Can We Really 3-D Print Limbs for Amputees?

For the approximately 1.7 million people in the United States living without one or more of their natural limbs, the process of acquiring a prosthetic one is exhausting. It’s a drain on time and money, involving mold fitting, laser body scanning, and hours upon hours in prosthetists’ offices.

But many of the approximately 34 million people around the world living without a natural limb don’t have access to this process at all.

The motivation to research and create more advanced prosthetic limbs is not financial. The money poured into research isn’t often recouped, simply because there aren’t enough customers. And it isn’t cheap for those customers, either.

3-D printing has the potential to change this.

When Scott Summit, the founder of Bespoke Innovations, started researching 3-D prosthetics six years ago, you had to go to Los Angeles to get a 3-D body scan and it cost about $800. Summit has been working for the past six years to reach a point where fully 3-D printed prosthetics become an easy reality. Everyone I talk to about the intersection of 3-D printing and prosthetics mentions Summit as the definitive expert in the field, and he says we can, right now, create a prosthetic limb with an iPhone and a 3-D printer. “I would like to see the creation of a prosthetic limb to be a viral app that’s usable by everyone,” Summit says.

The technology exists. Unfortunately, it costs a boatload of money.

3-D printing is, in layman’s terms, the ability to take a digital model and “print” it in all its three-dimensional glory. Generally, this process uses plastic as a medium, though it also works with metal and even biological material (though this is a slightly different process). 3-D printing offers higher customization of geometric models than ever before, and its nature allows for more trial and error in the actual creation process, since it makes prototyping cheap and quick.

The Media Hype

The Internet is full of stories about amputees creating entire prosthetic limbs in their homes, using a MakerBot Replicator-type home 3-D printer, but this is an extreme anomaly.

Jon Kuniholm, who lost his right arm to an IED as a Marine in Iraq, finds the media hype particularly egregious. Kuniholm founded The Open Prosthetics Project, a non-profit open-source collaborative resource for innovations in prosthetics, and he’s given several Tedx talks about the pros and cons of advancing of this technology.

Most prosthetic limbs are composed of two halves: the replacement limb and the part that connects with the body (generally called a socket). These parts are often made of a combination of materials from metals to plastics to electronics, which presents a problem for 3-D printing, which currently can only print one material at a time. The other issue 3-D printing faces is the connection to the body.

“The idea is—you’re trying to securely attach a hand or a foot or whatever to somebody’s skeleton—which is inside their body—through the soft tissue that’s still around it without damaging that soft tissue or it being uncomfortable,” Koniholm says. “Most of the time, a surface scan of somebody’s body isn’t going to create something that is going to be useful, because it has to interact with the bony part that’s inside.”

Generally, doing this requires that a plaster mold be made of the stump to capture its geometry. While a high-end laser body scanner, such as the one Summit remembers in Los Angeles, can do this work, Koniholm doesn’t think there is necessarily an advantage to it.

That said, scanners can help figure out the geometry of prototypes, which can then be created using a 3-D printing.

Prototyping

“If someone needs a prosthetic, then they’ll typically have another limb that’s intact, and they’ll use a white-light scanner or laser-based scanner to capture their intact limb and scan it to create their other limb,” says Rob Connelly, president of FineLine Prototyping. One of the advantages of 3-D printing is the absurd amount of customization available for the visual aspect of a prosthetic limb. While scanners vary in resolution, some exist that can “get down to even the fingerprint level,” Connelly says, allowing for a near-exact replica of an amputee’s remaining limb.

“There is a tremendous amount of engineering that goes into any prosthetics,” as Connelly says, but 3-D printing can still help create prototypes as engineers move toward an end goal.

For example, in 2009, then-25-year-old Joel Salder was honored by TIME for having one of the best 50 inventions that year—a prosthetic knee that only cost $20. The Stanford University Bio-X fellow used 3-D printing “to find out what forms work really well for a knee joint” when creating the JaipurKnee.

