A defining trait in humans is the upright walking on two legs, allowing them to move all over the environment in a much efficient manner. When a stroke occurs, this steady walking can change in the blink of an eye.
A clinical phenomenon called hemiparesis can be observed in almost 80% of patients post-stroke. In this phenomenon, one limb loses its ability to function normally. Even patients who recover walking mobility during rehabilitation retain abnormalities in their walk that prevents them form taking part in many activities, as they could risk falling down, and because they impose a more inactive lifestyle, can result in secondary health problems.
Rear view of the ankle-assisting exosuits with its soft robotic elements and the cable that transfers mechanical power from actuators operated from the hip to the ankle join. (Image courtesy of the Rolex Awards/Fred Merz)
Several robotics groups from academia and industry are developing exoskeletons in order to help stroke patients regain their walking abilities. These exoskeletons are powered wearable devices capable of restoring gait functions or assisting in rehabilitation. In the past, these devices restricted patients to a treadmill in a clinical setting, however, today portable systems have been manufactured that enable walking overground.
Focusing on the long-term goal of creating soft wearable robots capable of being worn as clothing, Researchers at the
Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), the Wyss Institute for Biologically Inspired Engineering, and Boston University’s (BU) College of Health & Rehabilitation Sciences: Sargent College have now developed a soft, lightweight, wearable ankle-assisting exosuit that has the potential to reinforce normal gait in people with hemiparesis after stroke.
In earlier studies conducted on healthy people, the Researchers established that their exosuit technology is capable of delivering assistive forces during jogging and walking and also producing marked reductions in energy costs. In a recent study published in Science Translational Medicine, a research team headed by Conor Walsh in association with BU faculty members Terry Ellis, Lou Awad and Ken Holt have proved the possibility of using exosuits in order to enhance walking after stroke — a vital step in -risking exosuit technology towards real-world clinical use.
This foundational study shows that soft wearable robots can have significant positive impact on gait functions in patients post-stroke, and it is the result of a translational-focused multidisciplinary team of Engineers, Designers, Biomechanists, Physical Therapists and most importantly patients who volunteered for this study and gave valuable feedback that guided our research.
Conor Walsh, the John L. Loeb Associate Professor of Engineering and Applied Sciences at SEAS, Wyss Core Faculty member and the founder of the Harvard Biodesign Lab
Compensatory walking strategies are developed by patients recovering from a stroke in order to deal with their helplessness to clear the ground with their affected limb and to push off at the ankle while moving forward. These patients will typically have to lift their hips (hip hiking) or move their foot in an outward circle forward (circumduction) instead of taking a straight line during walking. Rigid plastic braces worn around the ankle are generally prescribed in order to help patients with their walking, but these plastic braces fail to help in overcoming these abnormal gait patterns and almost 85% of those who suffered a stroke retain elements of their walking abnormalities.
Current approaches to rehabilitation fall short and do not restore the mobility that is required for normal life.
Terry Ellis, Director of the Center for Neurorehabilitation at BU’s College of Health & Rehabilitation Sciences: Sargent College and Assistant Professor at BU
In the new study, the Researchers asked whether the beneficial impact brought about by the exosuit on gait mechanics and energy expenditure during walking they observed in healthy people would also be detected in patients post-stroke who were enlisted and enrolled in the study with the help of the Wyss Institute’s Clinical Research Team.
Exosuits are attached to the affected limb of a hemiparetic stroke patient through a functional apparel, and they deliver gait-restoring forces to the ankle joint by transmitting mechanical power through a cable-based transmission from battery-powered actuators that are incorporated into a hip belt or an off-board cart placed next to a treadmill.
In treadmill experiments we found that a powered exosuit improved the walking performance of seven post-stroke patients, helping them to clear the ground and push off at the ankle, thus generating more forward propulsion.
Jaehyun Bae, a Co-first Author on the study and Graduate Student at SEAS
The Researchers also noticed a reduced functional asymmetry between the non-paretic and paretic limbs of participants and discovered that the exosuit’s assistance allowed them to walk in much more efficient manner.
The team further assessed the benefits provided by the exosuit in an overground walking experiment since walking dynamics and mechanics vary between controlled walking on a treadmill and walking overground in the communal environment or home.
“It was extremely encouraging to see that an untethered exosuit also had the ability to facilitate more normal walking behavior during overground walking. This is a key step toward developing exosuits as rehabilitation devices for patients to use outside of the clinic and in their normal lives,” stated Lou Awad, the study’s other Co-first Author, who, during the study, was a Postdoctoral Fellow with Walsh and since has become an Associate Faculty member at the Wyss Institute and Assistant Professor at BU’s College of Health and Rehabilitation: Sargent College.
In an ideal future, patients post-stroke would be wearing adjustable and flexible exosuits from the get-go in order to prevent them from developing incompetent gait behaviors in the first place.
The Researchers aim to further personalize exosuit assistance to particular gait abnormalities, explore assistance at other joints such as the knee and hip, and evaluate longer-term therapeutic effects of their technology in their future and current research. Besides this research, Wyss Institute staff member Kathleen O’Donnell heads the Wyss Institute’s efforts to translate the technology to the clinic along with industrial partner ReWalk Robotics.
“In an ideal future, patients post-stroke would be wearing flexible adjusting exosuits from the get-go to prevent them from developing inefficient gait behaviors in the first place,” said Ellis.
The other Authors of the study include Kenneth Holt, Associate Professor at BU’s College of Health & Rehabilitation Sciences: Sargent College, former and current members on Walsh’s team Stefano De Rossi, Lizeth Sloot, Pawel Kudzia, and Stephen Allen, as well as Katy Hendron, N.C.S., who worked in Ellis’ group at BU.
The study received supported from a Defense Advanced Research Projects Agency (DARPA) Warrior Web Program, grants from the National Science Foundation, the American Heart Association and the National Institutes of Health, a Rolex Award for Enterprise, a Harvard University Star Family Challenge as well as Wyss Institute and SEAS funding.