Biostability and Biocompatibility of Subretinal Electronic Devices after Subretinal and Subcutaneous Implantation in Rabbits

Abstract

Abstract: : Purpose: The proof of long term biostability and biocompatibility is a crucial precondition for electronic devices, which are intended to be implanted into human eyes. So the encapsulation of the chip with a stable passivation layer is a key element of a functional implant. Microphotodiode arrays (MPDAs) encapsulated with 4 different materials were evaluated after subretinal and subcutaneous implantation in rabbits. Methods: 2 mm x 2 mm microchips with TiN-electrodes, encapsulated with 4 different passivation layers ( A, B, C, D) were implanted into the subretinal space of rabbit eyes via an ab externo transchoroidal access and explanted after 3, 6, 12 months respectively. In addition, the test items were implanted into the dorsal paravertebral subcutaneous tissue of rabbits (n=3 each type of implant, time period and implantation site). The tissue reaction in the eye or in the subcutaneous tissue was examined by histology either after removal of the implant or in combined tissue/material preparations. The explanted chips were analysed for microstructural integrity. Alterations were compared after subretinal versus subcutaneous implantations. Results: MPDAs encapsulated with substance A and B remained intact after in vivo both subretinal and subcutaneous implantation for 12 months, whereas: almost all electrodes were detached and corrosion occurred in items with passivation layers consisting of substances C and D. Histologically, all implants were tolerated in the subretinal space without any inflammatory or foreign body reaction, nor any proliferative reaction of Mueller cells. Subcutaneous implants were surrounded by a fibrous pseudo-capsule that in general did not evoke any inflammatory signs. Only occasionally, a weak macrophage reaction was observed but was not related to a certain passivation layer. Long term stability and biocompatibility of the different test items corresponded well after subretinal and after subcutaneous implantation. Conclusions: Two materials for long term stable and biocompatible encapsulation of subretinal electronic devices were identified. In addition, we could demonstrate that subcutaneous implantation provides a valid, easy and animal sparing pretest for ocular electronic implants. (passivation layers are anonymous because of a patent application) Support: German Ministry of Research (BMBF), 01 KP 0012

Keywords: retina • vitreoretinal surgery • visual search