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Open Access Publications from the University of California

Mechanistic Electrochemical Characterization of Novel Microelectrode Arrays and Their Application in Mapping Brain Activity across Species and Humans

  • Author(s): Ganji, Mehran
  • Advisor(s): Dayeh, shadi
  • et al.

Electrocorticography (ECoG) arrays are used in clinical mapping for neurosurgical resection and hold the promise for less damaging brain-machine interfaces. Current clinical ECoG electrodes face physical limits to the number of contact sites, spatial resolution (centimeter scale), and contact diameter (millimeter scale), and thus cannot resolve the dynamically changing neural activity over sub-millimeter scales . In addition to these practical limitations, current clinical electrode arrays are constrained to non-conformal electrode-carriers/substrates and to less-optimal metal electrochemical interfaces. Increasing the flexibility of clinical electrodes may lead to higher signal-to-noise ratios as well as higher spatial specificity and this also requires overcoming substantial physical barriers due to the compromised metal electrochemical interface properties.

The objectives of this thesis, described in seven chapters, are to develop high performance, safe, and durable neural electrode interfaces to yield stable, high signal-to-noise ratio cortical recordings in animal models as well as in humans.

In the second chapter, we demonstrate that sterilization of PEDOT:PSS electrophysiology devices can be performed using an autoclave. We find that autoclaving is a viable sterilization method, leaving morphology unaltered and causing only minor changes in electrical properties. These results pave the way for the widespread utilization of PEDOT:PSS electrophysiology devices in the clinic.

In the third chapter, we translate the use of robust PEDOT:PSS microelectrode arrays for safe intraoperative monitoring of the human brain. PEDOT:PSS micro-electrodes measured significant differential neural modulation under various clinically relevant conditions. We report the first evoked (stimulus-locked) cognitive activity with changes in amplitude across pial surface distances as small as 400 μm, potentially enabling basic neurophysiology studies at the scale of neural micro-circuitry.

In the fourth and fifth chapters, we present the first systematic study of scaling effects on the electrochemical properties of Pt and Au metallic and PEDOT:PSS organic electrodes from neural recording and stimulation perspectives. PEDOT:PSS coating reduced the impedances of metallic electrodes by up to 18X. The overall reduced noise of the PEDOT:PSS microelectrodes enable a lower noise floor for recording action-potentials with high fidelity. We observed a substantial enhancement in charge injection capacity up to 9.5X for PEDOT:PSS microelectrodes compared to metal ones and 88% lower required power for injecting the same charge density. These results permit quantitative optimization of contact material and diameter for different ECoG applications.

In the sixth chapter, We report an effective method of mechanically anchoring the PEDOT within the Au nanorod (Au-nr) structure and demonstrate that it provides enhanced adhesion and overall PEDOT layer stability under various electrochemical (charge injection) and In vivo stability tests.

In the seventh chapter, we report the fabrication of pure Pt nanorods (PtNRs) by utilizing low-temperature selective dealloying to develop scalable and biocompatible 1D platinum nanorod (PtNR) arrays that exhibit superb electrochemical properties at various length scales for high-performance neurotechnologies. PtNR arrays record brain activity with cellular resolution from the cortical surfaces in birds, mice, and non-human primates; demonstrating the PtNR microelectrode system as a robust system for high performance and stable neural electrode interfaces.

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