Chronic In Vivo Evaluation of PEDOT/CNT for Stable Neural Recordings

Abstract

Objective Sub-cellular sized chronically implanted recording electrodes have demonstrated significant improvement in single-unit (SU) yield over larger recording probes. Additional work expands on this initial success by combining the subcellular fiber-like lattice structures with the design space versatility of silicon microfabrication to further improve the signal-to-noise ratio, density of electrodes, and stability of recorded units over months to years. However, ultra-small microelectrodes present very high impedance, which must be lowered for SU recordings. While poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS) coating has demonstrated great success in acute to early-chronic studies for lowering the electrode impedance, concern exists over long-term stability. Here, we demonstrate a new blend of PEDOT doped with carboxyl functionalized multi-walled carbon nanotubes (CNTs) which shows dramatic improvement over the traditional PEDOT/PSS formula. Methods Lattice style subcellular electrode arrays were fabricated using previously established method. PEDOT was polymerized with carboxylic acid functionalized carbon nanotubes onto high impedance (8.0±0.1 MΩ: M±S.E.) 250 µm2 gold recording sites. Results PEDOT/CNT coated subcellular electrodes demonstrated significant improvement in chronic spike recording stability over four months compared to PEDOT/PSS recording sites. Conclusion These results demonstrate great promise for subcellular sized recording and stimulation electrodes and long-term stability. Significance This project uses leading-edge biomaterials to develop chronic neural probes that are small (sub-cellular) with excellent electrical properties for stable long-term recordings. High density ultrasmall electrodes combined with advanced electrode surface modification are likely to make significant contributions to the development of long-term (permanent), high quality, and selective neural interfaces.

Ultrasoft microwire neural electrodes improve chronic tissue integration

“…Furthermore, methods need to be developed to fabricate multi-channel devices. In addition, conducting polymer and nanomaterial modifications of the electrode sites to improve neural recording specificity and long-term quality can greatly expand the versatility of this device [25,49,101]. Additional modifications to include bioactive coatings that promote neuronal health and reduce acute inflammation may further improve electrode tissue integration [51,53,102–105].…”

Two-photon imaging of chronically implanted neural electrodes: Sealing methods and new insights

“…For example, material failure is believed to range from recording site to insulation damages including delamination, crack propagation, hydration which leads to loss of dielectric properties and iconic contamination (Escamilla-Mackert et al, 2009; Gilgunn et al, 2013; Kim et al, 2014; Kozai et al, 2014a; Kozai et al, 2015a; Kozai et al, 2015b; Prasad et al, 2014; Prasad et al, 2012; Sankar et al, 2014; Ware et al, 2014). On the other hand, biological failure modes are believed to be due to the inflammatory reactive tissue response to the implanted electrode (Gilgunn et al, 2012; Jaquins-Gerstl et al, 2011; Karumbaiah et al, 2012; Kozai et al, 2014a; Kozai et al, 2014b; Kozai et al, 2012a; Kozai et al, 2014c; Kozai et al, 2010; Potter et al, 2013; Rennaker et al, 2007; Turner et al, 1999).…”

Thinking Small: Progress on Microscale Neurostimulation Technology

“…PEDOT-PSS also displayed a 15-fold improvement in charge-injection capacity of ~15 mC/cm 2 (55). The problem for PEDOT-PSS is durability, and while electrodeposition of PEDOT with a tetrafluoroborate (56,57) or perhaps inclusion of appropriately functionalized carbon nanotubes (58) improves electrochemical performance and stability, long term robustness especially for neural stimulation remains elusive. Instead, metallic/oxide-based coatings are more likely to demonstrate long term stability in vivo for neural stimulation applications.…”

“…For an exposed geometric surface area of 500 μm 2 , carbon fibers show impedance levels of greater than 1 MΩ at 1 kHz and a charge-injection limit below 0.05 mC/cm 2 . The majority of prior work with carbon fiber tips has relied on coatings with PEDOT-PSS or PEDOT-PSS with carbon nanotubes (58). Unfortunately, as previously noted, PEDOT is unlikely to provide a stable electrochemical interface for chronic neural stimulation.…”