Why do trees and grasses bend so easily in the wind without breaking? Why can wood and bamboo bear such huge loads relative to their weight and density?
Such questions occupy researchers in an area of science and technology called ``bio-mimicking.''
Their goal is to understand the structures of natural materials so that ``engineered,'' or man-made, materials can apply some of nature's secrets.
Among these researchers is Lorna Gibson, of the department of civil and environmental engineering at the Massachusetts Institute of Technology (MIT). Dr. Gibson has spent hours in her lab peering into the inner workings of northern spruce limbs, leafstalks from palms, bamboo twigs, and the stems of grasses and other plants.
She and her collaborators in this project - Gebran Karam, also of MIT, and Michael Ashby, Hugh Shercliff, and Ulrike Wegst of Cambridge University in England - have also borrowed from the animal world, analyzing porcupine quills and hedgehog spines.
Still other researchers are looking at the extraordinarily stiff and strong qualities of spider's silk, in the hopes of genetically engineering bacteria that could produce similar fibers. United States government agencies, like the National Science Foundation (NSF) and the armed services, fund much of this work. Gibson's project at MIT is underwritten by a NSF grant.
The ``microstructure'' of the plant life she's scrutinizing - intricate patterns of bundled tubes, fibers, and foams - could hint at ways to fabricate metals and other materials that would be both lighter and stronger than current products.
Gibson says materials that mimic the lightness and flexible strength of some plant structures would fit neatly with ``anything that's working to reduce weight and reduce energy costs'' - the next generation of spacecraft, for instance.
More down-to-earth applications could include more durable ``legs'' for offshore oil rigs. Such legs already have a hollow structure reinforced by welded plates. Gibson suggests that what she and others have learned about the added resistance to buckling provided by a foamlike inner core - such as that found in many plant stems - could be adapted to these and other man-made structures.
The creation of new materials that draws on researchers' insights into the natural world is already under way. Gibson says scientists and manufacturers in Ukraine have been able to fabricate ``a new steel product that claims to have this foamlike quality - essentially a porous metal.''
The Ukrainian project has caught the eyes of US officials, who are negotiating the transfer of the technology here, according to Gibson.
``Foaming'' is one approach to bio-mimicking, and bundling together parallel tubes is another. The latter attempts to replicate the parallel cellular structures that follow the grain of wood. ``Wood is very stiff per unit weight compared to engineered material like steel,'' Gibson says.
Fabricated materials using parallel tubes have shown a higher stiffness in ``beam-bending'' tests than solids, Gibson says. ``Prototypes of these materials exist,'' she says, and are in the process of being considered for commercial applications.
You might expect to see this evolving technology applied in the construction of buildings. But that isn't likely any time soon. Existing materials, including wood, are so much cheaper that it probably won't be economical to go to new engineered materials for a very long time.
Meanwhile, Gibson and her colleagues in various research institutes will continue their close examination of things that most of us take for granted, as we swing from a tree limb or walk through a grassy field.