Electrical neurostimulation with imbalanced waveform mitigates dissolution of platinum electrodes

Abstract

Objective Electrical neurostimulation has traditionally been limited to the use of charge-balanced waveforms. Charge-imbalanced and monophasic waveforms are not used to deliver clinical therapy, because it is believed that these stimulation paradigms may generate noxious electrochemical species that cause tissue damage. Approach In this study, we investigated the dissolution of platinum as one of such irreversible reactions over a range of charge densities up to 160 µC cm−2 with current-controlled first phase, capacitive discharge second phase waveforms of both cathodic-first and anodic-first polarity. We monitored the concentration of platinum in solution under different stimulation delivery conditions including charge-balanced, charge-imbalanced, and monophasic pulses. Main results We observed that platinum dissolution decreased during charge-imbalanced and monophasic stimulation when compared to charge-balanced waveforms. Significance This observation provides an opportunity to re-evaluate the charge-balanced waveform as the primary option for sustainable neural stimulation.

Electrochemical Evaluations of Fractal Microelectrodes for Energy Efficient Neurostimulation

“…With the increased current density, we expect the dissolution process for these high PSA electrodes to be accelerated as well. Therefore, further study on the effects of fractal design on electrode dissolution is warranted altough the concern for electrode integrity may be mitigated by utilizing non-Pt electrodes materials or via imbalanced stimulation waveforms 50 . Finally, it is essential to investigate whether a more energy efficient neural stimulation can actually be achieved in vivo using these fractal microelectrode designs to confirm our electrochemical results.…”

Evolving Applications, Technological Challenges and Future Opportunities in Neuromodulation: Proceedings of the Fifth Annual Deep Brain Stimulation Think Tank

“…A schematic representation of the electrode-electrolyte interface [from (Merrill et al, 2005 with permission) far left]. The concentration of Pt measured at different charge densities for cathodic-first (middle) and anodic-first (far right) stimulation waveforms (Kumsa et al, 2016 with permission).…”

“…Balancing the amount of charge injected during the stimulation phase by a subsequent phase of the opposite polarity was formerly thought to avoid undesirable faradaic reactions. However, imbalanced charge biphasic waveforms are now known to reduce the amount of platinum (Pt) electrode dissolution when compared to balanced charge biphasic waveforms (Kumsa et al, 2016 ). In addition to minimization of Pt dissolution, imbalanced charge biphasic waveforms extend the parameter space that could be explored for current steering to selectively activate a target brain region during DBS therapy.…”

In vivo microstimulation with cathodic and anodic asymmetric waveforms modulates spatiotemporal calcium dynamics in cortical neuropil and pyramidal neurons of male mice

“…Therefore, it has been proposed that modulation of the likelihood of a neuronal element being activated by electric field may change the neuronal response to electrical stimulation (McIntyre & Grill, 2000, 2002; Yi & Grill, 2018). Although monophasic waveforms have lower activation thresholds, convention is to use charge balanced biphasic waveforms to prevent electrode degradation; however, there can be safety benefits to a slight charge imbalance (Kumsa et al., 2016). Within these safety constraints, biphasic electrical stimulation pulse waveforms can be designed by altering the polarity of the leading or activation phase and/or the shape of each phase while maintaining an equivalent charge injection (so that the net injected charge is zero, or slightly reduced in the balance phase).…”