Soft exosuit improves walking speed and endurance for stroke survivors
In 2017, researchers from Harvard's Wyss Institute, the John A. Paulson School of Engineering and Applied Science and Boston University demonstrated a soft robotic exosuit designed to help stroke patients improve their mobility. Now an untethered version of the lightweight ankle-assisting device has been shown to increase walking speed and distance.
According to the Centers for Disease Control and Prevention, nearly 800,000 people in the United States have a stroke each year. Though it ranks number five in the number of deaths, most survive but may suffer long-term disability. Many survivors will have to endure weakness or paralysis on one side of the body, which can cause loss of balance, walking difficulty, muscle fatigue and lack of coordination.
And it's these mobility issues that the wearable ankle-assist exosuit was designed to address. Originally tethered to an external battery and motor, the team led by Conor Walsh and Louis Awad from Wyss and Boston University's Terry Ellis has demonstrated walking speed and endurance improvements using a version that includes its own battery and motor.
The exosuit is reported to weight less than 5 kg and provides gait assist at the ankles. Its battery and actuator are worn at the waist, with cables leading down to a textile wrap mounted to the weakened leg only. The device was designed to assist with the part of the gait cycle where the foot is pushed into the ground and the swing phase where the foot is raised off the ground and the toes drawn up toward the shin.
The researchers recruited a small cohort of six chronic hemiparetic stroke survivors to demonstrate the exosuit, each displaying weakness or impairment of varying severity and type. They were asked to move down a 30-meter walkway with the exosuit powered off and then with it powered on. Though wearing an unpowered exosuit didn't appear to result in any change in walking speeds or distances compared to not wearing the assistance device, improvements from powering it on were noticed immediately.
"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," said Ellis. "It’s these kind of clinically meaningful outcomes that stimulate excitement among physical therapists and others in the rehabilitation community."
Average walking speeds were increased by 0.14 meters per second compared to unassisted travel – though one member of the test group managed to move 0.28 m/s faster. When tasked with walking as far as they could manage in six minutes, the average distance increase came in at 32 meters – though again, one of the group managed to travel 100 meters farther.
"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," said Awad. "We are also eager to explore therapeutic applications in both clinical settings and day-to-day walking in the home and community."
A paper on the latest development has been published in the IEEE Open Journal of Engineering in Medicine and Biology.