After 3D printing now comes 4D printing

July 21, 2021 // By Christoph Hammerschmidt
After 3D printing now comes 4D printing
Researchers have developed a process to produce movable, self-adapting material systems in a commercially available 3-D printer. The systems can undergo complex shape changes under the influence of moisture, contracting and expanding in a pre-programmed way. There is already talk of the advent of the fourth dimension in additive printing.

In their development, the scientists from the University of Freiburg and the University of Stuttgart (both Germany) took their cue from the movement mechanisms of a twining climbing plant, the air potato (dioscorea bulbifera). Using the method, the team produced the prototype of a forearm splint that adapts to the wearer and can be further developed for medical applications.

3D printing (aka additive manufacturing) has established itself as a manufacturing process for a wide range of applications. It can also be used to create intelligent materials and material systems that are movable after production and change their shape independently by means of an external stimulus such as light, temperature or humidity. This so-called 4-D printing, with which a shape change triggered by a stimulus can be specified, greatly expands the application potential of the systems. Such shape changes are made possible by the chemical composition of the materials, which consist of stimuli-responsive polymers. However, the printers and starting materials used to produce such materials have so far been highly specialised, expensive custom-made products.

But now - as a result of the research teams from Stuttgart and Freiburg - materials can be produced with commercially available 3-D printers that react to changes in humidity. They consist of a swelling and a stabilising layer. Due to their structure, these material systems can undergo changes in the shape of the entire system as well as individual parts. The researchers combined two reactive material systems and were thus able to realise a complex movement mechanism: A sinuous structure that tightens when pressure pockets are unfolded and that can release on its own when the pressure pockets collapse and the sinuous structure returns to an open state.

For the process, the scientists used a mechanism from nature: the air potato climbs up trees by itself applying pressure force against the stem of the host plant. To do this, the

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