Call of the wild

Watching a buzzard soar, a dolphin swim or a lizard run up the wall can dramatically illustrate how millions of years of evolution can produce something that any top designer would be proud of.

Legend has it that Reginald Mitchell, designer of the Spitfire, was inspired by the flight of a seagull to ask why humans’ flying machines had to be ungainly contraptions held together with wire. Many of the things scientists and engineers have been struggling to master for years were achieved in nature thousands and often millions of years ago. It is not surprising, then, that many of those involved in designing and engineering are increasingly looking towards the natural world for answers to their technical problems.

Biomimetics is the production of materials and structures based onnaturally occurring forms. Among famous examples are Velcro, inspired by burred seed cases, and the Eiffel Tower, whose shape is based on the ulna bone in the lower arm. However, more recent advances in science and technology are increasing the possible applications of this field. ‘I think biomimetics has reached a new phase,’ says Prof George Jeronimidis, director of the Centre for Biomimetics at Reading University.

‘The first phase of the discipline – typified by Velcro – was driven by chance curiosity or accidental discoveries. The new phase is about having a specific problem and looking logically at all the areas of biology that might provide an answer.’

This shift has been due largely to improvements in analytical science. Researchers can now study the form and function of natural entities at micro-scale and even nanoscale levels. Understanding these complex structures is the first step towards developing synthetic analogues. ‘Biological shapes are complex, contain few straight lines and are often multilayered, which has in the past made them difficult to model or simulate. But with advances in computer technology and programming these barriers to progress and understanding are beginning to be lifted,’ says Jeronimidis.

Much of biomimetics is concentrated on medical research into the synthetic production of replacements for human tissues, such as muscle or bone. But the medical scope of biomimetic designs extends far further than this. One device being developed is a pain-free needle based on the proboscis of a mosquito. If you have ever encountered a large number of mosquitoes you will probably have found that although you can sense a few making a meal of you, several others will be happily feeding away without your knowledge. This ability to pierce human skin undetected is what mechanical engineer Seiji Aoyagi and his team have been studying at Kansai University, Osaka. Detailed study of the proboscis shows why it can break the skin painlessly.

‘One reason the proboscis is painless is because it is so very small, about 10th or 20th the size of a normal needle – decreasing the contact area between the needle and the skin. The second is its jagged shape – these serrations make the dermis much easier to cut open,’ says Aoyagi. The jagged edge also reduces contact with skin, reducing pain through nerve stimulation. Successful tests have been carried out on silicone rubber to simulate human skin, but the current form of the needle, also made of silicone, is still too brittle, so the researchers are looking into other substances.

‘Within five years there will be a painless and safe needle available, simply because of the tremendously large commercial need – it is possible that it could replace all existing stainless medical needles. Even if I fail to develop such a needle, other researchers will succeed,’ says Aoyagi.

Apart from potential applications in medicine, a great deal of interest in biomimetics centres on materials technology. The strength and resilience of natural materials is the inspiration behind much research and perhaps the field where results will most quickly be seen. For example, the qualities of spider’s silk – the fineness of its thread, its strength and elasticity – are all facets that make it of great interest.

Dr David Knight and Prof Fritz Vollrath, spider experts at Oxford University’s Department of Zoology, have been studying natural silks since around 1974, and are now part of a project to produce synthetic spider’s silk.

Spinox, the company formed to develop their research, is funded by TechnoStart, a leading German hi-tech venture capital fund, and the Oxford University Challenge Seed Fund.

Although spider’s silk has many advantages over other sorts of fibre, it is the material’s ability to dissipate energy that is of most interest. This ability has developed from the web’s need to deal with large amounts of kinetic energy. When a moth or fly collides with the web the silk has to withstand a large impact, absorbing the energy rather than breaking. ‘This web strength is the result of a long-running evolutionary arms race between the spider and its prey,’ explains Knight.

The group has studied the spider’s silk using electron microscopy, X-ray diffraction and mechanical testing to develop devices that mimic the unique way in which spiders and silkworm spin silk. Still at a relatively early stage, a prototype spinning device should be in operation in around three months. Although spider silk is being used to start with, a wide range of feedstocks might be used for biomimetic spinning, including artificially synthesised or genetically engineered protein analogues and natural ‘silk-like’ proteins from wheat or rice grains.

