Carbon nanotubes improve electrical stimulation therapy
7 October 2008
Researchers at University of Texas Southwestern Medical Center have
designed a way to improve electrical stimulation of nerves by coating
electrodes with a coating of basic black, formed from carbon nanotubes.
The nanotube sheathing improves the signals received and transmitted
by electrodes, which researchers say is a potentially critical step for
advancing electrical nerve stimulation therapy. This type of therapy
increasingly shows promise for diseases ranging from epilepsy to
depression to chronic leg and back pain.
By implanting electronic nerve stimulators, doctors elsewhere have
provided a quadriplegic patient with the ability to move a computer
cursor at will, and monkeys have been able to move objects in a virtual
world with mere mind power. For individuals who lose an arm or leg and
rely on prosthetics, implanted stimulators offer promise in restoring
feelings of sensation.
“The key to success for these types of brain-machine interfaces is
where the electrode meets the nerve tissue,” said Dr. Edward Keefer,
instructor of plastic surgery at UT Southwestern and lead author of the
study appearing in a recent issue of Nature Nanotechnology. “When
we coat the electrodes with carbon nanotubes, it improves the
stimulation of the nerve and the feedback from the sensors.”
Depending on the way the nanotubes are fashioned, researchers were
able to bolster either the stimulation or receptive capabilities to
improve performance. In some tests, the nanotube coating improved
performance by fortyfold, while in others it improved by a factor of as
much as 1,600.
Nanotubes look like lattices rolled into a tube on a microscopic
scale. Although they are 1/50,000 the width of a human hair, nanotubes
are nonetheless among the stiffest and strongest fibres known, as well
as excellent conductors of electricity.
Those properties proved to be just the attributes needed to help
electrophysiologists conquer some of the hurdles facing them — such as
battery power and chemical stability.
The carbon nanotube coating improves conductivity, which means less
energy is needed to power the nerve stimulator. That can help reduce
routine maintenance, such as the need to change batteries in implanted
stimulation devices, as well as reduce tissue damage caused by the
“Our process is like taking a Ford Pinto, pouring on this chemical
coating, and turning it into a Ferrari,” Dr Keefer said.
Researchers have tried several types of electrochemical coatings to
see if they could improve conductivity, but the coatings often break
down quickly or fail to stay affixed to the electrodes. The carbon
nanotube coating shows far more promise, although further research is
still needed, Dr Keefer said.
“The development of new technologies by Dr Keefer to potentially
restore function in wounded tissues and future transplantations is
exciting,” said Dr Spencer Brown, assistant professor of plastic surgery
who heads research in the Nancy Lee and Perry R Bass Advanced Plastic
Surgery and Wound Healing Laboratory at UT Southwestern.