A new collaborative research project led by an assistant professor in the Paul M Rady Department of Mechanical Engineering at the University of Colorado Boulder is working to improve ankle-foot orthoses (AFOs), otherwise known as ankle braces, which are key to helping stroke survivors to walk. Cara Welker’s team hopes to develop a next-generation AFO that doesn’t just support movement, it enhances it.
According to a study in the American Heart Association journal, nearly 80 per cent of stroke survivors experience walking issues. For some, the solution is simple: AFOs. These wearable, assistive devices are designed to enhance mobility and make walking easier post-stroke.
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However, the functionality of these braces is very limited. In fact, a report in the National Library of Medicine said that only a third of stroke patients see walking improvements when paired with an AFO.
‘Stroke survivors or others using these assistive devices walk slower, and it takes more effort for them to move,’ said Welker, who is also affiliated with the Biomedical Engineering Program, the Robotics Program and the BioFrontiers Institute. ‘Movement is important, not just for getting around, but for our quality of life and physical health. If we can help someone walk faster or get closer to how a healthy person walks, then we see that as a success.’
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Funded by the National Science Foundation (NSF), the three-year, US$600,000 project is a collaboration with associate professor Elisa Arch at the University of Delaware. It begins with a unique AFO prototype that the two believe has the potential to transform the way assistive devices are designed.
Current ankle brace technology offers only a single stiffness profile that operates like a simple spring. The braces can be effective for some, but Welker says the human ankle is much more complex than that.
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‘The single stiffness profile doesn’t mimic normal ankle function when walking,’ Welker said. ‘It can’t adapt to the stiffness or the biological angle of a human ankle, which means many brace users still have trouble walking.’
To address this, Arch developed a new AFO that can transition between two different stiffness profiles instead of one. Think of it as a more personalised brace that’s tailored to the complexity of the ankle – as a person walks and their ankle angle changes, the brace can change how it behaves to provide better support.
But the challenge of the research project isn’t necessarily in the design. Welker says brace customisation is currently largely based on trial and error. The lack of precise modelling makes it difficult to pair different stiffness profiles and properties with the needs of the user.
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‘The device we have is very promising, but we don’t know how to prescribe these different stiffnesses based on someone’s specific set of weaknesses,’ said Welker. ‘It might likely be different from one person to another since stroke manifests itself in many ways.’
Using her cutting-edge Welker Lab space – equipped with a powered exoskeleton, motion capture cameras, ground-integrated treadmills and force plates – Welker’s role is to test the device. The goal is to see the AFO in action, model how changing these device parameters affect walking and optimise along the way wherever possible.
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‘There’s a technique called human-in-the-loop optimisation. It involves changing behaviour of an assistive device and measuring how these changes affect certain user metrics that are deemed important,’ Welker said. ‘We want to use this technique to measure things like walking speed or energy expenditure. By doing this, we can select the parameters that best optimise for outcome metrics we care about for a specific person.’
Welker has aspirations beyond the NSF-funded project, as well. She believes their research can be manufactured at scale and prescribed in clinics, helping stroke survivors and brace users around the world achieve normal ankle function.
She also believes that the work done during this project can positively affect her other projects. Whether it’s in the realm of AFOs or other assistive devices such as prosthetics, Welker’s research is well rounded and diverse. But she says her unique lab space with different assistive devices and the ability to quantify how people interact with them ties it all together.
‘We work on many different projects, but it’s great because we can integrate them under the same human motion analysis system,’ said Welker. ‘I’m excited to work on these types of studies, not just for people post-stroke, but also amputees. I believe the work we do will help improve the quality of life for many people.’