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ENCHANTING WORLD of BIONICS Pavel KEJZLAR, Dora KROISOVA

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ENCHANTING WORLD of BIONICS Pavel KEJZLAR, Dora KROISOVA 23. - 25. 10. 2012, Brno, Czech Republic, EU ENCHANTING WORLD OF BIONICS Pavel KEJZLAR, Dora KROISOVA Technical University of Liberec, Studentska 1402/2, 461 17, Liberec, Czech Republic, [email protected] Abstract Bionics is a quite new scientific discipline connecting knowledge of biologists and technicians. It uses structures and principles appearing in nature. Living organisms on the Earth evolved and improved during nearly 3.5 billion years and achieved perfection from all points of view. In nature there is no space for any type of error or imperfection, everything what doesn't adapt to its living conditions, dies. This fact is a reason, why we are looking for natural smart solutions, studying them and trying to find a way, how to use achieved knowledge in ours modern technologies. Secrets of surviving and prosperity are often hidden in sub-micron scale that's why we have to use the most modern imaging technologies as scanning electron- or atomic force microscopy to be able to study fine structures having amazing functions. This article will take the reader on a journey to enchanting world of natural nano- and micro-sized structures and shapes and will show him their extraordinary functions. Everything what we now have to do is keep our eyes open and let ourselves to be inspired. Keywords: Bionics, Biomimetics, Structure, Nanomaterial, Nature 1. INTRODUCTION The birth of Earth is dated to so called Hadean period (4600 - 3800 million years ago). The Earth formed by accreation from solar nebula. Much of the Earth was molten because of extreme volcanism and frequent collisions with meteorites. During this period the heavier molten iron sank to the middle of the newly forming Earth to become a core, the lighter material rose to the surface. Volcanic outgassing of volatile molecules such as water, methane, ammonia, hydrogen, nitrogen and carbon dioxide likely created the primordial atmosphere. It contained almost no oxygen. Over time, cosmic bombardment ceased allowing the planet to cool and form a solid crust. Steam (water brought by comets and asteroids) condensed into clouds and the proto-ocean took shape. Earth was finally hospitable to life. Life arose on Earth during so called Archaean period (3800 - 2500million years ago). In this time the only inhabitants of the Earth were simple microscopic organisms comparable to today’s bacteria. These early cells belong to the group of prokaryotes. The oldest cyanobacteria-like fossils known are nearly 3500 million years old. Many cyanobacteria secrete a thick cell wall. They may form large layered structures called stromatolites or oncolites. These structures form as a mat of cyanobacteria growths in a marine environment, trapping sediment and sometimes secreting calcium carbonate. Life on Earth remained small and microscopic for at least one billion years. The conditions under which these organisms lived differed greatly from those prevailing today, but the mechanisms of evolution were the same. In the protezoroic era (2500 – 544 m. y.) both, primitive single celled and more advanced multicellular organisms, begin to appear in abundance in rocks. The oldest multi-cellular algae fossil dates to 1200 million years. Genetic mutations made some individuals better fitted than others to survive and to reproduce in a given environment. The principle of natural selection exerted great changes on physiology [1-4]. Through the mutations the evolution responds to all of life’s problems – to get nutrients, to move around or to survive and prosper in all extreme conditions from the highest mountain tops to the deepest ocean waters. 23. - 25. 10. 2012, Brno, Czech Republic, EU Organisms continuously evolve, adapt and develop, becoming ever more sophisticated and complex, taking on new forms or going extinct in response to an ever-changing planet. The solutions found in the nature work with smart materials which can be characterized by phenomena as self-repairing, self-cleaning, super- hydrophobia etc. In the beginning, the human was just a part of breath-taking biodiversity, but his large brain helped him to achieve an exclusive position. He stopped to adapt to nature, contrary, he has started to adapt the nature to his needs. The human used technology to solve life problems. Our species become extremely successful but with a great cost to our planet. At the start of the third millennium we started a new revolution where the nature and technology stand hand in hand. There is a new science, bionics, which looks to nature to find an inspiration to solve our technical problems in totally unexpected ways. The word of “BIONICS” has been used for the first time about fifty years ago. It is composed of two parts of two words - biology and technics. By the use of the most modern imaging devices such as scanning electron microscopes or atomic force microscopes the bionics looks into the enchanting world of weird structures and shapes to see smart natural materials and to reveal their secrets and principles. The acquired knowledge is then used as models for development of synthetic systems. Of course, the purpose of bionics is not only imitation, but mainly utilization of the nature’s creative potential and the inspiration for constructions and technologies. The authors of this paper would like to give the reader a short lesson from nature. The reader will be able discover secrets of extraordinary natural materials such as lotus leaves or butterfly wings. 