Nav: Home

'Peel-and-go' printable structures fold themselves

September 13, 2017

As 3-D printing has become a mainstream technology, industry and academic researchers have been investigating printable structures that will fold themselves into useful three-dimensional shapes when heated or immersed in water.

In a paper appearing in the American Chemical Society's journal Applied Materials and Interfaces, researchers from MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) and colleagues report something new: a printable structure that begins to fold itself up as soon as it's peeled off the printing platform.

One of the big advantages of devices that self-fold without any outside stimulus, the researchers say, is that they can involve a wider range of materials and more delicate structures.

"If you want to add printed electronics, you're generally going to be using some organic materials, because a majority of printed electronics rely on them," says Subramanian Sundaram, an MIT graduate student in electrical engineering and computer science and first author on the paper. "These materials are often very, very sensitive to moisture and temperature. So if you have these electronics and parts, and you want to initiate folds in them, you wouldn't want to dunk them in water or heat them, because then your electronics are going to degrade."

To illustrate this idea, the researchers built a prototype self-folding printable device that includes electrical leads and a polymer "pixel" that changes from transparent to opaque when a voltage is applied to it. The device, which is a variation on the "printable goldbug" that Sundaram and his colleagues announced earlier this year, starts out looking something like the letter "H." But each of the legs of the H folds itself in two different directions, producing a tabletop shape.

The researchers also built several different versions of the same basic hinge design, which show that they can control the precise angle at which a joint folds. In tests, they forcibly straightened the hinges by attaching them to a weight, but when the weight was removed, the hinges resumed their original folds.

In the short term, the technique could enable the custom manufacture of sensors, displays, or antennas whose functionality depends on their three-dimensional shape. Longer term, the researchers envision the possibility of printable robots.

Sundaram is joined on the paper by his advisor, Wojciech Matusik, an associate professor of electrical engineering and computer science (EECS) at MIT; Marc Baldo, also an associate professor of EECS, who specializes in organic electronics; David Kim, a technical assistant in Matusik's Computational Fabrication Group; and Ryan Hayward, a professor of polymer science and engineering at the University of Massachusetts at Amherst.

Stress relief

The key to the researchers' design is a new printer-ink material that expands after it solidifies, which is unusual. Most printer-ink materials contract slightly as they solidify, a technical limitation that designers frequently have to work around.

Printed devices are built up in layers, and in their prototypes the MIT researchers deposit their expanding material at precise locations in either the top or bottom few layers. The bottom layer adheres slightly to the printer platform, and that adhesion is enough to hold the device flat as the layers are built up. But as soon as the finished device is peeled off the platform, the joints made from the new material begin to expand, bending the device in the opposite direction.

Like many technological breakthroughs, the CSAIL researchers' discovery of the material was an accident. Most of the printer materials used by Matusik's Computational Fabrication Group are combinations of polymers, long molecules that consist of chainlike repetitions of single molecular components, or monomers. Mixing these components is one method for creating printer inks with specific physical properties.

While trying to develop an ink that yielded more flexible printed components, the CSAIL researchers inadvertently hit upon one that expanded slightly after it hardened. They immediately recognized the potential utility of expanding polymers and began experimenting with modifications of the mixture, until they arrived at a recipe that let them build joints that would expand enough to fold a printed device in half.

Whys and wherefores

Hayward's contribution to the paper was to help the MIT team explain the material's expansion. The ink that produces the most forceful expansion includes several long molecular chains and one much shorter chain, made up of the monomer isooctyl acrylate. When a layer of the ink is exposed to ultraviolet light -- or "cured," a process commonly used in 3-D printing to harden materials deposited as liquids -- the long chains connect to each other, producing a rigid thicket of tangled molecules.

When another layer of the material is deposited on top of the first, the small chains of isooctyl acrylate in the top, liquid layer sink down into the lower, more rigid layer. There, they interact with the longer chains to exert an expansive force, which the adhesion to the printing platform temporarily resists.

The researchers hope that a better theoretical understanding of the reason for the material's expansion will enable them to design material tailored to specific applications -- including materials that resist the 1-3 percent contraction typical of many printed polymers after curing.

