Abstract
This study presents the fabrication of three-dimensional (3D) microelectrodes for subretinal stimulation, to accommodate adjacent return electrodes surrounding a stimulating electrode. For retinal prosthetic devices, the arrangement of return electrodes, the electrode size and spacing should be considered together, to reduce the undesired dissipation of electric currents. Here, we applied the hexagonal arrangement to the microelectrode array for the localized activation of retinal cells and better visual acuity. To provide stimuli more efficiently to non-spiking neurons, a 3D structure was created through a customized pressing process, utilizing the elastic property of the materials used in the fabrication processes. The diameter and pitch of the Pt-coated electrodes were 150 μm and 350 μm, respectively, and the height of the protruded electrodes was around 20 μm. The array consisted of 98 hexagonally arranged electrodes, supported by a flexible and transparent polydimethylsiloxane (PDMS) base, with a thickness of 140 μm. Also, the array was coated with 2 μm-thick parylene-C, except the active electrode sites, for more focused stimulation. Finally, the electrochemical properties of the fabricated microelectrodes were characterized, resulting in the mean impedance of 384.87 kΩ at 1 kHz and the charge storage capacity (CSC) of 2.83 mC·cm−2. The fabricated microelectrodes are to be combined with an integrated circuit (IC) for additional in vitro and in vivo experiments.
Highlights
Retinal degenerative diseases are one of the causes that impair the vision of patients
The base of the array was made of transparent PDMS, so that the photodiodes of the integrated circuit (IC) connected to the electrodes can sense light directly
By a customized pressing process utilizing the elastic property of the used material, a 3D structure of the electrode array was created, resulting in the electrodes that protruded around 20 μm from the PDMS base
Summary
Retinal degenerative diseases are one of the causes that impair the vision of patients. If photoreceptors are lost because of AMD and RP, these signals cannot be generated and transmitted to non-spiking neurons in the inner nuclear layer (INL) [5]. This results in no responses of the retinal ganglion cells (RGCs) that transmit the signals to the optic nerve. The stimulating electrodes have been developed to stimulate retinal cells epiretinally or subretinally [6,7,8,9,10,11], which differ in their stimulation thresholds to electrically elicit the responses of RGCs. The stimulation threshold can vary depending on the type of pulse applied to the electrode (monMoipcrhomaascihcinoesr20b2i0p, 1h1a, xsic), pulse polarity (cathodic or anodic), and pulse duration [25,26,27,28,29]. Rweecofarrbercitciadteendtiafictahtrieoen-odfimsyemnbsoiolsn[a3l3(]3aDn)dma ihcirgoheelreceltercotdroedaerdraeynswityithwi9th8ienlethcetrloimdeitsedbadseevdicoen the transapraeraen[3t4b] acsaenabnedacnhtiacripaactteedri.zFeidnatlhlye, ewleectfraobcrhiceamtedicaaltphrroeep-edritmieesnosifotnhael f(3aDbr)icmaitcerdoeelleecctrtoroddeeasr,rpayrior to in vitwroithan9d8 einlecvtirvoodeesxbpaesreidmoenntths.e transparent base and characterized the electrochemical properties of the fabricated electrodes, prior to in vitro and in vivo experiments
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