In vitro and in vivo stability of black-platinum coatings on flexible, polymer microECoG arrays

Objective. Intracranial EEG (iEEG) or micro-electrocorticography (µECoG) microelectrodes offer high spatial resolution in recordings of neuronal activity from the exposed brain surface. Reliability of dielectric substrates and conductive materials of these devices are under intensive research in terms of functional stability in biological environments. Approach. The aim of our study is to investigate the stability of electroplated platinum recording sites on 16-channel, 8 micron thick, polyimide based, flexible µECoG arrays implanted underneath the skull of rats. Scanning electron microscopy and electrochemical impedance spectroscopy was used to reveal changes in either surface morphology or interfacial characteristics. The effect of improved surface area (roughness factor = 23 ± 0.12) on in vivo recording capability was characterized in both acute and chronic experiments. Main results. Besides the expected reduction in thermal noise and enhancement in signal-to-noise ratio (up to 39.8), a slight increase in the electrical impedance of individual sites was observed, as a result of changes in the measured interfacial capacitance. In this paper, we also present technology processes and protocols in detail to use such implants without crack formation of the porous platinum surfaces. Significance. Our findings imply that black-platinum coating deposited on the recording sites of flexible microelectrodes (20 microns in diameter) provides a stable interface between tissue and device.