A prosthetic arm controlled by your mind, invented by a teenager and made on an entry-level 3D printer.

Benjamin Choi was in third grade when he watched a documentary about the then-cutting edge techniques scientists were beginning to use for bionic prostheses, artificial limbs controlled by the user’s mind.

“I was really, really amazed at the time because this technology was so impressive,” he says. “But I was also alarmed that they require this really risky open brain surgery. And they’re so inaccessible, costing in the hundreds of thousands of dollars.”

The ‘really risky open brain surgery’ was exactly that – most mind-controlled prostheses involve dozens or even hundreds of tiny sensors implanted over the surface of the motor cortex. And they can cost into the literal millions of dollars.

In 2020, Choi was a sophomore in Virginia when the pandemic shut down the lab he’d intended to intern in over the summer. Suddenly overwhelmed with free time, he assembled his own laboratory in his parents basement, co-opted his sister’s $75-dollar 3D-printer, and tackled the prostheses issue.

In a few months, he had a working arm, controlled by two external electroencephalography (EEG) sensors which just rests against the skin. His first one was made of PLA and fishing line.

Now two years later, Choi’s prosthetic arm has been through 75 iterations, has an AI assist to interpret the movements a user wants, and is made of materials that can stand weight up to four tons, but still costs only about $300 to manufacture.

Choi is now a senior in high school, due to graduate this June, and his invention has put him as a finalist in this year’s Regeneron Science Talent Search, a prestigious STEM competition.

The WHO estimates that less than one in ten of the people worldwide who need assertive products, which includes prostheses along with wheelchairs and eyeglasses, have access to them, with cost being the most common obstacle. Choi not only invented a cheap way to make a very advanced prosthetic, but he made the plans for how to do so free online.

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