Mechanical failure modes of chronically implanted planar silicon-based neural probes for laminar recording

Abstract

Penetrating intracortical electrode arrays that record brain activity longitudinally are powerful tools for basic neuroscience research and emerging clinical applications. However, regardless of the technology used, signals recorded by these electrodes degrade over time. The failure mechanisms of these electrodes are understood to be a complex combination of the biological reactive tissue response and material failure of the device over time. While mechanical mismatch between the brain tissue and implanted neural electrodes have been studied as a source of chronic inflammation and performance degradation, the electrode failure caused by mechanical mismatch between different material properties and different structural components within a device have remained poorly characterized. Using Finite Element Model (FEM) we simulate the mechanical strain on a planar silicon electrode. The results presented here demonstrate that mechanical mismatch between iridium and silicon leads to concentrated strain along the border of the two materials. This strain is further focused on small protrusions such as the electrical traces in planar silicon electrodes. These findings are confirmed with chronic in vivo data (133–189 days) in mice by correlating a combination of single-unit electrophysiology, evoked multi-unit recordings, electrochemical impedance spectroscopy, and scanning electron microscopy from traces and electrode sites with our modeling data. Several modes of mechanical failure of chronically implanted planar silicon electrodes are found that result in degradation and/or loss of recording. These findings highlight the importance of strains and material properties of various subcomponents within an electrode array.

Elastomeric and soft conducting microwires for implantable neural interfaces

“…Spontaneous recording was conducted in a dark room. Visual stimuli were presented using the MATLAB-based Psychophysics Toolbox [73–75] on a 24 inch LCD (V243H, Acer, Xizhi, New Taipei City, Taiwan) monitor placed 20 cm from the eye contralateral to the implant, spanning a visual field of 60° wide by 60° high as previously described [29, 50]. Solid black and white bar gratings were presented drifting in a perpendicular direction and recorded at 24,414 Hz.…”

“…In this way, the mechanical properties of implants affect cellular structure, metabolism, motility, transcription/translation and viability [43, 48] impacting the glial scar, neuronal health and the overall cellular response at the electrode-tissue interface [15, 18, 26, 49]. Furthermore, stiff implants that include subcomponents with large mechanical mismatch within the device have exhibited material failure induced by mechanical strain [50]. …”

Photoelectric artefact from optogenetics and imaging on microelectrodes and bioelectronics: new challenges and opportunities

“…Advances in microfabrication and packaging techniques have increased the number or density of recording sites as well as a variety of designs. Advances in biomaterials have further reduced device size, strengthening durability, improving flexibility, increasing electrical properties, attenuating tissue inflammation, and enhancing tissue integration 7-18 .…”

Implications of chronic daily anti-oxidant administration on the inflammatory response to intracortical microelectrodes

“…One emerging hypothesis concerning microelectrode failure suggests a leading role for oxidative stress in altering neuronal cell viability and blood brain barrier stability at the device-tissue interface (McConnell et al, 2009; Potter et al, 2013). In addition, it has also been proposed that the same oxidative environment can result in breakdown/corrosion of both the insulator and the metals of the electrode itself (Schmitt et al, 1999; Barrese et al, 2013; Kozai et al, 2014; Prasad et al, 2014; Sankar et al, 2014). Therefore, given this possible role for oxidative stress events, the biological mechanisms that might create and propagate a local oxidative environment around implanted microelectrodes are being investigated.…”