Niederhoffer, Thomas;
(2024)
Electrochemical safety of neural implants: in vitro study of platinum electrodes behaviour near Shannon’s safe stimulation limit.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
In neural electrical stimulation, safe stimulation guidelines are crucial for effective treatment while avoiding neural damage and electrode degradation. Shannon’s parameter k sets conditions on stimulation parameters to prevent neural damage, though the underlying mechanisms remain unclear. An experimental approach was designed to explore the electrochemical mechanisms involved in the charge injection behaviour of platinum electrodes near Shannon’s safe limit. A custom stimulator was developed to deliver biphasic, cathodic-first, charge-balanced, asymmetric, current-controlled pulse trains, while monitoring electrode potential. The pulse trains were calibrated to approach and exceed Shannon’s limit. A characterisation and conditioning sequence, including electrochemical impedance spectroscopy and cyclic voltammetry, was implemented to ensure repeatability. The influence of various experimental parameters was investigated, such as electrode design (recess, electrode size, electrode shape), stimulation protocol (pulse width), and electrolyte composition (pH, ionic strength, density, buffer system, dissolved gas). Initial results in saline confirmed previous findings: positive potential ratcheting from irreversible charge injection linked to molecular oxygen reduction, and correlation of Shannon’s limit with oxide-mediated platinum dissolution. This mechanism held consistent despite parameter variations, though the onset k-value differed. Changes in electrode design affected current density distribution and diffusion profile; variations in pulse width influenced polarisation due to longer diffusion times; electrolyte composition changes impacted ionic interactions, including double-layer capacitance, faradaic mechanisms, and diffusion. Double-layer capacitance and diffusion profile emerged as key factors determining oxidemediated platinum dissolution threshold and rate. Future research should further examine how the in vivo environment impacts these parameters and work towards developing a standardised characterisation method for stimulation electrodes.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Electrochemical safety of neural implants: in vitro study of platinum electrodes behaviour near Shannon’s safe stimulation limit |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2024. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10199947 |
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