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In Vivo Electrochemical Analysis of a PEDOT/MWCNT Neural Electrode Coating.

Alba NA, Du ZJ, Catt KA, Kozai TD, Cui XT - Biosensors (Basel) (2015)

Bottom Line: Equivalent circuit analysis showed that the impedance increase is the result of surface capacitance reduction, likely due to protein and cellular processes encapsulating the porous coating.Some coated electrodes exhibited steady impedance while others exhibiting large increases associated with large decreases in charge storage capacity suggesting delamination in PBS.Despite the impedance increase, coated electrodes successfully recorded neural activity throughout the implantation period.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Pittsburgh, 5056 Biomedical Science Tower 3, 3501 Fifth Avenue, Pittsburgh, PA 15213, USA. nicolasaalba@gmail.com.

ABSTRACT
Neural electrodes hold tremendous potential for improving understanding of brain function and restoring lost neurological functions. Multi-walled carbon nanotube (MWCNT) and dexamethasone (Dex)-doped poly(3,4-ethylenedioxythiophene) (PEDOT) coatings have shown promise to improve chronic neural electrode performance. Here, we employ electrochemical techniques to characterize the coating in vivo. Coated and uncoated electrode arrays were implanted into rat visual cortex and subjected to daily cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for 11 days. Coated electrodes experienced a significant decrease in 1 kHz impedance within the first two days of implantation followed by an increase between days 4 and 7. Equivalent circuit analysis showed that the impedance increase is the result of surface capacitance reduction, likely due to protein and cellular processes encapsulating the porous coating. Coating's charge storage capacity remained consistently higher than uncoated electrodes, demonstrating its in vivo electrochemical stability. To decouple the PEDOT/MWCNT material property changes from the tissue response, in vitro characterization was conducted by soaking the coated electrodes in PBS for 11 days. Some coated electrodes exhibited steady impedance while others exhibiting large increases associated with large decreases in charge storage capacity suggesting delamination in PBS. This was not observed in vivo, as scanning electron microscopy of explants verified the integrity of the coating with no sign of delamination or cracking. Despite the impedance increase, coated electrodes successfully recorded neural activity throughout the implantation period.

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(a–d) Representative unit recording from a PEDOT/MWCNT/Dex-coated electrode at day 11 post-implantation. Red line indicates onset of visual stimulus. (a) Filtered (300 Hz–3 kHz) data stream; (b) Two example units sorted from the same coated electrode; (c) Peristimulus time histogram (PSTH) for each respective unit.; (d) Interspike interval (ISI) histogram of the two example units; (e) Average signal-to-noise ratio (SNR) values on representative days pre and post-release stimulus; (f) Average noise amplitude on representative days pre and post-release stimulus. All groups exhibited similar values within each day, suggesting equivalent performance. All data presented as mean ± SD. p > 0.01 for all.
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biosensors-05-00618-f004: (a–d) Representative unit recording from a PEDOT/MWCNT/Dex-coated electrode at day 11 post-implantation. Red line indicates onset of visual stimulus. (a) Filtered (300 Hz–3 kHz) data stream; (b) Two example units sorted from the same coated electrode; (c) Peristimulus time histogram (PSTH) for each respective unit.; (d) Interspike interval (ISI) histogram of the two example units; (e) Average signal-to-noise ratio (SNR) values on representative days pre and post-release stimulus; (f) Average noise amplitude on representative days pre and post-release stimulus. All groups exhibited similar values within each day, suggesting equivalent performance. All data presented as mean ± SD. p > 0.01 for all.

Mentions: Neurophysiological recording capability of coated electrodes compared to uncoated electrodes was evaluated through the visual stimulation of the array-implanted animals. Visual stimulation evoked robust firing rate change during the entire period of experimentation. A representative filtered (0.3–5 kHz) spike data stream from a coated channel on the last day of implantation is shown in Figure 4a, with visual stimulation initiation time indicated. Waveforms, inter-spike interval histograms, and PSTHs of two representative sorted single units on this channel are presented in Figure 4b–d. Average recording SNR (signal-to-noise ratio) and noise amplitude between the coated and uncoated electrodes are compared in Figure 4e,f. Same-day unit information is divided into groups before and after CV to evaluate the influence of CV on neural activity. Only channels exhibiting detectable spiking behavior were included in SNR computations, resulting in values of N between 8 and 15 per group. No significant difference was observed between pre and post-CV values of SNR or noise amplitude of either coated or uncoated electrodes at any time point (p > 0.01 for all). Performance was also not observed to be correlated with impedance during the initial week, as uncoated and coated probes exhibited the same noise amplitude and SNR despite having significantly different 1 kHz impedance. In general, the coated channels performed similarly in comparison with uncoated channels.


