Bauer CM1, Pauli CA1, Wirz M1, Graf ES1
1ZHAW, Health, Winterthur, Switzerland
Background: Globally circa 16 million people per year experience a stroke for the first time, of which 5 million remain limited in their mobility. Therapeutic strategies for patients with stroke and partial mobility limitations should specifically target walking to improve daily living activities. Current exoskeletons substitute function with active actuation. However, stroke patients with partial mobility limitations need support for their remaining function, not substitution.
Purpose: A soft biomimetic exoskeleton that supports walking could fill this gap. The project XoSoft (www.xosoft.eu) aims to develop such a device. It follows an iterative user-centered-design approach with subsequent prototype generations (Beta1, Beta2, Gamma). The aim of this study was to assess the biomechanical effects of these prototypes on a patient with stroke. Results from one prototype testing inform the development of the subsequent prototype.
Methods: A 69-year-old male who experienced a cerebrovascular stroke seven years ago was recruited for this study. He presents with unilateral gait impairment, with the right side affected.
The soft biomimetic exoskeleton has a flexible and adaptive structure. Its design is lightweight due to its basic garment. Actuation is provided at the right hip and knee joints. A central processor that receives input from foot pressure sensors embedded in shoes, which enable real-time gait-phase detection, controls actuation. In Beta1, mono-articular elastic bands in series with an electromagnetic clutch support hip and knee flexion in the initial swing phase. In Beta2 and Gamma, mono- respectively bi-articular elastic bands in series with textile-jamming based clutches and an external pneumatic source support hip flexion and knee extension during swing. The Gamma prototype integrated parts of the external pneumatic source in a backpack. The biomechanical effects were tested during level-floor walking in a movement laboratory, using an optoelectronic reflective marker based system.
Results: Without the exoskeleton, the participant had limited maximal right hip flexion and less maximal right knee flexion during swing phase. Further, he showed a whipping movement at the right knee and hip joints during mid-swing that accelerates shank progression but may increase stress on the knee joint. Beta1 increased knee flexion during swing due to the mono-articular support. The hip flexion support reduced maximal hip extension during stance and further accentuated the whipping movement during swing. Beta2's hip extension support improved maximal hip extension in stance, but maximal hip flexion in swing did not increase. Beta2's knee extension support reduced the whipping movement during swing. The backpack used with Gamma increased the whipping movement, likely because of its weight.
Conclusion(s): The support strategy was successful to improve gait. Increased knee flexion and reduced whipping during swing could signify better foot clearance, increased efficiency, and reduced risk of tripping. A combination of knee extension and knee flexion actuation could target both aspects of knee kinematics. Knee flexion actuation needs to be mono-articular. The backpacks weight needs reducing.
Implications: A soft biomimetic exoskeleton is useful to support and improve walking after stroke. An iterative user centered design approach with subsequent prototype generations is essential to develop successful support strategies, identify disadvantages, and advance this novel technology.
Keywords: Stroke, exoskeleton, assistive device development
Funding acknowledgements: This work has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No.688175 (XoSoft).
Purpose: A soft biomimetic exoskeleton that supports walking could fill this gap. The project XoSoft (www.xosoft.eu) aims to develop such a device. It follows an iterative user-centered-design approach with subsequent prototype generations (Beta1, Beta2, Gamma). The aim of this study was to assess the biomechanical effects of these prototypes on a patient with stroke. Results from one prototype testing inform the development of the subsequent prototype.
Methods: A 69-year-old male who experienced a cerebrovascular stroke seven years ago was recruited for this study. He presents with unilateral gait impairment, with the right side affected.
The soft biomimetic exoskeleton has a flexible and adaptive structure. Its design is lightweight due to its basic garment. Actuation is provided at the right hip and knee joints. A central processor that receives input from foot pressure sensors embedded in shoes, which enable real-time gait-phase detection, controls actuation. In Beta1, mono-articular elastic bands in series with an electromagnetic clutch support hip and knee flexion in the initial swing phase. In Beta2 and Gamma, mono- respectively bi-articular elastic bands in series with textile-jamming based clutches and an external pneumatic source support hip flexion and knee extension during swing. The Gamma prototype integrated parts of the external pneumatic source in a backpack. The biomechanical effects were tested during level-floor walking in a movement laboratory, using an optoelectronic reflective marker based system.
Results: Without the exoskeleton, the participant had limited maximal right hip flexion and less maximal right knee flexion during swing phase. Further, he showed a whipping movement at the right knee and hip joints during mid-swing that accelerates shank progression but may increase stress on the knee joint. Beta1 increased knee flexion during swing due to the mono-articular support. The hip flexion support reduced maximal hip extension during stance and further accentuated the whipping movement during swing. Beta2's hip extension support improved maximal hip extension in stance, but maximal hip flexion in swing did not increase. Beta2's knee extension support reduced the whipping movement during swing. The backpack used with Gamma increased the whipping movement, likely because of its weight.
Conclusion(s): The support strategy was successful to improve gait. Increased knee flexion and reduced whipping during swing could signify better foot clearance, increased efficiency, and reduced risk of tripping. A combination of knee extension and knee flexion actuation could target both aspects of knee kinematics. Knee flexion actuation needs to be mono-articular. The backpacks weight needs reducing.
Implications: A soft biomimetic exoskeleton is useful to support and improve walking after stroke. An iterative user centered design approach with subsequent prototype generations is essential to develop successful support strategies, identify disadvantages, and advance this novel technology.
Keywords: Stroke, exoskeleton, assistive device development
Funding acknowledgements: This work has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No.688175 (XoSoft).
Topic: Robotics & technology; Neurology: stroke; Human movement analysis
Ethics approval required: Yes
Institution: Canton Zurich
Ethics committee: Cantonal Ethics Committee
Ethics number: BASEC-Nr. 2016-01406
All authors, affiliations and abstracts have been published as submitted.
