Insertion of linear 8.4μm diameter 16 channel carbon fiber electrode arrays for single unit recordings

Abstract

Objective Single carbon fiber electrodes (d=8.4 μm) insulated with parylene-c and functionalized with PEDOT:pTS have been shown to record single unit activity but manual implantation of these devices with forceps can be difficult. Without an improvement in the insertion method any increase in the channel count by fabricating carbon fiber arrays would be impractical. In this study, we utilize a water soluble coating and structural backbones that allow us to create, implant, and record from fully functionalized arrays of carbon fibers with ~150 μm pitch. Approach Two approaches were tested for the insertion of carbon fiber arrays. The first method used a PEG coating that temporarily stiffened the fibers while leaving a small portion at the tip exposed. The small exposed portion (500 μm – 1 mm) readily penetrated the brain allowing for an insertion that did not require the handling of each fiber by forceps. The second method involved the fabrication of silicon support structures with individual shanks spaced 150 μm apart. Each shank consisted of a small groove that held an individual carbon fiber. Main results Our results showed that the PEG coating allowed for the chronic implantation of carbon fiber arrays in 5 rats with unit activity detected at 31 days post-implant. The silicon support structures recorded single unit activity in 3 acute rat surgeries. In one of those surgeries a stacked device with 3 layers of silicon support structures and carbon fibers was built and shown to readily insert into the brain with unit activity on select sites. Significance From these studies we have found that carbon fibers spaced at ~150 μm readily insert into the brain. This greatly increases the recording density of chronic neural probes and paves the way for even higher density devices that have a minimal scarring response.

Chronicin vivostability assessment of carbon fiber microelectrode arrays

“…Carbon fiber arrays were fabricated as previously described [42]. Briefly, individual fibers were secured to bare traces (152.4 μm pitch) of a custom made PCB with silver epoxy that was then heat cured.…”

“…Probe tips also received a site coating of PEDOT:pTS with the same formula and deposition parameters used on the fibers that underwent soak testing. The final preparation step was a coating of poly(ethylene glycol) (PEG) as described in [42]. …”

Thinking Small: Progress on Microscale Neurostimulation Technology

“…Softer, polymeric materials such as SU-8 and bio-inspired nanocomposites may decrease this gap by 3–4 orders of magnitude. Values for moduli of each substrate were taken from published literature: Iridium (24), carbon fiber (25,26), platinum (24), silicon (27), a-SiC (28), gold (29), SU-8 (30), Parylene C (31), nanocomposite (32), and human brain tissue (33). …”

“…For neural recording or stimulation, carbon fibers are electrically conductive and their small cross-sectional area makes them attractive due to their minimal invasiveness during implantation, minimal risk of blood-brain-barrier disruption, and reduced tissue displacement (37,61,62). Carbon fibers have a typical radii of about 4–7 μm and are mechanically stiff with a Young’s modulus of 241 - 380 GPa (25,26). The small cross-sectional area allows the fibers to be mechanically compliant within neuronal tissues (62).…”

“…The small cross-sectional area allows the fibers to be mechanically compliant within neuronal tissues (62). Implanted carbon fiber microelectrodes have provided high quality single and multi-unit recordings in acute and chronic experiments (25,26,62). Carbon fiber microelectrodes have been shown to record at high signal-to-noise from a variety of neuronal cell types, across a variety of brain regions at varying depth in different animal models including songbirds (26) and rat cortex (25,62).…”