By Thomas K. Grose
limbs are taking on new life thanks to advances in embedded-chip technology
that are giving wearers a freedom of movement that would have been impossible
a few years ago.
theme in popular science fiction of the late 20th century was the notion
that horribly injured humans could be repaired using cyber-replacements
for lost or badly damaged body parts. From the 70s television
show The Six Million Dollar Man to the 1987 film RoboCop,
heroes run on legs and throw punches with arms and hands crammed with
electronic gadgetry that's hardwired to their brains. But what
was once fiction is rapidly becoming a reality within the grasp of researchers
in these early days of the 21st century. Because of embedded chip technology,
artificial limbs permanently attached to amputees and controlled by
their brains could be available some time within the next decade or
two. And while it's unlikely that such prostheses could ever improve
upon a real arm or leg, bioengineering is nevertheless offering America's
1.3 million amputees the real possibility of mechanical limbs that closely
mimic nature's. Based on recent results at Caltech and elsewhere,
I can confidently say at this point it is a matter of when, and not
if, such technology will be ultimately realized, says Joel W.
Burdick, deputy director of the California Institute of Technology's
Center for Neuromorphic Systems Engineering.
that day, however, advances in embedded systems are already revolutionizing
the design of prosthetic devices, giving wearers a freedom of movement
that would otherwise have been impossible a few short years ago. For
instance, Paul H. Chappell, an electrical engineering professor at Southampton
University in England, is overseeing the design of an artificial hand
that will move beyond a pincer grip to one that incorporates all five
digits. Says Chappell: We would not be able to do this without
early 1980s, long after The Six Million Dollar Man had been
relegated to late-night reruns, we were still giving patients
a block of wood for a foot, they were still basically walking on a peg
leg, notes Stewart Atkinson at Seattle Systems, a leading manufacturer
of prosthetics. The company's origins, in fact, were based on the
marketing of an energy-returning foot that harnessed the energy of the
foot striking the ground to ease the workload on wearers and help propel
them forward. Other advances in recent years include a rolling-joint
foot that uses progressive resistance to give users a more natural gait.
In upper body prosthetics, the most popular designs use a patient's
own back, shoulder, or neck muscles to control steel cables that move
artificial elbows and handsa technology that evolved after the
Second World War. More recently, prosthetic arms, wrists, and hands
have relied on sensors that pick up the electrical signals that emanate
from an amputee's residual muscles. These electromyogram (EMG)
signals are then amplified and drive actuators in the replacement limb.
But as great and useful as these advances have been, they've all
fallen short of closely replicating natural movements. That's because
to make them more complex would mean making them heavierand weight
is inimical to prosthetics. Lightweight digital technology, however,
is ushering in an era where the gap between natural and mechanical will
be nearly, if not entirely, bridged.
vast majority of us, simple physical tasks like walking or picking up
a coffee cup are no-brainers. We just do them, unconscious of the amazing
amount of communication and mechanical dexterity our body is experiencing
every nanosecond. All the walking that you and I do, we never
have to think about it, says C. Michael Schuch, director of the
Center for Orthotics and Prosthetics Care at the Duke University Medical
Center. For every step we take, however, our nerves are shooting vital
bits of information to our brains about such things as terrain, speed,
and obstacles. And our brains just as quickly use the nerves to tell
our muscles how to react or compensate. For wearers of prosthetic devices,
that two-way communication is lost. Until recently, the most advanced
prostheses required users to clearly think about every movement. But
the chips installed into the latest generation of devices have introduced
some degree of thought-free movement. These microprocessors, constantly
fed data from sensors, allow the prostheses themselves to take over
some of the automatic tasks that were once the province of brains and
nerves. This devolution of control from person to machine is a significant
improvement. It makes, for example, an artificial hand more like
a real hand, autonomous, says Michael E. Tompkins, founder and
president of Animated Prosthetics, of Greensboro, N.C., which haswith
the help of the Duke Medical Centercreated two products based
on chip technology that improve upper body prostheses.
