Jiri Ehlich1, Ludovico Migliaccio1, Marta Nikić1,2, Imrich Gablech1, Eric Glowacki1

1Central European Institute of Technology (CEITEC), Bioelectronics Materials and Devices, Purkyňova 656/123 61200 Brno; 2University of Zagreb, Faculty of Science, Department of Physics

During electrical neural stimulation, charge-balanced biphasic current pulses are typically used to trigger action potentials in excitable tissues. Cathodic pulses depolarize cells, evoking action potentials, meanwhile subsequent anodic pulses are meant to reverse the products of possible electrochemical processes back to their original form. Balanced biphasic current pulses are thus generally considered to be safe for chronic applications [1]. However recently it has been found, that not all reactions that could possibly happen at the electrode-tissue interface during the stimulation are perfectly reversible. Products of these reactions can be possibly dangerous to the tissue or act as signalling molecules. The identity and the scale of such reactions still remains an unexplored area [2]. Our work examines oxygen reduction reactions at the electrodes made out of commonly used materials used for neural stimulation electrodes. Oxygen can be reduced either to water or hydrogen peroxide by 4- or 2-electron process. Both reactions can significantly reduce the quantity of dissolved oxygen near the electrode, creating hypoxic conditions harmful to neurons. Peroxide, meanwhile, can induce toxic reactions or act as a signalling molecule. We are examining the amount of reduced oxygen and produced peroxide by various biphasic stimulation protocols and comparing electrocatalytic activities of studied materials. Results of this study should help to engineer novel and potentially safer neurostimulation devices and protocols.

Acknowledgements: We acknowledge support from CzechNanoLab Research Infrastructure supported by MEYS CR (LM2018110) and funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme grant agreement No. 949191), and financial support from the city council of Brno.

[1]   Boehler, C., Carli, S., Fadiga, L., Stieglitz, T. & Asplund, M. Tutorial: guidelines for standardized performance tests for electrodes intended for neural interfaces and bioelectronics. Nat. Protoc. 15, 3557–3578 (2020).

[2]   Cogan, S. F., Ehrlich, J., Plante, T. D., Gingerich, M. D. & Shire, D. B. Contribution of oxygen reduction to charge injection on platinum and sputtered iridium oxide neural stimulation electrodes. IEEE Trans. Biomed. Eng. 57, 2313–2321 (2010).

Presenting author e-mail address: jiri.ehlich@ceitec.vut.cz