Comparison of the In Vitro and In Vivo Electrochemical Performance of Bionic Electrodes.

The electrochemical performance of platinum electrodes was assessed in vitro and in vivo to determine the impact of electrode implantation and the relevance of in vitro testing in predicting in vivo behaviour. A significant change in electrochemical response was seen after electrode polarisation. As a result, initial in vitro measurements were poor predictors of subsequent measurements performed in vitro or in vivo.

Electrode impedance changes after implantation of a dexamethasone-eluting intracochlear array.

Postoperative inflammation and the formation of fibrotic tissue around the intracochlear electrode array are often held responsible for negative outcomes in cochlear implant recipients. Here we test the effectiveness of intracochlear delivery of dexamethasone via a drug-eluting electrode array in reducing fibrotic tissue formation, assessed via measurement of both monopolar and four-point electrode impedance. Adult guinea pigs were bilaterally implanted with a dexamethasone-eluting array (left ear) and a standard non-eluting array (right ear).

Using Chronopotentiometry to Better Characterize the Charge Injection Mechanisms of Platinum Electrodes Used in Bionic Devices.

The safe charge injection capacity and charge density of neural stimulating electrodes is based on empirical evidence obtained from stimulating feline cortices. Stimulation induced tissue damage may be caused by electrochemical or biological mechanisms. Separating these mechanisms requires greater understanding of charge transfer at the electrode-tissue interface.

Protecting against electrode insertion trauma using dexamethasone.

Objective: To compare the benefits of a dexamethasone-eluting array for hearing preservation and cochlear histopathology in low trauma (soft-surgery) and high trauma models of cochlear implant surgery.

Methods: Adult guinea pigs were implanted with an intra-cochlear array using two different surgical procedures: either a soft-surgery approach or following generation of electrode insertion trauma (high trauma). Two methods of dexamethasone delivery were evaluated: elution from an electrode array alone, and elution from a cochlear implant electrode array in combination with a pre-operative systemic injection.

Measuring the effective area and charge density of platinum electrodes for bionic devices.

Objective: Neural stimulation is usually performed with fairly large platinum electrodes. Smaller electrodes increase the applied charge density, potentially damaging the electrode. Greater understanding of the charge injection mechanism is required for safe neural stimulation.

Electrode Impedance Fluctuations as a Biomarker for Inner Ear Pathology After Cochlear Implantation.

Objectives/hypothesis: Cochlear implant surgery now aims to preserve residual low frequency hearing. The current research explores whether fluctuations in the electrical impedance of cochlear implant electrodes may act as a biomarker for pathological changes that lead to the delayed loss of residual hearing.

Study Design: Secondary analysis of a double-blinded randomized trial, where methylprednisolone was administered intravenously before cochlear implantation with a view to preserving residual hearing.

Long-term electrode impedance changes and failure prevalence in cochlear implants.

Objective: This study assessed the prevalence of electrode failures and electrode impedance measures in Nucleus cochlear implants around initial activation (an average of 16 days after surgery) and after 8 to 12 years of device use.

Design: Retrospective data from the Melbourne Cochlear Implant Clinic was collated and analysed.

Study Sample: Included in this study were 232 adults, all of whom were implanted at the clinic between March 1998 and August 2005.

Meningitis and a safe dexamethasone-eluting intracochlear electrode array.

Objectives: To evaluate the potential risk of pneumococcal meningitis associated with the use of a dexamethasone-eluting intracochlear electrode array as compared with a control array.

Methods: In two phases, adult Hooded-Wistar rats were implanted via the middle ear with an intracochlear array and were inoculated with Streptococcus pneumoniae 5 days post-surgery. Phase I created a dosing curve by implanting five groups (n = 6) with a control array, then inoculating 5 days later with different numbers of S.

Electropermeabilization of adherent cells with cochlear implant electrical stimulation in vitro.

Cochlear implant stimulation creates a reduction in electrode impedance that returns to pre-stimulation levels following cessation of stimulation and is presumed to be associated with the fibrous tissue covering over the electrode array. This study assessed the possibility that transitory impedance reduction originates from a change in the membrane permeability of cells on the electrode (electropermeabilization). These changes can be recorded using the dye propidium iodide, which fluoresces upon entry into the leaky cell.

Development of a safe dexamethasone-eluting electrode array for cochlear implantation.

Objectives: Cochlear implantation can result in trauma leading to increased tissue response and loss of residual hearing. A single intratympanic application of the corticosteroid dexamethasone is sometimes used clinically during surgery to combat the potential effect of trauma on residual hearing. This project looked at the safety and efficacy of dexamethasone eluted from an intracochlear array in vivo.

Impedance changes in chronically implanted and stimulated cochlear implant electrodes.

Objectives: Electrode impedance increases following implantation and undergoes transitory reduction with onset of electrical stimulation. The studies in this paper measured the changes in access resistance and polarization impedance in vivo before and following electrical stimulation, and recorded the time course of these changes.

Design: Impedance measures recorded in (a) four cats following 6 months of cochlear implant use, and (b) three cochlear implant recipients with 1.

Computer modelling of the cochlea and the cochlear implant: a review.

In the last few decades, cochlear implants have experienced major developments with intensive studies carried out through experimental and computational analysis. With the rapid increase in computational resources available and the development of efficient computational techniques, computer models of the cochlea and the cochlear implant have become more sophisticated. It is now possible to analyze the micromechanics of the cochlea and the transient response of tissue to external stimulation.

Electrical stimulation causes rapid changes in electrode impedance of cell-covered electrodes.

Animal and clinical observations of a reduction in electrode impedance following electrical stimulation encouraged the development of an in vitro model of the electrode-tissue interface. This model was used previously to show an increase in impedance with cell and protein cover over electrodes. In this paper, the model was used to assess the changes in electrode impedance and cell cover following application of a charge-balanced biphasic current pulse train.

Changes in biphasic electrode impedance with protein adsorption and cell growth.

This study was undertaken to assess the contribution of protein adsorption and cell growth to increases in electrode impedance that occur immediately following implantation of cochlear implant electrodes and other neural stimulation devices. An in vitro model of the electrode-tissue interface was used. Radiolabelled albumin in phosphate buffered saline was added to planar gold electrodes and electrode impedance measured using a charge-balanced biphasic current pulse.

Micro-focus fluoroscopy - a great tool for electrode development.

The aim of this study was to utilise micro-focus X-ray fluoroscopy for viewing electrode movement in the cochlea. Various prototypes of newly designed cochlear implant electrodes were evaluated during insertion studies on human cadaver temporal bones. The magnified fluoroscopic images were observed in real-time and recorded for retrospective studies.

The effect of polypyrrole with incorporated neurotrophin-3 on the promotion of neurite outgrowth from auditory neurons.

This research aims to improve the nerve-electrode interface of the cochlear implant using polymer technology to encourage neuron survival, elongation and adhesion to the electrodes. Polypyrrole (Ppy) doped with p-toluene sulphonate (pTS) is an electroactive polymer into which neurotrophin-3 (NT3) can be incorporated. Ppy/pTS+/-NT3 was synthesised over gold electrodes and used as a surface for auditory neuron explant culture.

An in vitro model for investigating impedance changes with cell growth and electrical stimulation: implications for cochlear implants.

The impedance of stimulating electrodes used in cochlear implants and other neural prostheses often increases post-implantation, and is thought to be due to fibrous tissue encapsulation of the electrode array. Increased impedance results in higher power requirements to stimulate target neurons at set charge densities. We developed an in vitro model to investigate the electrode-tissue interface in a highly controlled environment.