give artificial arms and hands advantages over prosthetic legs because
they can receive some information from the brain by way of electric
impulses shooting through muscles. But they don't work for all
amputees. Old analogue versions that run off circuit boards are not
easily adjustable and often don't work if a patient's EMG
signal is too weak or scattered. If you don't have the right
signal, you're stuffed, Schuch says. But two digital products
that Animated Prosthetics has developed with Duke solve that problem,
and they can be adapted to any prosthetic. The Animation Control System
(ACS) relies on sensors and a microprocessor to better read and amplify
EMG signals and to manage power and movement. The Prosthesis Configuration
Unit (PCU) is a remote diagnostic tool that reads what's
going on inside the arm and sends the information to a handheld computer.
Now we can fit (a prosthesis) to any patient, no matter what the
EMG is, says Schuch, who uses the PCU to read the signals. Meanwhile,
because the onboard computer reacts to the data from the sensors and
the EMG signals, we take unnecessary energy and wasted motion
away from the patient. Once a hand is closed, for instance, it won't
try to close it again, Tompkins says. This makes things more natural
for the wearer. Using a conventional myoelectric arm, a patient must
tense a muscle to open a hand and tense it again to close it. A chip-enhanced
arm will close a hand once a muscle relaxes, which is how a normal hand
popular myoelectric arm is the Utah Arm, developed about 20 years ago
at the University of Utah and manufactured by Motion Control, which
is run by Harold Sears, a former University of Utah researcher. Motion
Control released a second version of the arm in 1997, which updated
its electronics but kept it an analogue-based product. It will soon,
however, launch a third version that will incorporate embedded chipsa
technology that it has already placed into its ProControl 2 wrist and
hand products. The current Utah Arm allows only one degree of freedom
at a time. The amputee must position and lock the elbow into place before
using the hand, for example. Chip technology will allow two functions
at once, moving the elbow and hand simultaneously, Sears explains.
and manufacturers expect embedded technology to add further refinements
to upper body prosthetics. Today's artificial hands make use of
only the thumb, forefinger, and index finger. The ring finger and pinky
are cosmetic, and the thumb moves only back to front, not side to side.
This enables a pincer grip, but not a full-hand grip that one would
use for, say, holding a baseball. At England's Southampton University,
Chappell is overseeing work on a hand that would allow use of all four
fingers and give the thumb a two-way motion. It would also increase
sensitivity to slip, so that the hand would automatically put a firmer
grasp on an object if it began to slip. Tompkins, who still works with
Duke researchers and patients, is also working along similar lines.
And he wants to develop better processing. Extracting information
from a patient is not easy to do with all the electrical activity in
the arm, so we need better signal processing, he says, which will
likely mean smaller processors moved closer to the residual arm. Tompkins
also hints at adopting wireless technology to send signals to and from
the focus in lower-body prosthetics is on the knee, because when it
comes to walking, it is the most critical joint. It must lock in place
to give us stability and it must flex to allow for the swing phase.
The first artificial leg to make use of a computer chip was based on
Japanese technology and manufactured by Britain's Chas. A. Blatchford
& Sons (Endolite North America in the United States). It was introduced
about a decade ago and used a processor to control the swing phase to
give amputees more control over speed. But Schuch says it was never
marketed well and, subsequently, not many were sold.
the U.S. Food and Drug Administration approved the C-Leg, made by German
manufacturer Otto Bock, which is now the industry standard. The original
concept for the C-Leg came from Kelvin James, a biomechanical engineer
in the Division of Neuroscience at the University of Alberta in Canada.
It has two processors and four sensorswhich relay data at a rate
of 50 times a secondto operate its mechanical and hydraulic systems.
