Prof Shea and her group have taken this approach one step further by developing a construction principle that allows them to control the deformation.
“The flat structures we produce do not change their configuration randomly, but rather exactly in the way we design them,” said Tian Chen, a doctoral student in Prof Shea's group. The ETH scientists claim to be the first to create these 4D printed objects that can also bear a load.
The structural principle depends on an actuating element developed by the scientists to take on two possible states: retracted or extended. The researchers combined these elements to create more complex structures. As the individual elements can assume only one of the two specific states, the researchers can predict the stable three-dimensional form of the overall structure. This also allows structures that can take on several stable forms. And as the researchers have also developed simulation software, they can accurately predict the shapes and the force that must be applied to produce the deformation.
The objects created by the ETH scientists comprise a rigid polymer that makes up most of the structure and an elastic polymer for the moving parts. The researchers print all parts in a single step with a multi-material 3D printer.
“4D printing has several advantages,” explains Prof Shea. “Printing a flat initial form with rigid and elastic sections in a single step is highly efficient. It would be much more complex and time-consuming to produce the three-dimensional object or assemble it from separate components.”
The flat structure also saves space in transport and can be deployed at its final destination. Similar approaches have been used in aerospace for some time; for example, to transport structures into space in a compressed space-saving state.
As well as aerospace applications, the scientists are also considering the simple construction of ventilation systems, systems for opening and closing valves or medical applications, such as stents.
Currently, the scientists are reconfiguring these structures by hand, but are working on a drive for their elements that will extend the structures in reaction to temperature. They also say it might be possible to control the structures using pneumatic tubing or swelling materials that change shape depending on humidity.
