July 7, 2005
Working with platinum nanowires 100 times thinner
than a human hair--and using blood vessels as conduits
to guide the wires--a team of U.S. and Japanese researchers
has demonstrated a technique that may one day allow
doctors to monitor individual brain cells and perhaps
provide new treatments for neurological diseases
such as Parkinson's.
Writing in the July 5, 2005, online issue of The
Journal of Nanoparticle Research , the researchers
explain it is becoming feasible to create nanowires
far thinner than even the tiniest capillary vessels.
That means nanowires could, in principle, be threaded
through the circulatory system to any point in the
body without blocking the normal flow of blood or
interfering with the exchange of gasses and nutrients
through the blood-vessel walls.
The team describes a proof-of-principle experiment
in which they first guided platinum nanowires into
the vascular system of tissue samples, and then successfully
used the wires to detect the activity of individual
neurons lying adjacent to the blood vessels.
Rodolfo R. Llinás of the New York University
School of Medicine led the team, which included Kerry
D. Walton, also of the NYU medical school; Masayuki
Nakao of the University of Tokyo; and Ian Hunter
and Patrick A. Anquetil of the Massachusetts Institute
"Nanotechnology is becoming one of the brightest
stars in the medical and cognitive sciences," said
Mike Roco, Senior Advisor for Nanotechnology at the
National Science Foundation (NSF), which funded the
Already, the researchers note, physicians routinely
use arterial pathways to guide much larger catheter
tubes to specific points in the body. This technique
is frequently used to study blood flow around the
heart, for example.
Following the same logic, the researchers envision
connecting an entire array of nanowires to a catheter
tube that could then be guided through the circulatory
system to the brain. Once there, the wires would
spread into a "bouquet," branching out into tinier
and tinier blood vessels until they reached specific
locations. Each nanowire would then be used to record
the electrical activity of a single nerve cell or
small groups of them.
If the technique works, the researchers say, it
would be a boon to scientists who study brain function.
Current technologies, such as positron emission tomography
(PET) scans and functional magnetic resonance imaging
(fMRI), have revealed a great deal about how neural
circuits process, say, visual information or language.
But the view is still comparatively fuzzy and crude.
By providing information on the scale of individual
nerve cells, or "neurons," the nanowire technique
could bring the picture into much sharper focus.
"In this case, we see the first-ever application
of nanotechnology to understanding the brain at the
neuron-to-neuron interaction level with a non-intrusive,
biocompatible and biodegradable nano-probe," said
Roco. "With careful attention to ethical issues,
it promises entirely new areas of study, and ultimately
could lead to new therapies and new ways of treating
diseases. This illustrates the new generations of
nanoscale active devices and complex nanosystems."
Likewise, the nanowire technique could greatly improve
doctors' ability to pinpoint damage from injury and
stroke, localize the cause of seizures, and detect
the presence of tumors and other brain abnormalities.
Better still, Llinás and his coauthors point
out, the nanowires could deliver electrical impulses
as well as receive them. So the technique has potential
as a treatment for Parkinson's and similar diseases.
According to researchers, it's long been known that
people with Parkinson's disease can experience significant
improvement from direct stimulation of the affected
area of the brain. Indeed, that is now a common treatment
for patients who do not respond to medication. But
the stimulation is currently carried out by inserting
wires through the skull and into the brain, a process
that can cause scarring of the brain tissue. The
hope is, by stimulating the brain with nanowires
threaded through pre-existing blood vessels, doctors
could give patients the benefits of the treatment
without the damaging side effects.
One challenge is to precisely guide the nanowire
probes to a predetermined spot through the thousands
of branches in the brain's vascular system. One promising
solution, the authors say, is to replace the platinum
nanowires with new conducting polymer nanowires.
Not only do the polymers conduct electrical impulses,
conductive, they change shape in response to electric
fields, which would allow the researchers to steer
the nanowires through the brain's circulatory system.
Polymer nanowires have the added benefit of being
20 to 30 times smaller than the platinum ones used
in the reported laboratory experiments. They also
will be biodegradable, and therefore suitable for
short-term brain implants.
"This new class of materials is an attractive tool
for nanotechnology," said MIT's Anquetil. "The large
degrees of freedom that they offer synthetically
allow the rational design of their properties."
Charles E. Blue, NSF (703) 292-5392 email@example.com
M. Mitchell Waldrop, NSF (703) 292-7752 firstname.lastname@example.org
Mihail C. Roco, NSF (703) 292-8301 email@example.com
Rodolfo Llinas, New York University Medical Center (212) 263-5415 firstname.lastname@example.org
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