Microelectrode arrays (MEAs) offer a powerful tool to both record activity and deliver
electrical microstimulations to neural networks either in vitro or in vivo. Microelectronics
microfabrication technologies now allow building high-density MEAs containing several
hundreds of microelectrodes. However, dense arrays of 3D micro-needle electrodes,
providing closer contact with the neural tissue than planar electrodes, are not achievable
using conventional isotropic etching processes. Moreover, increasing the number of
electrodes using conventional electronics is difficult to achieve into compact devices
addressing all channels independently for simultaneous recording and stimulation.
Here, we present a full modular and versatile 256-channel MEA system based on integrated
electronics. First, transparent high-density arrays of 3D-shaped microelectrodes were
realized by deep reactive ion etching techniques of a silicon substrate reported on
glass. This approach allowed achieving high electrode aspect ratios, and different
shapes of tip electrodes. Next, we developed a dedicated analog 64-channel Application
Specific Integrated Circuit (ASIC) including one amplification stage and one current
generator per channel, and analog output multiplexing. A full modular system, called
BIOMEA, has been designed, allowing connecting different types of MEAs (64, 128, or
256 electrodes) to different numbers of ASICs for simultaneous recording and/or stimulation
on all channels. Finally, this system has been validated experimentally by recording
and electrically eliciting low-amplitude spontaneous rhythmic activity (both LFPs
and spikes) in the developing mouse CNS. The availability of high-density MEA systems
with integrated electronics will offer new possibilities for both in vitro and in
vivo studies of large neural networks.
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