Researchers 3D Print Shape-Changing Structures That Expand with Heat

“Tensegrity” is a term that refers to a structural system of floating rods in compression and cables in continuous tension. It combines the words “tensional integrity,” and has been used as the structural basis for several architectural projects such as the roofs of the Georgia Dome stadium and the Olympic Gymnastics Arena in Seoul, South Korea, as well as a large pedestrian bridge in Brisbane, Australia. It’s also the system that was used by a research team from the Georgia Institute of Technology to create 3D printed objects that significantly expand when heated.

As a child, I loved playing with those capsules that would turn into spongy animal shapes in hot water, and that’s what I’m reminded of watching the crumpled, flattened 3D printed objects suddenly spring into neat, much larger geometric 3D structures when submerged in hot water. The objects are made up of rods connected by cables, and the rods were 3D printed from a shape memory polymer that unfolds and expands when heated.

“Tensegrity structures are extremely lightweight while also being very strong,” said Glaucio Paulino, a professor in Georgia Tech’s School of Civil and Environmental Engineering. “That’s the reason there’s a heavy amount of interest right now in researching the use of tensegrity structures for outer space exploration. The goal is to find a way to deploy a large object that initially takes up little space.”

The research was documented in a paper entitled “Programmable Deployment of Tensegrity Structures by Stimulus-Responsive Polymers,” which you can access here. To allow the 3D printed struts to be folded flat, they were designed as a hollow shape with a narrow opening running the length of the tube. Each strut has an attachment point at each end to connect to the cables, which are also 3D printed. Once the structures were heated to 65°C, they expanded, and retained their expanded shapes after they were cooled.

“We believe that you could build something like an antenna that initially is compressed and takes up little space, but once it’s heated, say just from the heat of the sun, would fully expand,” said Jerry Qi, a professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech.

The researchers were able to control the rate of expansion by adjusting at which temperature each strut expands, allowing for structures with struts that expand sequentially instead of all at once.

“For bigger and more complicated structures, if you don’t control the sequence that these struts expand, it tangles and you have a mess,” Paulino said. “By controlling the temperature at which each strut expands, we can have a phased deployment and avoid this entanglement…These active tensegrity objects are very elegant in design and open up a range of possibilities for deployable 3-D structures.”

The technology, according to the researchers, could be used for applications in space exploration, biomedical devices, or for shape-changing soft robots. The research was supported by the National Science Foundation and the Air Force Office of Scientific Research. Authors of the paper include Ke Liu, Jiangtao Wu, Glaucio H. Paulino, and H. Jerry Qi. Discuss in the Shape-Changing Objects forum at 3DPB.com.

[Source: Georgia Institute of Technology / Images: Rob Felt]