Devices

Arrays of 8.4 µm carbon fibers on about 150 µm pitch, inserted with a dissolvable coating or silicon backbone. Chestek lab, 2015, with a high-density follow-up in 2020.

Device — Intracortical

Carbon fiber electrode arrays (University of Michigan)

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carbon fiber · intracortical · single-unit · small footprint · Michigan · Chestek · academic · preclinical

Carbon fiber electrode arrays (University of Michigan)

One-line verdict: Single-unit recording on a fiber about 8 µm wide, solved the insertion problem that kept it from being an array, and tested in rats.

Quick tags: Recording · Intracortical · Species: Rat · First array paper: 2015

Overview

What it is: Each electrode is a carbon fiber 8.4 µm in diameter, insulated with parylene-C and coated with PEDOT:pTS. A single fiber had already recorded single units, but placing fibers one at a time with forceps does not scale to an array.

What the 2015 paper changed: Two insertion methods. A poly(ethylene glycol) coating stiffens the fibers temporarily, leaving 500 µm to 1 mm of tip exposed to penetrate the brain. Alternatively, silicon support structures hold each fiber in a groove, with shanks 150 µm apart.

Result: PEG-coated arrays were chronically implanted in five rats, with unit activity detected 31 days after implant. The silicon supports recorded single units in three acute rat surgeries, including a three-layer stacked device. The authors conclude that fibers spaced at about 150 µm insert readily, which raises recording density.

Follow-up: Patel et al. (J Neural Eng, 2020) describe high-density carbon fiber arrays for chronic electrophysiology, fast-scan cyclic voltammetry and correlative anatomy.

Spec Card Grid

Identity

  • Lab: Cynthia A. Chestek, University of Michigan
  • First array paper: Patel PR, Na K, Zhang H, Kozai TDY, Kotov NA, Yoon E, Chestek CA. J Neural Eng 12(4):046009, 2015
  • Species: rat

Geometry & Architecture

  • Fiber diameter: 8.4 µm
  • Insulation and site coating: parylene-C; PEDOT:pTS
  • Pitch: about 150 µm
  • Channel count in the 2015 paper: 16 channels (title: linear 16-channel arrays)

Evidence and limits

  • Chronic: 5 rats, unit activity at 31 days (PEG method)
  • Acute: 3 rats (silicon support method)
  • Not covered here: human use

Engineering Verdict

Strengths: a very small cross-section, which is the argument for lower tissue damage.

Limitations: handling and insertion of fibers this thin; connecting each fiber to electronics; the 2015 chronic evidence is one month.

References