Transforming materials

In collaboration with Harvard University, two TU Delft students have built a 3-D material with controllable shape and size.

Metamaterial made from extruded cubes (Photo: Bas Overvelde)
Metamaterial made from extruded cubes (Photo: Bas Overvelde)

Imagine a house that could fit in a backpack or a wall that could become a window with the flick of a switch.

PhD student Bas Overvelde MSc (Harvard University, 3mE graduate TU Delft 2012) and Twan de Jong MSc (Faculty of Aerospace Engineering) have designed a new type of foldable material that is versatile, tunable and self-actuated. It can change size, volume and shape; it can fold flat to withstand the weight of an elephant without breaking, and pop right back up to prepare for the next task.

The research was led by Katia Bertoldi, Professor of the Natural Sciences at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), James Weaver (Senior Research Scientist at the Wyss Institute for Biologically Inspired Engineering) and Chuck Hoberman, of the Harvard Graduate School of Design. Nature Communications published their article on March 11, 2016.

Foldable

Photo's: Bas Overvelde, animation JW
Photo's: Bas Overvelde, animation JW

"We've designed a three-dimensional, thin-walled structure that can be used to make foldable and reprogrammable objects of arbitrary architecture, whose shape, volume and stiffness can be dramatically altered and continuously tuned and controlled," said Overvelde, graduate student in Bertoldi's lab and first author of the paper.

The structure is inspired by an origami technique called 'snapology', and is made from extruded cubes with 24 faces and 36 edges. Like origami, the cube can be folded along its edges to change shape. The team demonstrated, both theoretically and experimentally by a centimeter-scale prototype, that the cube can be deformed into many different shapes by folding certain edges, which act as hinges. The team also embedded pneumatic actuators (inflatable cushions) that can deform certain hinges, changing the cube's shapes and size, without external application of force on the structure.

Scalable

Twan de Jong took a cube home (Photo: JW)
Twan de Jong took a cube home (Photo: JW)

The team connected 64 of these individual cells to create a 4x4x4 cube that can grow, and shrink, change its shape globally, change the orientation of its microstructure and fold completely flat. As the structure changes shape, it also changes stiffness — meaning one could make a material that's very pliable or very stiff using the same design. These actuated changes in material properties add a fourth dimension to the material. "We know exactly what we need to actuate in order to get the shape we want", said Bertoldi.

"This research demonstrates a new class of foldable materials that is also completely scalable," Overvelde said, "It works from the nano-scale to the meter-scale and could be used to make anything from surgical stents to portable pop-up domes for disaster relief."

Back home

"The material properties change enormously as the shape changes", said De Jong, who has returned to the Netherlands for his graduation on March 1st. "The volume changed at least by a factor 10 and the stiffness by a factor 100", he estimates.

Overvelde will also return to the Netherlands (in May) to start the Soft Robotic Matter Group at AMOLF, an Amsterdam-based research group that aims to 'design, fabricate and analyze materials with emergent behavior, that are capable of autonomously adapting to - and even harnessing - variations in their environment', as Overvelde explains. Previously, he worked with TU Delft students on the development of ballooning muscles that may be used in soft robotics.

--> Johannes T.B. Overvelde, Twan A. de Jong, et al., A three-dimensional actuated origami-inspired transformable metamaterial with multiple degrees of freedom, Nature Communications, March 11 2016, DOI: 10.1038/ncomms10929