“A house that could fit in a backpack or a wall that could become a window with the flick of a switch” are just two fantastical objects that could be made from a new self-folding metamaterial – according to its inventors at Harvard University in the US. Inspired by origami, the material will pop up and fold down on command, and can change both its shape and stiffness. Other possible applications for the new material include retractable roofs and medical implants.
The metamaterial was developed by a team led by Katia Bertoldi, James Weaver and Chuck Hoberman. It was inspired by “snapology”, which is a type of origami that uses modular units of folded paper to create larger objects. In the new approach, each unit cell is an extruded rhombus that has inflatable air pockets along three of its edges (see video). When an air pocket is pressurized, it causes an edge of the unit cell to try to fold flat. By pressurizing different combinations of pockets, the shape of the unit cell itself can be changed.
To create its metamaterial, the team combined 64 unit cells (each about 4 cm across) to make a large cubic structure. Control over the shape of the structure was achieved by dividing the air pockets into three subsets. Pockets in a subset are interconnected so that they can be activated using the same source of compressed air.
An important feature of the metamaterial is that its stiffness changes as it changes shape. As a result, the same metamaterial could have a number of different uses. While compressed air was used to activate their metamaterial, the researchers say thermal, electrical and hydraulic systems could also be used. Weaver adds that the control system could be integrated within the metamaterial, which could lead to the creation of “easily deployable transformable structures”.
“This structural system has fascinating implications for dynamic architecture, including portable shelters, adaptive building facades and retractable roofs,” says Hoberman. “Whereas current approaches to these applications rely on standard mechanics, this technology offers unique advantages such as how it integrates surface and structure, its inherent simplicity of manufacture, and its ability to fold flat.”
Team member Johannes Overvelde points out that the structure can be made over a range of sizes. “It works from the nanoscale to the metre-scale, and could be used to make anything from surgical stents to portable pop-up domes for disaster relief.”
The new metamaterial is described in Nature Communications.