Professor aspires toward the perfect prosthetic design

by Tomoko Otake

Staff Writer

“Functionality and aesthetics can co-exist.”

That’s the idea Shunji Yamanaka is trying to express through his design of next-generation prosthetic limbs. Yamanaka, a product designer and professor of media studies at Keio University’s Shonan Fujisawa Campus (SFC), became interested in prosthetics after seeing South African double-amputee runner Oscar Pistorius perform at the 2008 Beijing Paralympics. Pistorius’ masterful use of carbon-fiber feet, he felt, “symbolized a very special relationship between human beings and man-made products.”

Yamanaka’s research led him to Tokyo-based prosthetist Fumio Usui [see main article], who founded a track club for athletes with amputated limbs. Usui introduced him to the members and invited him to their competitions.

Yamanaka — one of the masterminds behind the SUICA/PASMO train-card system and a host of interior and household goods — was soon devoting himself to sketching artificial limbs. At first, though, he was hesitant to approach the athletes themselves with his ideas.

“I was half-scared,” he recalled recently at his SFC office in Fujisawa, Kanagawa Prefecture. “They all come from somewhat unfortunate circumstances. I thought they might think design is a luxury they have no room for.”

He needn’t have worried. “I explained to one of them how I was a designer, that prosthetics sometimes looked beautiful to me, and that I was wondering if there was anything I could do. Then the athlete — Paralympian cyclist Masaki Fujita — said he was glad to know that somebody thought prosthetics would be able to look cool.”

Encouraged by Fujita’s words, Yamanaka thought harder on the design concept for new prosthetics. One day, he had an epiphany.

“Many amputees, soon after losing their legs, want limbs that restore their pre-amputation look. But after awhile, they become less preoccupied with that, and they learn to view prosthetics as their tools. The new limbs, while functioning like human legs, look completely different. I realized that artificial limbs can be aesthetically designed, fitting the natural rhythm and tensions of the human body without mimicking its appearance.”

To put his ideas into action, Yamanaka looked to improve the design of existing prosthetics. He streamlined the segment that connects the carbon-fiber “foot” to the socket, which in previous designs had bolts sticking out of it — “like construction-site materials,” as Yamanaka puts it. Not only is this unsightly, it poses a danger to the runner’s other leg. Yamanaka also made an improvement to the sockets themselves, which are custom-built to fit the shape of the user’s leg. The traditional asymmetrical design followed the contour of the severed limb, which can make some people uncomfortable. So Yamanaka smoothed out the entire surface over a layer of plastic foam. To improve stability, he increased the width of the sole of the foot spring, and to boost the limb’s aesthetic appeal, he coated the entire package with sleek metal.

The process led Yamanaka and his students to research everything from basic biomechanics to the spatial relationship between the socket and the foot spring; they also had to teach themselves how to make prosthetics from scratch.

To test the new gear, Yamanaka chose Saki Takakuwa, a Keio University student and rising star among Japan’s amputee runners. Her numerous trial runs led to further design improvements.

“We provided four prototypes (to Takakuwa), and the latest one is the lightest and the coolest,” Yamanaka says. “Even though it took us four years to create an artificial limb for just one athlete, I feel we’ve achieved sophistication in both technology and design.”

Yamanaka is also working on a nonsports-type prosthetic limb, which reflects his pursuit of functionality and aesthetics and which is designed to look good when worn with regular clothes.

Takakuwa says she’ll bring the new prosthetic with her to London, though she isn’t sure if she’ll compete with it at the Paralympics — it only recently arrived and she hasn’t had enough time to practice with it. But Yamanaka already considers the project a success.

“She told us that when she first started changing into the prosthetic limb at practice (at Keio), her (able-bodied) teammates would behave like they shouldn’t look. Now, they openly ask her how the artificial limb works and what it feels like to run with it.

“A product with a well-thought-out design sends the message that it’s OK to talk about. And now I feel that’s what we’ve wanted to achieve with prosthetics all along.”