Studies on the Biocompatibility of Materials for Retinal Prosthesis

Abstract

Abstract: : Purpose:There are presently several concepts to restore vision in blind or highly visually handicapped persons by implantation of electronic device into the eye in order to partially restore vision. The purpose of the present study was to evaluate the biocompatibility of materials of retinal prosthesis (MRP) in vivo and vitro model. Methods: The materials (diameter; 0.15 mm2) considered to use as a parts of retinal prosthesis were implanted onto the rat retina. Inflammatory response was monitored by the measurement of the C–reactive protein (CRP) in rat serum during the experimental periods. After 2 months of the implantation, histological study was performed. For analysis of the inflammation related cytokines, the retinas were subject to RNA protection assay. In vitro study, purified retinal ganglion cells (RGC) were cultured with the presence of MRP in medium. After overnight of culture, the cell viability was determined by the metabolism of calcein–AM. The total number of living RGC in each well was counted in 5 fields (0.185mm2 / field). The average of these fields was considered as the total living cells in each well. Wells were counted in triplicate. Results:There were statistically no differences in CRP productions among MRPs (SiO2, Si, Pt, Ti and Al). Histological studies revealed that Al caused the thickness of outer nuclear layer (ONL). In vitro study, the RGC cell viability affected by MRPs [SiO2, Si, Pt, Ti, Al, Iridium, and polyimide (PIX, CRC, PIQ)] was measured. These results revealed that Iridium caused loss of the cell viability but the others were suitable for RGC cell culture. Conclusions:As a biomaterial, Al was reported to oxidize the membrane and subject to inhibit the Fe2+ channel events. This inhibition was known to reduce the cell viability. In vitro, there was no effect in cell viability of RGC with the presence of Al. However the implantation of Al in vivo caused severe destruction of the ONL. These results demonstrated that prolonged implantation induced the membrane oxidization and lead to the photoreceptor damage. In conclusion, excepted for Al and Iridium, the materials tested in this study are suitable for production of functional retinal prosthesis and no complications are to be expected from long–term implantations of them into the eye.

Keywords: inflammation • ganglion cells • cytokines/chemokines