arrays were found to be more prominent in the participant with a longer implantation time. Two IrOx arrays were subjected to brief survey stimulations, and one of these arrays showed loss of iridium from most of the stimulated sites. Recording performance appeared to be unaffected by this loss of iridium, suggesting that the adhesion of IrOx coating may have been compromised by the stimulation, but the metal layer did not detach until or after array removal. In summary, both tissue encapsulation and material degradation were more pronounced in the arrays that were implanted for a longer duration. Additionally, these arrays also had lower signal amplitude and impedance. New biomaterial strategies that minimize fibrotic encapsulation and enhance material stability should be developed to achieve high quality recording and stimulation for longer implantation periods.

Spatiotemporal spike-centered averaging reveals symmetry of temporal and spatial components of the spike-LFP relationship during human focal seizures

“…In these cases, characterization of the st-SCA may inform the appropriateness of such interventions in personalized patient treatment plans. Furthermore, because this method includes the spatial domain, the st-SCA method can be used for a broad scope of applications, such as MEA cultures 26 , 27 , Utah arrays implanted in monkeys completing tasks 28 – 30 , MEAs implanted in humans for sleep 31 , and for brain-computer interfaces 32 , 33 .…”

Surface Area and Local Curvature: Why Roughness Improves the Bioactivity of Neural Implants

“…Specifically, the effect of the surface modification on water contact angle was investigated in refs and , while we measured effects on zeta potential in ref . Additionally, the mechanisms of protein binding were investigated in ref . These effects were not remeasured in the present investigation because of the focus specifically on topographic effects.…”

In Vivo Penetrating Microelectrodes for Brain Electrophysiology

“…This type of microelectrode predominantly registers a large number (from hundreds to thousands) of neural signals at one level of the brain tissue (multisite horizontal recordings). Utah microelectrodes are FDA (U.S. Food and Drug Administration)-approved and applied in neuroscience research to understand the neural ensembles, as well as in brain–computer interfaces (BCIs) [ 38 , 39 , 40 , 41 , 42 ].…”