Several UW researchers are taking their inspiration from nature in designing new materials. In a revolution called "biomimetics"--mimicking biological systems--they are unlocking the secrets of natural materials and applying that knowledge in the hope of producing man-made substances that are stronger, lighter, cheaper than conventional materials, and easier on the environment to boot. In one instance, this research has yielded an important clue to a long-standing medical mystery as well.
![[Electron micrograph of abalone shell]](/research/pathbreakers/graphics/c_ju1.JPG) |
| Electron micrograph of abalone shell |
Consider the case of the common banana slug. You might not
think the slug could be a boon to science. But UW
bioengineering professors Pedro Verdugo and Christopher Viney,
together with zoology professor Ingrith Deyrup-Olsen, have been
studying the properties of slug mucus, and have found it's
quite a remarkable substance. Slugs use it for protection and
as a sort of slithery railway for transportation. Previously,
researchers thought that at the molecular level, slug slime was
like a bowl of spaghetti--the more tangled the strands,
the thicker the mucus. But in 1993, Verdugo and Viney showed
that slug mucus is not random; it is a highly organized
polymeric material. Furthermore, when secreted, the polymer
absorbs water extremely rapidly—up to 100 times its initial
volume.
"Add water and
stir" takes on explosive proportions when it comes to
mucus.
The UW researchers discovered that the thickness of mucus in
general is controlled by the swelling of the polymer network,
and that swelling, in turn, is governed by the saltiness of the
water it picks up. This discovery was the first direct link
between thick mucus and the defective transport of chloride ion
that are both characteristic of the disease cystic fibrosis.
Deyrup-Olsen has been studying the basic mechanisms by which slug mucus is secreted. The slug cells cleverly package up the mucus in granules, coating the mucus with a layer of cell membrane material, thereby keeping it dry until it is well outside the cell. Then these packets break open (apparently upon contact with extracellular ATP), exposing the mucus to water.
The researchers foresee many potential applications of slug slime technology in materials science and bioengineering: new drug delivery systems, pollutant traps for sewage treatment plants, and water-based lubricants, for example.
UW materials science and engineering professor Mehmet
Sarikaya describes another avenue of exploration in the
burgeoning field of biomimetics. The abalone, for instance,
produces a shell so tough it can be run over by a truck without
breaking. The organism manufactures its beautiful and lustrous
abode in the most benign of conditions: at sea-water
temperature, using readily available starting
materials--mainly calcium carbonate, or chalk. Studying
the structure under an electron microscope, Sarikaya and
colleagues have discovered that the part of the shell called
nacrethe shiny inner "mother-of-pearl"is made of thin layers of
laminate. Tiny stacks of overlapping, six-sided calcium
carbonate "bricks" are bound together by a mortar of protein
and sugars. The structure is as much as 30 times stronger than
calcium carbonate made in the laboratory.
Sarikaya and
former UW professor Ilhan Aksay, now at Princeton, initiated a
project with medical geneticist Clement Furlong and
microbiologist James Staley to develop techniques of
artificially "growing" novel materials patterned after the way
an abalone produces its shell.
Viney and colleagues have brought their expertise in liquid crystals to bear on the subject of silk spun by spiders and silkworms. Liquid crystals are liquids in a highly ordered state, something between a liquid and a solid crystal. They are most familiar as the display screens for digital watches.
In a 1991 paper published in the scientific journal Nature, Viney and colleagues reported that spider silk owes its exceptional strength to temporarily becoming a liquid crystal. The researchers found that as the spider secretes its silk, molecules in the droplets align themselves in rod-like structures, passing through a semi-ordered liquid crystal phase. The resultant solid material can support far more weight for its size than steel. Can new bulletproof fabrics and stronger suspension bridges be far away?
