Mechanically Dynamic Cortical Electrodes
Description
Recent advances in macromolecular science have produced mechanically
dynamic materials that can change their stiffness. This material has promise as a substrate for cortical interfaces. There are numerous
advantages of cortical electrodes to monitor brain function and restore
function, but available probes are not typically able to record single
unit activity over a several year lifetime. One factor generally
believed to contribute to the short lifetime is the mismatch between the stiffness of standard electrode materials (modulus between 4 – 100 GPa)
and the brain stiffness (modulus between 1 – 100 kPa). The novel polymer
is stiff for insertion followed by a compliant state once fully
implanted in the brain. A probe fabricated of this material is able to
pierce the pia mater of the brain for insertion while minimizing the
electrode-neural distance and overall probe footprint. In the brain’s
aqueous environment, the material’s modulus is dramatically reduced and
is similar to the modulus of the brain. Our hypothesis is that the
softer probe will result in a reduced cellular reaction and better
long-term connection to the neurons.
Preliminary Results
The dynamic material, a nanocomposite of a percolated cellulose scaffold
in a poly(vinyl acetate) (PVAc) polymer maxtrix, has been implanted into
rats with a speed-controlled mechanical inserter. The force of insertion
of the nanocomposite has been measured and compared to standard tungsten
microwires. After periods of one day, nine days, and two weeks, rat
brains were analyzed via immunohistochemistry. Preliminary analysis has
been performed to understand the cellular response from the
nanocomposite probes and tungsten microwires. Classic markers of glial
encapsulation: astrocytic condensation and neuronal die-back are being
investigated in addition to other markers of cell types manifested in
cortical injuries.
Clinical Significance
With increasing development of brain-machine interfaces, safe, long-term
cortical electrodes can restore abilities to individuals with spinal
cord injuries or amputees.
Chronic cortical electrodes are limited by their limited recording
lifetimes of typically six months to a year, and increases in longevity
are vital to viable prosthetic systems to regain function after
neurological trauma or disease. High density electrode arrays that can
record signals from the brain will also yield data on the plasticity of
the brain and allow for investigations into restoration of function
through retraining of the brain. Arrays that can be implanted over a
span of decades rather than months will also allow for further
investigation into disease progression in neurological disorders such as
MS, ALS, Alzeheimer's, Huntington's, and Parkinson's.
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