Evaluation of the Structural Retinal Changes After Implantation of Different Subretinal 3D Implants in Mini-Pigs

In this study, we evaluated the retinal changes of various three-dimensional (3D) microelectrodes implanted subretinally based on implant geometry. In the preliminary experiment, 75 μm-tall 3D electrodes on a 200 μm-thick right-angled polydimethylsiloxane (PDMS) substrate (group 1, n=3) and dome-shaped 40 μm-tall 3D electrodes on an 18 μm-thick parylene-C substrate (group 2, n=3) were implanted in the subretinal space of mini-pig. In the second experiment, a 140 μm-thick sloped PDMS substrate without electrodes (group 3, n=3)and with 20 μm-tall 3D electrodes (group 4, n=3) were implanted into the subretinal space of mini-pig, and 1 female mini-pig was used as a control for immunohistochemistry during examination. In all experiments, spectral-domain optical coherence tomography (SD-OCT) images were obtained at baseline and 2, 6, and 12 weeks after surgery. On OCT, 3D electrodes of group 1 touched the inner plexiform layer (IPL) directly, andsevere fibrous reaction was noted around the implant over time. On the other hand, in implants of groups 2, 3 and 4, the foreign materials remained in place without migration under the retina.Statement of SignificanceExcept group 1, retinal ganglion cells and bipolar cells were preserved intact without fibrosis over the retinal implants in immunostaining results in remaining 3 groups during the implantation period of 12 weeks. The analysis of four different designs of subretinal implants showed differences in the degree of reaction in the retinal tissue. A sloped substrate yielded better results than a right-angled substrate for preserving the retina over the implanted electrodes.