First shape-changing 3D printed objects

Posted Jun 15, 2017 by Karen Hardison
3D printing creates objects that compress and expand according to programmed heat changes. Tensional integrity forms bridges and domes on Earth and may form 3D compressible "tensegrity" structures in space or in soft robots.
Glaucio Paulino  a professor in Georgia Tech’s School of Civil and Environmental Engineering  and...
Glaucio Paulino, a professor in Georgia Tech’s School of Civil and Environmental Engineering, and Jerry Qi, a professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech, hold objects 3-D printed that use tensegrity, a structural system of floating rods in compression and cables in continuous tension.
(Credit: Rob Felt)
Using 3D printed struts and cables, the first 3D printed objects that can compress to compact size and expand to full size have been created. This breakthrough has implications for large structures that can be transported to outer space in a compressed state and expanded, by programmed heat memory in "shape memory polymers," to full size and functional capacity. Outer space exploration is one objective considered for these "extremely light weight" yet "very strong" new tensegrity objects, as reported by researchers at Georgia Institute of Technology (Georgia Tech).
Georgia Tech researchers 3-D printed an object made with tensegrity  a structural system of floating...
Georgia Tech researchers 3-D printed an object made with tensegrity, a structural system of floating rods in compression and cables in continuous tension.
(Credit: Rob Felt)
Shape memory polymers used in 3D printing of these new tensegrity objects are programmed to respond to specific temperatures. In the objects printed by the Georgia Tech research team, including Professors Glaucio Paulino and Jerry Qi, the shape memory polymers were programmed to 65 degrees Celsius (slightly above the glass transition temperature of 60 degrees Celsius). The cool-down temperature was programmed to 10 degrees Celsius, as explained in the team's report.
When the struts of the object were heated to 65 degrees Celsius, the team compressed the object into what resembled a W shape. Cooled to 10 degrees Celsius, the shape memory acrylate-based photopolymer held its shape. The cables, which form "a continuous network" and are printed from "stretchable elastomeric filament," are attached to the struts while in their W shape, as reported in the Nature journal, Scientific Reports. When the object is reheated to the programmed heat of 65 degrees Celsius, the W shaped object expands to form a tensegrity structure that is compressible, strong, lightweight and transportable.
Struts and Cables
The 3D printed objects are built of struts and cables. The struts give the shape and the cables give the unity, or, they give the "topography" and "geometry" of the tensegrity object. The struts are assembled first and have "arrowheads" that join with holes on the cables. The cables are attached after the struts have been compressed, through heating, to their cooled shape. The stretchability of the elastomeric filament cables allows for stability in the deployed tensegrity structure once it is expanded.
As described in Scientific Reports, the deployment occurs when the struts and cables "assemblage is thrown into a tank of hot water at ~65 °C. As the struts recover their original straight shapes, cables are stretched and self-stresses grow within the system. This renders 'life' to our tensegrity, i.e. it stands up, to reach its designated geometry, resulting in a giant configurational change...."
Kurilpa Bridge in Brisbane  Australia  at night  April 2010.
Kurilpa Bridge in Brisbane, Australia, at night, April 2010.
Tensional Integrity "Tensegrity" Concepts on Earth
The concept of tensional integrity, or tensegrity, has for many years been employed on Earth creating such flexible yet strong structures such as the Kurilpa pedestrian bridge in Brisbane, Australia, and the domed stadium roof of the Olympic Gymnastics Arena in Seoul, South Korea (and the Georgia Dome Stadium of Atlanta, which is scheduled for implosion in late 2017 as the Mercedes-Benz Stadium will replace it). Georgia Tech's research team suggests outer space structures such as antennas might be created as 3D printed tensegrity structures. They even foresee an application for "shape-change soft robots."