Publications
113 results found
Green RA, Toor H, Dodds C, et al., 2012, Variation in performance of platinum electrodes with size and surface roughness, Sensors and Materials, Vol: 24, Pages: 165-180, ISSN: 0914-4935
Ouyang L, Green R, Feldman KE, et al., 2011, Direct local polymerization of poly(3,4-ethylenedioxythiophene) in rat cortex, Progress in Brain Research, Vol: 194, Pages: 263-271, ISSN: 1875-7855
Glial scar encapsulation is thought to be one of the major reasons for the failure of chronic brain-machine interfaces. Many strategies, including modification of the probe surface chemistry, delivery of anti-inflammatory drugs, and changes of probe geometry, have been employed to reduce glial scar formation. We have proposed that a possible means to establish long-term, reliable communication across the scar is the in situ polymerization of conjugated polymers such as PEDOT in neural tissue. Previously, we exposed entire brain slices to the EDOT monomer. Here, we demonstrate that PEDOT can be polymerized by the direct delivery of EDOT monomer to the reaction site. The monomer was delivered into rat cortex via microcannula and simultaneously electrochemically polymerized within the tissue using a microwire electrode. We found that the resulting PEDOT polymer cloud grew out from the working electrode tip and extended far out into the brain tissue, spanning distances more than 1. mm. We also examined the morphology of resulting polymer cloud by optical microscopy. © 2011 Elsevier B.V.
Green RA, Duan C, Hassarati R, et al., 2011, Electrochemical stability of poly(ethylene dioxythiophene) electrodes, Cancun, Mexico, 5th International IEEE/EMBS Conference on Neural Engineering, NER 2011, Publisher: IEEE, Pages: 566-569
The conducting polymer poly(ethylene dioxythiopene) (PEDOT) has been investigated as a coating for visual prosthesis electrode arrays. The prototype electrode array was coated with PEDOT doped with two conventional anions: paratoluene sulfonate (pTS) and lithium perchlorate (LiClO4). PEDOT variants were analyzed for charge injection limit, electrochemical stability following continuous biphasic stimulation, accelerated ageing and steam sterilization conditions. It was found that PEDOT/LiClO4 was the most stable conducting polymer under chronic stimulation and high temperature circumstances. However, PEDOT/pTS exhibited acceptable stability in comparison to conventional platinum.
Green RA, Devillaine F, Dodds C, et al., 2010, Conducting polymer electrodes for visual prostheses., Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, Pages: 6769-6772, ISSN: 1557-170X
Conducting polymers (CPs) have the potential to provide superior neural interfaces to conventional metal electrodes by introducing more efficient charge transfer across the same geometric area. In this study the conducting polymer poly(ethylene dioxythiophene) (PEDOT) was coated on platinum (Pt) microelectrode arrays. The in vitro electrical characteristics were assessed during biphasic stimulation regimes applied between electrode pairs. It was demonstrated that PEDOT could reduce the potential excursion at a Pt electrode interface by an order of magnitude. The charge injection limit of PEDOT was found to be 15 x larger than Pt. Additionally, PEDOT coated electrodes were acutely implanted in the suprachoroidal space of a cat retina. It was demonstrated that PEDOT coated electrodes also had lower potential excursions in vivo and electrically evoked potentials (EEPs) could be detected within the vision cortex.
Green RA, Baek S, Poole-Warren LA, et al., 2010, Conducting polymer-hydrogels for medical electrode applications., Sci Technol Adv Mater, Vol: 11, ISSN: 1468-6996
Conducting polymers hold significant promise as electrode coatings; however, they are characterized by inherently poor mechanical properties. Blending or producing layered conducting polymers with other polymer forms, such as hydrogels, has been proposed as an approach to improving these properties. There are many challenges to producing hybrid polymers incorporating conducting polymers and hydrogels, including the fabrication of structures based on two such dissimilar materials and evaluation of the properties of the resulting structures. Although both fabrication and evaluation of structure-property relationships remain challenges, materials comprised of conducting polymers and hydrogels are promising for the next generation of bioactive electrode coatings.
