3-D printing: Wave of the future

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3-D printing: Wave of the future

If you’ve been wondering about 3-D printing, it’s probably for the same reason we are. On May 17, we learned that surgeons had placed a life-saving support — built on a 3-D printer — into the airway of Kaiba Gionfriddo.

Man holds model in front of computer screen, showing resemblance between model and MRI image.
Credit: The Why Files
Alejandro Roldan of the University of Wisconsin-Madison holds a printed, 3-D model of a heart against its computer design, which was based on a patient’s MRI scan. The system, still under development, could be used to guide surgery to repair defective organs. Using the realistic, printed model, the surgeon can perform “virtual surgery” to test the effect of heart-remodeling surgery on blood flow and pumping efficiency — without touching the patient.

Kaiba was an emergency case: Every day, his breathing stopped when his airway collapsed. The support was patterned on CT images of his airway, and printed in biodegradable plastic.

That welcome news came just three days after Forbes reported widespread interest in a handgun printed with similar technology.

A 3-D printer builds up objects layer by layer, using various methods to deposit and harden the “ink” where it is needed. Many materials, including plastic, metal, ceramic and even human cells, can now be printed, based on instructions from computer-assisted design (CAD) programs.

“Quite a few doctors said he had a good chance of not leaving the hospital alive,” says April Gionfriddo, about her son, Kaiba, who is now 20 months old. “We were desperate.”

With emergency clearance from the Food and Drug Administration, Glenn Green and Scott Hollister of the University of Michigan printed a tracheal splint, using a polymer that they expect to be absorbed by the body in three years.

On February 9, 2012, the splint was sewn around Kaiba’s airway to expand it and serve as a skeleton for proper growth. “It was amazing. As soon as the splint was put in, the lungs started going up and down for the first time and we knew he was going to be okay,” says Green.

How much hype? How much reality?

You’ve heard the 3-D hype: Factories are becoming obsolete. When you need a part, you’ll feed a downloaded file into your personal printer, and press “print.”

Today, many of those objects turn out to be trinkets, baubles, chess pieces or covers for slab-phones.

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The situation reminds us of the giga-hype over nanotechnology about 25 years ago, when invisible, nanometer-sized robots would supposedly emulate proteins or enzymes and usher in the era of self-assembly.

The over-sell is not that bad, “but there’s still an incredible amount of hype” in 3-D printing, says Tim Osswald, a professor of mechanical engineering at University of Wisconsin-Madison. In fact, he says, some are touting — as a legitimate business venture — the idea of printing whole motorcycles. “No, we can’t do that,” he says.

“We can’t 3-D print clothing, though people say they will,” says Osswald, who researches the raw material — the “ink” — for 3-D printing. “Why should we? We can sew clothing much easier, and besides we don’t have a powder tiny enough to make a fabric.”

And still, as the printed airway and the handgun demonstrate, the 3-D printing wave is getting legs. What can — and can’t — these gadgets do? How do they work?

Promise and hype of 3-D printing

Some of the features of 3-D printing lend themselves to designing, prototyping, visualizing and experimenting. Others can make parts that cannot be made any other way.

3-D printing can:

  • “Print” plastic, metal, even living cells. (After printing, ceramic and glass must undergo high-temperature firing).
  • Eliminate the need for a mold, which is a major expense for metal, plastic, ceramic and glass parts.
  • Create parts — even entire assemblies — that could never previously be made.

Building up the shape one layer at a time allows one part to be formed inside another. “It opens the ability to engineer in a different way,” says David Sheffler, in mechanical and aerospace engineering at the University of Virginia.

We wondered why we’re hearing so much about 3-D printing right now when a variant called stereolithography has been around for almost three decades. “It was used in the back rooms of design firms, and it always used to frustrate me,” says Hod Lipson of Cornell University. “I’d talk on the street about this incredible technology that could make anything you want, but nobody knew about it.”

