The strongest part of a tree lies not in its trunk or its sprawling roots, but in the walls of its microscopic cells, according to researchers from the Massachusetts Institute of Technology.

A single wood cell wall is constructed from fibers of cellulose, which is nature’s most abundant polymer, and the main structural component of all plants and algae, the researchers said. Within each fiber are reinforcing cellulose nanocrystals (CNCs), which are chains of organic polymers arranged in nearly perfect crystal patterns. At the nanoscale, CNCs are stronger and stiffer than Kevlar.

An MIT team has engineered a composite made mostly from cellulose nanocrystals mixed with a bit of synthetic polymer. 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 mollusks.

The team hit on a recipe for the CNC-based composite that they could fabricate using both 3D printing and conventional casting. “By creating composites with CNCs at high loading, we can give polymer-based materials mechanical properties they never had before,” said 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.”