The organic crystals take up about 60 to 90 percent of the material - the highest fraction of CNCs achieved in a composite to date.

The researchers found the cellulose-based composite is stronger and tougher than some types of bone, and harder than typical aluminum alloys. The material has a brick-and-mortar microstructure that resembles nacre, the hard inner shell lining of some molluscs, according to MIT News.

The team hit on a recipe for the CNC-based composite that they could fabricate using both 3D printing and conventional casting.

The researchers also machined the composite into the shape of a tooth to show that the material might one day be used to make cellulose-based dental implants - and for that matter, any plastic products - that are stronger, tougher, and more sustainable.

"By creating composites with CNCs at high loading, we can give polymer-based materials mechanical properties they never had before," says A. John Hart, professor of mechanical engineering. "If we can replace some petroleum-based plastic with naturally-derived cellulose, that's arguably better for the planet as well."

Each year, more than 10 billion tons of cellulose is synthesized from the bark, wood, or leaves of plants. Most of this cellulose is used to manufacture paper and textiles, while a portion of it is processed into powder for use in food thickeners and cosmetics.

The exceptionally strong crystals could be used as natural reinforcements in polymer-based materials. But researchers have only been able to incorporate low fractions of CNCs, as the crystals have tended to clump and only weakly bond with polymer molecules.

"We basically deconstructed wood, and reconstructed it," MIT researchers said. "We took the best components of wood, which is cellulose nanocrystals, and reconstructed them to achieve a new composite material."

They tested the material's resistance to cracks, using tools to initiate first nano- and then micro-scale cracks. They found that, across multiple scales, the composite's arrangement of cellulose grains prevented the cracks from splitting the material. This resistance to plastic deformation gives the composite a hardness and stiffness at the boundary between conventional plastics and metals.