Researchers at MIT have 3D-printed graphene structures that resemble sponge or coral, which are up to ten times stronger than steel but have much lower densities.

The team started by compressing small flakes of graphene using a combination of heat and pressure. This produced a strong, stable structure whose form resembles that of some corals and microscopic creatures called diatoms. These shapes have a massive surface area in comparison to their volume, and also proved to be exceptionally strong.

"Once we created these 3D structures, we wanted to see what's the limit - what's the strongest possible material we can produce," said Zhao Qin, a research scientist at MIT’s Department of Civil and Environmental Engineering (CEE).

To explore the capabilities of the structures, the researchers created a variety of 3D models and subjected them to a range of tests. In computational simulations that mimic a tensile loading machine, one of the samples had five per cent the density of steel, but 10 times the strength. The configurations were then 3D-printed in the lab, with the physical samples matching up to the performance of the simulations. The material could be used in any application that requires a combination of low weight and extreme strength.

"You could either use the real graphene material or use the geometry we discovered with other materials, like polymers or metals," said Markus Buehler, the head of MIT's CEE Department.

"You can replace the material itself with anything. The geometry is the dominant factor. It's something that has the potential to transfer to many things."

According to the team, the geometry could also be applied to large-scale structural materials, such as to concrete for bridges and buildings. This approach would have the additional benefit of providing good insulation due to the large amount of enclosed airspace within the structure.

The findings are reported in Science Advances.