3D-printed structures that ‘remember’ original shapes

In this series, a 3-D printed multimaterial shape-memory minigripper, consisting of shape-memory hinges and adaptive touching tips, grasps a cap screw. Credit: Qi (Kevin) Ge

A team of engineers has used light to print 3D structures that “remember” their original shapes even after being stretched, twisted and bent at extreme angles

The structures — from small coils to an inch-tall replica of the Eiffel Tower — sprang back to their original forms within seconds of being heated to a certain temperature “sweet spot,” said the team from Massachusetts Institute of Technology (MIT) and Singapore University of Technology and Design (SUTD).

For some structures, the researchers were able to print micron-scale features as small as the diameter of a human hair.

According to Nicholas X Fang, associate professor of mechanical engineering at MIT, shape-memory polymers can be useful for soft actuators that turn solar panels toward the Sun to tiny drug capsules that open upon early signs of infection.

“We ultimately want to use body temperature as a trigger. If we can design these polymers properly, we may be able to form a drug delivery device that will only release medicine at the sign of a fever,” said Fang.

The material can bounce back to its original printed form, within a specific temperature range — in this case, between 40 and 180 degrees Celsius.

The team printed a variety of structures, including coils, flowers and the miniature Eiffel Tower.

According to Qi “Kevin” Ge, assistant professor at SUTD, the process of 3D printing shape-memory materials can also be thought of as 4-D printing, as the structures are designed to change over the fourth dimension — time.

“Our method not only enables 4-D printing at the micron-scale, but also suggests recipes to print shape-memory polymers that can be stretched 10 times larger than those printed by commercial 3-D printers,” Ge noted in a paper published in the journal Scientific Reports.

The team hopes to find combinations of polymers to make shape-memory materials that react to slightly lower temperatures to design soft, active and controllable drug delivery capsules.

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