Mechanistic drivers of platinum dissolution in neural prosthetic electrode pulsing: decoupling electrochemistry, biological interfaces, and electrode degradation products.

Abstract

Implantable neuromodulation devices rely on platinum (Pt) electrodes for safe and effective operation. However, accumulating evidence shows that Pt electrodes can corrode and release ionic and particulate Pt material into the environment. This dissolution behaviour can impair device performance and introduces unresolved biocompatibility concerns, since its mechanistic drivers in biologically relevant environments remain poorly defined. This study evaluated electrochemical and biological factors governing Pt dissolution in neural prosthetic electrodes. Using biphasic charge-balanced pulses delivered over acute and subchronic one-week intervals, the effects of charge density, frequency, and cumulative charge were decoupled while quantifying dissolution in the presence of proteins, and fibrotic-tissue mimics. Charge density emerged as the dominant determinant, explaining ~86% of dissolution variability, whereas frequency and aggregate charge exerted weaker but significant influences. Acute pulse produced highly variable Pt release linked to removal of loosely bound material, whereas subchronic dissolution reflected more uniform electrochemical degradation. Protein-model solutions reduced Pt loss by 2-5×, and fibrotic-tissue mimics suppressed release by up to two orders of magnitude. Although these interfaces increased impedance and altered charge-storage behaviour, electrochemical metrics alone did not predict dissolution, indicating that biological interfaces function primarily as physicochemical barriers. New quantification strategies revealed that particulate Pt dominated acute degradation (≥68%), whereas ionic species were more prevalent subchronically. Conventional ICP-MS underestimated total Pt by 66-99% in particulate-rich samples. These findings reconcile longstanding inconsistencies in the literature and stress the need of distinguishing ionic from particulate Pt when evaluating cytotoxicity, electrode longevity, and the long-term safety of neural interfaces.