-end-

Additional background

PAPER: 3D-printed self-folding electronics http://web.mit.edu/subras/www/ACS_AMI_17.pdf

ARCHIVE: Toward printable, sensor-laden "skin" for robots http://news.mit.edu/2017/goldbug-beetle-printable-sensor-laden-skin-robots-0323

ARCHIVE: Customizing 3-D printing http://news.mit.edu/2015/customizing-3-d-printing-0903

ARCHIVE: "MultiFab" 3-D prints a record 10 materials at once, no assembly required http://news.mit.edu/2015/multifab-3-d-print-10-materials-0824

ARCHIVE: Bake your own robot http://news.mit.edu/2014/bake-your-own-robot-0530

Massachusetts Institute of Technology

Related Polymer Articles:

World first: New polymer goes for a walk when illuminated
Scientists have developed a new material that can undulate and therefore propel itself forward under the influence of light.
Polymer-coated silicon nanosheets -- an alternative to graphene
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene.
New polymer additive could revolutionize plastics recycling
Only 2 percent of the 78 million tons of manufactured plastics are currently recycled into similar products because polyethylene (PE) and polypropylene (PP), which account for two-thirds of the world's plastics, have different chemical structures and cannot be efficiently repurposed together.
Responsive filtration membranes by polymer self-assembly
Polymer self-assembly is a crucial tool for manufacturing membranes using scalable methods, enabling easier commercialization.
Biodegradable polymer coating for implants
Medical implants often carry surface substrates that release active substances or to which biomolecules or cells can adhere better.
Praise for polymer science
Engineer Glenn Fredrickson receives the William H. Walker Award for Excellence in Contributions to Chemical Engineering Literature.
When it comes to polymer fragility, size does matter
By combining a number of tools and techniques, a team of researchers from the US, Italy and China was able to find a more complete picture of the glass transition phenomenon in polymers and to point out where the polymers differ from small molecular liquids.
Better, stronger: Polymer breakthrough to improve things we use everyday
Medicine, mobile phones, computers and clothes could all be enhanced using the process for making paint, according to research by the University of Warwick.
CWRU researcher scaling up knotty polymer research
Researchers at Case Western Reserve University developed a technique that produces a long chain molecule in the shape of a trefoil knot.
New 3-D printed polymer can convert methane to methanol
Lawrence Livermore National Laboratory scientists have combined biology and 3-D printing to create the first reactor that can continuously produce methanol from methane at room temperature and pressure.

Best Science Podcasts 2017

We have hand picked the best science podcasts for 2017. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: Radiolab

Oliver Sipple
One morning, Oliver Sipple went out for a walk. A couple hours later, to his own surprise, he saved the life of the President of the United States. But in the days that followed, Sipple's split-second act of heroism turned into a rationale for making his personal life into political opportunity. What happens next makes us wonder what a moment, or a movement, or a whole society can demand of one person. And how much is too much?  Through newly unearthed archival tape, we hear Sipple himself grapple with some of the most vexing topics of his day and ours - privacy, identity, the freedom of the press - not to mention the bonds of family and friendship.  Reported by Latif Nasser and Tracie Hunte. Produced by Matt Kielty, Annie McEwen, Latif Nasser and Tracie Hunte. Special thanks to Jerry Pritikin, Michael Yamashita, Stan Smith, Duffy Jennings; Ann Dolan, Megan Filly and Ginale Harris at the Superior Court of San Francisco; Leah Gracik, Karyn Hunt, Jesse Hamlin, The San Francisco Bay Area Television Archive, Mike Amico, Jennifer Vanasco and Joey Plaster. Support Radiolab today at Radiolab.org/donate.
Now Playing: TED Radio Hour

Future Consequences
From data collection to gene editing to AI, what we once considered science fiction is now becoming reality. This hour, TED speakers explore the future consequences of our present actions. Guests include designer Anab Jain, futurist Juan Enriquez, biologist Paul Knoepfler, and neuroscientist and philosopher Sam Harris.