Green RA, Baek S, Poole-Warren LA, et al., 2010, Micro and nanostructured conducting polymer hydrogel composites for medical electrode applications, Science and Technology of Advanced Materials, ISSN: 1468-6996
Poole-Warren LA, Lovell NH, Baek S, et al., 2010, The development of bioactive conducting polymers for neural interfaces, Expert Review of Medical Devices, Vol: 7, Pages: 35-49, ISSN: 1743-4440
Green RA, Baek S, Poole-Warren LA, et al., 2010, Conducting polymer-hydrogels for medical electrode applications, Science and Technology of Advanced Materials, Vol: 11, Pages: 1-13, ISSN: 1468-6996
Conducting polymers hold significant promise as electrode coatings; however, they are characterized by inherently poor mechanical properties. Blending or producing layered conducting polymers with other polymer forms, such as hydrogels, has been proposed as an approach to improving these properties. There are many challenges to producing hybrid polymers incorporating conducting polymers and hydrogels, including the fabrication of structures based on two such dissimilar materials and evaluation of the properties of the resulting structures. Although both fabrication and evaluation of structure–property relationships remain challenges, materials comprised of conducting polymers and hydrogels are promising for the next generation of bioactive electrode coatings.
Poole-Warren LA, Lovell NH, Baek S, et al., 2010, Development of bioactive conducting polymers for neural interfaces, Expert Review of Medical Devices, Vol: 7, Pages: 35-49, ISSN: 1743-4440
Green RA, Lovell NH, Poole-Warren LA, 2010, Impact of co-incorporating laminin peptide dopants and neurotrophic growth factors on conducting polymer properties, ACTA Biomaterialia, Vol: 6, Pages: 63-71, ISSN: 1742-7061
Green RA, Martens P, Nordon RE, et al., 2009, Bio-synthetic encapsulation systems for organ engineering: focus on diabetes, Stem Cell Engineering, Editors: Artmann, Hescheler, Minger, New York, Publisher: Springer, ISBN: 9783642118647
Green RA, Suaning GJ, Poole-Warren LA, et al., 2009, Bioactive conducting polymers for neural interfaces: Application to vision prosthesis, Antalya, Turkey, 4th International IEEE/EMBS Conference on Neural Engineering, NER `09
Bioactive conducting polymers (CPs) have the potential to provide superior neural interfaces to conventional metal electrodes by lowering interfacial impedance, reducing strain-mismatch and controlling the interaction of surrounding tissue. Application to vision prosthesis is demonstrated in this study where cell adherence and neurite outgrowth were stimulated via biomolecules entrapped within the CP matrix. The responses of two different cell types to biologically modified poly(ethylene dioxythiophene) (PEDOT) were studied by incorporating the appropriate differentiation factors for each cell type. For the PC12 cell line, nerve growth factor (NGF) was incorporated and for the clonal retinal ganglion cell (RGC-5), staurosporine (SS) was used. Platinum (Pt) electrodes coated with bioactive PEDOT promoted superior cell responses when compared to the bare Pt electrodes for both cell types. It was also demonstrated that cells preferentially adhered to the PEDOT surface, indicating that these CPs have surface topography more suited to cell attachment than conventional smooth metal surfaces. ©2009 Crown.
Green RA, Lovell NH, Poole-Warren LA, 2009, Cell attachment functionality of bioactive conducting polymers for neural interfaces, Biomaterials, Vol: 30, Pages: 3637-3644, ISSN: 0142-9612
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 DEDEDYFQRYLI, but attachment on both peptide doped polymers could be enhanced by coating with whole native laminin. © 2009 Elsevier Ltd. All rights reserved.
