MIT Engineers Claim Plants Display a Wide Range of Mechanical Properties

A group of engineers from MIT complied data on the microstructures of a number of different plants ranging from apples to potatoes to willow and spruce trees, and discovered that plants exhibit an enormous range of mechanical properties, based on their arrangement of cell wall's four building blocks that consist of cellulose, hemicellulose, lignin and pectin.

Lorna Gibson, the Matoula S. Salapatas Professor of Materials Science and Engineering at MIT, says 'Understanding plants' microscopic organization may help engineers design new, bio-inspired materials. "If you look at engineering materials, we have lots of different types, thousands of materials that have more or less the same range of properties as plants. But here the plants are, doing it arranging just four basic constituents. So maybe there's something you can learn about the design of engineered materials."

The new study that was published this month in the Journal of the Royal Society Interface focused on three main plant materials: woods, such as cedar and oak; parenchyma cells, which are found in fruits and root vegetables; and arborescent palm stems, such as coconut trees.

Based on the experiments previously conducted the researcher analyzed two main mechanical properties in each plant: stiffness and strength. She noticed Fruits and vegetables such as apples and potatoes were the least stiff, while the densest palms were 100,000 times stiffer. Similarly, apples and potatoes fell on the lower end of the strength scale, while palms were 1,000 times stronger.

Thereason for the large range stiffness was due to  intricate combination of plant microstructures. Taken together, the cell walls occupy a large portion of a cell, providing structural support. The cells in woods are organized in a honeycomb pattern a geometric arrangement that gives wood its stiffness and strength. Parenchyma cells, found in fruits and root vegetables, are much less stiff and strong than wood, because they have no lignin; combined with their thin walls and the random arrangement of their cellulose fibers.

Gibson sees plant mechanics as a valuable resource for engineers designing new materials. 

"Plants are multifunctional," Gibson says. "They have to satisfy a number of requirements: mechanical ones, but also growth, surface area for sunlight and transport of fluids. The microstructures plants have developed satisfy all these requirements. With the development of nanotechnology, I think there is potential to develop multifunctional engineering materials inspired by plant microstructures."

 Karl Niklas, a professor of plant biology at Cornell University, says Gibson's engineering parallels are fitting. Plants, in a way, he says, are "largely structural things chemical factories that are architecturally arranged."