Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
We can conclude that B-NCD offers several advantages when
compared to metallic materials. Its carbon surface offers high
biocompatibility, and the B-NCD potential window is about
twice that of Pt.
We can also see on Figure 5 that retinal ganglion cells can
grow their neurites onto electrodes. Cells can be seen to
organize along lines (Fig. 5B) whereas they do not show any
organization in the absence of similar patterns (Fig. 5A).
Such fabricated B-NCD MEAs were also tested to record the
spontaneous neural activity on mouse spinal cord, and they
were compared with standard Pt MEAs in term of noise level
found to be around 10µV peak to peak, Figure 6.
Different procedures are still under investigation to obtain
other significant biological measurable signals.
Figure 6. Illustration of B-NCD MEAs used to record
spontaneous neural activity.
IV.
Recorded spontaneous activity
Rms noise: 10µV peak to peak
MEA APPLICATION TO RETINAL IMPLANTS
10 µV
A
Figure 4. Retinal Ganglion Cell survival on different
substrates.
B
At present time, in the case of retinal diseases, affecting
around 12 Million people in both Europe and US, among the
most frequent pathologies, photoreceptor degeneration is
causing blindness in both hereditary diseases like retinitis
pigmentosa and non-hereditary diseases like age-related
macular degeneration (AMD).
In such cases of retinal dystrophies, the number of
photoreceptor cells is significantly reduced, causing a
progressive reduction of visual acuity and, in worst cases,
complete blindness. It can cause photoreceptor degeneration
following which other layers of the retina, including bipolar
and ganglion cells, partially remain [13]. Amongst several
strategies, the concept of retinal prostheses was developed to
restore useful vision in blind patients by activating this
remaining inner retinal network using subretinal stimulation,
as illustrated on Figure 7 [14].
This concept was also validated in several clinical trials
showing that patients were able for instance to follow moving
light targets and were able to identify specific known
contrasted objects [15, 16]. The first existing system (from
Second Sight, US) is composed by an implanted stimulating
device, using a micro-electrode array (MEA), coupled with an
external camera and a coding device [17].
Figure 5. Retinal ganglion cell cultures on multi-electrode
arrays. Note in (B) the presence of cells organized along lines
when a square pattern is aligned with electrodes.
Based on the patterning of nanodiamond seeds prior to growth
as described in part II, it comes possible to process structured
MEAs where the active area is diamond (B-NCD). Here an
additional challenge is to propose a fabrication of diamond
electrodes compatible with a soft substrate material, which is
achieved using a sacrificial substrate lift-off technique,
resulting in retinal implants embedded into polyimide.
Such implants are based on 16, 32 or 64 electrodes arrays and
are tested in-vivo on rats, as one can see on Figure 8.
Biologists developed a surgical technique to introduce the
implants in the subretinal space of blind P23H rats. After 14
weeks in vivo, the eye can be fixed and histological sections of
the eye are obtained to visualize the retinal tissue with respect
to the implant. These preliminary results are very encouraging
because no major reactive gliosis is detected in contact with
the implant. The significant reduction of glial cells appearance
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