Research is being performed in adding a fourth dimension to 3D printers — the dimension of time. This technique, called 4D printing, creates moveable and shape-variable objects, such as flat components, that can be folded into three-dimensional objects at a later point, or even objects that can change their shape as a function of external influences.

This object is printed flat (left) and can later be altered in two stable and load-bearing forms (middle and right). (ETH Zurich/Tian Chen)

A construction principle has been developed that enables control of the deformation. The flat structures produced do not change their configuration randomly, but rather exactly in the way they are designed. The structures can also support weight, enabling load-bearing, 4D-printed objects.

The structural principle depends on an actuating element taking on two possible states: retracted or extended. These elements were combined to create more complex structures. As the individual elements can assume only one of the two states, the stable three-dimensional form of the overall structure can be predicted.

The structures were created with a multi-material 3D printer that can print objects from up to 40 different materials. A rigid polymer was used for most of the structure, and an elastic polymer for the moving parts. All parts were made in a single step.

Printing a flat initial form with rigid and elastic sections in a single step is highly efficient; the flat structure saves space in transport, and can then be deployed at the final destination. Similar approaches have been used in aerospace for quite some time; for example, to transport structures into space in a compressed, space-saving state.

In addition to aerospace, other possible applications of 4D printing include the simple construction of ventilation systems, systems for opening and closing valves, or medical applications such as stents.

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