To design the prosthetic Ferrell and a group of volunteers took measurements of Katelyn's arms, and used a design provided on the internet from the e-NABLE community, a global network of volunteers. Ferrell told The Huffington Post that the designs for Katelyn's prosthetic are publicly available, already tested and have been adopted by many users around the world. It is not a FDA-approved device, but the material used for 3D printing is a well-known, non-toxic plastic called polylactic acid. "[The prosthetic we built] is generally recognized as a beneficial alternative to more expensive professional prosthetics," Ferrell told HuffPost. The hand device that Ferrell and his team made is pink and purple, Katelyn's favorite colors, and includes fingers and a thumb that allow Katelyn to grasp objects. It is attached to Katelyn's arm by Velcro straps and is controlled by her elbow.

After spending more than a year on a waiting list for a functional prosthetic hand, a Texas girl's needs were met by her local public library-- which happens to have a 3-D printing lab. Katelyn Vincik, 5, was born with a left hand that wasn't fully formed, but hasn't let that difference slow her down, Click 2 Houston reported. "She's very determined, she does everything," her mother, Kimberly Vincik, told the news channel. "It's never held her back." But during her nightly prayers, Katelyn always asks when the doctors will fix her hand.