Stronger yet lightweight artificial materials made by 3D-printing lattices with multiple orientations are reported in a paper published in this week’s Nature. The new lattice designs are based on the principle that underlies strong metal alloys.

With a 3D printer, designed materials can be produced with a lattice structure of repeating nodes and connecting struts, which can make them both lightweight and strong. When these materials fail, however, they do so catastrophically, limiting their practical use. This failure results from how these materials are structured - a lattice with a single overall orientation. The same phenomenon occurs in metallic single crystals, which are structured similarly and deform through internal slips along specific planes. However, in polycrystalline materials, which contain crystal grains of different orientations, the boundaries between grains help to stop developing slips and cracks from propagating. This increases the ability of these materials to withstand deformation.

Minh-Son Pham and colleagues emulate polycrystalline materials to design new lattice-like metamaterials with granular structures, giving different regions of the internal lattice different orientations. The authors find that, when deformed, the granular metamaterial - which they dub a ‘meta-crystal’ - is far stronger and more damage-tolerant than conventional metamaterials. As with polycrystalline materials, the strength of the meta-crystals can be increased by reducing the size of each grain-like lattice region.

The authors also create specific meta-crystals structured to twist into a different configuration when force is applied, mimicking similar rearrangements in crystalline materials. Together, these findings could lead to tougher, lightweight 3D-printed materials suitable for a variety of applications.