Browsing by Author "Wallace, Gordon"

Now showing 1 - 4 of 4
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    Biocompatibility of Immobilized Aligned Carbon Nanotubes
    (Wiley, 2011) Nayagam, David; Williams, Richard; Chen, Jun; Magee, Kylie; Irwin, Jennifer; Tan, Justin; Innis, Peter; Leung, Ronald; Finch, Sue; Williams, Chris; Clark, Graeme; Wallace, Gordon
    In vivo host responses to an electrode-like array of aligned carbon nanotubes (ACNTs) embedded within a biopolymer sheet are reported. This biocompatibility study assesses the suitability of immobilized carbon nanotubes for bionic devices. Inflammatory responses and foreign-body histiocytic reactions are not substantially elevated when compared to negative controls following 12 weeks implantation. A fibrous capsule isolates the implanted ACNTs from the surrounding muscle tissue. Filamentous nanotube fragments are engulfed by macrophages, and globular debris is incorporated into the fibrous capsule with no further reaction. Scattered leukocytes are observed, adherent to the ACNT surface. These data indicate that there is a minimal local foreign-body response to immobilized ACNTs, that detached fragments are phagocytosed into an inert material, and that ACNTs do not attract high levels of surface fouling. Collectively, these results suggest that immobilized nanotube structures should be considered for further investigation as bionic components.
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    Development and Characterization of a Sucrose Microneedle Neural Electrode Delivery System
    (Wiley, 2017-12) Apollo, Nicholas; Jiang, Jonathon; Cheung, Warwick; Baquier, Sebastien; Lai, Alan; Mirebedini, Azadeh; Foroughi, Javad; Wallace, Gordon; Shivdasani, Mohit; Prawer, Steven; Chen, Shou; Williams, Richard; Cook, Mark; Nayagam, David; Garrett, David
    Stable brain–machine interfaces present extraordinary therapeutic and scientific promise. However, the electrode–tissue interface is susceptible to instability and damage during long-term implantation. Soft, flexible electrodes demonstrate improved longevity, but pose a new challenge with regard to simple and accurate surgical implantation. A high aspect ratio water-soluble microneedle is developed based on sucrose which permits straightforward surgical implantation of soft, flexible microelectrodes. Here, a description of the microneedle manufacturing process is presented, along with in vitro and in vivo safety and efficacy assessments. Successful fabrication requires control of the glass transition temperature of aqueous sucrose solutions. The insertion force of 5 different microneedle electrode vehicles is studied in agarose brain phantoms, with the sucrose microneedle eliciting the lowest insertion force and strain energy transfer. Short- and long-term assessments of the pathological response to sucrose microneedle implantations in the brain suggest minimal tissue reactions, comparable to those observed following stainless-steel hypodermic needle punctures. Finally, microelectrodes fabricated from graphene, carbon nanotubes, or platinum are embedded in sucrose microneedles and implanted into an epileptic rat model for 22 d. All electrodes are functional throughout the implantation period, with the graphene electrode exhibiting the largest seizure signal-to-noise ratio and only modest changes in impedance.
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    Promoting neurite outgrowth from spiral ganglion neuron explants using polypyrrole/BDNF-coated electrodes
    (Wiley Periodicals, 2009-10) Evans, Alison; Thompson, Brianna; Wallace, Gordon; Millard, Rodney; O'Leary, Stephen; Clark, Graeme; Shepherd, Robert; Richardson, Rachael
    Release of neurotrophin-3 (NT3) and brain-derived neurotrophic factor (BDNF) from hair cells in the cochlea is essential for the survival of spiral ganglion neurons (SGNs). Loss of hair cells associated with a sensorineural hearing loss therefore results in degeneration of SGNs, potentially reducing the performance of a cochlear implant. Exogenous replacement of either or both neurotrophins protects SGNs from degeneration after deafness. We previously incorporated NT3 into the conducting polymer polypyrrole (Ppy) synthesized with para-toluene sulfonate (pTS) to investigate whether Ppy/pTS/NT3-coated cochlear implant electrodes could provide both neurotrophic support and electrical stimulation for SGNs. Enhanced and controlled release of NT3 was achieved when Ppy/pTS/NT3-coated electrodes were subjected to electrical stimulation. Here we describe the release dynamics and biological properties of Ppy/pTS with incorporated BDNF. Release studies demonstrated slow passive diffusion of BDNF from Ppy/pTS/BDNF, with electrical stimulation significantly enhancing BDNF release over seven days. A three-day SGN explant assay found neurite outgrowth from explants was 12.3-fold greater when polymers contained BDNF (p<0.001), although electrical stimulation did not increase neurite outgrowth further. The versatility of Ppy to store and release neurotrophins, conduct electrical charge and act as a substrate for nerve-electrode interactions is discussed for specialized applications such as cochlear implants.
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    Soft, Flexible Freestanding Neural Stimulation and Recording Electrodes Fabricated from Reduced Graphene Oxide
    (John Wiley and Sons, 2015-05-04) Apollo, Nicholas; Maturana, Matias; Tong, Wei; Nayagam, David; Shivdasani, Mohit; Foroughi, Javad; Wallace, Gordon; Prawer, Steven; Ibbotson, Michael; Garrett, David
    There is an urgent need for conductive neural interfacing materials that exhibit mechanically compliant properties, while also retaining high strength and durability under physiological conditions. Currently, implantable electrode systems designed to stimulate and record neural activity are composed of rigid materials such as crystalline silicon and noble metals. While these materials are strong and chemically stable, their intrinsic stiffness and density induce glial scarring and eventual loss of electrode function in vivo. Conductive composites, such as polymers and hydrogels, have excellent electrochemical and mechanical properties, but are electrodeposited onto rigid and dense metallic substrates. In the work described here, strong and conductive microfibers (40–50 μm diameter) wet-spun from liquid crystalline dispersions of graphene oxide are fabricated into freestanding neural stimulation electrodes. The fibers are insulated with parylene-C and laser-treated, forming “brush” electrodes with diameters over 3.5 times that of the fiber shank. The fabrication method is fast, repeatable, and scalable for high-density 3D array structures and does not require additional welding or attachment of larger electrodes to wires. The electrodes are characterized electrochemically and used to stimulate live retina in vitro. Additionally, the electrodes are coated in a water-soluble sugar microneedle for implantation into, and subsequent recording from, visual cortex.