Platinum dissolution and tissue response following long-term electrical stimulation at high charge densities

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dc.contributor.authorShepherd, Robert
dc.contributor.authorCarter, Paul
dc.contributor.authorDalrymple, Ashley
dc.contributor.authorEnke, Ya Lang
dc.contributor.authorWise, Andrew
dc.contributor.authorNguyen, Trung
dc.contributor.authorFirth, James
dc.contributor.authorThompson, Alex
dc.contributor.authorFallon, James
dc.date.accessioned2021-02-15T05:56:13Z
dc.date.available2021-02-15T05:56:13Z
dc.date.issued2021-02
dc.description.abstractOBJECTIVE: Established guidelines for safe levels of electrical stimulation for neural prostheses are based on a limited range of the stimulus parameters used clinically. Recent studies have reported particulate platinum (Pt) associated with long-term clinical use of these devices, highlighting the need for more carefully defined safety limits. We previously reported no adverse effects of Pt corrosion products in the cochleae of guinea pigs following 4 weeks of electrical stimulation using charge densities far greater than the published safe limits for cochlear implants. The present study examines the histopathological effects of Pt within the cochlea following continuous stimulation at a charge density well above the defined safe limits for periods up to 6 months. APPROACH: Six cats were bilaterally implanted with Pt electrode arrays and unilaterally stimulated using charge balanced current pulses at a charge density of 267 C/cm2/phase using a tripolar electrode configuration. Electrochemical measurements were made throughout the implant duration and evoked potentials recorded at the outset and on completion of the stimulation program. Cochleae were examined histologically for particulate Pt, tissue response, and auditory nerve survival; electrodes were examined for surface corrosion; and cochlea, brain, kidney, and liver tissue analysed for trace levels of Pt. MAIN RESULTS: Chronic stimulation resulted in both a significant increase in tissue response and particulate Pt within the tissue capsule surrounding the electrode array compared with implanted, unstimulated control cochleae. Importantly, there was no stimulus-induced loss of auditory neurons or increase in evoked potential thresholds. Stimulated electrodes were significantly more corroded compared with unstimulated electrodes. Trace analysis revealed Pt in both stimulated and control cochleae although significantly greater levels were detected within stimulated cochleae. There was no evidence of Pt in brain or liver; however, trace levels of Pt were recorded in the kidneys of two animals. Finally, increased charge storage capacity and charge injection limit reflected the more extensive electrode corrosion associated with stimulated electrodes. SIGNIFICANCE: Long-term electrical stimulation of Pt electrodes at a charge density well above existing safety limits and nearly an order of magnitude higher than levels used clinically, does not adversely affect the auditory neuron population or reduce neural function, despite a stimulus-induced tissue response and the accumulation of Pt corrosion product. The mechanism resulting in Pt within the unstimulated cochlea is unclear, while the level of Pt observed systemically following stimulation at these very high charge densities does not appear to be of clinical significance.en_US
dc.description.sponsorshipThis work was supported by NIDCD (R01DC015031) and Cochlear Ltd. The Bionics Institute acknowledges support of the Victorian Government through Operational Infrastructure Support Programen_US
dc.identifier.citationShepherd, R. K., P. Carter, A. Dalrymple, Y. L. Enke, A. K. Wise, T. Nguyen, J. Firth, A. Thompson, and J. B. Fallon. 2021. Platinum dissolution and tissue response following long-term electrical stimulation at high charge densities. Journal of Neural Engineering: [online ahead of print].en_US
dc.identifier.issn1741-2552
dc.identifier.urihttp://repository.bionicsinstitute.org:8080/handle/123456789/418
dc.language.isoenen_US
dc.publisherIOP Publishingen_US
dc.subjectElectrical stimulationen_US
dc.subjectNeural prosthesisen_US
dc.subjectPlatinum electrodeen_US
dc.subjectStimulation safetyen_US
dc.subjectCorrosionen_US
dc.subjectCochlear implanten_US
dc.subjectNeurotechnologyen_US
dc.titlePlatinum dissolution and tissue response following long-term electrical stimulation at high charge densitiesen_US
dc.typeArticleen_US
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