Two piezoelectric strain gauges measure pressures on the leg and how
often the heel strikes, while magnetic sensors keep tabs on the angle
of the knee. Schuch explains that before the C-Leg, artificial knees
sacrificed speed for stability. Each time a heel strikes the ground,
a human knee must flex a tiny bit, just 5 to 7 degrees, then relock
before opening to allow for the swing. All that maneuvering is done
within split seconds, and it's a bit too much for a conventional
artificial knees had to lock fully in place between swings so they could
accommodate the patient's weight, and all that locking wasn't
helpful in negotiating anything but a clear, flat surface. All
it takes is a rock under the heel to trip someone up, Schuch notes.
And because an artificial leg is just so much weight affixed to a stump,
descending stairs meant going slowly, one step at a time. But the C-Leg's
microprocessor compensates for those nuances, and users can walk naturallyand
with little forethoughtover all sorts of terrain, and they can
dash down stairs. That last advantage turned into a life-saver for Curtis
Grimsley, a computer programmer for the Port Authority of New York.
He worked in the World Trade Center, and when terrorists smashed two
commercial jetliners into the twin towers, eventually collapsing them
both, Grimsley escaped because his C-Leg enabled him to vault down 70
flights of stairsan accomplishment that earned both him and his
German-made leg worldwide attention and admiration. It's
really beautiful technology, he told the New York Times.
is competition afoot, however. At the Massachusetts Institute of Technology's
Leg Laboratory, researchers are developing a knee that will keep adjusting
itself to the wearer. Co-director Hugh Herr declined to talk about the
MIT project, saying he was waiting until it is commercially available
(from Ossur, a manufacturer in Iceland). But previous accounts and discussions
with other researchers indicate that the MIT knee will use a magnetorheological
fluid, rather than oil-based hydraulics, to shift metal plates and control
resistance within the knee.
Systems, in conjunction with the U.S. Department of Energy's Sandia
National Laboratories, is working on a smart leg it has
christened SILL, for Smart Integrated Lower Limb, and much of the research
is being carried out in Russia by scientists at a former nuclear weapons
facility. Seattle System's Atkinson says a working prototype is
about a year away, but if all goes according to plan, the SILL will
incorporate about a dozen sensors feeding data to just one microprocessor
that will control not only the knee but the ankle, foot, and socket,
as well. Its ankle, knee, and socket will be powered by piezoelectric
motors and hydraulic joints, and kinetic energy from knee and foot motion
will be recaptured and used to aid propulsion. Atkinson admits that
despite nearly $5 million in research money, it's been a difficult
project that's behind schedule. It's not easy having
all those components communicating with one another, he says.
This is research, so there are no guarantees.
Pitkin, an assistant professor of bioengineering at the Tufts University
School of Medicine who designed the rolling-joint foot, says he's
not convinced that digital technology is particularly needed for below-the-knee
prosthetics. Advanced mechanics that attempt to mimic the human skeleton
can provide all the needed stability and propulsion, he says. His foot,
for instance, uses the natural limitations of progressive resistance
to move smoothly. Pitkin likens progressive resistance to the feeling
one gets when rocking back and forth in a rocking chairthe roll
starts easily but gradually slows to a stop, then a reverse motion begins.
Schuch, of Duke, agrees with Pitkin: We are able to do so much
now (below the knee) with simple technology, that (an embedded system)
is not necessary.
the C-Leg is clearly a major accomplishment, there is one thing it can't
help a patient do: walk up stairs easily. The current state of battery
power isn't enough to let the knee lift a wearer's weight.
Indeed, C-Leg originator James says further breakthroughs in prosthetic
devices will need to come from better power sources. The limiting
factor is carrying enough power battery storage. The limiting technology
is not chip technology, but battery technology, James explains.
