Despite being bent, twisted or stretched at extreme angles, special three-dimensional (3D) structures being manipulated by an international team of scientists can still "remember" their original shapes.

In a new research, engineers from the Massachusetts Institute of Technology (MIT) and the Singapore University of Technology and Design (SUTD) use light to print these special 3D structures and turn them into small coils to an inch-replica of France's Eiffel Tower.

Within seconds of being heated to a specific temperature, the 3D-printed structures sprang back to their original forms, researchers found.

Memory-Shape Polymers

Polymers that can remember their original shape can stretch and deform based on external stimuli such as light, electricity and heat. These materials can switch between a low-temperature, amorphous state to a rubbery, high-temperature state.

For some of the objects, MIT and SUTD scientists successfully printed micron-scale features that were as tiny as the diameter of human hair. These are dimensions one-tenth as big as what other experts have achieved with memory-shape materials.

Qi “Kevin” Ge, co-author of the research and an assistant professor at SUTD, says the process of printing 3D memory-shape materials can be thought of as 4D printing because the structures are intended to change over the fourth dimension - time.

Ge and colleagues pioneered a method called microstereolithography to print memory-shape polymers in great detail. This process allows engineers to use projector light to print patterns on a series of layers of resin.

Nicholas Fang, lead author of the study and an engineering associate professor at MIT, says it's like they're printing light "layer by layer."

He compares the process to how dentists produce replicas of teeth to fill cavities. The difference is that researchers are doing it with high-quality lenses from the semiconductor industry for intricate parts.

Practical Applications

Ge believes that developing memory-shape polymers that stretch 10 times bigger than commercial 3D printers will advance 4D printing in a wide range of applications.

Fang agrees. He says such memory-shape structures that can morph in response to a certain temperature can be useful for a variety of applications.

These include advancement in biomedical devices, the development of tiny drug capsules that open up early stages of infection, deployable aerospace structures, and soft actuators that shift solar panels toward the sun.

If scientists can design the memory-shape polymers properly, they may be able to produce a drug delivery service that can release medicine at the sign of a fever, he says.

“We ultimately want to use body temperature as a trigger,” says Fang.

Details of the new research were published in the journal Scientific Reports.

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