Development of High-Resolution Electrode Arrays for Retinal Prostheses
Milan Djilas, post-doc à l'institut de la vision

vendredi 8 octrobre 2010 à 10h
Salle E223 - LIRMM


Résumé
In normal-sighted individuals vision begins when light enters the eye and hits photoreceptor cells in the retina. The role of these cells is to convert light into bioelectric signals which are subsequently processed by complex inner retinal circuitry. Processed visual information is eventually encoded in form of electric impulse trains that are sent to the brain via the optic nerve. In cases of retinal degeneration caused by diseases like age-related macular degeneration and retinitis pigmentosa, the number of photoreceptor cells is significantly reduced, causing a reduction of visual acuity and, in worst cases, complete blindness. Following photoreceptor degeneration, parts of the inner layers of the retina, including bipolar and ganglion cells, remain. The concept of retinal electrical prostheses has been developed to restore useful vision in blind patients by activating the remaining inner retinal network. The system can either consist of an implanted stimulating device coupled with an external camera and a coding device or all these functions can be integrated into a single chip. Eventually the recorded image is encoded into an electrical pattern and sent to the dystrophic retina using a stimulation electrode array. The resolution of the electrode array remains a general and important challenge. Planar electrode arrays show limited activation selectivity of cells underlying the electrode array. Three-dimensional electrode arrays were proposed to decrease inter-electrode cross-talk and provide improved bio-electronic interfacing.
The presentation will give a short summary of the research conducted at the Institute of Vision (INSERM/CNRS, Paris, France) towards developing high-resolution retinal prostheses. Finite-element modeling and geometry optimization of 3D electrode structures were conducted to maximize electric field focalization in retinal tissue targeted for stimulation. Implant prototypes with optimized geometries were microfabricated and implanted into the subretinal space of blind rats. Histological analysis confirmed our starting hypothesis that retinal bipolar cells, but not reactive glial cells, would migrate into and integrate with the implants. Future work will include in vivo optical imaging of the visual cortex in rats to evaluate responses to electrical stimulation of the retina. Future implants will also be coated with boron-doped diamond; a potential new biomaterial that recently raised great interest for use in neuroprostheses because of its semi-conductive properties. Its biocompatibility has been investigated on retinal neuron cultures in our lab and the preliminary in vivo tests are very promising.