Abstract
Neural interfaces for neuroscientific research are nowadays mainly manufactured using standard microsystems engineering technologies which are incompatible with the integration of carbon as electrode material. In this work, we investigate a new method to fabricate graphitic carbon electrode arrays on flexible substrates. The devices were manufactured using infrared nanosecond laser technology for both patterning all components and carbonizing the electrode sites. Two laser pulse repetition frequencies were used for carbonization with the aim of finding the optimum. Prototypes of the devices were evaluated in vitro in 30 mM hydrogen peroxide to mimic the post-surgery oxidative environment. The electrodes were subjected to 10 million biphasic pulses (39.5 μC/cm2) to measure their stability under electrical stress. Their biosensing capabilities were evaluated in different concentrations of dopamine in phosphate buffered saline solution. Raman spectroscopy and x-ray photoelectron spectroscopy analysis show that the atomic percentage of graphitic carbon in the manufactured electrodes reaches the remarkable value of 75%. Results prove that the infrared nanosecond laser yields activated graphite electrodes that are conductive, non-cytotoxic and electrochemically inert. Their comprehensive assessment indicates that our laser-induced carbon electrodes are suitable for future transfer into in vivo studies, including neural recordings, stimulation and neurotransmitters detection.
Highlights
Laser technology was recently investigated and developed as an alternative for mid-scale integration densities to traditional photolithographic methods, for patterning the silicone rubber substrate and platinum/iridium electrodes and tracks[22,23,24], and for carbonizing the electrode sites[25]
Afterwards, the electrode sites were laser-structured in an inert atmosphere (N2) to obtain laser-induced carbon electrodes and the devices were released from the ceramic carrier
The analysis reveals an atomic percentage of graphitic carbon of 75% and 74%, for the pristine P20 and P40 electrodes respectively, and confirms that both laser parameters yield a graphitic type of carbon by pyrolyzing the parylene C insulation layer on top of the platinum-iridium tracks
Summary
Laser technology was recently investigated and developed as an alternative for mid-scale integration densities to traditional photolithographic methods, for patterning the silicone rubber substrate and platinum/iridium electrodes and tracks[22,23,24], and for carbonizing the electrode sites[25]. The referred fabrication method surely has the potential to have a high impact on the carbon electrodes technology towards clinical trials, as it represents a rapid, simple and economic way to make on-demand electrodes for patients with different anatomies and for various applications where carbon can improve the performance of the implanted devices (e.g. cuff electrodes for peripheral nerve stimulation, retinal implants, ECoG and micro-ECoG arrays for brain-computer interfaces (BCI) and deep brain stimulation (DBS) devices for closed-loop systems) Such devices have electrode-site dimensions that are rather suited to record local field potentials and mass signals or stimulate populations of fibers and cell bodies, than for single unit access. Our goal was to find a rapid way for prototyping robust graphitic carbon electrode arrays on flexible substrates, optimize their performance, and potentially refine the role of carbon as electrode material in the field of neural prostheses
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