Bio–Hybrid Retinal Implant: Micro/Nano–Fabrication of Conductive Polymer for Molecular Electrodes

Abstract

Abstract: : Purpose: As can be seen in ARVO’99 abstracts, we have developed a bio–hybrid retinal implant, which consists of cultured neurons on MEMS (Microelectromechanical System). In this implant, axons of the cultured neurons are guided toward the central nervous system (CNS) with a peripheral nerve graft. Although the first prototype of MEMS has been completed, the main remaining issue is the interface problems between electrodes and neural tissue caused by conventional metallic electrodes and extra–cellular stimulation. In order to solve this problem, we have focused on conductive polymers. They are expected to improve electrical functionality and bio–compatibility at the molecular level so that a neuron will be stimulated intra–cellularly or quasi–intra–cellularly to decrease the threshold current dramatically. Methods: We have been developing the micro/nano–fabrication technique of conductive polymer, and evaluating the bio–compatibility of the polymer in in vitro neuron culture experiments. We have focused on polypyrrole (PPy) as an electrode material. Our fabrication is a photolithography technique using photochemical reaction of oxidative polymerization agents. After fabrication, neurons were cultured on the electrode to test its biocompatibility. Results: When an electrode array was fabricated with this technique, the minimum line width was 3um, which is small enough for stimulating neural tissues. The cultured cells on PPy extended their neurites and survived over 4 weeks. These results suggest that micro–patterns of PPy can be applied to electrodes, and PPy have good affinity to neurons. Conclusions: Although the conductivity of the present electrode must be improved in further study, we have obtained promising data in our pilot studies. In the next phase, we will perform axon guidance experiments with this conductive polymer electrode, evaluate its functionality in electrophysiology testing.

Keywords: visual impairment: neuro-ophthalmological disease • regeneration • cell membrane/membrane specializations