An arms race: Building better prosthetic limbs
From: McCormick - Spring 2007 - page 6
By: Kyle Delaney

As you hold this magazine, you're probably not thinking about the thousands
of electrical signals traveling between your fingertips and your brain. These
signals control your hands' grip on the magazine and produce motions to
adjust it to the right angle or to turn the page (though hopefully you're not
ready to do that just yet). They also provide an equally rich amount of data
back to your brain that constantly refines your movement and allows you to
feel the weight and temperature ot the paper. These very same electrical
signals may someday help arm amputees control their prosthetic hands and arms
just as you control yours - without even thinking about it. 

Researchers at McCormick, in collaboration with members of Northwestern's
Feinberg School of Medicine and the Rehabilitation Institute of Chicago
(RIC), are exploring ways to build and control better prostheses for arm
amputees. Some truly revolutionary breakthroughs here have given hope to
people who have lost limbs and are playing a major role in the rapid
advancement of prosthetic technology. 

The need for improved prostheses is driving a $48.5 million national push
from the Defense Advanced Research Projects Agency (DARPA). Todd Kuiken (PhD
`89, Feinberg `90), associate professor of biomedical engineering and
physical medicine and rehabilitation and director of the Neural Engineering
Center for Artificial Limbs at RIC; Richard Weir (MS `89, PhD `95), clinical
professor of biomedical engineering and research associate professor of
physical medicine and rehabilitation; Michael Peshkin, professor of
mechanical engineering; and Ed Colgate, Pentair-D. Eugene and Bonnie L.
Nugent Teaching Professor and professor of mechanical engineering, are
pursuing collaborative research that aims to speed the development of a
lifelike prosthetic arm and hand. 

Engineering from both sides 

It's one of the first rules of engineering design: design with the user in
mind. But what if you can also modify the user to better interact with the
design? That's the key concept in Todd Kuiken's work in nerve transfer, which
began almost 20 years ago when he was a PhD student at McCormick. 

Kuiken takes the nerves that would have gone to a missing arm and transfers
them into the pectoral muscle, which no longer has a purpose once the arm is
gone. The nerves then grow into the new muscle, telling it to contract and
relax based on the signals that would have controlled the missing arm. The
signals from nerves that have not been transferred are too small to measure
reliably for long periods of time. By rerouting the nerve endings into the
pectoral muscle, the signals become stronger, and Kuiken and his team are
able to use sensors to detect them. Using these signals, the patient is able
to intuitively control a motorized prosthetic arm. A patient's thought to
"close my hand" becomes a command to close the prosthetic hand. 

"This process has a number of advantages," explains Kuiken, "the biggest
being that you use muscle as a biological amplifier as opposed to relying on
hardware. It never breaks down and has an infinite energy supply - as long as
you eat your Wheaties."  

Kuiken's first challenge was to decode the meaning of the electrical signals,
differentiating the signals that cause the hand to open from those that cause
it to close. One of his first collaborators at McCormick was Allen Taflove,
professor of electrical engineering and computer science. "I went to Allen
and toid him I was interested in using finite element modeling and wanted his
help?' Kuiken says. "He was wonderful in helping me to get started, figure
out the modeling, and get our first grant. He was so generous with his time,
support, and enthusiasm during a very critical time?"  

Kuiken spent several years working through decoding problems and doing the
bench work and animal studies necessary to prove the feasibility of his
concept. Ready to begin clinical trials, Kuiken identified his first patient:
Jesse Sullivan, an electrical line worker who burned his arms so severely
that both were amputated at the shoulder. Following his successful nerve
transfer in 2003 and the fitting and implementation of new prosthetic arms,
Sullivan has been dubbed the world's first "bionic man" and serves as a
living example of the promise of this technology. 

After transferring four of Sullivan's nerves into his pectoral muscle, Kuiken
had modest goals: to allow Sullivan to open and close his arm and bend and
straighten his elbow in a natural way. Using sensors that picked up the
electrical signals rerouted to Sullivan's chest to operate the three-motor
prosthetic arm, Sullivan was able to control his arm so well that Kuiken set
his sights even higher. 

