Biomedical Engineering Reference
In-Depth Information
Attracting Retinal Cells to Electrodes
Migration of Retinal Cells into Perforated Membrane
We have discovered a robust property of retinal tissue that promises to reliably
provide an extremely close proximity of the retinal cells to the implant, thus
allowing high-resolution electrical stimulation. In experiments in vitro, in which
retinas were placed photoreceptor-side down upon the membrane, a robust
migration of retinal tissue into small apertures was observed in all samples of the
rat, chicken, and rabbit retina [15]. Migration of the outer nuclear layer, outer
plexiform layer, and inner nuclear layer occurred through apertures larger than
5m (Figure 14.6). The cellular invasion of the aperture appeared to include
both glial and neural cellular elements, and the rate of tissue migration increased
with aperture size. A transmission electron micrograph of a section through an
aperture demonstrated the presence of neuronal processes and synaptic structures
connecting the migrating cells. These findings indicate the possibility of signal
transduction from the stimulated cells to rest of the retina [14-16]. Culturing of
the retina upside down (tested on the P7 rat retina), i.e. nerve fiber layer toward
the membrane, did not result in cellular migration, as shown in Figure 14.6.
The RCS rats were used as a model for in vivo experiments, since their
photoreceptors degenerate as in RP. Experiments with subretinal Mylar films
perforated with apertures of 15-40m in diameter showed robust migration of
the inner nuclear layer after 5 and 9 days [14]. Since unlimited tissue migration
through a membrane could be problematic (draining retinal cells and proliferating
Figure 14.6. Histological sections of the RCS rat retina 3 days after explantation onto a
perforated 13-m-thick Mylar film. (Left) Retinal tissue placed photoreceptors down onto
the membrane migrates through the aperture. (Right) Retina placed with its nerve fiber
layer onto the perforated membrane does not migrate even when the ILM was removed.
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