Glassy Carbon Electrocorticography Electrodes on Ultra-Thin and Finger-Like Polyimide Substrate: Performance Evaluation Based on Different Electrode Diameters

Abstract

Glassy carbon (GC) has high potential to serve as a biomaterial in neural applications because it is biocompatible, electrochemically inert and can be incorporated in polyimide-based implantable devices. Miniaturization and applicability of GC is, however, thought to be partially limited by its electrical conductivity. For this study, ultra-conformable polyimide-based electrocorticography (ECoG) devices with different-diameter GC electrodes were fabricated and tested in vitro and in rat models. For achieving conformability to the rat brain, polyimide was patterned in a finger-like shape and its thickness was set to 8 µm. To investigate different electrode sizes, each ECoG device was assigned electrodes with diameters of 50, 100, 200 and 300 µm. They were electrochemically characterized and subjected to 10 million biphasic pulses—for achieving a steady-state—and to X-ray photoelectron spectroscopy, for examining their elemental composition. The electrodes were then implanted epidurally to evaluate the ability of each diameter to detect neural activity. Results show that their performance at low frequencies (up to 300 Hz) depends on the distance from the signal source rather than on the electrode diameter, while at high frequencies (above 200 Hz) small electrodes have higher background noises than large ones, unless they are coated with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS).

Flexible Bioelectronic Devices Based on Micropatterned Monolithic Carbon Fiber Mats

“…Average impedance magnitude dropped after stimulation but maintained the same shape, while the phase showed a more pronounced constant phase characteristic at low frequencies (Figure g). This behavior is consistent with what has been previously observed in other studies on the activation of glassy carbon ECoG electrodes via electric pulses . The charge storage capacity, determined from the area of the CV ran within the CF electrodes water window (−0.9 to 1.1 V, also see Figure S4, Supporting Information) increased from 2.3 to 7.1 mC cm −2 after stimulation (Figure h; Figure S5, Supporting Information), which is another known sign of activation.…”

“…Device functionality for neural applications was tested on one adult Long Evans rat (400–500 g) in three different positions over the S1BF. The surgical procedure to expose the rat barrel cortex (A‐P: between 1 and 4 mm from bregma, M‐L: between 3 and 5 mm from the midline), implant the array and record SEPs were performed using the protocols described elsewhere . To calculate the SNR, the signal power was estimated by computing the integral of the spectral power density (SPD in the 3–1000 Hz band) of the signal (evoked activity, 60 intervals of 100 ms after the whiskers stimulation) and the noise power computed as the integral of the SPD of the noise (spontaneous activity, 60 intervals of 100 ms before the whiskers stimulation).…”

“…When they are flexible and able to conform to curvilinear bodies, they allow for high amplitude recordings up to the resolution of spikes even if the Young's modulus of the device is orders of magnitude higher than the tissue underneath . Surface biocompatibility of the implant materials ensure intended interactions with the target cells …”

Electrodeposited PEDOT:Nafion Composite for Neural Recording and Stimulation

“…26, 4/3/2014), and an approved protocol by the Ethics Committee for animal research of the University of Ferrara and by the Italian Ministry of Health (authorization no. 332/2015‐PR) …”

Revisiting thin film of glassy carbon

“…In particular, glassy carbon is attracting the interest of materials scientists and industrial companies for its large and original physical properties compared to other carbonaceous materials, such as high electrical conductivity, excellent mechanical resistance and gas impermeability. GC is also biologically compatible with living tissues [17][18][19]. Finally, GC has the particularity of being the carbonaceous material with the lowest mass density (1.5 g/cm 3 ) [19] without open porosity, thus combining the properties of vitreous and ceramic materials with those of graphite.…”