Working with Richard Weir - whom Kuiken met when they were both PhD students
at McCormick and other collaborators from around the world, Kuiken developed
a six-motor arm that provided six degrees of freedom. This was a vast
improvement over the three-motor arm hut still fell far short of the 22
degrees of freedom in a human arm. Cobbling together an elbow from Boston, a
shoulder from Scotland, a hand from China, a rotator from Vienna, and humeral
rotator from Weir's lab, Kuiken and Weir created a new arm with twice the
functionality of Kuiken's original model. 

"In the first two weeks, Jesse did remarkably," Kuiken says. "He's an
absolutely wonderful guy to work with. Those results got us going and got us
excited."  

Unexpected results 

While nurses prepped Jesse Sullivan's chest with rubbing alcohol during one
of his many visits to RIC, a remarkable thing happened: Sullivan felt the
cooling effect of the alcohol as though it were on his hand. Searching for an
explanation for this phenomenon, Kuiken discovered that the nerves
transferred into Sullivan's chest actually grew into the skin on his chest, a
process known as targeted sensory reinnervation. Both the outgoing and
incoming nerve signals for the arms had regrown into the pectoral muscle and
skin. With this unexpected finding, Kuiken saw even greater potential. "This
gives you a portal to let the person feel what they touch as if it were in
their missing hand," he says. 

While Kuiken was excited about this advance, he knew that he didn't have the
expertise to put it to work. Richard Weir and Jon Sensinger, a PhD student in
biomedical engineering, worked to develop a proof of concept for a device
that could communicate the sense of touch to a patient's chest. After seeing
that it could work, the team connected with Michael Peshkin and Ed Colgate in
the mechanical engineering department at McCormick, who have based a
significant part of their research on the study of haptics, or the sense of
touch, mostly in relation to robotics. 

Colgate and Peshkin are now developing tactors - microrobots that can convey
haptic sensations to a patient's chest - for use in conjunction with
prosthetic arms. Using inputs from the prosthetic arm, these tactors recreate
the same sensation on a scale appropriate to the area of skin on the chest
where the nerves have reattached. 

While the research is still in its early phases, the results have been
remarkable. The device can apply force in several directions and even heat up
and cool down based on temperature sensors. In testing, Sullivan and Claudia
Mitchell, a single-arm amputee who became the first woman to be outfitted
with the bionic arm, have been able to differentiate between satin ribbon and
sandpaper and feel temperature changes. This advance has both practical and
social importance. 

"When I asked Jesse what he wanted to do with a sense of touch, he said he
wanted to be able to hold his wife's hand," explains Colgate. "A big part of
that is warmth. There's a big social dimension to this work that is sometimes
underappreciated."  

While developing the tactor, Colgate and Peshkin have struggled with a
variety of unique challenges. The device must be thin enough to fit in the
vest that holds the prosthetic device in place, it must consume as little
energy as possible, and it must stay in the appropriate place despite being
on a moving body.  

"At this point it is very experimental. You want to try different
capabilities to see what you actually need, "Peshkin says. "Yet even at the
experimental level, it's very tricky engineering."  

A friendly competition 

As Kuiken's research began its clinical phases, the Pentagon also started
planning a push for more realistic prosthetic devices. The need for better
prosthetic limb systems has become increasingly important as a result of the
continuing casualties in Iraq and Afghanistan. Improved body armor and
medical treatment have led to higher survival rates: About 90 percent of
those injured in Iraq and Afghanistan survive. However, those who survive are
increasingly likely to have lost a limb. And while hand and arm amputees make
up just 5 percent of civilian amputees, nearly a quarter of the amputees who
come home from Iraq have lost an arm or hand. 

All four researchers are working on both major projects that have been funded
by DARPA to accelerate the pace of prosthetic research - and at times, based
on the differing roles and approaches to the project, they even find
themselves in competition with one another. Colgate and Peshkin through their
company, Chicago PT - and Richard Weir are developing two different designs
for prosthetic arms and hands. 

Weir and his colleagues are working on an intrinsic design, meaning that all
of the motors and gears are located near the point of use. For example, the
prosthetic hand they are designing has 15 miniature motors, with another
three in the wrist. Weir's team works with a variety of corporate and
academic partners, including Otto Bock, the leading manufacturer of
prosthetic devices. They recently completed their first prototype - a model
that brings together a variety of components already in development. As they
test that model with patients at RIC, they are busy developing an improved
second prototype. 

