Scientists have created shape-shifting '4D' printed objects that dramatically transform when heated. The objects are made from shape-memory plastics created using a 3D printer, but are labelled as 4D printed because they can change their shape after production. The researchers say that the morphing materials could be used for super light-weight structures needed for space exploration or even shape-change soft robots. The new objects use tensegrity, a structural system of compressed floating rods, known as struts, and cables in continuous tension. The researchers, from the Georgia Institute of Technology, made the struts from shape memory plastics that unfold when heated. 'Tensegrity structures are extremely lightweight while also being very strong,' study coauthor Professor Glaucio Paulino said. '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 researchers used 3D printers to create the struts that make up one of the primary components of the tensegrity structure. The researchers designed them to be hollow with a narrow opening that runs the length of the tube so that they can be temporarily folded flat. Each strut had an attachment point on each end to connect to a network of elastic cables, which were also made with 3-D printers. Once the struts were heated to 65°C (149°F), the researchers could partially flatten and fold them into a shape resembling the letter W. When cooled the structures permanently retained the temporary shape. The shape memory polymers enabled the researchers to fine-tune how quickly each strut expanded by adjusting at which temperature the expansion occurred. That enabled structures to be designed with struts that expand sequentially.