window of this study, up to 6 weeks postoperatively, the neurons maintain their normal narrowly defined small molecular signatures in the presence of the implant, indicating normal metabolic status [9].

7.3.3  Pillar Arrays

While chamber arrays effectively improved neuron-implant proximity, the migrated tissue was somewhat isolated from the rest of the retina. Pillar arrays were designed to provide proximity to cells by utilizing retinal migration, while avoiding this isolation. The pillars used in this study were made from uncoated SU-8, approximately 10 mm in diameter, spaced 20, 40 and 60 mm center-to-center and 65 mm in height (Fig. 7.4c, d). The devices were implanted into P45 RCS rats for 6 weeks.

Figure 7.6 shows retinal histology 6 weeks after implantation. In the area with lower pillar density (Fig. 7.6a, 40 mm spacing) some cell bodies appear to be pulled down past the tops of the pillars, but many cell bodies remain apposed to the electrode surface at the top of the pillars. At the higher pillar density (Fig. 7.6b, 20 mm spacing) the space between the pillars seems to be filled almost entirely with neuropil and the cell bodies remain stable near the tops of the pillars. The inner retina appears well ordered and healthy for RCS retina. CMP results show that the neurons retain their phenotype and

Fig. 7.6  Pillar implant in subretinal space of RCS rat 6 weeks post-op. Scale bar is 50 mm. (a) Area with 40 mm pillar spacing. (b) Area with 20 mm pillar spacing. Figure reprinted from [9], with permission