Biomimetics: learning from nature

Meeting chaired by Andy Pepperdine

Thomas Hesselberg

Centre for Biomimetics & Natural Technologies

Dept of Mechanical Engineering, University of Bath

17 June 2005

Biomimetics is a new interdisciplinary field that identifies potential useful processes & mechanisms in biological systems & organisms & imitates them in engineering systems. A brief introduction is given to biomimetics, followed by a case study involving the potential use of locomotion systems from marine worms in self-moving endoscopes.

 

Ever since the earliest days of tool making, man has tried to imitate the skills of nature. In pre-historic times this ranged from wearing fur to keep warm to the actual development of bone- and stone-tools to emulate teeth and claws of animals. However, the ingenuity of man was not limited to blindly copying nature and soon human technology started to diverge from nature. The most conspicuous example of this is, of course, the invention of the axle and the wheel, which has no counterparts in nature. Nature, however, continued to inspire either by supplying vague concepts or in some cases even providing a full design. A case of the latter is the early unsuccessful attempt at building flying machines. In as early as 1488 Leonardo da Vinci designed a flying machine based on bats and 400 years later Otto Lilienthal built gliders based on avian design. Although the first successful aeroplane, built by the Wright brothers in 1903, involved a radical new design, it was based on the pioneering work done by Lilienthal. It is, furthermore, likely that humans would never have had the determination and conviction of eventual success, if they could not see from animals in nature that flying is possible.

 

In the first half of the 20th century the idea that biological studies could provide inspiration for developing new technology was slowly gaining ground in the scientific community. In the late 50s the word bionics was used for technological designs and ideas learned from nature, but this word is now more associated with the replacement of body parts with artificial electronic devices, although it retains its original meaning in the German speaking countries. The word ‘biomimetics’ made its first appearance in the title of a paper in 1969 and was included in Webster’s dictionary in 1974. The exact definition of biomimetics (or biomimicry as it is also sometimes called) has been broadened since and can now be used in many contexts, which involves the transfer of skills or information from biology to applied science.

The most famous example of the biomimetic approach is the invention of Velcro. In the late 1940s a Swiss engineer, George de Mestral, was taking his dog for a walk, when he noticed cockleburs sticking to both his clothes and the dog’s fur. Upon returning home he examined the burs and discovered the small hooks that enables the seed-bearing bur to be transported to new areas. By trial and error experiments he could, in 1955, patent Velcro, an artificial design based on the cockleburs. Velcro is a unique two-sided fastener, one side with stiff hooks like the burs and the other side with soft loops like the fabric of his pants.

A recent and promising example of the power of the biomimetical approach is the Lotus Effect. This effect was discovered by the botanist Wilhelm Barthlott during a systematic scanning electron microscopy study of the leaf surface of some 10.000 plant species. Barthlott and one of his students observed that species with a smooth leaf surfaces always had to be cleaned before examination, while those with a rougher and more irregular surface were almost completely free of contamination. From further studies and experiment they discovered that small wax crystals covered the surface of the rough leaves. Water droplets are balancing on the top of these crystals with only little surface contact to the leaf and will therefore roll off easily. The adhesion between dirt particles and crystals is similarly minimised, so the particle is attracted to the larger surface of the passing water droplet and with that removed from the leaf surface. They called this the Lotus-Effect, after the leaves of the sacred lotus or sacred water lily, which give a particular impressive demonstration of this effect. The Lotus-Effect has great potential for commercialisation and currently a house-paint is distributed under the name Lotusan. A further potentially lucrative application is to manufacture a self-cleaning paint for cars.

