Impedance optimization by electrophoretic deposition of laser-generated colloidal nanoparticles on the surface of platinum-iridium macroelectrodes for deep brain stimulation and platinum-tungsten microelectrodes for recording of neural activity

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Electrodes are routinely used for chronic stimulation or recording of neuronal activity during therapeutic or diagnostic neurosurgical interventions. The quality of these electrodes is critically affected by their impedance. While low and stable impedance is needed for reduced energy consumption during chronic deep brain stimulation (DBS), high impedance is required for recording of neuronal activity in order to achieve good signal to noise ratios. In this project we aim to examine if coatings composed of platinum and tungsten oxide nanoparticles (NP) can be used to tune the impedance and to elucidate a systematic correlation between coating properties (surface coverage, particle size, material) and electrophysical characteristics of the electrodes in vitro and in vivo. During the first term of our joint proposal we successfully developed a coating process based on electrophoretic deposition (EPD) using laser-fabricated, ligand-free nanoparticles and determined in vitro that impedance positively correlates with nanoparticle surface coverage, surface charge and surface oxidation of the new electrodes. Long term in vivo deep brain stimulation experiments in rats revealed that coating the electrodes with Pt NP significantly stabilizes impedance. Furthermore, the coatings endured mechanical tear and did not negatively affect biocompatibility. During the second phase of our proposal, we intend to explore the correlation between the initial impedance of the electrode in vitro and the subsequent alteration of impedance in vivo. We will use coating parameters optimized for low impedance, clinically relevant for chronic stimulation. Furthermore, long term in vitro stimulation experiments will be used to explore whether reported changes in impedance with time originate from the electrode alone or they are due to electrode-tissue interactions. In addition to PtIr electrodes, the project will further focus on PtW recording electrodes, which will be coated with tungsten oxide and platinum NP for high impedance. Consecutive in vivo recording experiments will verify whether the corresponding coating can improve the quality of the neuronal signal, i.e., the signal to noise ratio. An important issue during in vivo applications of coated is the stability of the coating. Therefore, detailed examinations of the binding state of the nanoparticles on the electrode as well as thorough evaluations of biocompatibility will be conducted. The project will be complemented by particle-based simulations of the EPD process in order to more precisely correlate electrode properties with coating parameters.