Researchers at MIT and Northeastern University have developed a new class of “scale-rich network-based metamaterials” that use controlled disorder to improve impact resistance and durability.
The team published their findings on Wednesday in the journal Nature, detailing how these materials deviate from traditional, uniform lattice structures.
Traditional metamaterials typically rely on repeating unit cells, such as square or hexagonal grids. While these ordered patterns are easy to design, they often suffer from localized failure; if one part of the material buckles, the damage quickly spreads to identical neighboring cells. By contrast, the new “scale-rich metamaterials” feature non-uniform beams of varying lengths and thicknesses, modeled after complex natural networks like leaf veins and dragonfly wings.
To create these structures, the researchers designed an algorithm that generates a virtual network of beams based on physical constraints. The program places points at random coordinates and draws lines at varying angles, creating a dense web that avoids the repetition of standard lattices.
By adjusting two parameters—the thickness of the initial lines and the rate at which subsequent lines thin—scientists can tune the material’s stiffness and mechanical properties.
Physical tests, including 3D-printed polymer samples, confirmed that these networks effectively distribute energy during impacts. Measurements showed that the scale-rich designs maintained a localization parameter (ℒ) of less than or equal to 0.2 through 25 percent macroscopic strain. This represents a 37 percent reduction in localization compared to the Voronoi geometry. Using a “checkerboarding” approach to nucleation, the team further constrained the localization parameter to 0.08, a 74 percent reduction over the Voronoi value.
The research team manufactured centimeter-scale resin structures using a vat photopolymerization 3D printer with a printing resolution of about 100 micrometers. To evaluate average mechanical properties while reducing outer edge effects, the total number of beams in the specimens was set to 500.
Compression tests with stress-strain curves integrated up to 40 percent engineering strain demonstrated that the scale-rich network showed toughness equal to or greater than square lattices, hexagonal lattices, and irregular Voronoi tessellations.
The researchers analyzed how these networks perform across different relative densities. The analysis showed that scale-rich networks covered 77 percent of the combinations of relative density and anisotropy that were investigated.
“This is a completely new way of thinking for metamaterials,” said Carlos Portela, associate professor of mechanical engineering at MIT. “Unlocking this network design for materials really frees us to think of new microstructures and mechanical benefits that haven’t been possible before.”
“We’ve spent years looking at periodic and ordered microstructures, and we’ve learned there are a lot of limitations and non-ideal responses, such as this localization effect,” Portela added.
The research team suggests the material could be used to print next-generation sports helmets, lightweight body armor, and precision acoustic lenses that focus sound waves and vibrations with unprecedented control. Beyond impact protection, the team investigated the potential for controlling elastic waves.
By spanning a wide range of effective refractive indices, these materials could be used to create precise acoustic lenses. Future development will focus on scaling the approach to three-dimensional bulk structures and testing performance in materials such as metals and ceramics under complex loading conditions.