Biomaterials and structures is one of the main areas where the biomimetical approach is expected to be profitable. One of the best examples is that of producing artificial spider silk. Silk is a biopolymer consisting of a keratin-like protein called fibroin. Spider silk is an interesting material from a commercial perspective due to its high tensile strength (1100 MPa for radial threads of the cross spider compared with around 500 MPa for steel) and its strong viscoelastic effects. However, despite the huge research effort into spider silk, large problems still exists before any products are ready for the market. The main problem is that not only is the exact structure of the silk important for its physical properties, but these in turn also depend on the complex weaving pathway through the ducts and spinnerets of the spider, where the silk is changed from a liquid soup of proteins to solid threads. So far the most promising candidate is BioSteel developed by Nexia Biotechnologies. They took some genes from the spider and incorporated them into the milk glands of goats. Milk from the resulting transgenic goats then contained water-soluble silk proteins, which by spinning can be turned into silk fibres, although with inferior mechanical properties compared to the original spider silk. The company aims to employ BioSteel in the manufacture of fishing lines and bulletproof vests. However, major obstacles still lay ahead, not least the question of durability. In nature the spider continuously produce new silk since it is affected by changes in temperature and moisture. Inspiration from biological materials is also thought to be useful in development of new composite materials, such as artificial wood and ceramics based on nacre, a natural composite found in the hard shell of molluscs.

 

Publications containing words with the root biomimetic in the title, abstract or in keywords.
The data is obtained from searching the ISI Web of Science database (SCI-EXPANDED) writing the term biomimetic* in the topic field. The bars show the number of publications found in the database for each year &the line represents the percentage of publications found out of the total number of publications in the database for each year.
The area of robotics has in recent years turned some attention to the advantages of a biomimetic approach. An imitation of the various forms of animal locomotion will be especially useful for robots required to move in more structural complex and tortuous environments, where the standard engineering solution of wheeled locomotion may not be applicable. In the Biomimetic Underwater Robot Program at Northeastern University, USA, a robot was developed by reverse engineering from the American lobster. The auto-nomous robot uses shape memory alloys for emulating muscles, where electrical current generates the heat necessary for a phase transformation, and it copies the sensor system of the lobsters to detect water flow and obstacles. This and other similar studies, although still simple in their robotic design, successfully show the potential of the biomimetical approach. Another area that has received considerable attention, especially from the military, is the development of micro air vehicles (MAVs). The aim is to create small reconnaissance drones based on the principles of flight in insects. However, the technical difficulties to overcome in order to recreate these complex and not yet fully understood flight mechanisms are substantial and, despite massive funding available for this line of research, significant progress remains to be seen. Robotic engineers are not restricted to studying biomechanics if they want to be inspired by nature. The neurobiology of invertebrates is now so well understand that robot models can successfully replicate aspects of the behaviour of real animals. Especially, navigation strategies in insects have with some success been applied to robot navigation.

 

As is hopefully clear from the above, current research in biomimetics covers a very wide range of disciplines. And then I have not even mentioned the more exotic approaches of combining natural processes with creative thinking or the ambitious project of linking biology to the TRIZ (the theory of inventive problem solving) method with the aim of facilitating a systematic harvest of the knowledge of nature. Although the biomimetical approach, with the exception of Velcro, still lacks spectacular success stories, it is my belief that it will play an increasing role in improving our technology in the coming decades. However, before we uncritically attempt to copy the ways of nature some caution is required. As the biologist Steven Vogel points outs, natural technology has evolved under several major constraints, which should not limit our technology. Nature, for instance, uses only a very limited number of materials, where our technology, which is not constrained by organic environments, has a far greater variety of materials available. Furthermore, designs in nature are usually not optimised for any single function, but instead have multiple functions. For example, the spider web’s primary function is to detain prey long enough for the spider to catch it. However, it also functions as a communication channel during courtship behaviour and in camouflage by blurring the outline of the spider. Therefore uncritical copying of biological structures will often not give useful results. Instead, a careful analysis and assessment of the functions in nature is required before potential aspects can be identified and attempts made to imitate them. This will often be a complex process and it is here that cooperation between biologists and engineers is of vital importance for a successful outcome.

 

The three most advanced prototypes yet developed by the BIOLOCH consortium.

A ragworm (Nereis diversicolor) swimming by sending sinusoid waves from the tail towards the head.
An example of a biomimetical project is the BIOLOCH (BIOmimetic structures for LOComotion in the Human body), which is funded by the European Commission and consists of an interdisciplinary consortium of six European institutions (University of Bath, engineering/biology; SSSA and University of Pisa, engineering; FORTH Greece computer science; Steinbeis University and University of Tübingen, surgery).

