Matthew Kramer

Born with a left arm that ends just below his elbow, 9-year-old Aidan Robinson has had his share of prosthetic arms. As a baby, he wore a passive arm, plastic and immovable like a doll’s arm, which trained his brain to develop motor skills equally on both sides. As he grew, he graduated to more complex prostheses. Most children with an upper-limb difference—a catch-all term used to describe conditions in which limbs don’t develop to their full length—start with a body-powered prostheses, a system which use a series of cables attached to the opposite shoulder to create motion. But Robinson immediately jumped to myoelectric arms, which use electrodes to respond to subtle muscle movements. His first myoelectric arm could open at will but close automatically after a few seconds. His next arm was more complex, capable of reading two types of muscle movements instead of one, closing when he lifted his arm up and opening when he lowered it.

While the science of prosthetics has advanced dramatically, the most sophisticated prosthetic technology is still not available for children. Arms with fingers that articulate or that can do complicated motions like turning a wrist while simultaneously opening a hand often don’t even come in children’s sizes. And for some good reasons. These advanced prosthetics are expensive—basic myoelectric systems start around $15,000—whereas basic, body-powered arms for kids are far cheaper, starting around $5,500. That price difference is particularly significant when you considering that the child might outgrow the arm in a year. Kids also might not have the muscle control needed to use a myoelectric arm effectively. And children simply might not be responsible enough to make sure the arm doesn’t get wet or to charge the battery every night.

So while Robinson's myoelectric arms were more complex than the body-powered ones that most kids with upper-limb differences use, they left a lot to be desired. The arm with an automatically closing hand, for example, is also known as a “cookie crusher” in the prosthetics community because kids who are not careful might accidentally crush something they forgot they were holding. The arm that came with a hand that opened when he lowered his arm made it difficult for him to pick up anything that dropped on the floor. When asked what he wanted out of a prosthetic, Robinson said, “When I’m doing my pushups, I want to open my hand. I don’t want to [have to] balance on it.” Two years ago, he stopped wearing his prosthetic altogether.

Even without the prosthetic, Robinson does many of the things kids his age like to do—play on the computer, compete on the swim team, study karate (he’s a green belt), and even throw perfectly round bowls on the pottery wheel. But in the coming weeks, Robinson’s prosthetic-free streak may come to an end. Last July, Robinson attended Superhero Cyborg Camp, a one-week design education workshop for kids with varying degrees of upper-limb loss. At camp, which was run by the San Francisco nonprofit KIDmob, Robinson and nine other students learned problem-solving, design and prototyping skills, and used them to design a new arm with its own superpowers.

For Robinson, being able to hold a Wii remote controller was an important power to acquire. Using old toys and parts donated from a hardware store, he fashioned together a prosthetic prototype made of a threaded metal rod onto which he could screw on different parts: his Wii remote, a fork, and a life-size version of the hands found on LEGO figurines.

One of the volunteers, a prosthetist named Erik Tompkins, helped him attach the rod to his arm by embedding it into a socket made of Aquaplast, a type of plastic that stays hard at room temperature but becomes gooey and moldable when heated to 140 degrees Fahrenheit, and securing it with masking tape. Though the prototype was less sophisticated than the prosthetics he had used, Robinson was much more excited to wear it and dream up fun, new ideas for his prosthetic.