Shoval et al recently tested the efficacy of TiN electrodes, fabricated on oxidized silicon substrates and coated with multi-wall carbon nanotubes, as a multielectrode array for the treatment of retinal degeneration. Vision loss due to retinal degradation is common, but since the output retinal ganglion cells remain intact, it has been suggested that a retinal implant may be able to circumvent the photoreceptors and restore visual information transfer. Carbon nanotubes have a diameter of 82nanometers with a narrow distribution. Due to their chemical inertivity, resistance to mechanical damage, high conductivity, and ease of production, they are an attractive material to interface between electrodes and neural tissue.
Specifically, the researchers tested their design on rodent retinal brain splices and analyzed data from electrodes that had activity of 0.2 Hz or above. Compared to commercial TiN electrodes, the carbon nanotube interfaced electrodes had both 1) Increased variability in the amplitude distribution (up to ~250 μV as opposed to ~100 μV for TiN electrodes), suggesting an improved electrical coupling between the neurons and the electrodes, and 2) Increased signal-to-noise ratio, again suggesting an improved coupling between tissue and electrode, perhaps due to an increase in surface area contact between the cell’s processes (i.e., neurites) and the electrodes.
There are many other technical considerations to overcome in engineering the retinal implants, such as biocampatability, stability, a lack of current spread throughout the retina following focal stimulation, and an insufficient ratio of electrodes to ganglion cells. But given that age related macular degeneration affects 30% of individuals aged 75-85, this is a pressing issue that deserves attention.
Age-Related Macular Denegeration Info: http://www.agingeye.net/maculardegen/maculardegeninformation.php.