In Vivo Electrochemical Analysis of a PEDOT/MWCNT Neural Electrode Coating.

Alba NA, Du ZJ, Catt KA, Kozai TD, Cui XT - Biosensors (Basel) (2015)

(a–d) Representative unit recording from a PEDOT/MWCNT/Dex-coated electrode at day 11 post-implantation. Red line indicates onset of visual stimulus. (a) Filtered (300 Hz–3 kHz) data stream; (b) Two example units sorted from the same coated electrode; (c) Peristimulus time histogram (PSTH) for each respective unit.; (d) Interspike interval (ISI) histogram of the two example units; (e) Average signal-to-noise ratio (SNR) values on representative days pre and post-release stimulus; (f) Average noise amplitude on representative days pre and post-release stimulus. All groups exhibited similar values within each day, suggesting equivalent performance. All data presented as mean ± SD. p > 0.01 for all.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4697137&req=5

biosensors-05-00618-f004: (a–d) Representative unit recording from a PEDOT/MWCNT/Dex-coated electrode at day 11 post-implantation. Red line indicates onset of visual stimulus. (a) Filtered (300 Hz–3 kHz) data stream; (b) Two example units sorted from the same coated electrode; (c) Peristimulus time histogram (PSTH) for each respective unit.; (d) Interspike interval (ISI) histogram of the two example units; (e) Average signal-to-noise ratio (SNR) values on representative days pre and post-release stimulus; (f) Average noise amplitude on representative days pre and post-release stimulus. All groups exhibited similar values within each day, suggesting equivalent performance. All data presented as mean ± SD. p > 0.01 for all.
Mentions: Neurophysiological recording capability of coated electrodes compared to uncoated electrodes was evaluated through the visual stimulation of the array-implanted animals. Visual stimulation evoked robust firing rate change during the entire period of experimentation. A representative filtered (0.3–5 kHz) spike data stream from a coated channel on the last day of implantation is shown in Figure 4a, with visual stimulation initiation time indicated. Waveforms, inter-spike interval histograms, and PSTHs of two representative sorted single units on this channel are presented in Figure 4b–d. Average recording SNR (signal-to-noise ratio) and noise amplitude between the coated and uncoated electrodes are compared in Figure 4e,f. Same-day unit information is divided into groups before and after CV to evaluate the influence of CV on neural activity. Only channels exhibiting detectable spiking behavior were included in SNR computations, resulting in values of N between 8 and 15 per group. No significant difference was observed between pre and post-CV values of SNR or noise amplitude of either coated or uncoated electrodes at any time point (p > 0.01 for all). Performance was also not observed to be correlated with impedance during the initial week, as uncoated and coated probes exhibited the same noise amplitude and SNR despite having significantly different 1 kHz impedance. In general, the coated channels performed similarly in comparison with uncoated channels.

Bottom Line: Equivalent circuit analysis showed that the impedance increase is the result of surface capacitance reduction, likely due to protein and cellular processes encapsulating the porous coating.Some coated electrodes exhibited steady impedance while others exhibiting large increases associated with large decreases in charge storage capacity suggesting delamination in PBS.Despite the impedance increase, coated electrodes successfully recorded neural activity throughout the implantation period.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Pittsburgh, 5056 Biomedical Science Tower 3, 3501 Fifth Avenue, Pittsburgh, PA 15213, USA. nicolasaalba@gmail.com.

ABSTRACT
Neural electrodes hold tremendous potential for improving understanding of brain function and restoring lost neurological functions. Multi-walled carbon nanotube (MWCNT) and dexamethasone (Dex)-doped poly(3,4-ethylenedioxythiophene) (PEDOT) coatings have shown promise to improve chronic neural electrode performance. Here, we employ electrochemical techniques to characterize the coating in vivo. Coated and uncoated electrode arrays were implanted into rat visual cortex and subjected to daily cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for 11 days. Coated electrodes experienced a significant decrease in 1 kHz impedance within the first two days of implantation followed by an increase between days 4 and 7. Equivalent circuit analysis showed that the impedance increase is the result of surface capacitance reduction, likely due to protein and cellular processes encapsulating the porous coating. Coating's charge storage capacity remained consistently higher than uncoated electrodes, demonstrating its in vivo electrochemical stability. To decouple the PEDOT/MWCNT material property changes from the tissue response, in vitro characterization was conducted by soaking the coated electrodes in PBS for 11 days. Some coated electrodes exhibited steady impedance while others exhibiting large increases associated with large decreases in charge storage capacity suggesting delamination in PBS. This was not observed in vivo, as scanning electron microscopy of explants verified the integrity of the coating with no sign of delamination or cracking. Despite the impedance increase, coated electrodes successfully recorded neural activity throughout the implantation period.

Show MeSH
Related in: MedlinePlus