Research from the Engineering Design and Computing Laboratory at ETH Zurich in Switzerland, demonstrates multimaterial 4D printing of tetrahedrons. The shapes are initially 3D printed to be flat, but when heat is applied the tetrahedrons move to assemble a predefined structure.

4D tetrahedron assembly when heat is applied. Clip via Engineering Design and Computing Laboratory on YouTube

The 4D printing revolution 

The term 4D printing was first coined by MIT research Skylar Tibbits in a TED Talk about the method. It can be defined simply as design that uses 3D printing to create structures capable of taking on another permanent form when conditions such as heat, or moisture are applied.

Other research in the field includes the use of composite materials for a direct 4D printing approach, and SLA 3D printing of a net that forms a bucky ball in 65 ̊C water.

Challenges to heat activated assembly

In the ETH Zurich study, researchers first examined areas of improvement in a previous method of 4D printed structures. The desired features for the tetrahedron were then identified as “predictable reversibility”, “defined load bearing capability” and an ability to be precisely controlled.

Realization of these features is achieved by taking advantage of bistable actuators – small mechanical systems that have two “stable”, i.e. firm, positions. These are based on the geometric shape of a Von Mises Truss, i.e. two bars attached to a central moving member by a pin axis.

The two positions of a 3D printed Von Mises Truss actuator as used in the ETH Zurich study. Shows the actuator open (right) and closed (left). Figure via Chen, Mueller & Shea

The two positions of a 3D printed Von Mises Truss actuator as used in the ETH Zurich study. Shows the actuator open (right) and closed (left). Note the four moving bars connected by pins to the central figure. Image via Chen, Mueller & Shea

By linking these actuators together, the researchers make a tetrahedron shape, that rises in warm water.

Afterwards the actuators are reconfigured to propose multiple dome shapes. These are activate and deactivated by sliding the actuators open and closed.

Extended actuators making a dome. Clip via “Deployment and simulation of a multistable dome” by Engineering Design and Computing Laboratory on YouTube.

The researchers also demonstrate how these tetrahedral structures can support weight.

A tetrahedral configuration supporting the weight of a camera lens cap. Clip via “Deployment and simulation of a multistable dome” by Engineering Design and Computing Laboratory on YouTube.

Possible uses of such systems are clear in equipment applications. For example, if scaled up, the configuration could create self-assembling shelters, stands, or even scaffolding – flat packed for transport, but 3D dimensional when needed.

Further work

On open article on this research is published online in Nature’s Scientific Reports journal as Integrated Design and Simulation of Tunable, Multi-State Structures Fabricated Monolithically with Multi-Material 3D Printing. It is co-authored by Tian Chen, Jochen Mueller and Kristina Shea.

Future work, as stated in the conclusion, “includes developing computational design methods to explore the design space and optimise active structures.”

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Featured image: 4D printed, self-assembling tetrahedron from ETH Zurich. Image courtesy of Tian Chen

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