Nanocomposites of iridium oxide and conducting polymers as electroactive phases in biological media

Nanocarbon-Iridium Oxide Nanostructured Hybrids as Large Charge Capacity Electrostimulation Electrodes for Neural Repair

Nanostructuring nanocarbons with IrO_x yields to material coatings with large charge capacities for neural electrostimulation, and large reproducibility in time, that carbons do not exhibit. This work shows the contributions of carbon and the different nanostructures present, as well as the impact of functionalizing graphene with oxygen and nitrogen, and the effects of including conducting polymers within the hybrid materials. Different mammalian neural growth models differentiate the roles of the substrate material in absence and in presence of applied electric fields and address optimal electrodes for the future clinical applications.

Controlling Nerve Growth with an Electric Field Induced Indirectly in Transparent Conductive Substrate Materials

Innovative neurostimulation therapies require improved electrode materials, such as poly(3,4-ethylenedioxythiophene) (PEDOT) polymers or IrO_x mixed ionic-electronic conductors and better understanding of how their electrochemistry influences nerve growth. Amphibian neurons growing on transparent films of electronic (metal) conductors and electronic-ionic conductors (polymers and semiconducting oxides) are monitored. Materials are not connected directly to the power supply, but a dipole is created wirelessly within them by electrodes connected to the culture medium in which they are immersed. Without electrical stimulation neurons grow on gold, platinum, PEDOT-polystyrene sulfonate (PEDOT-PSS), IrO_x , and mixed oxide (Ir-Ti)O_x , but growth is not related to surface texture or hydrophilicity. Stimulation induces a dipole in all conductive materials, but neurons grow differently on electronic conductors and mixed-valence mixed-ionic conductors. Stimulation slows, but steers neurite extension on gold but not on platinum. The rate and direction of neurite growth on PEDOT-PSS resemble that on glass, but on IrO_x and (Ir-Ti)O_x neurites grow faster and in random directions. This suggests electrochemical changes induced in these materials control growth speed and direction selectively. Evidence that the electric dipole induced in conductive material controls nerve growth will impact electrotherapies exploiting wireless stimulation of implanted material arrays, even where transparency is required.

Biosafety assessment of conducting nanostructured materials by using co-cultures of neurons and astrocytes

Neural electrode implants are made mostly of noble materials. We have synthesized a nanostructured material combining the good electrochemical properties of iridium oxide (IrOx) and carbon-nanotubes (CNT) and the properties of poly(3,4-ethylenedioxythiophene) (PEDOT). IrOx-CNT-PEDOT charge storage capacity was lower than that of IrOx and IrOx-CNT, but higher than that of other PEDOT-containing hybrids and Pt. Cyclic voltammetry, SEM, XPS and micro-Raman spectroscopy suggest that PEDOT encapsulates IrOx and CNT. In our search for a cell culture platform that could optimize modelling the in vivo environment, we determined cell viability, neuron and astrocyte functionality and the response of astrocytes to an inflammatory insult by using primary cultures of neurons, of astrocytes and co-cultures of both. The materials tested (based on IrOx, CNT and PEDOT, as well as Pt as a reference) allowed adhesion and proliferation of astrocytes and full compatibility for neurons grown in co-cultures. Functionality assays show that uptake of glutamate in neuron-astrocyte co-culture was significantly higher than the sum of the uptake in astrocytes and neurons. In co-cultures on IrOx, IrOx-CNT and IrOx-CNT-PEDOT, glutamate was released by a depolarizing stimulus and induced a significant increase in intracellular calcium, supporting the expression of functional NMDA/glutamate receptors. LPS-induced inflammatory response in astrocytes showed a decreased response in NOS2 and COX2 mRNA expression for IrOx-CNT-PEDOT. Results indicate that neuron-astrocyte co-cultures are a reliable model for assessing the biocompatibility and safety of nanostructured materials, evidencing also that hybrid IrOx-CNT-PEDOT nanocomposite materials may offer larger resistance to inflammatory insults.

Long-Term Stable Adhesion for Conducting Polymers in Biomedical Applications: IrOx and Nanostructured Platinum Solve the Chronic Challenge

Conducting polymers (CPs) have frequently been described as outstanding coating materials for neural microelectrodes, providing significantly reduced impedance or higher charge injection compared to pure metals. Usability has until now, however, been limited by poor adhesion of polymers like poly(3,4-ethylenedioxythiophene) (PEDOT) to metallic substrates, ultimately precluding long-term applications. The aim of this study was to overcome this weakness of CPs by introducing two novel adhesion improvement strategies that can easily be integrated with standard microelectrode fabrication processes. Iridium Oxide (IrOx) demonstrated exceptional stability for PEDOT coatings, resulting in polymer survival over 10 000 redox cycles and 110 days under accelerated aging conditions at 60 °C. Nanostructured Pt was furthermore introduced as a purely mechanical adhesion promoter providing 10-fold adhesion improvement compared to smooth Pt substrates by simply altering the morphology of Pt. This layer can be realized in a very simple process that is compatible with any electrode design, turning nanostructured Pt into a universal adhesion layer for CP coatings. By the introduction of these adhesion-promoting strategies, the weakness of CP-based neural probes can ultimately be eliminated and true long-term stable use of PEDOT on neural probes will be possible in future electrode generations.

