Biocompatibility of photodiode structures used for epiretinal prosthesis extended by an integrated epiretinal recording (OPTO-EPIRET)

Purpose : In patients suffering from retinal degenerative diseases, e.g., retinitis pigmentosa, functionality can be regained by epiretinal prostheses, where microelectrodes electrically stimulate the remaining functional retinal cells. Within the OPTO-EPIRET proposal, the common approach is extended by an integrated circuit (IC) based epiretinal recording of the visual field. An array of photodiodes at the frontside of the IC will record the images that would normally fall onto the retina. The optical information will be converted by the circuit in appropriate stimulation pulses that are forwarded to the electrodes on the backside of the IC embedded in the prosthesis. Here, we analyzed the biocompatibility of the photodiode structures after direct and indirect cell contact in terms of cell proliferation and viability. Methods : The photodiode structures were provided by our partner from the University Duisburg-Essen and fabricated at the Fraunhofer Institute of Microelectronic Circuits and Systems. Growth rates and survival of L-929 and retinal precursor (R28) cells were determined after direct and indirect contact. For indirect contact, cells were cultivated in medium pre-incubated with the photodiode structures and analyzed using a luminescent cell viability assay. Direct cell contact was evaluated using a fluorescein-diacetate/ propidiumiodide-based life-dead assay. Results : Regarding indirect contact, the extractive medium of the photodiode structures had no significant influence on cell growth rates, as compared to different reference materials that showed defined levels of cytotoxicity. Regarding direct contact, both cell types exhibited good proliferation properties and showed less than 2% dead L-929 cells and less than 1% dead R28 cells. Conclusions : The photodiode structures showed a good biocompatibility profile and no aspects of cytotoxicity, neither after direct or indirect contact. This is the first step towards the biocompatibility testing of the OPTO-EPIRET structures in-vivo in a rabbit animal model. This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.