Saturday, April 07, 2007

Nature- the master designer

In his book, “Pulse : How Nature is inspiring Technology of the 21st century”, Robert Freaney provides a fascinating glimpse into advances in - inter alia- material science, made possible by adopting some astonishing designs and features that Nature has used in the creation of so many living organisms.

Take elastin. That’s the stuff that forms the big ligament on the back of a grazing animal’s neck- as in a cow- connecting the base of the skull to the joint of its shoulders. The ligament is a strong elastic band which counterbalances the weight of the head and the neck more than or less in the manner of the spring balancing an overhead garage door. Elastin functions by storing energy when mechanically stretched and providing the recoil. And the primary ligament in the cattle is a beautiful example. As are the aortic arch and the walls of the descending aorta which are made of elastin.

Inspired by these, synthetic elastin sheets that respond to temperature have been developed. If the temperature is lowered slightly, the sheet will expand and if the temperature rises slightly it will contract. You can add a weight on it, and when it contracts it will pick up the weight. Some can lift more than a thousand times their dry weight.

Hedgehogs fall out of trees all the time without getting hurt. What scientists have found is that the sharp hollow spines protecting it from attack are also exceptionally good shock absorbers. The core of its spines are filled with a natural honeycomb that prevents the tubes from collapsing like crimped drinking straws when they are bent by an attacking predator or when hitting the ground. So much so that a puncture-proof tire has been designed by ringing a wheel with a bristling fringe of hedgehog spines.

When looking to Nature for lessons, dandelions provide a good illustration. Their flowering stems are only 7 percent solids and yet grow nearly a foot tall and withstand all kinds of weather. A good example for lightweight buildings and aerospace design.

Or consider how a spider handles one of the toughest problems in engineering- attaching one kind of material to another at a right angle. When a spider glues the main support for its web to a leaf, it does so with one hundred tiny threads that it generates, by dropping its bottom on the ground twice for about half a second. In that brief moment it achieves a near-perfect adhesive joint, of a quality equal to what you may find at the terminus of a well-designed bridge.

Then there’s the a project looking at pinecones and transpiration methods in leaves in order to design military clothing that adapts to different weather conditions by changing its ‘breathability’. A study of the cockroach’s excellent sensing mechanisms, for use in fighter aircraft is paralleled by a scheme to use beetle carapaces as models for light, superstrong body armour. Another looks at how insect wings unfold as clue to designing deployable arrays for space missions. NASA engineers imagine a plane with wings that change their shapes in reaction to changing flight conditions just as those of birds do,

This aping of nature has to be tempered with the skeptical realism of a good engineer. Many of the materials used by nature are effective only within the fairly small temperature ranges inhabited by the plants and animals that create them. Spider silk is a case in point; synthetic versions are avidly being sought due to its tremendous strength, but it degrades above 80 degree centigrade. Also when nature makes materials, it takes its time. There are trees a century old. Simple creatures like mollusks may need years to form their shells.

A major difference between human creations and the way nature does things lies in our overall approach to design. Taking a linear, machine age approach, we are normally concerned with finding a specific answer to some specific questions. But a living thing is a complex answer drawn from nature’s response to a multitude of questions- and from a need to answer them all at once. The humble swallow can fly and has a very good visioning system and coordination for capturing prey and it reproduces. Then this very small creature can travel thousands of miles, migrating to the south and back north again. That’s quite an extraordinary thing when you think of it .It’s that integration of many different systems, the optimization of all those systems that is the real impressive thing about nature.

Another extraordinary thing about Nature is the surprisingly few components from which natural materials are made. For their ceramics, most organisms use only two calcium salts. Organic fibres in animals are largely collagen, a protein. In plants they are mostly cellulose, a sugar polymer. Chitin, a strong fiber related to cellulose, turns up in anthropods- insects, spiders, crabs, prawns, and fungi. And then there are keratins, another protein family, which figure in various guises as nails, horns, hair and feathers, not to mention hedgehog spines.

Broadly speaking, Nature has no more than two main types of ceramics, two fibrous sugar polymers, four fibrous proteins and some globular structural protein. Compare these with the surfeit of artificial material we’ve come up with; ten main types of ceramics, fifteen plastics, ten fibres all of which require vast amount of energy during production.

Given the subtlety economy and infinite variety of nature’s designs and how simple and clean her methods are, we still have a lot to learn.


Anonymous said...

i like the way u present facts in an enjoyable writeup... i wud possibly not read all these facts if i had to read them on some nature-related site... but i enjoyed reading this blog...


Anonymous said...

Am always amazed by nature's technology when I see an enormous jackfruit attached to its tree with its impossibly skinny looking stalk:)

Raj said...

cheeku,actually it helps me understand and remember the subject better, when I blog about it.

dipali, how true!