People involved with 3-D printing in a vast array of fields — techies printing their own computer parts, doctors printing human organs, artists printing jewelry, entrepreneurs making printers that are more and more accessible to consumers — all agree on one thing: The revolution has arrived.

"It's beyond, really, your imagination," said Dr. Paul Wang, a cardiovascular medicine and bioengineering professor at Stanford University who has been using 3-D printers to create models of human hearts as well as devices such as coronary catheters, valves and stents.

Though the first working 3-D printer was built in the 1980s, advances in technology in the last few years have propelled the process forward, redefining the way things are made and the speed with which they are produced.

The 3-D printing process begins with a digital model of a 3-D object, which is typically designed using software such as computer-aided design, or CAD. Files are then exported to printers, much like clicking "control-P" prints a document.

The actual printing process is additive, meaning layers of material — usually plastic — are laid down on top of one another successively in different shapes to create an object. The two main plastics used by today's 3-D printers are PLA, or polylactic acid, which is made from corn, and ABS, or acrylonitrile butadiene styrene. ABS has been used by manufacturers to make a range of items such as Legos, musical instruments, whitewater canoes and some small kitchen appliances.

"When (3-D printing) first came out, so many people were just using it for tchotchke stuff — I can print Yoda's head or whatever you can come up with," said Jesse Harrington, a program manager at Autodesk, a leading 3-D design software company headquartered in San Rafael. "Now, we're really starting to see usable things."

The resolution of printers has improved exponentially, according to Wang's colleague, postdoctoral research fellow Jeff Caves. One machine at Stanford can print down to 30 microns, or 30 thousandths of a millimeter.

"Even though the basics of these tools have been around for maybe 10 years or more, it's just the gradual, incremental improvement is really resulting in something that is becoming exponentially more useful," Caves said.

In the Stanford Biodesign building one recent afternoon, Wang and Caves pointed at a 3-D-printed plastic replica of a human heart sliced open to show minuscule anatomical details.

"What we're trying to do is understand the anatomic, structural elements and constraints that are offered by the heart as we design new tools for treating heart conditions," Wang said.

It starts with Caves designing these tools — which are often no bigger than a few millimeters — on CAD. He can then export the file to one of Stanford's many 3-D printers and, by the next day, hold the printed part in his hand.

"It's literally like designing a house and then building it in front of your eyes," Wang said. "It's that kind of feeling. It's really very cool."

They make tools that are precisely designed to match the contours of the heart's chambers. They then have a device that they can test, redesign and improve.

"It really allows us to do things that I think we were pretty imperfect in terms of doing before," Wang said. "It's that ability to really translate the concept into practice that really is a revolution."

Previously, specialists handmade custom parts at such a small scale that getting a working model could take months, hugely slowing down the design — and redesign — process, Wang said.

"Jeff can design this on the computer and overnight we get something we can test," he said. "So you can imagine how that accelerates your process and your ability to look at different designs. The first design naturally needs to be adjusted and so you could do that on a daily basis rather than wait a few months and try it again — and it's very costly."

The cost of 3-D printing itself is going down, with many printers becoming accessible to people beyond engineers and designers. Makerbots, the industry's leading desktop printers, sell for $2,199 a pop. The printer looks like a small, futuristic microwave that prints using its version of "ink," a spool of plastic that feeds into the machine.

New materials are also being experimented with, such as nylon and wood.

3-D printing "is on the downside of the hype cycle but on the rise as far as usability," Harrington said. "It's been on the market forever, but on the consumer level, really the last five years."

A longtime player in the printing industry, the Palo Alto Research Center, located in the Stanford Research Park, is also experimenting with 3-D printing. PARC's focus is printed electronics. Just as regular printers use ink in different colors, PARC uses chemically synthesized ink to print semi-conducting materials with different functions, such as circuit boards or sensors. One recent project, born out of a request from the U.S. Army, culminated in the creation of a "smart" label printed with memory and sensors that can process information about what happens to a soldier in the field.

Janos Veres, who manages PARC's printed electronics team, is excited about adding intelligence and functionality to products. It's a chance not only to reinvent a dying printing industry but to increase innovation.

"When you think about it like that, the potential of this is way beyond being able to make just a smart label. ... You look back at the early days of computing, (when) people weren't exactly sure what computers could do for you. Is it really going to go in your mobile phone? Is it really going to go into your eyeware? And now it has."

It's the same thing with 3-D printing, Veres said.

"Will this technology literally come to your desktop? ... Will it go and help people who are in the printing industry do something way more complex? That's the thing: All of those are possibilities."

Another group of researchers exploring 3-D printing potential is at the Stanford Center for Computer Research in Music Acoustics (CCRMA), an interdisciplinary institute where composers and researchers collaborate on the latest in music technology. 3-D printers there are being used to create customized wind instruments, such as flutes.

With wind instruments, the resonator — the element that creates sound — is the air itself, so the material is less important than it would be for instruments in which the material itself vibrates to create sound.

John Granzow, a doctoral candidate and teaching assistant in Stanford's Department of Music and CCRMA colloquium coordinator, has been building instruments for years the traditional way. When he started researching auditory perception at Stanford about two years ago, a professor prompted him to find out if they had access to 3-D printers on campus. They did and soon began experimenting with printing instruments and devices to test and explore acoustics.

In August, Granzow is co-leading a workshop titled "3-D Printing for Acoustics," a collaboration between CCRMA and Stanford's Product Realization Lab. The workshop is the first of its kind at CCRMA. Students will model instruments on CAD, either modifying 3-D scans of pre-existing objects or creating their own, Granzow said. At the end of the workshop, a composer will lead a concert using instruments printed by workshop participants.

"This is part of a phase in 3-D printing where a lot of peoples' concept projects are happening," Granzow said. "People are wondering: 'Can we print something that looks, sounds and feels like a real flute even if doesn't last or suffers from some quality problems? Or can we print a real acoustic guitar, like Scott Summit did?'"

It turns out they can, and Granzow has. But he said he and his colleagues are more interested in the experimental side of 3-D printing.

"We don't want to replicate necessarily nearly perfected instruments. We would rather use the tool for what it's good for: producing geometries that are very different and have yet to be seen and seeing how they resonate in certain ways. Or more simply, using it as a tool to test acoustic predictions with geometry."

Granzow said that 3-D printing also allows for a re-imagining of instruments' structures, combining tradition with high-tech.

For example, one could design a printed guitar bridge (the piece that the strings are attached to), which are traditionally made out of bone. Or, a kalimba, also known as a thumb piano, which can fit in a person's hands and has historically been made out of wood or bamboo, could be made with a printed body and bamboo tines, which are plucked to make sound.

From catheters to clarinets, being able to leverage 3-D printing to experiment and redesign overnight is nothing short of revolutionary — but it's still just the beginning, according to the researchers.

Wang and Caves said they are far from achieving the possibilities within their field — tailoring parts to individual patients, printing a model of a specific patient's heart or implanting printed devices in patients. They currently use CT scans, which are layered and then reproduced by the printer. Wang called the process "still relatively labor-intensive."

"When that becomes a lot simpler, more straightforward, then we can look at the whole range of different disorders, heart sizes, body sizes, everything," Wang said. "That's definitely the promise, and I'm totally convinced that we'll be able to do it."