Now, a material that can fold from full 3D to flat by itself

What if there was a house that could fit in a backpack or a wall that could become a window with the flick of a switch? A new material could actually make this possible.

Harvard researchers 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.

"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 first author Johannes T. B. Overvelde.

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, that the cube can be deformed into many different shapes by folding certain edges, which act like hinges. The team embedded pneumatic actuators into the structure, which can be programmed to deform specific hinges, changing the cube's shape and size, and removing the need for external input.

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 not only understand how the material deforms, but also have an actuation approach that harnesses this understanding," said lead researcher Katia Bertoldi. "We know exactly what we need to actuate in order to get the shape we want."

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

It is described in Nature Communications.