The main objective of the project is to design and fabricate biologically inspired micro-robots able to navigate in tortuous and slippery environments, in particular inside the human body. This idea originates from the medical need to develop more mobile and autonomous devices for endoscopy. After a

Scanning electron microscopy photos of the parapodium & seta of the ragworm.

left to right:
The parapodium with the three seta-bundles highlighted.

centre:
A single seta.

right above:
the serrated blade.

right below:
the joint between the blade & the shaft.
preliminary survey of locomotion systems in lower animal forms two animals were identified to serve as models for the locomotion unit in the robotic endoscope. The earthworm (segmented worm in the class oligochaeta, moving by sending longitudinal waves along the body) and the ragworm (segmented worm in the class polychaeta, moving by sending sinusoid waves along the body). As I am personally involved in research on the latter a more thorough description of the ragworm follows below. Promising prototypes, using recent technological advances such as smart memory alloys for actuation, have been developed based on both models. However, all prototypes currently either move too slowly or are too large for endoscopy, but once problems with generating sufficient thrust and friction have been overcome, biologically inspired robots potentially offer a less damaging and painful alternative to current endoscopes. The ragworm, Nereis diversicolor, was identified as a suitable model organism partly because it inhabits sandy and muddy

environments in shallow marine waters and estuaries and partly because it shows a diverse range of locomotion methods. It is capable of burrowing through the substrate slow and fast crawl over the substrate, and swimming in the open water. During fast crawling and swimming sinusoid body waves aid the movement of the lateral appendages on, each segment (parapodia), which in the former acts as legs and in the latter as paddles. Interestingly the body waves in these worms move from the tail towards the head. This is opposite to what is found in other animals, such as snakes and eels, which move using sinusoid body waves that travels from the head towards the tail. This is possible in the ragworm because the main thrust is not generated by the body wave itself but by the backward movement of the parapodia

At the distal end of the parapodium bundles of fine hair (setae) protrude. A seta consists of a serrated blade that is joined to a shaft, so that restricted movement of the blade relative to the shaft is possible. This movement is entirely passive as no muscles or nerves are found in the seta. The main function of the seta is probably to generate friction between the worm and the substrate during crawling, but other functions include anchoring in burrows and thrust generation during swimming. From a biomimetic perspective these passive setae offers a solution of how to generate friction between the robotic endoscope and the mucous lined gut wall. But the locomotion system in the ragworm also offers wider biomimetic potential. For instance a possible application would be for underwater multipurpose explor-ation robots which are required to swim in the open water, crawl on the bottom and burrow in the substrate.

Thomas Hesselberg

Further reading.

Barthlott W & Neinhuis C. ‘Purity of the sacred lotus, or escape from contamination in biological surfaces’ Planta 202 (1997):1-8.

Benyus, JM. Biomimicry: Innovation inspired by nature (William Morrow & Co. Inc, NY, 1997).

Gould P. ‘Exploiting spiders’ silk’ Materials Today December (2002): 42-47.

La Spina G, Hesselberg T, Williams J. & Vincent JFV. ‘A biomimetic approach to robot locomotion in unstructured & slippery environments’ Journal of Bionics Engineering 2 (2005): 1-14.

Scaps P. A review of biology, ecology & potential use of the common ragworm Hediste diversicolor (OF Müller) (Annelida: Polychaeta), Hydrobiologia 470 (2002): 203-218.

Tsakiris DP, Sfakiotakis M, Menciassi A, La Spina G & Dario P. Polychaete-like undulatory robotic locomotion. International Conference on Robotics & Automation, Barcelona (2005).

Vincent, JFV. ‘Smart by name, smart by nature’, Smart Materials & Structures 9 (2000): 255-259.

Vogel S. Copying nature: a biologist’s cautionary comments. Biomimetics 1(1992): 63-79.

Internet resources

Centre for Biomimetic & Natural Technologies, University of Bath: .http://www.bath.ac.uk/mech-eng/biomimetics/

BIOLOCH: http://zeus.ics.forth.gr/bioloch/

http://istresults.cordis.lu/index.cfm/section/news/tpl/article/BrowsingT...

Biomimetics general:

http://www.biomimicry.net/

http://www.extra.rdg.ac.uk/eng/BIONIS/