The shape of tomorrow: Reprogrammable materials

Material scientists at Harvard University have created structures that can change shape and behaviour on demand. Frances Marcellin looks at how the findings could impact on building design.

What if house could fold up into a weekend bag, or a wall could transform into a window? While these might seem like architectural design fantasies, a new structure for materials, inspired by the origami technique “snapology”, means that these previously unimaginable ideas could become reality in the future.

This new structure has been developed by a group of researchers from Harvard. It can be applied to a range of different materials, from cardboard to steel, which then allows the materials to change size, volume and shape. The structure is so durable and strong that it is able to withstand the weight of an elephant when folded, and then return back to its original shape ready for the next transformation.

From foldable structures to shape-shifting materials

“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,” explains Johannes Overvelde, a Harvard graduate and one of the researchers on the project.

Overvelde is now Scientific Group Leader of the Soft Robotic Matter group at AMOLF, one of the research laboratories of the Netherlands Organisation for Scientific Research (NWO).

During several years of research, Overvelde and a team of three other researchers, discovered that space-filling assemblies of polyhedra can be used as a template for the design of reconfigurable, thin-walled structures that consist of rigid plates connected by flexible hinges. A report detailing the research was published in Nature in January 2017.

The cutting-edge of design

Chuck Hoberman, Pierce Anderson Lecturer in Design Engineering from the Harvard University Graduate School of Design is renowned for skilfully fusing the worlds of art, architecture and engineering in his work. He is most famous for inventing the Hoberman Sphere in the nineties, an isokinetic structure that can expand and contract to a fraction of its size due to its scissor-like folding mechanism.

It was Hoberman’s original designs for a “family of foldable structures”, which included a prototype of an extruded cube, which kick-started the research back in 2014.

"We realised that these simple geometries could be used as building blocks to form a new class of reconfigurable metamaterials."

“We were amazed by how easily it could fold and change shape,” says Katia Bertoldi, John L Loeb Associate Professor of the Natural Sciences at the Harvard John A Paulson School of Engineering and Applied Sciences (SEAS). “We realised that these simple geometries could be used as building blocks to form a new class of reconfigurable metamaterials, but it took us a long time to identify a robust design strategy to achieve this.”

During the research, the structures were made from extruded cubes, with 24 faces and 36 edges, which change shape by folding certain edges, and act like hinges. The team then programmed actuators, which were embedded in the structure to deform certain hinges, so that the size and shape of the structure could be changed without the need for any further external input.

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

Nanoscale, metre-scale and everywhere in between

By using computational modelling, the team were able to quantify all the different ways the material could bend and how that affected functionality, such as stiffness. It allowed them to scan close to a million different designs, and select those with the preferred response.

“By combining design and computational modelling, we were able to identify a wide range of different deformations and rearrangements and create a blueprint or DNA for building these materials in the future,” says Overvelde.

While the prototypes were created from laser-cut cardboard and double-sided tape, and were also 3D printed with a multi-material printer, Overvelde says that other materials can be used.

"In principle all materials can be used to fabricate the samples."

“In principle all materials can be used to fabricate the samples, however some care has to be taken with materials such as concrete and steel, to make sure that the materials locally don’t undergo permanent deformation like fracture or plasticity,” he says. “Other than that the specific reconfigurability doesn’t depend on the materials that have been used.”

He explains how they fabricated larger-scale samples, on an architectural scale, using steels and hinges for Hoberman’s recent exhibit 10 degrees. Held at Le Laboratoire in Cambridge, Massachusetts, the exhibition presented four kinetic sculptures (with one, two, three and four degrees of mobility) that could be transformed by “hands-on play” by visitors.

“This research demonstrates a new class of foldable materials that is also completely scalable,” says Overvelde, adding that 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.

A toolkit for building reconfigurable materials

Although still in the early stages, the possibilities for potential usage are endless. A formalised design framework such as this could benefit a wide range of professions, including aerospace engineers, material scientists, physicists, robotic engineers, biomedical engineers, designers and architects.

Final costs will depend largely on the scale of final designs and the type of material used, but Overvelde says a step needs to be taken to make fabrication more efficient. “I believe we could benefit from input from architects and designers,” he says.

Those interested in applying this structural system to materials for design work should start off by making a paper prototype. “It is hard to really understand what these structures can do,” says Overvelde, “you need to play with them – I have some tutorials on my website.”

Hoberman believes that the structural system has “fascinating implications for dynamic architecture”, including portable shelters, adaptive building facades and retractable roofs.

“This technology offers unique advantages, such as how it integrates surface and structure, its inherent simplicity of manufacture, and its ability to fold flat,” he says, adding that the framework they have discovered is like a toolkit to build reconfigurable materials.

“These building blocks and design space are incredibly rich, and we’ve only begun to explore all the things you can build with them.”