Abstract
In order to provide high-quality visual information to patients who have implanted retinal prosthetic devices, the number of microelectrodes should be large. As the number of microelectrodes is increased, the dimensions of each microelectrode must be decreased, which in turn results in an increased microelectrode interface impedance and decreased injection current dynamic range. In order to improve the trade-off envelope between the number of microelectrodes and the current injection characteristics, a 3D microelectrode structure can be used as an alternative. In this paper, the electrical characteristics of 2D and 3D Au microelectrodes were investigated. In order to examine the effects of the structural difference, 2D and 3D Au microelectrodes with different base areas but similar effective surface areas were fabricated and evaluated. Interface impedances were measured and similar dynamic ranges were obtained for both 2D and 3D Au microelectrodes. These results indicate that more electrodes can be implemented in the same area if 3D designs are used. Furthermore, the 3D Au microelectrodes showed substantially enhanced electrical durability characteristics against over-injected stimulation currents, withstanding electrical currents that are much larger than the limit measured for 2D microelectrodes of similar area. This enhanced electrical durability property of 3D Au microelectrodes is a new finding in microelectrode research, and makes 3D microelectrodes very desirable devices.
Highlights
Retinal degenerative diseases such as age-related macular degeneration (ARMD) and retinitis pigmentosa (RP) result in progressive degeneration of the photoreceptors in the retina and eventually lead to complete blindness [1]
We have previously reported about the surface-area dependent electrical characteristics of 2D and 3D Au microelectrodes at a conference [13]
Each microelectrode is parameterized by the three-element-circuit model, and the maximum allowable current injection limit is simulated using the SPICE software [13]
Summary
Retinal degenerative diseases such as age-related macular degeneration (ARMD) and retinitis pigmentosa (RP) result in progressive degeneration of the photoreceptors in the retina and eventually lead to complete blindness [1]. Despite a near-total loss of the macular photoreceptors in the final stages of RP or ARMD, there are reports that the inner nuclear and retinal ganglion layers are partially preserved [4]. These results support the notion that the approach of restoring vision by electrical stimulation of the surviving neurons using neural prosthetic devices may be viable as a vision-recovery methodology in retinal degenerative diseases [5]. MEAs are used to replace the functions of the degenerated natural photoreceptors by delivering electrical signals to the surviving inner nuclear and ganglion cell layers [6]
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