Jose Delgado, 53, was born without most of his left arm. He has a prosthetic hand that uses muscle signals from the forearm to open and close the fingers. Cost: $42,000, half of which was out of pocket. He recently got in touch with Jeremy Simon, who maintains the 3D Universe blog, to see about 3D printing a prosthetic hand. The so-called Cyborg Beast device cost approximately $50 in ABS material, and Delgado prefers it! He spends a lot of time lifting and moving boxes at his job, and he finds the 3D-printed hand to be more functional and to have a better grip. Plus, if a part breaks, a new one can be printed in a matter of hours. Delgado talks about the 3D-printed hand with Simon in the video below.

Simon describes the mechanical design of the Cyborg Beast, the design of which is derived from the famous Robohand, on his blog. "There are a series of nonflexible cords running along the underside of each finger, connecting to a "tensioning block" on the top rear of the device (the "gauntlet")," he writes. "Tension is caused by bending the wrist downward. With the wrist in its natural resting position, the fingers are extended with a natural inward curve. When the wrist is bent 20 to 30 degrees downward, the non-flexible cords are pulled, causing the fingers and thumb to bend inward. A second series of flexible cords run along the tops of the fingers, causing the fingers to return automatically when tension is released."

Since fitting Delgado with the prosthetic, Simon has fine-tuned the tension on the tendon cords. He plans to print another iteration of the device using Bridge nylon, which is lightweight but with enhanced strength properties.

Simon, who describes himself as a 3D printing evangelist, has an interesting story to tell, as well. A college dropout, he started a consulting firm specializing in information security that became quite successful. After 14 years of that, he asked himself, "If money weren't an issue, is this what I would be doing with my time?" The answer was obvious, so he sold his shares in the company in 2012 and started dabbling in 3D printing, which he writes about with enthusiasm and conviction on his blog, 3D Universe.

— Norbert Sparrow

Norbert Sparrow is Senior Editor at PlasticsToday. Follow him on twitter @norbertcsparrow and Google+.