Walking the walk: Soft robotics help post-stroke patients walk

Benjamin Boettner explains how post-stroke patients reach terra firma with Wyss Institute's soft robotic exosuit technology.

A soft wearable robotic suit is promoting normal walking in stroke patients, opening new approaches to gait re-training and rehabilitation. Upright walking on two legs is a defining trait in humans. This can all change when a stroke occurs. In about 80% of patients’ post-stroke, it is typical that one limb loses its ability to function normally - a clinical phenomenon called hemiparesis. And even patients who recover walking mobility during rehabilitation retain abnormalities in their gait that hinder them from participating in many activities, pose risks of falls, and, because they impose a more sedentary lifestyle, can lead to secondary health problems.

To help stroke patients regain their walking abilities, various robotics groups from industry and academia are developing powered wearable devices – exoskeletons – that can restore gait functions or assist with rehabilitation. Historically, these systems restricted patients to a treadmill in a clinical setting, but in recent years portable systems have been developed that enable walking overground. Working towards the long-term goal of developing soft wearable robots that can be worn as clothing, researchers at the Wyss Institute for Biologically Inspired Engineering, the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Boston University's (BU) College of Health & Rehabilitation Sciences: Sargent College have developed a lightweight, soft, wearable ankle-assisting exosuit that could help reinforce normal gait in people with hemiparesis after stroke.

In a new study published in Science Translational Medicine, a research team led by Conor Walsh collaborating with BU faculty members Terry Ellis, Lou Awad, and Ken Holt have demonstrated that exosuits also can be used to improve walking after stroke - a critical step in de-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," said Wyss Core Faculty member Walsh, who is also the John L. Loeb Associate Professor of Engineering and Applied Sciences at SEAS and the Founder of the Harvard Biodesign Lab.

Patients recovering from a stroke develop compensatory walking strategies to deal with their inability to clear the ground with their affected limb and to ‘push off’ at the ankle during forward movement. Typically, they have to lift their hips (hip hiking) or move their foot in an outward circle forward (circumduction) rather than in a straight line during walking. Usually, rigid plastic braces worn around the ankle are prescribed to help with walking, but they do not help overcome these abnormal gait patterns and about 85% of people who suffered a stroke retain elements of their gait abnormalities.

"Current approaches to rehabilitation fall short and do not restore the mobility that is required for normal life," said 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 team asked whether the exosuit's beneficial impact on gait mechanics and energy expenditure during walking they observed in healthy people would also be observed in patients post-stroke who were recruited and enrolled in the study with the help of the Wyss Institute's Clinical Research Team.

Exosuits are anchored to the affected limb of a hemiparetic stroke patient via functional apparel, and they provide gait-restoring forces to the ankle joint by transferring mechanical power via a cable-based transmission from battery-powered actuators that are integrated into a hip belt or an off-board cart located next to a treadmill.

"Indeed, 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," said Jaehyun Bae, a co-first author on the study and graduate student at SEAS..

Because walking mechanics and dynamics differ between controlled walking on a treadmill and walking overground in the home or communal environment, the team went on to assess exosuit-provided benefits in an overground walking experiment.