That's not to say there haven't been improvements in power
sources. An internal lithium ion battery keeps the C-Leg moving for
up to 35 hours. Animated Prosthetics' ACS also uses a lithium ion
battery that Schuch calls a vast improvement over the nicad batteries
that powered previous myloelectric arms. The nicad batteries needed
very regular recharging, had low memory, and lasted just a year. Improved
power plants will, however, be needed to make permanently attached prosthetics
a reality. One potential solution may be miniature fuel cells, which
use a clean chemical reaction to generate energy. Says James: We're
all waiting on the chemical engineers.
history, prostheses have been detachable devices. But in Sweden, one
researcher is pioneering the permanent attachment of above-knee artificial
legs to the femur bone using a titanium implant. Known as osseointegration,
it's a technique developed by dentists to attach false teeth. Schuch
calls the procedure a moderate success and says the main
problem is bacterial infectionsalways a risk when the skin is
penetrated. Nonetheless, he and other experts expect that problem will
eventually be overcome. And that will be a triumph, because a direct
skeletal fit would eliminate the need for a socket. That solves an ongoing
problem with all artificial limbs: obtaining a smooth interface between
the socket and the residual limb.
to the Source
Grail of prosthetics, however, is a direct link between a human-made
limb and the wearer's brain. Truly the stuff of sci-fi. But, as
noted by Caltech's Burdick, it is a future that will be realized
relatively soonthough many hurdles must first be overcome. The
human body is an incredible piece of engineering, so artificial replacements
aren't that easy to do, says Chappell of Southampton. Nevertheless,
within the last two years there have been impressive strides in neural
prosthetics. Caltech and three other research groups have used signals
extracted from monkey brains to control an external mechanical device
and images on a computer screen. The research at Caltech looks to implant
custom-designed chips into the brain as close as possible to the neurons.
So much for the hard wiring. Transmission of the signals from the implants
to the prosthetic would likely be wireless, thus minimizing the risk
of infection that a wire into the head would run. Powering the chips
would have to be done wirelessly, as well. But powering them is a delicate
task. If they're too powerful and emit too much heat, surrounding
brain tissue could be damaged.
researchers are looking at ways to connect a semiconductor chip to nerve
cells. This is also a difficult area because there is a conductive cleft
between the neurons and the chip that acts as a barrier. Get the chip
too close to the cells' membrane, and they disconnect. Peter Fromherz,
of Germany's Max Planck Institute for Biochemistry, recently presented
a paper that described the creation of a pulsating hybrid circuit whose
signals can be read both ways across the cleft. Fromherz has said the
technique could open the door to neural connections for prosthetics.
limbs, bionics may some day give vision to the blind. In 1996, Wentai
Liu, an electrical engineering professor at North Carolina State University,
oversaw a team that created an Artificial Retinal Component Chip, a
microchip that could be implanted in an eye to replace a damaged retina.
Light hitting the chip's sensors is converted into electrical signals,
read by optic nerves, and translated by the brain. Liu's team has
since worked on improving the chip while awaiting FDA and Federal Communications
Commission approval for the first implant, which could finally happen
in early 2003. Since its creation, the chip has gone from containing
an array of 25 pixels to 64, and Liu says 1,024, or even 10,000 pixels,
may ultimately be needed. That would require a big boost in power, and
like Caltech's electrodes, that means finding a way of controlling
heat. And the chip must be properly sealed so as not to be corrupted
by body fluids. Sighs Liu, It's a continuing process.
considering the pros and cons of neural connections and osseintegration,
Schuch is convinced that somewhere down the road, those technologies
will hook up. But these solutions will almost certainly be very
expensive. Nothing on the market now, for instance, is particularly
cheap. The C-Leg costs $40,000, a tidy annual salary for many people.
And even the chip-less current version of the Utah Arm sells for $60,000.
Because the market for prosthetics is limited and rather small, economies
of scale never kick in. So while permanent cyber-limbs might be good
value for amputees who are young adults or children, that may not be
the case for older patients. And, the sad fact is, the majority of amputees
are elderly and often suffering from diabetes. Nonetheless, embedded
chip technology will soon give us the chance to fuse human beings and
machines. And that's an opportunity we're unlikely to walk
C. Grose is a freelance writer based in Great Britain. He can be reached
by e-mail at firstname.lastname@example.org.