Green RA, Ordonez JS, Schuettler M, et al., 2009, Cytotoxicity of implantable microelectrode arrays produced by laser micromachining, Biomaterials, Vol: 31, Pages: 886-893, ISSN: 0142-9612
Green RA, Baek S, Lovell NH, et al., 2009, Nanostructured Conductive Polymers as Biomaterials, Nanostructured Conductive Polymers, Editors: Eftekhari, USA, Publisher: Wiley Press, Pages: 707-736, ISBN: 9780470745854
Green RA, Lovell NH, Poole-Warren LA, 2009, Impact of co-incorporating laminin-peptide dopants and neurotrophic growth factors on conducting polymer properties, ACTA Biomaterialia, Vol: 6, Pages: 63-71, ISSN: 1742-7061
Green RA, Lovell NH, Wallace GG, et al., 2008, Conducting polymers for neural interfaces: Challenges in developing an effective long-term implant, Biomaterials, Vol: 29, Pages: 3393-3399, ISSN: 0142-9612
Metal electrode materials used in active implantable devices are often associated with poor long-term stimulation and recording performance. Modification of these materials with conducting polymer coatings has been suggested as an approach for improving the neural tissue-electrode interface and increasing the effective lifetime of these implants. Neural interfaces ideally have intimate contact between the excitable tissue and the electrode to maintain signal quality and activation of neural cells. The outcomes of current research into conducting polymers as coatings has potential to enhance this tissue-material contact by increasing the electrode surface area and roughness as well as allowing delivery of bioactive signals to neural cells. However, challenges facing conducting polymers include poor electroactive stability and mechanical properties as well as control of the mobility, concentration and presentation of bioactive molecules. The impact of biological inclusions on polymer properties and their ongoing performance in neural prosthetics requires a greater understanding with future research aimed at controlling and optimising film characteristics for long-term performance. Optimising the electrode interface will require a trade-off between desired electrical, mechanical, chemical and biological properties. © 2008 Elsevier Ltd. All rights reserved.
Green RA, Williams CM, Lovell NH, et al., 2008, Novel neural interface for implant electrodes: Improving electroactivity of polypyrrole through MWNT incorporation, Journal of Materials Science - Materials in Medicine, Vol: 19, Pages: 1625-1629, ISSN: 0957-4530
Multi-walled carbon nanotubes (MWNTs) can be incorporated into conductive polymers to produce superior materials for neural interfaces with high interfacial areas, conductivity and electrochemical stability. This paper explores the addition of MWNTs to polypyrrole (PPy) through two methods, layering and codeposition. Conductivity of PPy doped with polystyrene sulfonate (PSS), a commonly used dopant, was improved by 50% when MWNTs were layered with PPy/PSS. The film electrochemical stability was improved from 38% activity to 66% activity after 400 cycles of oxidation and reduction. Growth inhibition assays indicated that MWNTs are not growth inhibitory. The electroactive polymer-MWNT composites produced demonstrate properties that suggest they are promising candidates for biomedical electrode coatings. © 2008 Springer Science+Business Media, LLC.
Green RA, Poole-Warren LA, Lovell NH, 2007, Novel neural interface for vision prosthesis electrodes: Neurite outgrowth through biomolecule incorporation
Lovell NH, Hallum LE, Chen SC, et al., 2007, Advances in Retinal Neuroprosthetics, Handbook of Neural Engineering, Editors: Metin Akay, Piscataway, New Jersey, USA, Publisher: IEEE Press, Pages: 337-356, ISBN: 9780470056691
Green RA, Poole-Warren LA, Lovell NH, 2007, Novel Neural interface for vision prosthesis electrodes: Improving electical and mechanical properties through layering., Kohala Coast, Hawaii, IEEE EMBS conference on Neural Engineering
The rationale for this research is to address the problem of long-term function of neural interfaces. The approach followed is surface modification of traditional electrode materials using electically conducting polymers and biological factors with the aim of establishing a functional neural interface between stimulating electrode and neural tissue. Polyethylene dioxythiophene films have good electrochemical stability but are very difficult to handleand are subject to failure by brittle fracture. The specific aim of this study was to evaluate layering of different conductive polymers for optimization of film properties. Layering of the films was shown to produce composite materials with properties superior to does of the individual components. Conductivity of the layered film was between that of each film alone and mechanical stability was similar to the more flexible PPy films. Neurite outgrowth was improved on the layered film. These layered films show promise as conductive coatings for electrodes.
Green RA, Martens P, Middeldorp L, et al., 2006, Novel neural interface technique for use in vision prostheses: Neurite ingrowth to electrode stimulation sites, Rotorua, New Zealand
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