It can only do that because its actuation mechanisms are at the micron scale.” “For example, a flower can release pollen in milliseconds. “The reality is that, if you’re able to make it to much smaller dimensions, these materials can actually respond very quickly, within seconds,” Fang says. Fang says this size restriction also limits how fast the material can recover its original shape. However, using conventional 3-D printers, researchers have only been able to design structures with details no smaller than a few millimeters. To fabricate shape-memory structures, some researchers have looked to 3-D printing, as the technology allows them to custom-design structures with relatively fine detail. The bent and stretched shapes can be “frozen” at room temperature, and when heated the materials will “remember” and snap back to their original sturdy form. Shape-memory polymers are particularly intriguing: These materials can switch between two states - a harder, low-temperature, amorphous state, and a soft, high-temperature, rubbery state. These new and emerging materials, which include shape-memory polymers, can stretch and deform dramatically in response to environmental stimuli such as heat, light, and electricity - properties that researchers have been investigating for use in biomedical devices, soft robotics, wearable sensors, and artificial muscles. “This will advance 4-D printing into a wide variety of practical applications, including biomedical devices, deployable aerospace structures, and shape-changing photovoltaic solar cells.”įang and others have been exploring the use of soft, active materials as reliable, pliable tools. “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 says. Ge says the process of 3-D 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. “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.”įang’s coauthors include former MIT-SUTD research fellow Qi “Kevin” Ge, now an assistant professor at SUTD former MIT research associate Howon Lee, now an assistant professor at Rutgers University and others from SUTD and Georgia Institute of Technology. “We ultimately want to use body temperature as a trigger,” Fang says. Fang, associate professor of mechanical engineering at MIT, says shape-memory polymers that can predictably morph in response to temperature can be useful for a number of applications, from soft actuators that turn solar panels toward the sun, to tiny drug capsules that open upon early signs of infection. The team’s results were published earlier this month in the online journal Scientific Reports. Even after being stretched, twisted, and bent at extreme angles, the structures - from small coils and multimaterial flowers, 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.”įor some structures, the researchers were able to print micron-scale features as small as the diameter of a human hair - dimensions that are at least one-tenth as big as what others have been able to achieve with printable shape-memory materials. Engineers from MIT and Singapore University of Technology and Design (SUTD) are using light to print three-dimensional structures that “remember” their original shapes.
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