Mimic termites to generate new materials

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Inspired by how termites build their nests, Caltech researchers have developed a framework for designing new materials that mimic fundamental rules hidden in nature’s growth patterns. The researchers showed that by using these rules, it is possible to create materials designed with specific programmable properties.

The researchled by Chiara Daraio, G. Bradford Jones Professor of Mechanical Engineering and Applied Physics and Heritage Medical Research Institute Investigator, was published in the journal Science.

“Termites are only a few millimeters long, but their nests can reach 4 meters high, the equivalent of a human building a house at the height of Mount Whitney in California,” Daraio explains. If you look inside a termite mound, you will see a network of asymmetrical, interconnected structures, like the inside of a loaf of bread or a sponge. Made up of grains of sand, dust, dirt, saliva, and dung, this messy, irregular structure seems arbitrary, but a termite mound is specifically optimized for stability and ventilation.

“We thought that by understanding how a termite contributes to nest building, we could define simple rules for designing architectural materials with unique mechanical properties,” says Daraio. Architected materials are foam-like or composite solids that comprise the building blocks that are then organized into 3D structures, from the nanoscale to the microscale. So far, the field of architected materials has mainly focused on periodic architectures – these architectures contain a unit cell with uniform geometry, such as an octahedron or a cube, and then these unit cells are repeated to form a lattice structure. However, focusing on orderly structures limited functionality and the use of architectural materials.

“Periodic architectures are convenient for us engineers because we can make assumptions in analyzing their properties. However, if we think about applications, they are not necessarily the optimal design choice,” says Daraio. Disordered structures, like that of a termite mound, are more common in nature than periodic structures and often exhibit superior functionality, but until now engineers had not found a reliable way to design them.

“We first approached the problem by thinking about the limited number of resources a termite has,” says Daraio. When building its nest, a termite does not have a blueprint of the overall nest design; he can only make decisions on the basis of local rules. For example, a termite may use grains of sand it finds near its nest and assemble the grains following procedures learned from other termites. A round grain of sand can fit next to a half moon shape for added stability. These basic adjacency rules can be used to describe how to build a termite mound. “We created a numerical program for material design with similar rules that define how two blocks of different materials can adhere to each other,” she says.

This algorithm, which Daraio and his team dub the “virtual growth program”, simulates the natural growth of biological structures or the making of termite nests. Instead of a grain of sand or a grain of dust, the virtual growth program uses unique material geometries, or building blocks, along with adjacency guidelines on how those building blocks can fit. attach to each other. The virtual blocks used in this initial work include an L-shape, an I-shape, a T-shape, and a +-shape. Additionally, the availability of each building block is assigned a set limit, alongside the limited resources a termite may encounter in the wild. Using these constraints, the program builds an architecture on a grid, then these architectures can be translated into 2D or 3D physical models.

“Our goal is to generate disordered geometries with properties defined by the combinatorial space of certain essential shapes, such as a straight line, a cross or an “L” shape. These geometries can then be 3D printed with a variety of different building blocks materials depending on application requirements,” says Daraio.

Reflecting the randomness of a termite mound, each geometry created by the virtual growth program is unique. Changing the availability of L-shaped building blocks, for example, results in a new set of structures. Daraio and his team experimented with virtual inputs to generate over 54,000 simulated architected samples; samples could be grouped into groups with different mechanical characteristics that could determine how a material deforms, its stiffness, or its density. By graphically representing the relationship between building block layout, resource availability, and resulting mechanical characteristics, Daraio and his team can analyze the rules underlying disordered structures. This represents a completely new framework for materials analysis and engineering.

“We want to understand the fundamental rules of material design so that we can then create materials that perform better than what we currently use in engineering,” says Daraio. “For example, we are considering the creation of materials that are lighter but also more resistant to breakage or better absorbing mechanical shocks and vibrations.”

The Virtual Growth Program explores the uncharted frontier of disordered materials by mimicking the way a termite builds its nest rather than replicating the configuration of the nest itself. “This research aims to control disorder in materials to improve mechanical and other functional properties using previously untapped design and analysis tools,” says Daraio.

– This press release was originally published on the California Institute of Technology website

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