An implantable microelectrode array for chronic in vivo epiretinal stimulation of the rat retina

The design, fabrication, and testing of a microelectrode array for chronic in vivo stimulation of the rat retina is presented. Epiretinal positioning of the array introduced design challenges associated with the surgical implantation approach into the rat ocular orbit. These anatomical and surgical challenges were overcome using microfabrication of thin-film Parylene C and platinum to create the array followed by thermal post-processing steps to achieve the required array geometry. An electroplated platinum-iridium coating was employed to increase the electrode charge storage capacity and then verified in benchtop electrochemical characterization. Preliminary in vivo implantations with sham devices containing no metal revealed chronic biocompatibility (up to 6 weeks) and acute trials with functional arrays illustrated device robustness against surgical trauma. This work represents the first epiretinal implant development for the rat animal model via a suitable soft neural interface device enabled through polymer MEMS micromachining.