Diagram shows how selective laser sintering works: laser beam selectively fuses power layer by layer and unsintered particles are removed later.
Modified from Materialgeeza
A layer of powder on the work surface is selectively heated with a laser. The process called sintering solidifies the powder into the part; the unsintered powder can later be removed. Laser sintering allows low-volume production of complex parts in metal and plastic. Programming the laser light determines what becomes part, and what gets blown away to form voids.

Printing medical miracles

The life-saving replacement airway in Michigan is “a perfect example of different ways in which 3-D printing can be used to improve life,” says Lipson, co-author of a new book on the technology1.

The technology is also infiltrating medicine, says Lipson. “There are hundreds of bone implants, printed in titanium, usually for hip replacements, based on an MRI scan.”

At Cornell, Lipson says, “We almost routinely print plastic bone for the veterinary school before a complex procedure, so the surgery is like putting a puzzle together the second time.”

3-D printing is also used in Invisalign plastic braces, which “have to be custom-made in a series that will gradually pull your teeth into the right place. Most people don’t know that 50,000 of these are 3-D printed each day. Someone you encountered today is wearing this 3-D printed prosthetic.”

3-D printing: the hard cell

3-D printing is not just for plastics. A “cell printer” that works like an ink-jet printer can spray a precise stream of gel containing living cells. Early tests are looking at using cell printing to form a meniscus, a tissue that cushions the knee.

Other simple tissues that may be printed include bone and cartilage, Lipson adds. “As the technology becomes more complex, the kidney, liver and spinal disks” are likely to be future targets.

Ideally, some replacement tissues should have the capacity to grow, Lipson says. “If a plastic heart valve was implanted in a child, it would have to be replaced” as the child matured. A valve made of the patient’s own cells might grow with the child, he says. “That’s revolutionary!”

Testing your mettle

Although 3-D printing began with plastic, metal can be printed in an inert environment that prevents oxidation. A laser sinters the metal powder after each layer is laid down. “The properties of the resulting metal are almost identical to bulk metal; it’s a very viable, engineering-tested way of making metal parts,” says Lipson.

But there’s little sense copying conventional metal parts, says Lipson, who points to growing interest in the aerospace industry for parts with new shapes. “What you made with a forge you can still make, but you can also make hollow or organic shapes, and end up with a shape with the same performance, but half the weight.”

Under consideration is 3-D printing of jet-engine turbine blades with air channels for better cooling.

Ball courtesy Tim Osswald/University of Wisconsin-Madison; video by The Why Files.
A one-piece fútbol made with 3-D printing actually bounces on springy plastic internal struts. “Now engineering becomes open ended,” says Tim Osswald. “To make something like this with traditional molds, you would have to glue it together by hand. These are things that you could not make before. Now you can rethink engineering.”

Aircraft are produced in small quantities, have very complex parts and can be very expensive. “That’s where the technology has the best value,” says Lipson. “You are not going to be printing toothbrushes.”

Mark Ganter, professor of mechanical engineering at the University of Washington, has come up with some interesting new printing materials, including ceramic. He is currently working on glass-ceramic composites, and says, “We see these being used in everything from armor to building materials. Disposable ceramic armor would be a big deal for a flak jacket; you could custom-tailor the inserts.”

3-D printing may also be used to print molds for casting metal — sidestepping the highly skilled job of mold-maker.

On the other hand…

After all this enthusiasm, it’s time for some cautions. For medium- and large-sized production runs of plastic parts, injection-molded plastic is cheap, fast, automated and reliable, even considering the cost of the mold.

Even the staunchest advocates warn that 3-D printing is not suited to every task, and issues concerning raw material, strength and deformation all need to be addressed as the field matures.

One issue is post-printing change of shape, “You get shrinkage, warpage, issues with dimensional stability,” says Osswald. “This has been a problem since plastic has existed. When Alexander Parkes made cellulose in 1856, a few months later, all the parts had warped because the plasticizer had evaporated.”

Printed plastic can shrink as much as 5 percent, Osswald says.

A second limitation concerns particle size in the “ink.” “We are using 50 to 100 micrometers now,” Osswald says, which creates the characteristic roughness on printed plastic, “but are hoping to get much smaller. We can make particles as small as 5 micrometers, but they still need to flow through the machine.”

