3D Diamond Electrode Array for High-Acuity Stimulation in Neural Tissue

Abstract

Innovations in micro-and nanofabrication technologies enable the manufacture of multielectrode arrays for use in neuromodulation and neural recording. Multielectrode arrays make possible medical implants such as pacemakers, deep-brain stimulators, or visual and hearing aids, to treat numerous neural disorders. An optimal neural interface requires a high density of electrodes to precisely record from and stimulate the nervous system while minimizing the overall size of the array. For example, people with retinal degenerative diseases can benefit from retinal prostheses implanted inside the eye. However, at present the visual acuity provided by such implants is well below the threshold for functional vision, mainly due to the limited spatial resolution. In this work, we present a design of 3D nanostructured conductive diamond electrodes, integrated within a polycrystalline diamond housing, offering a high electrode density and count, which simultaneously satisfies spatial resolution and biocompatibility goals. The array is composed of height adjustable pillar electrodes that are 80 μm in diameter and separated by 150 μm. A holistic characterization of the electrodes was performed and the device tested for stimulation performance in a whole-mounted retina. Electrochemical testing showed impedance of 20 kΩ and a wide water window of 2.47 V. The pillar structure allows the distance between the electrodes and the retinal ganglion cells to be reduced which is key to more confined stimulation at lower current levels, leading to potentially higher-acuity stimulation without damaging retinal tissue.

3D Electrodes for Bioelectronics

“…For example, boron-doped diamond (BDD) is a p-type semiconductor, and the conductivity of BDD can be controlled by the doping level. [83][84][85] Piret et al developed 3D nanostructured BDD electrodes (Figure 5d) and used of the electrodes for recording the electrophysiology of hippocampal cells. [84] This nanostructured BDD had an impedance of 50 kΩ at 1 kHz, based on a 20 µm diameter electrode.…”

Recent Advances in Monitoring Cell Behavior Using Cell-Based Impedance Spectroscopy

“…Compared to the cancer research, there is less reported research that utilizes CBI devices to study neuron behavior and neurodegenerative diseases. These few studies demonstrated the capability of the CBI devices to monitor the behavior of neurons in physiological and pathogenically conditions using 2D and 3D in vitro models [84][85][86][87][88][89][90][91].…”

“…The CBI system was also used to study the neural signals using an in vitro model [87,88]. Zuo et al [87] designed a multiple microelectrode array, with 105 electrodes, to stimulate and record the extracellular neural signals of mouse brain slices.…”

“…Recently, a diamond 3D microelectrode array, with a hexagonal shape and high electrode density was developed for neuronal stimulation. An in vitro model of rat retina was used to test the performance of the device, which showed that the 3D diamond electrodes could provide a localized stimulation of retinal ganglion cells [88].…”

Diamond in medical devices and sensors: An overview of diamond surfaces

“…From the same laboratory group, Ahnood et al describe a system with upscaled information density for retinal implants (Ahnood et al, 2017), as well as another method of generating charge in diamond electrodes through near‐infrared light (Chambers et al, 2020). Improved methods of micro‐ and nano fabrication enabled the formation of a 3D nanostructured array by Stamp et al, subsequently used for electrophysiological tests for subretinal stimulation in explanted animal retinas and found capable of localized stimulation of retinal ganglion cells (Stamp et al, 2020). Overall, CVD fabricated diamond has shown great promise as a material for electrodes, sensors and bionic interfaces, with multimodality an emerging prospect of interest from this versatile material.…”