Polymerization of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) around living neural cells (original) (raw)
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Acta Biomaterialia, 2014
Poly(3,4-ethylenedioxythiophene) (PEDOT) films have attracted substantial interest as coatings for platinum neuroprosthetic electrodes due to their excellent chemical stability and electrical properties. This study systematically examined PEDOT coatings formed with different amounts of charge and dopant ions, and investigated the combination of surface characteristics that were optimal for neural cell interactions. PEDOT samples were fabricated by varying the electrodeposition charge from 0.05 to 1 C cm À2 . Samples were doped with either poly(styrenesulfonate), tosylate (pTS) or perchlorate. Scanning electron micrographs revealed that both thickness and nodularity increased as the charge used to produce the sample was increased, and larger dopants produced smoother films across all thicknesses. X-ray photoelectron spectroscopy confirmed that the amount of charge directly corresponded to the thickness and amount of dopant in the samples. Additionally, with increased thickness and nodularity, the electrochemical properties of all PEDOT coatings improved. However, neural cell adhesion and outgrowth assays revealed that there is a direct biological tradeoff related to the thickness and nodularity. Cell attachment, growth and differentiation was poorer on the thicker, rougher samples, but thin, less nodular PEDOT films exhibited significant improvements over bare platinum. PEDOT/pTS fabricated with a charge density of <0.1 C cm À2 provided superior electrochemical and biological properties over conventional platinum electrodes and would be the most suitable conducting polymer for neural interface applications.
Electrochemical polymerization of conducting polymers in living neural tissue
Journal of neural engineering, 2007
A number of biomedical devices require extended electrical communication with surrounding tissue. Significant improvements in device performance would be achieved if it were possible to maintain communication with target cells despite the reactive, insulating scar tissue that forms at the device-tissue interface. Here, we report that the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) can be polymerized directly within living neural tissue resulting in an electrically conductive network that is integrated within the tissue. Nano and microscale PEDOT filaments extend out from electrode sites, presumably forming within extracellular spaces. The cloud of PEDOT filaments penetrates out into the tissue far enough that it should be possible to bypass fibrous scar tissue and contact surrounding healthy neurons. These electrically functional, diffuse conducting polymer networks grown directly within tissue signify a new paradigm for creating soft, low impedance implantable electrodes.
Applied biochemistry and biotechnology, 2006
A novel conducting polymer, poly(hydroxymethylated-3,4-ethylenedioxythiophene) (PEDOT-MeOH), was electrochemically deposited onto the electrodes of micromachined neural probes. Uniformly distributed film was obtained from aqueous solution when doped with polystyrenesulfonate. The surface morphology was rough and had good cellular adhesion. Impedance spectroscopy showed that the magnitude of coated electrode was lower than that of the bare gold over a range of frequencies from 10 0 to 10 5 Hz. Since the biocompatibility of the interface between the neural probes and brain tissue plays an important role when the probes are implanted in the central nervous system for long-term application, biomolecules were incorporated into the coating. Nonapeptide CDPGYIGSR was codeposited as the counterion in the conducting films. The surface morphology of the coating was fuzzy, providing many bioactive sites for interaction with neural cells. The magnitude of impedance was as low as 53 kΩ at the biologically relevant frequency of 1 kHz. An in vitro experiment demonstrated that the neuroblas-118 Xiao et al.
Composite biomolecule/PEDOT materials for neural electrodes
Biointerphases, 2008
Electrodes intended for neural communication must be designed to meet both the electrochemical and biological requirements essential for long term functionality. Metallic electrode materials have been found inadequate to meet these requirements and therefore conducting polymers for neural electrodes have emerged as a field of interest. One clear advantage with polymer electrodes is the possibility to tailor the material to have optimal biomechanical and chemical properties for certain applications. To identify and evaluate new materials for neural communication electrodes, three charged biomolecules, fibrinogen, hyaluronic acid ͑HA͒, and heparin are used as counterions in the electrochemical polymerization of poly͑3,4-ethylenedioxythiophene͒ ͑PEDOT͒. The resulting material is evaluated electrochemically and the amount of exposed biomolecule on the surface is quantified. PEDOT:biomolecule surfaces are also studied with static contact angle measurements as well as scanning electron microscopy and compared to surfaces of PEDOT electrochemically deposited with surfactant counterion polystyrene sulphonate ͑PSS͒. Electrochemical measurements show that PEDOT:heparin and PEDOT:HA, both have the electrochemical properties required for neural electrodes, and PEDOT:heparin also compares well to PEDOT:PSS. PEDOT:fibrinogen is found less suitable as neural electrode material.
