Browsing by Author "Huynh, Mario"
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- ItemElectrochemical and biological characterization of thin-film platinum-iridium alloy electrode coatings: a chronic in vivo study(IOP Publishing, 2020-05) Dalrymple, Ashley; Huynh, Mario; Nayagam, Bryony; Lee, Curtis; Weiland, Greg; Petrossians, Artin; Whalen, John; Fallon, James; Shepherd, RobertOBJECTIVE: To evaluate the electrochemical properties, biological response, and surface characterization of an electrodeposited Platinum-Iridium (Pt-Ir) electrode coating on cochlear implants subjected to chronic stimulation in vivo. APPROACH: Electrochemical impedance spectroscopy (EIS), charge storage capacity (CSC), charge injection limit (CIL), and voltage transient (VT) impedance were measured bench-top before and after implant and in vivo. Coated Pt-Ir and uncoated Pt electrode arrays were implanted into cochlea of normal hearing rats and stimulated for ~4 hours/day, 5 days/week for 5 weeks. Neural function was monitored using electrically-evoked auditory brainstem responses. After explant, the electrode surfaces were assessed, and cochleae examined histologically. MAIN RESULTS: When measured on bench-top before and after stimulation, Pt-Ir coated electrodes had significantly lower VT impedance (p < 0.001) and significantly higher CSC (p < 0.001) and CIL (p < 0.001) compared to uncoated Pt electrodes. In vivo, the CSC and CIL of Pt-Ir were significantly higher than Pt throughout the implantation period (p = 0.047 and p < 0.001, respectively); however, the VT impedance (p = 0.3) was not. There was no difference in foreign body response between material cohorts, although cochleae implanted with coated electrodes contained small deposits of Pt-Ir. There was no evidence of increased neural loss or loss of neural function in either group. Surface examination revealed no Pt corrosion on any electrodes. SIGNIFICANCE: Electrodeposited Pt-Ir electrodes demonstrated significant improvements in electrochemical performance on the bench-top and in vivo compared to uncoated Pt. Neural function and tissue response to Pt-Ir electrodes were not different from uncoated Pt, despite small deposits of Pt-Ir in the tissue capsule. Electrodeposited Pt-Ir coatings offer promise as an improved electrode coating for active neural prostheses.
- ItemElectrochemical and biological performance of chronically stimulated conductive hydrogel electrodes(IOP Publishing, 2020-03) Dalrymple, Ashley; Robles, Ulises; Huynh, Mario; Nayagam, Bryony; Green, Rylie; Poole-Warren, Laura; Fallon, James; Shepherd, RobertOBJECTIVE: Evaluate electrochemical properties, biological response, and surface characterization of a conductive hydrogel (CH) coating following chronic in vivo stimulation. APPROACH: Coated CH or uncoated smooth platinum (Pt) electrode arrays were implanted into the cochlea of rats and stimulated over a 5 week period with more than 57 million biphasic current pulses. Electrochemical impedance spectroscopy (EIS), charge storage capacity (CSC), charge injection limit (CIL), and voltage transient (VT) impedance were measured on the bench before and after stimulation, and in vivo during the stimulation program. Electrically-evoked auditory brainstem responses were recorded to monitor neural function. Following explant, the cochleae were examined histologically and electrodes were examined using scanning electron microscopy. MAIN RESULTS: CH coated electrodes demonstrated a bench-top electrochemical advantage over Pt electrodes before and after the electrical stimulation program. In vivo, CH coated electrodes also had a significant advantage over Pt electrodes throughout the stimulation program, exhibiting higher CSC (p = 0.002), larger CIL (p = 0.002), and lower VT impedance (p < 0.001). The CH cohort exhibited a greater tissue response (p = 0.003) with small deposits of particulate material within the tissue capsule. There was no loss in auditory neuron density or change in neural response thresholds in any cochleae. SEM examination of the electrode surface revealed that most CH electrodes exhibited some coating loss; however, there was no evidence of corrosion in the underlying Pt. SIGNIFICANCE: CH coated electrodes demonstrated significant electrochemical advantages on the bench-top and in vivo and maintained neural function despite an increased tissue response and coating loss. While further research is required to understand the cause of the coating loss, CH electrodes provide promise for use in neural prostheses.
- ItemElectrochemical and mechanical performance of reduced graphene oxide, conductive hydrogel, and electrodeposited Pt-Ir coated electrodes: an active in vitro study(IOP Publishing, 2019-10) Dalrymple, Ashley; Huynh, Mario; Robles, Ulyises; Marroquin, Jason; Lee, Curtis; Petrossians, Artin; Whalen, John; Li, Dan; Parkington, Helena; Forsythe, John; Green, Rylie; Poole-Warren, Laura; Shepherd, Robert; Fallon, JamesOBJECTIVE: To systematically compare the in vitro electrochemical and mechanical properties of several electrode coatings that have been reported to increase the efficacy of medical bionics devices by increasing the amount of charge that can be delivered safely to the target neural tissue. APPROACH: Smooth platinum (Pt) ring and disc electrodes were coated with reduced graphene oxide, conductive hydrogel, or electrodeposited Pt-Ir. Electrodes with coatings were compared with uncoated smooth Pt electrodes before and after an in vitro accelerated aging protocol. The various coatings were compared mechanically using the adhesion-by-tape test. Electrodes were stimulated in saline for 24 hours/day 7 days/week for 21 days at 85 masculineC (1.6-year equivalence) at a constant charge density of 200 muC/cm2/phase. Electrodes were graded on surface corrosion and trace analysis of Pt in the electrolyte after aging. Electrochemical measurements performed before, during, and after aging included electrochemical impedance spectroscopy, cyclic voltammetry, and charge injection limit and impedance from voltage transient recordings. MAIN RESULTS: All three coatings adhered well to smooth Pt and exhibited electrochemical advantage over smooth Pt electrodes prior to aging. After aging, graphene coated electrodes displayed a stimulation-induced increase in impedance and reduction in the charge injection limit (p < 0.001), alongside extensive corrosion and release of Pt into the electrolyte. In contrast, both conductive hydrogel and Pt-Ir coated electrodes had smaller impedances and larger charge injection limits than smooth Pt electrodes (p < 0.001) following aging regardless of the stimulus level and with little evidence of corrosion or Pt dissolution. SIGNIFICANCE: This study rigorously tested the mechanical and electrochemical performance of electrode coatings in vitro and provided suitable candidates for future in vivo testing.
- ItemVagus nerve stimulation to treat inflammatory bowel disease: a chronic, preclinical safety study in sheep(Future Medicine, 2019-02) Payne, Sophie; Burns, Owen; Stebbing, Martin; Thomas, Ross; de Silva, Angel; Sedo, Alicia; Weissenborn, Frank; Hyakumura, Tomoko; Huynh, Mario; May, Clive; Williams, Richard; Furness, John; Fallon, James; Shepherd, RobertAim: Electrical stimulation of the left cervical vagus nerve is a feasible therapy for inflammatory bowel disease (IBD). However, due to the location of the electrode placement, stimulation is often associated with side effects. Methods: We developed a cuff electrode array, designed to be implanted onto the vagus nerve of the lower thorax or abdomen, below branches to vital organs, to minimize off-target effects to stimulation. Results: Following chronic implantation and electrical stimulation, electrodes remained functional and neural thresholds stable, while there were minimal off-target affects to stimulation. No nerve damage or corrosion of stimulated electrodes was observed. Conclusion: This novel electrode array, located on the vagus nerve below branches to vital organs, is a safe approach for the treatment of inflammatory bowel disease.