That’s one of the biggest advantages of 3-D printing, the ability to quickly print highly customizable forms. This opens the practice up to mechanical extrapolations, such as producing cheaper components for traditional prosthetic limbs.

Take Willow Wood, a company that produces prosthetic limbs and components. “We can print out a socket that can be used definitively, but attached to that socket is generally some sort of suspension device,” says director of research Jim Colvin. “To print that [component] in the same printer is not possible today.… You’re trying to replace a part of the body, and that part of the body isn’t homogenous.”

Still, by using either traditional casting or a combination of digital modeling software and laser body scanning to gather the geometry of the stump, the company successfully prints sockets, saving both time and money without sacrificing customization. It’s progress, but it isn’t the same as being able to have a fully-created prosthetic limb hot off the printer.

“There’s a dream that in the future, we’ll be sitting in our home and hit a button to print our prosthetics from scratch,” Sadler says. “That might be a further out vision.”

But some people think we’re already there.

The 3-D Printed Prosthetics of Today

Sadler agrees with Kuniholn about the difficulty of attaching printed prosthetics, saying, “The fitting is a whole other black art. 3-D printing only gets you part of the way.” Of course, that’s for high-end prosthetics, the kind you hope to have. In some parts of the world, the choice is between having a mediocrely-fitting prosthetic and not having one at all. This is the situation that spurred Summit to action, as well as Patrice Johnson, who, according to Sadler, is, “the only person to have successfully designed and sold [a] functional upper limb prosthesis that used 3-D printing.”

Johnson was the former chief technical officer of Physionetics, a start-up company that successfully created both the hook hand replacements and sockets of upper-limb prosthetics that could be 3-D printed.

These limbs were printed on a $500,000 3-D printer owned by ExOne. This particular printer, housed in Pittsburg, can print metal, a stronger material than the plastic of most printers. While attempting to create a cheap prosthetic arm that could be used by people around the world, Johnson found that “in the long-term, it made much more sense, just from a money sense, to use 3-D printing” citing “one of the ways that it made a crucial difference for us is if you had a good idea … you’re quickly able to create your good idea and see if it’s feasible.”

It proved feasible, as the company began creating metal hooks and sockets for military amputees, who wanted to use them for strenuous activities such as rock climbing. “One of us actually hung from one of the hooks to see if it was strong enough,” Johnson remembers.

As the start-up continued making the prosthetics, 3-D printing continued to advance. Strength and versatility rose while price decreased. Soon, Johnson was spreading the technology across the world.

“Right on the border of Burma and Thailand, there are landmines like you wouldn’t believe,” he says. These landmines leave many residents as amputees, residents who “would typically never see a prosthesis because of [the] fitting and time it would take.” Armed with Physionetics’ technology and good will, Johnson went to Burma and fitted two amputees with the printed arms. “We donated them,” he says. “All I had to do is go out there, show them how it was fit, and within an hour and a half, we had them on these two guys.”

Stories like this are what drive Summit to continue his quest for a “self-use viral app for developing countries” that can create prosthetics. “There will simply never be enough prosthetists to meet their needs.”

This isn’t his dream for the future; he thinks it’s a scientific possibility now. And he strongly disagrees that the materials 3-D printing can handle aren’t strong enough to work as limbs. He points out that, “the [human] bones that we have are not as strong as titanium,” a material used in many prosthetic limbs.

“When you have great flexibility of geometry, as we do with 3-D printing, you can overcome what strength you don’t have,” Summit says. He says he’s found a way to overcome this strength barrier by creating a hollow prosthetic, then filling it with a lattice structure, similar to the construction of a bird’s bone. “Nature’s been doing this for a long time,” he says.

Johnson is currently working for a new start-up (connected with the University of Denver) called Levity. Its goal is to create entire 3-D printed exoskeletons that fit as comfortably as a shirt, so that children with cerebral palsy can avoid painful (and continuous) surgeries to correct their growth/form. Summit continues to work toward a day when a viral app can help create prosthetic limbs at the touch of a button.

“We’re not waiting for a new breakthrough,” Summit says. “We are waiting for [a] cost breakthrough.”