Abstract
Objective. Electrode arrays for chronic implantation in the brain are a critical technology in both neuroscience and medicine. Recently, flexible, thin-film polymer electrode arrays have shown promise in facilitating stable, single-unit recordings spanning months in rats. While array flexibility enhances integration with neural tissue, it also requires removal of the dura mater, the tough membrane surrounding the brain, and temporary bracing to penetrate the brain parenchyma. Durotomy increases brain swelling, vascular damage, and surgical time. Insertion using a bracing shuttle results in additional vascular damage and brain compression, which increase with device diameter; while a higher-diameter shuttle will have a higher critical load and more likely penetrate dura, it will damage more brain parenchyma and vasculature. One way to penetrate the intact dura and limit tissue compression without increasing shuttle diameter is to reduce the force required for insertion by sharpening the shuttle tip. Approach. We describe a novel design and fabrication process to create silicon insertion shuttles that are sharp in three dimensions and can penetrate rat dura, for faster, easier, and less damaging implantation of polymer arrays. Sharpened profiles are obtained by reflowing patterned photoresist, then transferring its sloped profile to silicon with dry etches. Main results. We demonstrate that sharpened shuttles can reliably implant polymer probes through dura to yield high quality single unit and local field potential recordings for at least 95 days. On insertion directly through dura, tissue compression is minimal. Significance. This is the first demonstration of a rat dural-penetrating array for chronic recording. This device obviates the need for a durotomy, reducing surgical time and risk of damage to the blood-brain barrier. This is an improvement to state-of-the-art flexible polymer electrode arrays that facilitates their implantation, particularly in multi-site recording experiments. This sharpening process can also be integrated into silicon electrode array fabrication.
Highlights
Electrode arrays for implantation in the brain are a technology critical to both fundamental neuroscience and clinical treatments for diseases including epilepsy (Toth et al, 2016), retinal degeneration (Luo and da Cruz, 2016), Parkinson’s, and depression (Lozano et al, 2019)
We report successful implantation and recording of local field potential (LFP) and single units from devices targeted to the orbitofrontal cortex (OFC), for at least 95 days
One planar shuttle successfully penetrated dura over the right hippocampus, but was excluded from subsequent calculations because it penetrated dura only after buckling to an extent that would likely have caused separation from an attached polymer probe
Summary
Electrode arrays for implantation in the brain are a technology critical to both fundamental neuroscience and clinical treatments for diseases including epilepsy (Toth et al, 2016), retinal degeneration (Luo and da Cruz, 2016), Parkinson’s, and depression (Lozano et al, 2019). 2003, Rousche and Normann, 1998) or other hard metal (Nicolelis et al, 2003) While these devices can be effective in recording single units (Mols et al, 2017), the longevity of recordings is limited (Polikov et al, 2005, Jeong et al, 2015). Implanted in animal models, polymer devices can yield single-cell recordings spanning months (Chung et al, 2019, Jeong et al, 2015, Fu et al, 2016, Luan et al, 2017), with many of the same individual neurons recorded continuously for at least ten days (Chung et al, 2019)
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