Cutting Edge 5 min
Bio-inspired, a new life for polymers
Although it is nothing new, the science of biomimicry, which seeks to take inspiration from nature’s strengths, has recently had a second wind, thanks to polymers, which are once again displaying an incredible ability to adapt.
Bio-inspired, a new life for polymers
Bio-inspired, a new life for polymers

Polymers get into mechanics

Nylon, the ancestor of modern biomimicry

Biomimicry… Pessimists might say that there is nothing new under the sun. Did Leonardo da Vinci not already apply the principle when he designed a tank directly inspired by a tortoise’s shell, or flying machines using the same biomechanical principles as bats’ wings? It is true that the principle has been used before, but biomimicry is not just found in mechanical applications, it is also found in chemicals and is based on industrial developments in the field, and, in particular, those relating to polymers. The invention of Velcro is a perfect example of this. The story is well-known by now: in 1941, while taking a walk through the forest, Swiss engineer Georges de Mestral noted how difficult it was to remove burdock flowers from his clothes. Rather than getting angry, he observed them under a microscope and found that the flowers had small hooks that were sufficiently elastic to attach themselves to the fibres of the fabric.

bioinspirés velcro

He then came up with the idea of reproducing the flower synthetically, with the aim of competing with the zipper. With the help of an industrialist, they developed a system made up of two bands of the recently-developed Nylon, a polyamide, one with microloops and the second with microhooks. The patent was filed in 1951 and the invention was christened Velcro, a portmanteau of the French words “velours” (velvet) and “crochet” (hook). Success came immediately. However, Georges de Mestral was entirely unaware of the fact that he had just invented modern biomimicry at the same time.

Composites have a good nose

Nature is fortunate, it has had millions of years to adapt to its environment. Some species have been able to finetune their morphology to increase their aerodynamics or hydrodynamics. Man simply has to observe to find inspiration. Did the Concorde not look like a crane in flight? Sometimes, observations can take longer. This happened to the Japanese engineers who designed the Shinkansen, the high-speed train that reaches speeds of up to 300km/h. The engineers were faced with a problem: every time the train entered a tunnel, the train compressed the air around it, which would then expand a few tenths of a second later. The physical phenomenon would slow down the train and create a large explosive sound far exceeding the standards for passenger comfort. Certain in the knowledge that nature had a solution to their problem, they began studying various animals that might be faced with the same issue.

Nature is fortunate, it has had millions of years to adapt to its environment. Some species have been able to finetune their morphology to increase their aerodynamics or hydrodynamics. Man simply has to observe to find inspiration. Did the Concorde not look like a crane in flight? Sometimes, observations can take longer. This happened to the Japanese engineers who designed the Shinkansen, the high-speed train that reaches speeds of up to 300km/h. The engineers were faced with a problem: every time the train entered a tunnel, the train compressed the air around it, which would then expand a few tenths of a second later. The physical phenomenon would slow down the train and create a large explosive sound far exceeding the standards for passenger comfort. Certain in the knowledge that nature had a solution to their problem, they began studying various animals that might be faced with the same issue.

Bumps for a smoother ride

There are many other examples similar to that of the Japanese train. Some are so surprising that one could rightfully wonder what was going through the engineers’ minds at the time. Few could immediately see the link between a wind turbine and a whale, for instance. Yet, the concept of a bumpy wind turbine was developed at the prestigious Harvard University in the United States. Humpback whales have long been a fascinating subject for researchers. Many biologists have wondered how the mysterious animal could be so agile despite its large mass. Having noted the peculiar form of the whale’s fins, and more particularly the bumps on their leading edges, the researchers at Harvard made a mathematical model based on the feature. The results were very clear: the bumps have extraordinary hydrodynamic properties which give the creature its agility. The discovery inspired a Canadian wind turbine manufacturer who decided to test a new type of blade with bumps reminiscent of those on the whale’s fins.

The idea proved an excellent one, as the invention helped to reduce noise, improve stability and “capture” more wind energy. As a result of its improved stability, the blade is subject to less stress and can be made lighter using composite materials made from a mixture of fibreglass, carbon fibre, polyester resin and epoxy resin.

A little peck to avoid a big shock

Are motorcycle helmets effective? They are, if they meet current standards. They must therefore successfully pass various tests, the most remarkable of which involves dropping the helmet onto a steel cylinder from a height of 15 metres, which corresponds to an impact at 100km/h on a pole. However, if the same helmet had to withstand the pressure endured by a woodpecker (a bird that digs 10cm holes in trees to find its food, and which can make up to 10,000 pecks per day), the helmet would undoubtedly disintegrate despite the high level of robustness of the polycarbonate used to make the helmet. With each peck, the woodpecker’s head is subjected to an amount of pressure that would kill any human being, even wearing a helmet. It has many tricks up its sleeve: its very hard beak rests on an absorbent cushion, another elastic layer stretches from the base of the tongue and surrounds a particularly hard skull.

400

Pic-epeicheFinally, a layer of spongy bone envelops the brain. English engineer James Powell designed a helmet inspired by the woodpecker. Like the bird, it has four layers: the first is made from carbon fibre for rigidity, the second is the traditional polyurethane foam for absorption, the third is made from fibreglass, which is as fibrous as bone and prevents the shockwave from travelling to the centre (the brain), and finally, microbeads are injected between the first two layers to reproduce the bone of the skull. Computer simulations seem conclusive. All that’s left to do is to find a manufacturer interested in the project.

The dragonfly saves the giraffe

G-force induced loss of consciousness (G-LOC) is a phenomenon that can cause fighter pilots to lose consciousness from excessive and sustained g-forces. During sharp turns, pilots are subjected to forces in excess of ten times their own weight (i.e. 10g*)180228That is huge! The organs can move by up to fifteen centimetres, and blood pools in the ends of the limbs. The brain is less irrigated, and then comes the blackout or “G-LOC” in pilot jargon. In the 1960s, the problem was solved with the creation of g suits, an invention directly inspired by the working of a giraffe’s neck. In order to irrigate its brain, a giraffe has blood pressure twice that of a human being. Logically, the blood pressure in its brain should be so high when it leans down to drink that the giraffe should lose consciousness.

However, this is not the case as its neck is filled with small muscles that contract to control blood flow. This principle was used in the 1950s to develop special suits for pilots fitted with small rubber, then vinyl, inflatable cushions. However, this method reached its limits with the appearance of a new generation of airplanes able to subject their pilots to over 10g of pressure.

libéllule

Another animal, this time the dragonfly, inspired the new suits. Dragonflies seem to be impervious to the effects of acceleration. A dragonfly can easily withstand pressure of 30g when suddenly changing direction. Its secret? It has no veins or arteries, and its blood flows freely throughout its body; circulation is provided by its heart, which also floats in the liquid. Its blood acts as a sort of liquid padding. Modern flight suits are filled with two litres of water which circulates freely and automatically compresses the body’s lower limbs in high-gravity situations. The materials used are kept top secret. We can only know for sure that polymer fibres are involved, as the suits have to be both flexible and watertight.

* A g (“g” denotes gravity) is a unit of acceleration corresponding approximately to the acceleration of gravity on the surface of the Earth.

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