2. LECTURE FROM NATURE 2.1. Lotus leaf Self-cleaning properties of Lotus plant (Nelumbo nucifera – Fig. 1 [5]) has been known for more than 2000 years. Dirt on the Lotus leaf can be easily picked up by running water droplets and eventually be removed from the leaf. This self-cleaning ability is believed to be why this plant is regarded as a symbol of purity in many Asian religions and has been the inspiration for many biomimetic inventions. Fig. 1: Sacred Lotus (Nelumbo Nucifera) is known due to its self-cleaning properties [5]. In 1964 scanning electron microscope images revealed that the leaf surface is not smooth but double structured (Fig. 2, 3). Its epidermis shows little bumps with a distance of 10 – 30 µm. Furthermore the epidermis is covered by a thin layer of wax crystals, which are water-repellent and so they repel water droplets and help prevent wetting of the leaf surface. The combination of these micro- and nano-scale 23. - 25. 10. 2012, Brno, Czech Republic, EU features greatly reduces the contact area between the surface and water droplets, which is the key to the cleaning process and explains how even a light rain shower is enough to wash the leaves clean (Fig. 4) [7- 13]. Fig. 2: SEM image of lotus leaf surface, top view. Fig. 3: SEM image of lotus leaf surface, side view. Fig. 4: Principle of lotus effect [8]. 23. - 25. 10. 2012, Brno, Czech Republic, EU 2.2. Butterfly wing Butterflies possess some of the most striking colour displays found in nature. Butterflies actually get their colours from two different sources: ordinary (or pigmented) colour and structural colour. A butterfly wing is made of a thin membrane webbed with veins. Thousands of microscopic scales cover the membrane, overlapping like roof shingles (Fig. 5). Each scale is composed of multiple thick layers separated by air. The scales strengthen and stabilize the wings. Each scale is a flattened outgrowth of a single cell and is about 100 µm long and 50 µm wide. They are anchored in the double wing membrane with a short protrusion (Fig. 6). If a butterfly loses a lot of scales, the underlying membrane may become more prone to tears, and that could affect its ability to fly. A butterfly can’t regenerate lost scales. All colours arise in those small scales. We can imagine them as a flat transparent box with a plenty of small chambers that contain coloured pigment or air. On the outer side they are finely ribbed (Fig. 7) and this fine structure is responsible for colours. When light hits the different layers of the butterfly wing, it is reflected numerous times, and the combination of all these reflections causes the very intense colours. Variations in the spacing of the pattern often gives rise to an iridescent effect, as seen in peacock feathers, soap bubbles, films of oil, and mother-of- pearl. The reflected colour depends upon the angle of view that’s why we see the shimmering colours. For many butterfly species is that opalescence intended by their own pigment. Most butterflies get their different shades of brown and yellow from melanin, the same pigment that makes you tan in summer and gives some people freckles. Other colours - silver, gold, blue, purple, green and pearl are formed by a light refraction inside the scales or on their surface. White can also be the result of light reflection similar to snowflakes [14- 17]. Fig. 5: Scales on the butterfly wing arranged as roof tiles. Fig. 6: Anchoring of scales to the wing membrane with a short protrusion. 23. - 25. 10. 2012, Brno, Czech Republic, EU Fig. 7: The fine structure of the scales that causes light diffraction and refraction 3. CONCLUSION The evolution of fauna and flora on the Earth lasted an extremely long time. The origin of Earth is estimated to be 4.6 billion years, the origin of life 3.5 billion years. Humans stand at the end of this process and it is necessary to confess, that nature creates materials and constructions for a much longer time. It would be good to look at ordinary things that surround us with more interest. Just watch it isn’t enough, it’s necessary also see and understand, because what we understand, we can perhaps utilize.
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