Abstract
Implantable brain electrophysiology electrodes are valuable tools in both fundamental and applied neuroscience due to their ability to record neural activity with high spatiotemporal resolution from shallow and deep brain regions. Their use has been hindered, however, by the challenges in achieving chronically stable operations. Furthermore, implantable depth neural electrodes can only carry out limited data sampling within predefined anatomical regions, making it challenging to perform large-area brain mapping. Minimizing inflammatory responses and associated gliosis formation, and improving the durability and stability of the electrode insulation layers are critical to achieve long-term stable neural recording and stimulation. Combining electrophysiological measurements with simultaneous whole-brain imaging techniques, such as magnetic resonance imaging (MRI), provides a useful solution to alleviate the challenge in scalability of implantable depth electrodes. In recent years, various carbon-based materials have been used to fabricate flexible neural depth electrodes with reduced inflammatory responses and MRI-compatible electrodes, which allows structural and functional MRI mapping of the whole brain without obstructing any brain regions around the electrodes. Here, we conducted a systematic comparative evaluation on the electrochemical properties, mechanical properties, and MRI compatibility of different kinds of carbon-based fiber materials, including carbon nanotube fibers, graphene fibers, and carbon fibers. We also developed a strategy to improve the stability of the electrode insulation without sacrificing the flexibility of the implantable depth electrodes by sandwiching an inorganic barrier layer inside the polymer insulation film. These studies provide us with important insights into choosing the most suitable materials for next-generation implantable depth electrodes with unique capabilities for applications in both fundamental and translational neuroscience research.
Highlights
Array CNT fibers were dry-drawn from a vertically super-aligned array of CNTs grown by chemical vapor deposition (CVD) on a silicon substrate (Jia et al, 2011)
The second type of CNTFs are floating catalyst CNT fibers, which were spun from the CNT membrane grown with a floating catalyst CVD method using a liquid source of carbon and an iron nanocatalyst (Zhou et al, 2021)
While for the GFs, the scanning electron microscopy (SEM) image shows a porous structure with rough surface
Summary
Implantable depth neural electrodes constitute the basis for a wide range of applications, including deciphering how information is encoded inside the brain (Buzsáki, 2004; Stanley, 2013), treating various neurological diseases (Borchers et al, 2012; Lozano and Lipsman, 2013; Cash and Hochberg, 2015), and realizing brain-machine interfaces (BMIs) (Bensmaia and Miller, 2014; Shenoy and Carmena, 2014; Choi et al, 2016; Lebedev and Nicolelis, 2017). The capability of spatiotemporal mapping at the single-neuron level is advantageous over electroencephalography (EEG) or electrocorticography (ECoG) surface probes (Kim et al, 2010; Buzsáki et al, 2012), or noninvasive brain imaging methods such as functional magnetic resonance imaging (fMRI) (Logothetis et al, 2001; Weiskopf et al, 2007; Gosselin et al, 2011; Figee et al, 2013) or functional near infrared spectroscopy (fNIR) (Izzetoglu et al, 2005; Bunce et al, 2006; Ayaz et al, 2007, 2009; Harrison et al, 2014) Despite this advantage, single neuronal recordings with implantable depth electrodes remain limited in several aspects, including the limited number of sampling sites and challenges in achieving chronically stable operation (Vitale et al, 2015). Implantable depth electrodes with high MRI compatibility are important for combining highresolution electrophysiological measurements with more global MRI mapping of brain activity for fundamental neuroscience studies, as well as clinical evaluation and monitoring
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