Poor flow can leave voids in parts that become prone to cracking. In a tiny structure, Osswald says, pores and valleys become even more problematic. “You can get a mess, a part that will fall apart.”

Useful plastics, such as polylactic acid, a biodegradable substance used in medicine, can also be hard to powder, Osswald says. “You can freeze it and grind it into a very fine powder, but it’s very jaggedy, and does not flow easily.”

Man holds cylindrical machine in his hand.

Credit: The Why Files
Tim Osswald holds a prototype “micropelletizer” that produces tiny pellets of new plastics. “We have made powders and are trying to scale up, making polymers that can’t now be made into spheres” for 3-D printing, he says.
A orange box contains a white shape with many wires, and belts used to position ink-jet head.
Courtesy: Bre Pettis
When it was sold in 2011, the stripped-down MakerBot Cupcake CNC cost $455.

How expensive? How cheap?

3-D printers have a long way to go before they can compete with injection-molded plastic, one of the cheapest technologies ever invented. But cost is falling, says Sheffler. “The cost of bigger printers is following Moore’s law [which predicted a geometric decline in the cost of computer memory] very closely. We bought one for $30,000 two years ago, and now it costs $20,000.”

It’s the same trend evident in plasma TVs and many other new-fangled technologies, Sheffler adds.

3D printed airplane
Courtesy David Sheffler, University of Virginia
This printed plane actually flies! A summer project for two students, the printed plane has a skin that takes the load. “There are no spars inside, it was fully printed,” says Sheffler. A standard battery-powered electric motor supplies the power. “This is a snap-together plastic airplane that’s very stable. We pulled off something amazing.”

A key advance came in the mid 2000s with the introduction of two open-source 3-D printers, says Lipson. “We went from a vicious cycle, where it was expensive, and therefore had a narrow market, and was therefore expensive, to an open-source, cheap, hackable system that anybody could use.”

Lipson, who helped usher “Fab@Home” into being in 2006, says it and another called RepRap, “seeded the transition, and since then hundreds, then thousands of 3-D printers were made… This has brought the technology to the attention of the masses, and the media.”

The airplane “would be incredibly complicated to build by hand, but we designed, engineered, did the analysis in a CAD program, and printed out exactly what we designed,” Sheffler says. “No manual labor was involved.”

And there’s a significant fringe benefit to 3-D printing, Sheffler says. “Students love it, and it’s not just students, it’s me. The students are out there doing real research, applications; we are learning as we go. It’s great stuff, we’re having a ball!”

Pie chart shows 5 biggest uses: functional models, artistic items, spare parts, research/education, and direct part production.
Credit: The Why Files. Data from Statistical Studies of Peer Production.
Researchers from Finland surveyed people around the globe who are involved in 3-D printing; 350 people responded.

Osswald agrees. “Students are now thinking, ‘I can make this!’ They get weird ideas, ideas that we [older people] would not get because our brains are hard-wired. Young people can think outside the box, they don’t have the same restrictions that we have grown accustomed to.”

With 3-D printing, “There are a lot less restrictions on what you design.”

Summing up

So will a 3-D printer be fraternizing with your ink-jet printer in five years? Possibly… Prices are dropping, and capabilities are rising. But to really get the best from the printer, you my need some rare expertise, says Ganter. “The reality is that every one can own these things, but the difference is, to make an object on a 3-D printer, you need some kind of CAD background, you need skills that ordinary people don’t seem to possess.”

And even though an increasing range of printer instructions is available for download, who knows if you will find data on the broken widget on your essential gadget? If not, as Ganter stresses, you may not have the computer-assisted design necessary to control the printer. “I tell my engineering students, you possess skills that the average person may not possess. It’s not that it’s impossible, but not everybody is an engineer, not everybody is a designer, not everybody is an artisan.”

– David J. Tenenbaum
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Terry Devitt, editor; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer; Amy Toburen, content development executive