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. 2023 Apr 28;13(1):6973.
doi: 10.1038/s41598-023-32976-9.

Full-field, conformal epiretinal electrode array using hydrogel and polymer hybrid technology

Muru Zhou  1 , Benjamin K Young  2 , Elena Della Valle  3 , Beomseo Koo  3 , Jinsang Kim  1   3   4   5   6   7 , James D Weiland  8   9   10
Affiliations

Full-field, conformal epiretinal electrode array using hydrogel and polymer hybrid technology

Muru Zhou et al. Sci Rep. .

Abstract

Shape-morphable electrode arrays can form 3D surfaces to conform to complex neural anatomy and provide consistent positioning needed for next-generation neural interfaces. Retinal prostheses need a curved interface to match the spherical eye and a coverage of several cm to restore peripheral vision. We fabricated a full-field array that can (1) cover a visual field of 57° based on electrode position and of 113° based on the substrate size; (2) fold to form a compact shape for implantation; (3) self-deploy into a curvature fitting the eye after implantation. The full-field array consists of multiple polymer layers, specifically, a sandwich structure of elastomer/polyimide-based-electrode/elastomer, coated on one side with hydrogel. Electrodeposition of high-surface-area platinum/iridium alloy significantly improved the electrical properties of the electrodes. Hydrogel over-coating reduced electrode performance, but the electrodes retained better properties than those without platinum/iridium. The full-field array was rolled into a compact shape and, once implanted into ex vivo pig eyes, restored to a 3D curved surface. The full-field retinal array provides significant coverage of the retina while allowing surgical implantation through an incision 33% of the final device diameter. The shape-changing material platform can be used with other neural interfaces that require conformability to complex neuroanatomy.

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Conflict of interest statement

Author JDW has a financial interest in electrodeposited PtIr. Remaining author do not have any competing interest to declare.

Figures

Figure 1
Figure 1
(a) Illustration of implanting the compact FFA into the eye. FFA unfolds with a fully swollen hydrogel layer. Notably, the illustrated metal electrodes were only an indication of the location of the electrodes, and the electrodes were opened on the same side as the hydrogel. (b) Layer-to-layer composition of the FFA. (c) A photo of the curved FFA placed on a supportive platform in 0.01 M phosphate-buffered saline (PBS).
Figure 2
Figure 2
Impedance characterization of electrodes. (a) A box-and-whisker plot shows the distribution of impedance of the electrodes at 1 kHz (14 electrodes in total). The box represents the range of data between the first and the third quartile, and the whiskers represents the maximum and minimum data points without outliers (labeled in dots). The solid line inside the box represents the median value. (b) Two representative EIS trends of two out of the 14 electrodes.
Figure 3
Figure 3
Representative plot of model fitting of the EIS measurements of one electrode before electrodeposition using an equivalent circuit model. The experimental data is reported in solid blue line for impedance and solid orange line for phase. The fitted impedance and phase are reported as blue dashed line and orange dashed lines separately. The inset shows the equivalent circuit model used to fit the experimental data.
Figure 4
Figure 4
CV of one electrode before (purple) and after (blue) the Pt/Ir electrodeposition, and after hydrogel coating (black).
Figure 5
Figure 5
SEM image and EDS characterization of one representative electrode. (a) SEM image of one electrode shows the insulation of polyimide and the Pt/Ir alloy coating on the electrode surface. (b) Chemical spectra from the EDS map on the electrode active surface indicates two different peaks associated to Pt and Ir both at 9 keV and 11 keV. EDS map is generated using The EDAX TEAM EDS software suite. URL to the software: https://www.edax.com/-/media/ametekedax/files/eds/product_bulletins/team%20eds%20software%20suite.pdf.
Figure 6
Figure 6
Simulation surgery to implant the multilayered device. (a) Preparation of the device before implantation. The multilayered prosthesis was rolled up with PVA film and placed into a straw with one side cut open. The inset is the cross-section of the rolled-up device, and the diameter is measured as 8 mm. After dehydration and the removal of the straw, the device stayed fixed and compact at a diameter of 8 mm. (b) Photo of the fully deployed multilayered electrode in pig eye after removal of the cornea and scleral rim. The dotted white line outlines the edges of the 6 petals.
Figure 7
Figure 7
Impedance characterization of electrodes (n = 6). (a) A box-and-whisker plot demonstrates the impedance of electrodes at 1 kHz after hydrogel coating and after implantation. The box represents the range of data between the first and the third quartile, and the whiskers represents the maximum and minimum data points without outliers (labeled in dots). The solid line inside the box is the median value. (b) CV curve of one electrode shows CV after hydrogel coating in black and after implantation in red.
Figure 8
Figure 8
(a) Schematic illustration of sequential fabrication processes for polyimide-based electrode array. The bottom layer of polyimide was spin coated on the wafer and partially cured. Then, metal electrodes and conductive lines were patterned on polyimide by photolithography. Finally, the top of layer of polyimide was spin coated on top and patterned with electrode sites open. (b) Illustration of procedures to build sandwiched electrode array. Fabrication of the bottom layer and the top layer of PDMS with the guidance of back alignment marks. Then sandwich the polyimide-based electrode array between two layers of PDMS.
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