Every
40 seconds, someone in the United States has a stroke. According to the
U.S. Centers for Disease Control and Prevention, that totals about
795,000 strokes each year. More than 80 percent of stroke survivors
experience gait challenges, often relating to a loss of control over
ankle movement. As survivors progress into the chronic stage of stroke,
most continue to walk slower and less efficiently.
An agile,
untethered, and easy-to-use ankle exosuit could change that. Designed
for independent use in community settings, the new exosuit could help
stroke survivors improve their gait outside of the lab and during their
daily routines. A proof-of-concept study suggests the community-use
ankle exosuit could help stroke survivors improve their walking
propulsion and boost their overall walking confidence and ability while
ambulating around their own homes, workplaces, and neighborhoods. The
work, led by Conor Walsh’s team at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), is published online in Annals of the New York Academy of Sciences.
Recent
studies have proven that post-stroke study participants can improve
their walking speed, distance, propulsion, and gait symmetry with the
help of an assistive robotic exosuit, but those studies have all
occurred in labs or clinical settings.
“We saw an opportunity to leverage wearable technology to rethink how we approach physical therapy and rehabilitation” says Walsh,
senior author on the paper and the Paul A. Maeder Professor of
Engineering and Applied Sciences at SEAS. “If we can shift some of these
clinical services from the clinic to the home and community, we can
improve access, reduce costs and deliver better care. It is exciting to
see the fields of engineering and physical therapy come together to make
this happen.”
For
over a decade, Walsh’s Biodesign Lab at Harvard has been developing
assistive and rehabilitative exosuit technologies for various
applications. Some of that technology has already been licensed and
commercialized by ReWalk Robotics and been given breakthrough status by
the U.S. Food and Drug Administration. To design an ankle exosuit meant
for use in the community, Walsh’s team need to simplify the exosuit’s
mechanical components and make it easy for wearers to control.
“In
the past, our ankle exosuits had two active actuators – one that helped
with dorsiflexion to keep the wearer’s toes up, and another to help
with plantarflexion, propelling the foot and body away from the ground,”
says Richard Nuckols, a former postdoctoral fellow in Walsh’s lab at
SEAS, and co-first author of the paper.
Instead of an active
dorsiflexion actuator, the new exosuit contains a passive material that
flexes and performs like a spring, helping the toes stay up during the
foot’s swing phase and preventing the wearer from catching their toes on
the ground. “By replacing an active actuator with a passive actuator,
the exosuit is inherently safer; in the case of an unexpected power loss
or controller failure, the default state will keep the users toes up
and reduce risk of a trip and fall,” Nuckols says.
“We
also developed a mobile app to enable wearers to easily interact with
the device and remotely check in with our team,” says Chih-Kang Chang, a
Ph.D. candidate in Walsh’s lab and a co-first author on the paper. “The
app allows wearers to turn the device on themselves and tell the
exosuit when they want to start walking.”
In addition, the team
incorporated sensors to allow for remote monitoring of the wearer’s
progress over time. “We are collecting data while people are walking in
the exosuit, and measuring how they improve their gait over time,” Chang
says. “Going forward, this information could be a really powerful
aspect of using this exosuit for long-term rehabilitation in partnership
with a physical therapist.”
“These
sensors – located on the foot, shank, and pelvis – are converted using a
machine-learning algorithm into estimates of propulsion, helping us
understand how well people are generating proper ankle mechanics and how
effectively they are walking,” Nuckols says.
“Collecting
the amount of data needed to train a typical machine learning model
from individual wearers is extremely challenging, given the limited
ability to walk for extended periods of time post-stroke,” says Daekyum
Kim, a postdoctoral fellow in Walsh’s lab, and co-first author of the
paper. “The key advantage of our approach is that it leverages walking
data gathered from multiple individuals to better tune a machine
learning model to each user.”
To test the community ankle exosuit,
Walsh’s team partnered with the labs of Lou Awad and Terry Ellis from
Boston University’s Sargent College of Health & Rehabilitation
Sciences. They recruited four participants to use the device in their
own community settings for four weeks, walking independently three to
five times each week. All participants safely completed the study and
reported no safety issues. Due to individual variability in response
(participants with lower baseline walking propulsion saw more benefit
from wearing the exosuit), therapeutic benefit was not observed across
the whole group. But two of the participants improved their propulsion
by an average of 27 percent. They also walked an average of 4,000 steps
further in the week after the study than they had walked in the week
before the start of the study.
“I was 33 when I had my stroke. As a
result of the stroke, I have diminished sensitivity on my entire left
side,” says Bryant Butler, 51, one of the study’s participants. “Walking
is a challenge. I can’t feel my toes very well when I am walking, and I
have difficulty bending my leg. I frequently scuff the toe of my shoe,
and sometimes I trip.”
During the study, Butler used the exosuit
on Boston’s Commonwealth Avenue Mall, walking 20 to 30 minutes at a time
several days a week.
“The experience of walking with the exosuit
was liberating, because I no longer had to expend so much mental energy
when going from one place to another,” he says. “The exosuit gradually
corrected my gait with every step. I learned how my leg muscles, knee,
and toes should feel when I walk without it. [Even] when I wasn’t using
[the exosuit], my walking improved, because the device taught me how to
better compensate for the shortcomings of my left leg post-stroke.”
Butler
adds: “The device became an extra piece of clothing – [except for the]
wires and a battery pack – that I wore for a specific purpose. Most of
the time, I forgot it was there. The exosuit nudged me into being a
better walker. It inspired me to walk more, and to enjoy it.”
Additional
authors on the paper include Asa Eckert-Erdheim, Dorothy Orzel, Lauren
Baker, Teresa Baker, Nicholas C. Wendel, Brendan Quinlivan, Patrick
Murphy, Jesse Grupper, and Jacqueline Villalobos.
Harvard
University’s Office of Technology Development is exploring commercial
opportunities stemming from this intellectual property.
This work
was supported by the National Institutes of Health (BRG-R01HD088619),
the National Science Foundation (CMMI-1925085), a MassTech Collaborative
Research and Development Matching Grant, and support from a Blavatnik
National Award for Young Scientists.
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