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Hollywood's "Bionic Man"
may still be more fantasy than reality, but advances in medical technology
are beginning to meld man and machine, according to one biomedical engineer.
Researchers surveyed the current
and future capacity of machines that can interact with the brain and nerve
cells to help restore some function to people with lost or paralyzed limbs,
including victims of spinal cord injury, amputation and stroke.
One current area of research
uses brain-machine interfaces, which attempt to interpret commands from
the brain and initiate a response by a computer-controlled prosthesis.
In one experiment, researchers
have fitted severely paralyzed patients -- who can't even blink their eyes
to communicate -- with a brain-implanted chip that they can direct to select
letters on a computer screen and thus restore interaction with the outside
world.
Other devices circumvent the
brain and use functional electrical stimulation to communicate directly
with muscles and nerves. Some are commercially available, including the
FDA-approved FreeHand, which restores grasping ability in patients with
weakened arms who use shoulder movements to trigger radio waves that in
turn activate electrodes in their forearms to move.
Another device currently under
development is the RoboWalker, which allow patients who have lost motor
skills in their legs to walk. The patients use their hands to send messages
to their leg muscles, which are stimulated by implanted electrodes.
One of the many obstacles in
bionics is that the electronic devices needed to receive the message are
often too large to fit inside the brain. "It's a problem of the size
of the hardware," Craelius said. "Presently, the brain is not
big enough to contain all the power you would need to do things."
However, as long as Moore's
law continues to hold true, which states that the number of transistors
on a computer chip will double every 18 months, sufficient miniaturization
could be reached in a decade.
Another barrier to bionics
is the difficulty of integrating the prosthesis with the body's natural
tissue. Trying to make a decent place where skin can merge with an artificial
limb are decades away from being solved. When you're talking about living
cells that have to grow over it, that's a totally difficult magnitude
of problem.
Science February 8, 2002;295:1018-1021
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