Sharpened and mechanically robust carbon fiber electrode arrays for neural interfacing

Objective: Bioelectric medicine offers therapeutic diagnoses and treatments for disorders of the nervous system unresponsive to pharmacological treatments. While current neural interfaces effectively treat many disorders with stimulation, recording specificity is often limited to gross averages across many neurons or axons. Here, we develop and describe a novel, robust carbon fiber electrode array adaptable to many neural structures for precise neural recording. Approach: Carbon fibers were sharpened using a blowtorch method made reproducible by using the reflection of fibers against the surface of a water bath. Arrays of carbon fibers were developed by partially embedding carbon fibers in medical-grade silicone to improve robustness to fracture. Acute spontaneous electrophysiology was recorded from the rat cervical vagus nerve, feline dorsal root ganglia, and rat brain. Acute brushing and bladder pressure electrophysiology was recorded from feline dorsal root ganglia as well. Main results: Blowtorching resulted in fibers of 72.3 ± 33.5 degree tip angle with 146.8 ± 17.7 μm exposed carbon. Silicone-embedded carbon fiber arrays were robust to bending (87.5% of fibers remained unbroken, 50,000 passes). Observable neural clusters were recorded using sharpened carbon fiber electrodes from rat cervical vagus nerve (41.8 μVpp, N=3 electrodes), feline dorsal root ganglia (101.1 μVpp, N=32 electrodes), and rat brain (80.7 μVpp, N=7 electrodes). Recordings from the feline dorsal root ganglia included physiologically-relevant signals from increased bladder pressure and cutaneous brushing. Significance: These results suggest that this carbon fiber array is a uniquely robust and adaptable neural recording device, useful for specific electrophysiology measurements. In the future, this device may be useful as a bioelectric medicine tool for diagnosis and closed-loop neural control of therapeutic treatments and monitoring systems.