Weir points to one major benefit in their team's design: It is adaptable for
different levels of arm amputation. Because the motors are located near the
place of use, they don't require additional space for a central motor.
However, that also limits the amount of space for their equipment. "We have
to fit everything into the space of the hand and do it in a form for an
average female while providing enough strength for an average male." says
Weir. "It's very challenging."  

Colgate and Peshkin's work focuses on developing an arm based on their work
in cobotics, a class of robotic devices intended for direct physical
collaboration with human operators. In contrast to Weir's arm, their
prosthetic hand is an extrinsic design that runs off of a central motor in
the forearm to control the hand through a series of simulated tendons. One
major advantage of this technology is that it is inherently flexible,
allowing the arm to have a similar amount of give as a human arm. 

Like Weir, Colgate and Peshkin also struggle with space and weight issues.
Any prosthesis must weigh less than a real arm because it isn't attached to
the shoulder like a real arm. "As an engineer, it feels unfair," says
Peshkin. "In biological systems the actuators are above the body part. Both
our actuators and the power supply have to be in the space of the arm itself.
Compared with biological systems, you're always at a disadvantage. It's
really an uphill battle."  

Despite the challenges, the team sees promise in their work. "I think this
project may really advance the state of the art." says Colgate. "Coupled with
Todd Kuiken's research, it has a shot at being really helpful."  

New possibilities for user control 

Kuiken's research in nerve transfers has presented new possibilities for the
development of other prosthetic technologies for patients with upper-arm
amputations. Other ongoing research between McCormick, Feinberg, and RIC has
the potential to provide similar improvements for those who lose their hands,
lower arms, or even legs. 

Weir is studying one exciting possibility: wireless sensors that could be
implanted into the muscle to detect electrical signals and control a
prosthetic device. The wireless sensors convey the muscle signals to an
external coil around the limb and could be applied to amputees who have lost
part of their hand or forearm. Weir hopes that in addition to cutting down
the number of wires required for the prosthesis, they will provide a more
robust system of reading the body's electrical signals. In order to better
interpret those signals and understand the desired motion of the user, the
group is working with Wendy Murray, a new assistant professor of biomedical
engineering at McCormick, to conduct fundamental research into the nature of
neuromuscular control. 

While the research into upper-arm prosthetics is progressing at a rapid pace,
Kuiken is also keeping his eye on other opportunities to help amputees. "I
have a lifetime of work ahead of me with the arm, but the leg is an exciting
area to try as well," he explains. "There are 10 times as many leg amputees
as arm amputees. They've just come out with the first motorized legs. and we
think we can add steering to them."  

As researchers continue to make revolutionary advances in this field, it's
almost easy to overlook the significance of each step. "I got a call from
people working at our company, Chicago PT, telling me that they had tested
our tactors and that they had successfully conveyed the sensation of touch to
Jesse," Peshkin says. "I realized that they had done something really special
that day. Working with Todd and Jesse gives you the opportunity to do things
that never have been done before."  

Photo captions:
Photo 1 - Todd Kuiken
Photo 2 - Richard Weir
Photo 3 - A model of a tactor
Photo 4 - Jesse Sullivan with his bionic arm
Photo 5 - Ed Colgate and Michael Peshkin

Links:
Todd Kuiken
http://www.ric.org/search/kuiken.php

Building the Bionic Man  
http://www.poptech.com/kuiken/

Todd Kuiken and Jesse Sullivan
http://www.itconversations.com/shows/detail763.html

Neural Engineering Center for Artificial Limbs Lab
http://www.smpp.northwestern.edu/index.php?option=com_content&task=view&id=61&Itemid=76

New Technique Allows 'Feeling' in Artificial Arm
http://ww3.komotv.com/Global/story.asp?S=6026896
http://www.medicinenet.com/script/main/art.asp?articlekey=79282

Photo of Jesse Sullivan, Claudia Mitchell, and Todd Kuiken
http://www.wfaa.com/perl/common/slideshow/sspop.pl?recid=1824&nextimage=1