Design Engineering

Spring Loaded Technology’s hydraulic knee brace turns disabled legs ‘bionic’

By Treena Hein   

Fluid Power Materials Power Transmission Medical

Halifax-based startup hopes to change human mobility with unpowered, mechanical Levitation knee brace.

15-Oct-SpringLoaded-Levitation-Brace-360Like many parts of the human body, like the eye or the brain, the knee is an engineering marvel, a polycentric hinge with two axes of rotation that withstands 700 plus pounds of pressure every time you lean down to tie your shoes. So to protect the knee as we age or deal with an injury or other condition, wouldn’t it be wonderful to slip on a lightweight brace that provides power and mobility, enhances strength and increases stability?

That’s exactly what Spring Loaded Technology of Halifax has invented. Founded in early 2013, the firm has garnered numerous awards, most recently capturing the $100,000 Grand Prize 2015 BDC ‘Young Entrepreneur Award.’ According to the company, its Levitation bionic knee brace does nothing less than redefine the limits of human movement. Individuals with good mobility can use it to improve endurance and performance, while those with various mobility issues can use it for rehab or to regain independence.

“Our brace is essentially a fully-functional and completely reliable quadricep,” notes Spring Loaded Chief Technical Officer and co-founder Bob Garrish. “In a crouch, it exerts full body strength for someone who has lost that due to neurological issues or injury.”

The knee brace is a very old idea – and one that’s frequently given as a challenge to engineering students. In fact, the first patents for a knee brace that could help people stand back up, Garrish points out, were granted in the 1920’s, for polio and other muscle wasting diseases.


“There have been many patents, but that doesn’t mean they work,” he says. “There are exoskeleton designs now that provide the power that’s needed, and other braces that provide joint stability, but they don’t really help, don’t stay put or they are too bulky or expensive for most people. Our system is passive, just using body weight, and the cost is very reasonable.”

Before they began designing, the Spring Loaded team wanted to learn everything possible about braces. They spoke to doctors, physiotherapists, athletes with injuries and without injuries, people with MS and more. Once they learned the issues and the needs, they were ready to proceed. Overall, what was required was a hinge mechanism able to absorb a lot of energy, just like a human knee.

“It sounds simple – a rotary-to-linear coupling that would store a large amount of force – but it’s on a miniature scale,” Garrish says. “When you look at energy suspension systems – bicycle suspension, prosthetics, the ballast systems for keeping oil rigs balanced and so on – you have to keep that in mind and materials become very important. There is no material that you can make a small spring out of that can do the job, so springs were out. Pneumatics were out because, when you store energy with air, it’s not a linear situation, so what’s left is hydraulics.”

In the final design (the fifteenth, arrived at two years in), a high-tensile cable is pulled around a shaped cam, resulting in a shaped-force response, which compresses a cylindrical ultra-high strength hydraulic system similar to aircraft landing gear. According to Garrish, the small piece of cable involved put the focus squarely on material selection.

“The way steel fails, the way aluminum or polymer fails, they’re all different,” he says. “If you bend some cable around a pulley, the outside is stretched more than the inside, but if you pull it over a shaped piece so that it flattens out, then the outside and inside are pulled more evenly.”

“You can’t just look at a chart that says something will fail if bent around a two-inch pulley a thousand times,” Garrish adds. “You have to look at it microscopically. You need to know where the stresses are and why.”

In the end, polymer was the only option. For the shaped cam and brace ‘arms,’ strong and light carbon fibre was the obvious choice. In fact, the team found that the arms of the brace could be hollow and still do the job. But the geometry was impossible to achieve with a single mold, so the design had to include multiple pieces glued together to form a single piece.

The hydraulic system was another major challenge. “These systems lose fluid over time but we obviously don’t want that to happen to our customers for quite a few years, so we spent a lot of time on seals and went through a lot of technologies,” Garrish says. “It’s pretty tough to make a dry seal. We got them custom-made, then we made our own but they were no better, and then we realized we had to make custom components around the seal.”

However, the pressures involved were so high that things got pretty weird. “We got new types of seal failures and no one could find a reason for them,” Garrish says. “We realized what was going on – materials change their properties at high pressures, liquids turn to solids. That was off the books, totally uncharted.”

Not only did Spring Loaded come up with a brace able to withstand pressures handled by a healthy human knee, but created two different customizable designs. The A-Series brace is designed to reduce fatigue, enhance performance and protect the knees of people who can walk, but need help climbing stairs or crouching. The M-Series restores mobility for those with injuries or mobility impairments that prevent them from getting out of a chair.

“Along with fit, the force curve itself, the shape and the force of the curve can be changed for activity and weight,” Garrish explains. “It depends how much force a person wants and where.”

Currently, Spring Loaded is manufacturing for a test group, and Garrish says the eventual market cost will be comparable to an unpowered custom knee brace. The company has also obtained the medical device licences in Canada and the U.S. for commercialization and the company is about to start ‘crowd funding’ to push ahead with manufacturing. Garrish says that he anticipates that Spring Loaded brace will go to retail by the early in 2016.

Even though there were difficult challenges along the way, and occasional periods of wondering if the braces would ever be commercialized, Garrish never felt like he was wasting his time.

“We always had companies looking to hire us and still do,” he says. “Industry recognizes that the ability to solve problems is valuable and the start-up community is watched closely. Our skills and experience are valued, even as we work to bring our own idea to market.”


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