Researchers have demonstrated the ability to 3D print objects that can then change shape, even folding and unfolding, when heated through an electrical current or with ambient air temperature.

The scientists, with the Lawrence Livermore National Laboratory (LLNL) in California, used what they described as "smart ink" made from soybean oil along with polymers and carbon nanofibers, which they were able to "program" into a temporary shape at an engineered temperature that was determined by the chemical composition.

The technology, the researchers said, could have applications in healthcare, in aerospace for solar arrays or antennae that can unfold, and for flexible circuits and robotic devices.

Photos by Julie Russell/LLNL Lawrence Livermore National Laboratory researchers have successfully demonstrated the 3D printing of shape-shifting structures that can fold or unfold to reshape themselves when exposed to heat or electricity. Here, researchers Jennifer Rodriguez and Jim Lewicki examine a stent that can expand when exposed to heat.

The process of creating objects via 3D printing that can shift shape on their own is also known as 4D printing in the additive manufacturing industry.

Originally, "4D printing" referred to 3D printed objects that used "smart materials" that could then self-assemble. Now, the term covers 3D printed objects that can change shape and conform to their environment.

For example, a biomedical splint that can correct medical conditions and can change shape over time as a child grows is just one example of how 4D printing has been put to use in recent years.

Photos by Julie Russell/LLNL. Through a direct-ink writing 3D printing process, Lawrence Livermore National Laboratory researchers produced several types of structures, including a stent that expanded after being exposed to heat.

The researchers with LLNL, however, said their version of 4D printing is unique in that it is the first to combine the process of 3D printing and subsequent folding (via origami methods) with conductive smart materials to build complex structures.

The research, published in the journal Scientific Reports, demonstrated a 4D material capable of creating boxes, spirals and spheres from shape memory polymers (SMPs) that can change shape when resistively heated or when exposed to the "appropriate temperature."

"It's like baking a cake," Jennifer Rodriguez, the paper's lead author and a post-doctoral reseracher in LLNL's Materials Engineering Division, stated in a news release. "You take the part out of the oven before it's done and set the permanent structure of the part by folding or twisting after an initial gelling of the polymer."

The researchers envision the new material creating extremely complex parts.

Using 3D printed smart ink, the researchers were able to produce several types of structures, including a bent conductive device that morphed to a straight one when exposed to an electric current or heat, a collapsed stent that expanded after being exposed to heat, and boxes that either opened or closed when heated.

"We have these materials with 3D structures but they have extra smart properties; they can retain a memory of the previous structure," LLNL staff scientist James Lewicki said. "It opens up a whole new property set. If you can print with these polymer composites you can build things and electrically activate them to unfold. Instead of a dumb lump, you are left with this sentient, responsive material."