Journal of Neural …, 2011
We investigated using poly(3,4-ethylenedioxythiophene) (PEDOT) to lower the impedance of small, gold recording electrodes with initial impedances outside of the effective recording range. Smaller electrode sites enable more densely packed arrays, increasing the number of input and output channels to and from the brain. Moreover, smaller electrode sizes promote smaller probe designs; decreasing the dimensions of the implanted probe has been demonstrated to decrease the inherent immune response, a known contributor to the failure of long-term implants. As expected, chronically implanted control electrodes were unable to record well-isolated unit activity, primarily as a result of a dramatically increased noise floor. Conversely, electrodes coated with PEDOT consistently recorded high-quality neural activity, and exhibited a much lower noise floor than controls. These results demonstrate that PEDOT coatings enable electrode designs 15 microns in diameter.
In Vivo Electrochemical Analysis of a PEDOT/MWCNT Neural Electrode Coating
2015
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.
Cell attachment functionality of bioactive conducting polymers for neural interfaces
Biomaterials, 2009
Bioactive coatings for neural electrodes that are tailored for cell interactions have the potential to produce superior implants with improved charge transfer capabilities. In this study synthetically produced anionically modified laminin peptides DEDEDYFQRYLI and DCDPGYIGSR were used to dope poly(3,4-ethylenedioxythiophene) (PEDOT) electrodeposited on platinum (Pt) electrodes. Performance of peptide doped films was compared to conventional polymer PEDOT/paratoluene sulfonate (pTS) films using SEM, XPS, cyclic voltammetry, impedance spectroscopy, mechanical hardness and adherence. Bioactivity of incorporated peptides and their affect on cell growth was assessed using a PC12 neurite outgrowth assay. It was demonstrated that large peptide dopants produced softer PEDOT films with a minimal decrease in electrochemical stability, compared to the conventional dopant, pTS. Cell studies revealed that the YFQRYLI ligand retained neurite outgrowth bioactivity when DEDEDYFQRYLI was used as a dopant, but the effect was strongly dependant on initial cell attachment. Alternate peptide dopant, DCDPGYIGSR was found to impart superior cell attachment properties when compared to DEDE-DYFQRYLI, but attachment on both peptide doped polymers could be enhanced by coating with whole native laminin.
2003
Micromachined neural prosthetic devices facilitate the functional stimulation of and recording from the central nervous system (CNS). These devices have been fabricated to consist of silicon shanks that have gold or iridium sites along their surface. Our goal is to improve the biocompatibility and long-term performance of the neural prosthetic probes when they are implanted chronically in the brain. In our most recent efforts we have established that electrochemical polymerization can be used to deposit fuzzy coatings of conducting polymers specifically on the electrode sites. For neural prosthetic devices that are intended for long term implantation, we need to develop surfaces that provide intimate contact and promote efficient signal transport at the interface of the microelectrode array and brain tissue. We have developed methods to rapidly and reliably fabricate nanostructured conducting polymer coatings on the electrode probes using templated and surfactant-mediated techniques. Conducting polymer nanomushrooms and nanohairs of polypyrrole (PPy) were electrochemically polymerized onto the functional sites of neural probes by using either nanoporous block copolymers thin films, "track-etched" polycarbonate films or anodic aluminium oxide membranes as templates. Nanofibers of conducting polymers have also been successfully obtained by polymerizations in the presence of surfactants. The influence of current density, monomer concentration, surfactant concentration, and deposition charge on the thickness and morphology of the nanostructured conducting polymer coatings has been studied by optical, scanned probe, scanning electron and transmission electron microscopy. As compared with the normal nodular morphology of polypyrrole, the nanostructured morphologies grown from the neural electrode result in fuzzy coatings with extremely high surface area. The electrical properties of the polymer coatings were studied by Impedance Spectroscopy (IS) and Cyclic Voltammetry (CV). The significant drop in impedance in magnitude and phase angle is consistent with an increase of the surface area due to the roughened surface morphology.