Soft Exosuit Technology can Improve Walking Speed in Stroke Survivors

Around 17 million people in the United States experience stroke every year. Stroke is mainly responsible for causing serious long-term disability in U.S. individuals.

“Hemiparesis” is a paralysis that usually affects the facial muscles and limbs in stroke patients. Around 8 out of 10 stroke survivors experience hemiparesis on one side of their bodies, and this condition usually leads to severe difficulties, like difficulty in walking, muscle fatigue that rapidly manifests during exertions, and a loss of balance with a high risk of falling.

Most often, such impairments also make it difficult for stroke survivors to perform their basic daily activities.

To enable the patients to recover from a stroke, several rehabilitation centers have investigated robotic exoskeletons. An array of exciting devices are now available that are aiding people to walk again, especially those who were completely unable to do so at first. However, significant active research is still ongoing to figure out the most optimal way to apply wearable robotics for rehabilitation following stroke.

In spite of this promise, new clinical practice guidelines have now recommended against using robotic treatments when the aim is to enhance the distance or walking speed.

Back in 2017, a multidisciplinary group of apparel designers, electrical and mechanical engineers, and neuro-rehabilitation experts has demonstrated that an ankle-assisting soft robotic exosuit can significantly benefit stroke patients. When attached to an external motor and battery, this exosuit considerably enhanced the biomechanical gait functions in these patients when they wore it while walking on a treadmill.

The multidisciplinary team was from Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) and Wyss Institute for Biologically Inspired Engineering and also from Boston University’s College of Health & Rehabilitation Sciences—Sargent College.

The cross-disciplinary and cross-institutional team effort was headed by Wyss faculty members Conor Walsh, PhD and Lou Awad, P.T., D.P.T., PhD, along with Terry Ellis, PhD, P.T., N.C.S. from Boston University.

The same research team has now taken a major leap in converting their new technology towards a rehabilitation approach.

With the help of an untethered model of the exosuit that carries its own motor and battery, the researchers demonstrated in a group of six post-stroke survivors suffering from hemiparesis that their device could considerably boost their walking speed by an average 0.14 m per second, with one person walking as much as 0.28 m per second faster.

When the same group of individuals was encouraged to walk as far as they can in 6 minutes, they were able to walk 32 m farther, on an average basis, with one individual traveling more than 100 m farther. These results were published in IEEE Open Journal of Engineering in Medicine and Biology (OJEMB).

The vast majority of people who have had a stroke walk slowly and cannot walk very far. Faster and farther walking after physical therapy are among the most important outcomes desired by both patients and clinicians. If neither speed nor distance are changed by a therapy, it would be difficult to consider that therapy to be effective.

Lou Awad, P.T., D.P.T., PhD, Study First Author and Associate Faculty Member, Wyss Institute

Awad has also co-corresponded the findings published in IEEE OJEMB along with Walsh.

Awad continued, “The levels of improvement in speed and distance that we found in our exploratory study exceeded our expectations for an immediate effect without any training and highlight the promise of the exosuit technology.”

Awad is also the Director of the Neuromotor Recovery Laboratory and Assistant Professor at Boston University’s College of Health and Rehabilitation—Sargent College.

Weighing less than 5 kg, the exosuit used in this analysis targets the limbs of post-stroke survivors during the clear phases of the gait cycle. The exosuit is completely mobile, and is driven by a battery and activated by an actuator unit, both worn at the hips.

The exosuit sends mechanical power to the ankles through a cable-based mechanism, in which the cables and other components of the exosuit are fastened to the body through lightweight functional textiles. Moreover, patients can wear the exosuit only on their impaired paretic side, adding further to its low weight and the possibility to reduce gait asymmetries. This is different from the rigid exoskeleton systems, most of which had to be worn on both sides.

The exosuit was developed by Walsh’s research team to help with dorsiflexion, wherein the toes are pulled toward the shin and the foot is lifted during the swing phase of the gait cycle, and with plantar flexion—the ankle movement that forces the foot down into the ground during the stance phase of the gait cycle.

These two movements are unevenly affected in post-stroke hemiparetic walking, and survivors usually show a “drop foot”, a kind of inability to lift the foot from the ankles.

Over the last years, Walsh’s research team had pioneered and extensively validated the soft exosuit technology. Walsh is also the Founder of the Harvard Biodesign Lab and the Gordon McKay Professor of Engineering and Applied Sciences at SEAS.

To prove the wide applicability of their method in stroke survivors, suffering from hemiparesis, the researchers targeted six hemiparetic patients who had varying types and severities of impairments that had all entered a chronic phase.

Following a primary clinical evaluation of patients, and making adjustments to the exosuit according to the individuals, the scientists carried out a battery of tests on a 30-m walkway. Wearing the unpowered exosuit did not cause any drawbacks with respect to the participants’ walking speeds, energy costs, or distances when compared to the test in which they did not wear the exosuit.

But when the exosuit was subsequently powered on, “we saw important and immediate improvements in walking speed and distance which are meaningful outcomes that make a real difference in everyday lives of individuals who have sustained a stroke,” stated the study’s co-author Ellis.

It’s these kind of clinically meaningful outcomes that stimulate excitement among physical therapists and others in the rehabilitation community.

Terry Ellis, PhD, P.T., N.C.S., Study Co-Author, Associate Professor, and Chair of Physical Therapy, Boston University

Ellis is also the Director of the Center for Neurorehabilitation at Sargent College.

“Our engineering and clinical teams at Harvard and Boston University are highly motivated by these results to refine the technology and study its immediate impact in stroke survivors with a wide range of walking abilities. We are also eager to explore therapeutic applications in both clinical settings and day-to-day walking in the home and community,” added Awad.

This study by the team beautifully shows how exosuit technology developed at the Wyss Institute and its partners could make a real difference in the lives of many stroke survivors, and it is a compelling demonstration of how the Institute’s translation model rapidly creates and drives new solutions to some of our major health problems that can change the lives of patients for the better.

Donald Ingber, MD, PhD, Founding Director, Wyss Institute

Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and the Vascular Biology Program at Boston Children’s Hospital. He is also the Professor of Bioengineering at SEAS.

Journal Reference:

Awad, L. N., et al. (2020) Walking Faster and Farther With a Soft Robotic Exosuit: Implications for Post-Stroke Gait Assistance and Rehabilitation. IEEE Open Journal of Engineering in Medicine and Biology. doi.org/10.1109/OJEMB.2020.2984429.

Source: https://wyss.harvard.edu/