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When Garrison Hayes started designing a prosthetic foot in engineering school, he wanted to challenge the assembly-line approach taken by major prosthetic companies.
“A lot of them treat prosthetics like shoes,” explains Hayes, who completed his bachelor’s degree in biomedical engineering this spring at Colorado State University. “But not everyone wears the same shoe. Some people need orthotics; some people need small adjustments. We wanted to make that kind of customization widely available, so someone can come to us and say, ‘Hey, I have this specific need—can you make it work?’”
That approach is rare in the industry, he adds, because big manufacturers often focus on mass production rather than individual needs. By contrast, Hayes’ device can be easily tweaked to fit the user’s lifestyle, preferences, and goals—“just right” for every wearer. That explains the name he and his project team settled on: the Goldilocks foot.
Hayes learned the principles of user-focused problem solving long before engineering school. When he was just six years old, he was diagnosed with osteosarcoma in his knee. His doctors offered three options for treatment: an above-knee amputation; a knee replacement, which would preserve appearances but limit mobility; or rotationplasty, which repurposes the ankle as a knee joint and functions similar to a below-knee amputation.
“The doctor asked me, ‘What surgery do you want to have?’” Hayes recalls. “My parents were shocked, because here’s this five- or six-year-old being asked to decide. They said, ‘Why aren’t you asking us?’ The doctor told them, ‘He’s the one who has to live with it.’”
The choice came down to one thing: movement. “I told him I wanted to be able to play soccer with my friends,” Hayes recalls. “And the doctor said, ‘I think I have the right thing for you.’” Rotationplasty preserved more natural leg function and mobility than the other two options, making it the best fit for an active lifestyle.
That decision opened the door to a childhood spent in motion. Hayes dove into athletics with restless determination, trying so many sports that he once joked it might be easier to list the ones he didn’t play than the ones he did. Over the years, that passion shaped his persistence and problem-solving instincts, which eventually guided him toward a career in engineering.
“It goes back to sports,” Hayes says. “When I was younger, I was trying to find the right thing that worked for me. I was doing basketball, hockey, skiing—I was doing as much as I could. And I found out that my [prosthetic] foot couldn’t take everything that I was putting into it and would break. I kept thinking, ‘When will I be allowed to just be a kid and do what I want and push it as hard as I want to?’”
Because of those experiences, Hayes placed a premium on two qualities when designing the Goldilocks foot: durability and versatility. “We understood that there’s no ‘one size fits all’ prosthetic foot,” he explains, “so let’s make our goal be the foot that fits ‘just right.’ That was the inspiration. We wanted to make something that was custom and catered to amputees, so they could have something comfortable that they could use at all times.”
The process wasn’t always smooth. There were moments when prototypes didn’t perform as expected, forcing them to rethink their approach and examine the problem from a new angle. The team’s first attempt used a thermoplastic material called TPU, which was strong but too rigid. The foot was uncomfortable to wear, and it even squeaked with every step—not quite the solution they were looking for.
After exploring different options, they experimented with a material called polyamide. Built up layer by layer in a lattice structure, this synthetic fiber enables each foot to be adapted to an individual’s physical shape and functional needs.
Because amputees’ needs are diverse and idiosyncratic, the team spent months gathering opinions from a wide spectrum of lower-limb prosthesis users. The responses were all over the map, with various people desiring a foot that would allow them to hike, wear high heels, do yoga, play sports, and almost anything else you can think of. They built a prototype for one of their sources, a boxer, who tried it during a training session and was surprised by how light and comfortable it felt. The Goldilocks is nearly half a pound lighter than most prosthetic feet, with a design that absorbs impact yet rebounds like natural muscle tissue.
“We wanted to make sure this was adaptable across the board,” Hayes says. “The long-term plan is to develop a database that factors in height, weight, body type, and other measurements so the design can be customized for anyone — including individuals with double amputations.”
Nearly everyone expressed a desire for affordable, easy-to-maintain devices. To meet those needs, the team engineered a modular design with replaceable parts. “If you’re like me,” Hayes explains, “you break your prosthetic foot a lot regardless of how well it’s built. With this design, if you break a certain part, we can replace just that piece. Instead of paying $1,000 for a brand-new foot, you might spend less than $50 to replace one part.”
The Goldilocks foot remains in the prototype stage for now, but Hayes and his team would like to make it into a commercial venture. They envision a price point well below $1,000 per unit, Hayes says, because “we want this to be something everyone can access. But whatever growth comes in the future, our core values have to stay the same. It’s always the customer first—their needs above everything else.”
“Big companies have been making prosthetic feet for a long time,” he adds. “It’s hard to look at that and say, ‘We can do this better.’ But hearing someone actually say they’d wear our foot—it tells us we’re not just reinventing the wheel for no reason. It means we’re on to something.”
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