Enable Fluidic Interface with Brain
by Warren Grill, senior technical editor and James Cavuoto,
Neural interfaces for recording information from the brain or transmitting
information to the brain are dominated by electrical signaling.
However, communication between neurons in the brain primarily occurs
by chemical transmission across synapses. A new generation of microfluidic
devices promises to offer both electrical and chemical signaling.
Ruben Rathnasingham and colleagues from Daryl Kipkes neural
engineering laboratory at the University of Michigan recently
reported on the characterization of silicon-based microprobes that
incorporate fluid ports to allow local chemical delivery into the
brain. After using bench-top experiments to demonstrate a linear
relationship between the applied pressure and the resulting flow
rate, the efficacy of the devices was evaluated in vivo. The Michigan
researchers injected an excitatory neurotransmitter to the inferior
colliculus (IC) of the guinea pig brain while recording firing from
IC neurons using five discrete recording sites on the same probes
used for microinjection.
The firing rate of IC neurons increased dramatically following injection
while control injections of Ringer solution did not impact the firing
rate. Further, the duration over which the firing rate was increased
could be manipulated by changing the injected volume.
A team headed by Steve DeWeerth at Georgia
Techs Laboratory for Neural Engineering is also working
on a microfluidic/electronic neural interfacing system. They have
constructed a microfabricated neuronal interfacing system to interface
with a three-dimensional, in vitro neural network. DeWeerths
team is working with neural cell cultures and slices up to 2 mm
thick with the aim of understanding the behavior of functional networks
of neurons, neural plasticity in the networks, and the effects of
injury on network behavior.
The neuronal interfacing system consists of a planar substrate onto
which are grown vertical towers, up to 1 mm high, that feature connecting
crossbridges, microfluidic channels, and electrical contacts. The
microfluidic ports will be able to deliver nutrients, trophic factors,
and neurotransmitters to stimulate localized regions of tissue.
The electrical contacts on the tops and sides of the towers will
interface with custom integrated circuits that perform amplification,
multiplexing, and other forms of neural processing. The team hopes
to create a new form of hybrid tissue-engineered implants capable
of simultaneous stimulating, recording, and signal processing.
Interfaces such as these that enable local delivery could improve
the efficacy of pharmaceutical treatments by allowing much greater
control of the spatial and temporal pattern of delivery. For example,
substances could be delivered only to that brain area required for
the desired clinical effect, and not to other areas where side effects
might be produced.