Electrospinning of PELA/PPY Fibrous Conduits: Promoting Peripheral Nerve Regeneration in Rats by Self-Originated Electrical Stimulation

Peripheral nerve injuries represent a great challenge for surgeons. The conductive neural scaffold has experienced increasing interest because of its good biocompatibility and similar electrical properties as compared to those of a normal nerve. Herein, nerve conduits made from poly(d,l-lactide)-co-poly(ethylene glycol) and polypyrrole (20%, 30%, and 50%) (PELA-PPY) were prepared by electrospinning, and used in regeneration of peripheral nerve defects. The results of an in vitro experiment indicated a high biocompatibility for the as-prepared materials, supporting the attachment and proliferation of a rat pheochromocytoma PC-12 cell. Furthermore, the PELA-PPY nerve conduit implanted in the sciatic nerve defects (10 mm) of the Spraguee-Dawley rats for 12 weeks showed similar results with the autograft, while it demonstrated a better outcome than the PELA nerve conduit in electrophysiological examination, sciatic function index, total amount of regenerated myelinated nerve fibers, axon diameter, myelin thickness, and several immunohistochemistry indices (S-100, laminin, neurofilament, bromodeoxyuridine, and glial fibrillary acidic portein). We supposed that the bioactivity is mainly generated by the PPY in composite nanofibers which could transmit self-originated electrical stimulation between cells. Due to the facile preparation and excellent in vivo performance, the PPY-PELA nerve conduit is promising for use as a bioengineered biomaterial for peripheral nerve regeneration.

Coatings of nanostructured pristine graphene-IrOx hybrids for neural electrodes: Layered stacking and the role of non-oxygenated graphene

The need to enhance charge capacity in neural stimulation-electrodes is promoting the formation of new materials and coatings. Among all the possible types of graphene, pristine graphene prepared by graphite electrochemical exfoliation, is used in this work to form a new nanostructured IrOx-graphene hybrid (IrOx-eG). Graphene is stabilized in suspension by IrOx nanoparticles without surfactants. Anodic electrodeposition results in coatings with much smaller roughness than IrOx-graphene oxide. Exfoliated pristine graphene (eG), does not electrodeposit in absence of iridium, but IrOx-nanoparticle adhesion on graphene flakes drives the process. IrOx-eG has a significantly different electronic state than graphene oxide, and different coordination for carbon. Electron diffraction shows the reflection features expected for graphene. IrOx 1-2 nm cluster/nanoparticles are oxohydroxo-species and adhere to 10nm graphene platelets. eG induces charge storage capacity values five times larger than in pure IrOx, and if calculated per carbon atom, this enhancement is one order magnitude larger than the induced by graphene oxide. IrOx-eG coatings show optimal in vitro neural cell viability and function as cell culture substrates. The fully straightforward electrochemical exfoliation and electrodeposition constitutes a step towards the application of graphene in biomedical systems, expanding the knowledge of pristine graphene vs. graphene oxide, in bioelectrodes.

Assessment by Ames test and comet assay of toxicity potential of polymer used to develop field-capable rapid-detection device to analyze environmental samples

There is need for devices that decrease detection time of food-borne pathogens from days to real-time. In this study, a rapid-detection device is being developed and assessed for potential cytotoxicity. The device is comprised of melt-spun polypropylene coupons coated via oxidative chemical vapor deposition (oCVD) with 3,4-Ethylenedioxythiophene (EDOT), for conductivity and 3-Thiopheneethanol (3TE), allowing antibody attachment. The Ames test and comet assay have been used in this study to examine the toxicity potentials of EDOT, 3TE, and polymerized EDOT-co-3TE. For this study, Salmonella typhimurium strain TA1535 was used to assess the mutagenic potential of EDOT, 3TE and the copolymer. The average mutagenic potential of EDOT, 3TE and copolymer was calculated to be 0.86, 0.56, and 0.92, respectively. For mutagenic potential, on a scale from 0 to 1, close to 1 indicates low potential for toxicity, whereas a value of 0 indicates a high potential for toxicity. The comet assay is a single-cell gel electrophoresis technique that is widely used for this purpose. This assay measures toxicity based on the area or intensity of the comet-like shape that DNA fragments produce when DNA damage has occurred. Three cell lines were assessed; FRhK-4, BHK-21, and Vero cells. After averaging the results of all three strains, the tail intensity of the copolymer was 8.8 % and tail moment was 3.0, and is most similar to the untreated control, with average tail intensity of 5.7 % and tail moment of 1.7. The assays conducted in this study provide evidence that the copolymer is non-toxic to humans.