Biomedical and materials engineers at the University
of Michigan have developed a nanotech coating for brain implants that helps
the devices operate longer and could improve treatment for deafness, paralysis,
blindness, epilepsy and Parkinson's disease.
Currently, brain implants can treat Parkinson's disease, depression and epilepsy.
These and the next generation of the devices operate in one of two ways. Either
they stimulate neurons with electrical impulses to override the brain's own
signals, or they record what working neurons are transmitting to non-working
parts of the brain and reroute that signal.
On-scalp and brain-surface electrodes are giving way to brain-penetrating microelectrodes
that can communicate with individual neurons, offering hope for more precise
control of signals.
In recent years, researchers at other institutions have demonstrated that these
implanted microelectrodes can let a paralyzed person use thought to control
a computer mouse and move a wheelchair. Michigan researchers' say their coating
can most immediately improve this type of microelectrode.
Mohammad Reza Abidian, a post-doctoral researcher in the Department of Biomedical
Engineering who is among the developers of the new coating, says the reliability
of today's brain-penetrating microelectrodes often begins to decline after they're
in place for only a few months.
"You want to be able to use these for at least a couple years," Abidian
said. "Current technology doesn't allow this in most cases because of how
the tissues of the brain respond to the implants. The goal is to increase their
efficiency and their lifespans."
The new coating Abidian and his colleagues developed is made of three components
that together allow electrodes to interface more smoothly with the brain. The
coating is made of a special electrically-conductive nanoscale polymer called
PEDOT; a natural, gel-like buffer called alginate hydrogel; and biodegradable
nanofibers loaded with a controlled-release anti-inflammatory drug.
The PEDOT in the coating enables the electrodes to operate with less electrical
resistance than current models, which means they can communicate more clearly
with individual neurons.
The alginate hydrogel, partially derived from algae, gives the electrodes mechanical
properties more similar to actual brain tissue than the current technology.
That means coated neural electrodes would cause less tissue damage.
The biodegradable, drug-loaded nanofibers fight the "encapsulation"
that occurs when the immune system tells the body to envelop foreign materials.
Encapsulation is another reason these electrodes can stop functioning properly.
The nanofibers fight this response well because they work with the alginate
hydrogel to release the anti-inflammatory drugs in a controlled, sustained fashion
as the nanofibers themselves break down.
"Penetrating microelectrodes provide a means to record from individual
neurons, and in doing so, there is the potential to record extremely precise
information about a movement or an intended movement. The open question in our
field is what is the trade-off: How much invasiveness can be tolerated in exchange
for more precision?" said Daryl Kipke, a professor in the Department of
Biomedical Engineering and the director of the U-M Center for Neural Communication
In these experiments, the Michigan researchers applied their coating to microelectrodes
provided by the U-M Center for Neural Communication Technology.
A paper on this research, called "Multifunctional Nanobiomaterials for
Neural Interfaces," is published in Advanced Functional Materials. It is
the cover story on the February 24 issue.
Abidian's co-author is David Martin, a professor in of Materials Science and
Engineering; Biomedical Engineering; and Macromolecular Science and Engineering.
Biotectix, a U-M spin-off company founded by Martin, is actively working to
commercialize coatings related to those discussed in this paper. This research
is supported by the National Institutes of Health, the Army Research Office
Multi-disciplinary University Research Initiative and College of Engineering
Translational Research funding.