ADVERTISEMENT
2 /3 FREE ARTICLES LEFT THIS MONTH Remaining
Chemistry matters. Join us to get the news you need.

If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.

ENJOY UNLIMITED ACCES TO C&EN

Materials

Self-folding electronics take shape

A mechanically active ink causes flat, 3-D-printed electronic components to spontaneously fold

by Katherine Bourzac
September 11, 2017

Credit: Subramanian Sundaram/MIT
An electrochromic device that came out of a 3-D printer flat folds up its legs in a few minutes to assume this shape.

After being peeled from the platform of a three-dimensional printer, a flat electronic component begins to fold its four legs into position. In just a few minutes, it is fully formed and can stand. Researchers can now print self-folding electronic devices like this one thanks to a new polymer ink that builds up mechanical strain during the 3-D-printing process (ACS Appl. Mater. Interfaces 2017, DOI: 10.1021/acsami.7b10443).

Credit: Subramanian Sundaram/MIT
A device spontaneously begins to fold after being peeled from the platform of a 3-D printer.

Using 3-D printing allows engineers to make objects rapidly. But making electronic devices that have unusual 3-D shapes is quite challenging, says Subramanian Sundaram of Massachusetts Institute of Technology, who developed the new ink in collaboration with Ryan C. Hayward, a polymer scientist at the University of Massachusetts, Amherst.

Semiconductor inks must be printed on a flat surface or else they will dribble out of bounds and become smeary because of the runny solvents used to make them. Researchers typically print electronic devices flat, then reshape them into a 3-D form. Methods for reshaping these flat components include heating and bending, or using printable materials that expand in the presence of water or another solvent. But exposure to liquids and heat isn’t good for electronics, Sundaram says.

Credit: Subramanian Sundaram/MIT
A self-folding electrochromic device lights up when a voltage is applied.

He and his colleagues discovered their folding ink by accident while testing materials in their lab-built 3-D printer. Plastic parts usually shrink after they’re cured or solidified with ultraviolet light, but the researchers noticed that one of their inks did the opposite. “You could see it expand in front of your eyes,” Sundaram says.

The ink they developed is made up of long-chain and short-chain acrylic polymers. As the 3-D printer deposits layers of ink on top of one another, the short polymer chains from one layer migrate into the underlying, partially cured layer deposited earlier, like water soaking into a sponge. During that absorption, the ink layers swell, causing mechanical stress to build up within that polymer as it becomes rigid. The residual stress cannot be released until the printed piece is pried off the substrate.

To make a self-folding device, the researchers alternate layers of the folding ink with rigid polyacrylate. By controlling different parameters such as the ratio of long and short polymer chains in the ink, the intensity of the UV light, the temperature of the curing step, and the thickness of the ink layer, the researchers could program particular folds into a printed object and control the folding angles within a few degrees. As a proof of principle, the group made a self-folding four-legged electrochromic device, which changes color in response to an applied voltage.

“The idea of using mechanically active substrate materials to transform planar electronics into 3-D, curvilinear shapes is interesting,” says John A. Rogers, a materials scientist at Northwestern University. With further development, he says, researchers could use this method to make bio-inspired devices and medical devices.

Sundaram says they hope to use 3-D printing to build microsystems and robots that can assume complex shapes. To make that happen, they’re developing printable materials for moving parts.

X

Article:

This article has been sent to the following recipient:

Comments
John Rupkalvis (September 12, 2017 9:08 PM)

The fact that this ink expands, while most others contract during curing is potentially very important. This would indicate that by combining different printed layers using different inks on some layers than on others, different parts of the same object could be designed to "fold" in opposite directions, and by different amounts, thereby making the three-dimensional printing of some very complex components possible. With the additional combining of magnetic and/or electrically conductive ink layers, the possibilities are open to some very creative component engineering.
Min Han (September 13, 2017 11:40 PM)
This is an innovative and very important work. Just as Prof. Rogers said," the methodology of using mechanically active materials to transform flat electronics into 3D, curvelinear shapes is very intertesting", which may promote the future development of smart soft robotics and high-performance biomedical devices.

Leave A Comment

*Required to comment