The applications for such a substance are widespread and products for both medical and textile applications are being looked into: training shoe insoles, protective clothing, replacement for medical sutures and even surgical implants. The product also offers environmental and possibly cost benefits: the spinning process is sustainable and highly energy efficient and does not require high temperatures, strongly acidic solutions or toxic organic solvents. It shows excellent properties over a wide range of temperatures and can withstand magnetic or electric currents.

‘Organic alternatives have to be as good as their synthetic counterparts or they simply don’t succeed. I have no doubt in the future of biomimetic clothing, I just hope that we are involved when it does happen,’ says Knight.

In a similar project to mimic a triumph of nature, Bath Institute for Biomimetics and researchers at Qinetiq are separately looking into composites based on the structure of mother-of-pearl. Although mother-of-pearl is made largely from chalk it has much greater resistance to erosion than would be expected. This is attributed to its unique structure, forming composites at both the micro and macro level.

Director of Bath centre for Biomimetics Julian Vincent and his team are designing metal matrix composites that use the same principle but in a much stronger form. This may have applications in producing new, more durable cylinder-heads in diesel engines.

Qinetiq is interested in its resistance to impact erosion, which it has demonstrated by firing high-speed water droplets at mother-of-pearl. When these drops collide with most other materials, they cause shock waves that can create cracks; after impact the jets of water produced by the droplet open up these cracks causing further erosion. Scientists at Qinetiq are looking to make analogous composites for use in aerospace, such as coatings for the leading edges of helicopter rotor blades.

Another structure stronger than it may first appear is the outer skeleton of creatures such as centipedes, spiders and crustacea. Researchers at Reading Centre for Biomimetics are studying the exoskeleton to see why the sense organs make only minimum impact on structural integrity. ‘Generally, if you drill a hole in a structure you weaken it, but the sense organ holes in the insect’s exoskeleton do not because they are part of the design from the moment it’s formed,’ says Jeronimidis.

Another project involving Reading, in conjunction with Southampton and Bath Universities, is interested not in the strength of natural materials but their stiffness. The three-year project aims to produce variable-stiffness devices to combat vibration. The team is developing gels based on principles from mammals’ muscles and plant cells, which use diffusion to produce movement. The gels work like the cells of a muscle or a plant causing expansion through diffusion of a solvent. Fibres are used to control direction of expansion and strengthen these polyacrylic gels; the gels are being reduced in size to speed up diffusion, but as long as they are in contact with the solvent can be bundled together to produce greater forces. The applications of this gel are varied but most promising is the area of stopping vibration in vehicles. It could then be scaled up: ‘Once we have fully addressed the gel’s problems of reversibility and speed of response I don’t see why it couldn’t be used in larger-scale structures like replacing the dampers on the Millennium Bridge,’ says Jeronimidis. ‘Biomimetics is not just about copying nature; nature should be the inspiration but the scale and materials used are up to us.’

Scale is important to engineering consultant Arup, one of the companies taking an interest in the use of biomimetics in buildings. ‘On the macroscale biomimetics is usually just the inspiration for a building. But when creating a functional building so many compromises have to be made that although it may slightly resemble the original organic form the end product does not work in the way the organic form does,’ says Tony Sheehan, Arup knowledge manager.

Peter Bryans, a mechanical engineer involved with smart materials at Arup adds: ‘For us the real applications of biomimetics are where it will make structures smaller and stronger. Biomimetics is about minimising the need for materials while at the same time maintaining structural integrity.’ Nature has always been an influence for design and engineering, but the way this inspiration manifests itself has changed. Increased understanding of form and function in nature will help to answer many very human problems.

Sidebar: Velcro: The catch is in the hooks

Velcro is often cited as the archetypal example of biomimetics. It was invented in 1948 by the Swiss engineer and amateur mountaineer George de Mestral.His discovery came about during a hike with his dog, when many cockleburrs became attached to his clothes.

Returning home, he removed the burrs and examined them under the microscope. When he saw the hooks magnified de Mestral realised they had been catching on to the small loops in the fabric of his clothes. From this he had the idea to use strips of opposing hooks and loops to develop a fastener that would replace the zip.

De Mestral’s idea originally met with resistance, and some ridicule. But he stood by his idea and together with a weaver from a textile plant in France perfected the hook and loop fastener.

In 1955, after much development and experimentation, his idea was patented and given the name Velcro – a combination of the French words velour and crochet.Since patenting, George de Mestral’s invention has become part of our lives with a great many applications.