Not too long ago, Liam had no fingers on his right hand. The South African five-year old was born with Amniotic Band Syndrome, which causes amputation of digits before birth. But since November, Liam has been using a series of prosthetic hands designed by two men living on opposite sides of the planet, using open source software and 3D-printing technology.

Now, those two men—Ivan Owen in Bellingham, Washington and Richard Van As in South Africa—have published the design for Robohand, the mechanical hand prosthesis, on MakerBot's Thingiverse site as a digital file that can be used to produce its parts in a 3D printer. They've intentionally made the design public domain in the hopes that others around the world who don't have access to expensive commercial prosthetics (which can cost tens of thousands of dollars) can benefit from it.

The project began with a mechanical hand Owen made for a science fiction convention in 2011. He works for a school supply business during the day, but he also works from home creating special effects. When a video of Owen demonstrating the oversized hand went viral, it got the attention of Van As, who had lost most of four fingers on his right hand in a woodworking accident. Van As had been told that prosthetic fingers, such as the X-Finger, would cost him at least $10,000 per finger replaced, so he set about in his workshop trying to design his own.

Van As contacted Owen, and the two started collaborating long-distance and documenting the project on their blog, Coming up Shorthanded. Van As first sent Owen a plastic cast of his hand to use as a reference for design work. Initially, Owen had to physically ship Van As prototypes—a process that was expensive and added weeks to each iteration of their effort.

Last November, the two prepared to meet for the first time. "Our initial plan for the trip in November was to finalize and polish and improve the prosthesis we had designed for Rich," Owen told Ars in an interview. But then Van As got an e-mail from Liam's mother after she discovered the project online. "When he was contacted by (Liam's mother) Yolandi, we decided we would have a go at trying to build an initial prototype for Liam in the space of time that I was there as well. We only had 3 and a half days, so, you know, it was an arduous task, but it was something we felt we should definitely do while we were in the same place at the same time."

When Owen left, Liam had his first prototype hand, but it still needed some work. That work accelerated when Makerbot donated two Replicator 2 printers to the project in mid-January—one for Owen and one for Van As—allowing them to rapidly iterate their designs. "I actually didn't really know much about 3D printing until not too long ago," Owen said. Rich and I have been amazed at how useful it is, even for producing functional parts. It's been an incredible boost to the speed with which we can do this."

Owen has done most of the design work for 3D printed components using OpenSCAD—an open-source 3D computer-aided design modeling program. OpenSCAD isn't an interactive tool; rather, designs are created in a scripting language. Owen, who has a background in programming, taught himself how to use the software to produce the designs.

The OpenSCAD files for Robohand are relatively small—under 2 megabytes—so they can easily be pushed back and forth between Owen and Van As by e-mail. "There have been times Rich and I have been awake at the same time," Owen said, "and I e-mail him a file, and he prints it out, and can send me feedback. And then within 15 to 20 minutes, I can send him a modified version. It's made it a lot more like working right next to each other. Turnaround has gone from two weeks to two minutes."

Earlier this week, Liam received a finalized working version of the hand, printed on the MakerBot. The PLA plastic resin used by the MakerBot machine is strong enough to be used day to day, Owen said. We've found we can control the in-fill percentage—the ratio of plastic to air in the part," he said. "So actually, from the experiments we've done, the force to break the plastic exceeds the strength of the human hand." It also means that, as Liam grows, the design can just be scaled up and reprinted for him; when he's fully grown, the hand could be metal fabricated.

From the beginning, the project was intended to be open-sourced, Owen said. "Rich and I have been very happy to have the opportunity to do this," he explained. "Not only did we find a design partner, but we’re kindred spirits in that we're both frustrated by the fact that there are some things that just shouldn’t be commercialized—they're needs instead of wants—that are." The pair plan to continue to develop the design as a mechanical prosthesis in the long term because it is low-tech and could be more easily produced and supported around the world. "But if there is somebody who can utilize the design for a robotic prosthesis, we'd be excited to work with them," Owen added.

Owen also hopes to get his hand into the hands of the Defense Department and Department of Veterans Affairs to help veterans who have lost digits or hands. "I live not too far from Seattle, and [we] have Joint Base Lewis McChord near us," he said. "I would like to talk to on-base occupational therapists. If they have the funding to get a 3D printer, they could work with this—and the cost to produce them for each veteran is brought down because they don't have to pay royalties."