title: Insertion of linear 8.4 μm 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
  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.
  
  
  METHODS
  Two approaches were tested for the insertion of carbon fiber arrays. The first method used a poly(ethylene glycol) (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.
  
  
  RESULTS
  Our results showed that the PEG coating allowed for the chronic implantation of carbon fiber arrays in five rats with unit activity detected at 31 days post-implant. The silicon support structures recorded single unit activity in three acute rat surgeries. In one of those surgeries a stacked device with three layers of silicon support structures and carbon fibers was built and shown to readily insert into the brain with unit activity on select sites.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Biomedical Engineering, College of Engineering, University of Michigan, USA.
authors.forename: Paras R
authors.initials: PR
authors.lastname: Patel
authors.forename: Kyounghwan
authors.initials: K
authors.lastname: Na
authors.forename: Huanan
authors.initials: H
authors.lastname: Zhang
authors.forename: Takashi D Y
authors.initials: TD
authors.lastname: Kozai
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Kotov
authors.forename: Euisik
authors.initials: E
authors.lastname: Yoon
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Chestek
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002244:Carbon / Q000737:chemistry*; D000077482:Carbon Fiber; D004553:Electric Conductivity; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008297:Male; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D019919:Prosthesis Implantation / Q000379:methods; D051381:Rats; D020318:Rats, Long-Evans; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D046888:Tissue Array Analysis / Q000295:instrumentation
chemical_list: D000077482:Carbon Fiber; D002244:Carbon