Material is as light as aerogel but 10,000 times stronger

Designed to maintain a nearly constant stiffness across more than three orders of magnitude in density, the micro-architected metamaterials were created using a 3D printing technique called projection microstereolithography. This works on a microscopic level and involves using a micro-mirror display chip to create highly complex 3D microstructures, one layer at a time, from photosensitive feedstock materials. "This allows us to rapidly make many sample pieces and see how they behave mechanically," said MIT's Nicholas Fang. To start, the researchers made a polymer template coated with a metal film 200 to 500nm thick. The polymer base was then melted away, leaving behind the metal in the form of thin-film tubes. The team then used the same technique but replaced the metal with ceramic to create ceramic tubes about 50nm thick, which produced a material with the properties of an extremely stiff aerogel, four orders of magnitude stiffer than conventional aerogel, but with the same density. Lastly, the researchers used a slightly different process to create a ceramic-polymer hybrid. In this incidence, the polymer was removed thermally, allowing the ceramic particles to densify into a solid. When the polymer was removed, the result was a stiff, ultralight ceramic solid instead of hollow tubes. "This material is among the lightest in the world," said LLNL's Christopher Spadaccini. "It has been shown to withstand a load of at least 160,000 times its own weight." The key to this ultra high stiffness, according to Spadaccini, is that all the micro-structural elements are designed to be over constrained and do not bend under applied load. So far, the researchers have tested the process using three engineering materials (metal, ceramic and polymer) – all of which showed the same properties of being stiff and lightweight. In the future, the team sees the materials being used to develop ultra stuff, ultra lightweight parts and components for cars and aircraft