[Progress in Optics] Progress in Optics Volume 57 Volume 57 || Microstructures and Nanostructures in...

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Microstructures and Nanostructures in NatureDora KroisovaTechnical University of Liberec, Department of Material Science, Studentska 2, Liberec, Czech Republic

CHAPTER TWO

Progress in Optics, Volume 57 © 2012 Elsevier B.V. ISSN 0079-6638, http://dx.doi.org/ All rights reserved.10.1016/B978-0-44-459422-8.00002-3

Contents

1. Introduction 932. Sample Preparation and Electron Microscopy 963. Microstructures and Nanostructures of Selected Natural Objects 964. Discussion 1285. Conclusion 131Acknowledgments 131References 131

1. INTRODUCTION

Plants and animals have been subjected to many changes during mill-ion years of their evolution. The reason for these changes was the evolution of species connected with living conditions. Plant and animal species had to adapt to climate conditions in order to fulfill their lasting object—to reproduce. There was extinction of species where it had not been able to reproduce. Optimal designs, structures, chemical compositions, protective elements, means of communications, and sensors have been created as a consequence of this evolution. Nowadays it is possible to observe and study the factors mentioned above to inspire ourselves by analyzing former opti-mal materials, constructions, or technologies with the most modern techni-cal equipments (Bhushan, 2009). A rapid development has been realized in the area of nanotechnology during last decades. Nanoparticles, nanofibers, and nanosurfaces have already been prepared. The generally produced nano-materials are quite expensive and are mainly available in small amounts. Compared to the development of nanomaterials which has been continu-ing during past decades, there is the evolution of fauna and flora lasting a much longer time. Sophisticated technologies using biogenic elements,

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self-assembly, self-healing, and biodegradation without more energy requirement than just the sun shining are at the end of the evolution. Almost perfect parameters related to chemical composition and structure from the materials and designs points of view have been reached (Bar-Cohen, 2006).

Natural materials structures often reveal more levels. Their creation starts at the molecular level, getting through on the nanostructure level and micro-structure level where there is typical combination of more materials. These materials coexist mutually together, thus creating an excellent architecture object. The structure hierarchy is clearly evident in the case of plants and ani-mals objects. There are, e.g., the hydrophobic plant surfaces created by different structure types where the macrostructure presence of visible naked eye, micro-structures of different surface cells, and nanostructures on cells surface built up of various waxy shapes are evident (Koch, Bhushan, & Barthlott, 2009).

Specific and mostly nanostructured waxy shapes covering plant surfaces grow up from protective layer called cuticla which covers stems, leaves, and petals surfaces. Cuticla generally provides plant protection against excessive water evaporation at transpiration process, reflects or absorbs ultraviolet radia-tion, and protects plants from pathogen influence of fungi and bacteria. Cuticla is composed of cutan and another type of lipid marked as term wax. Waxes are embedded right in cuticla (intracuticular waxes) but also form specific surface shapes called epicuticular waxes. One can see by naked eye epicuticular waxes on plants and fruits surfaces (plums, grapes, etc.) because they form there blu-ish surface coloring. Only scanning electron microscopy (SEM) made it pos-sible for a detailed observation of three-dimensional waxy objects of different shapes (platelets, rodlets, spiral shapes), which are truly essential for plants due to their surface protective functions. Epicuticular waxes are crystalline, hydro-phobic, soluble in organic solvents, exhibit solid state at room temperature, and are soft. Some studies about the possibilities of recrystallization of these waxes in the other environment were carried out. These successful experiments revealed first results about waxy structures formed up by the self-assembly (Barthlott et al., 1998; Koch & Barthlott, 2009; Koch & Ensikat, 2008).

The basic condition for a plant’s growth and reproduction is photo-synthesis. This is a complicated biochemical multilevel process taking place in chloroplasts and chromatophores. Color pigments absorb light during the first light phase thus obtaining energy for subsequent process. Water is decomposed and oxygen is released. Biochemical processes in the sec-ond darkness phase do not need light but use the energy that is actually received during the first light phase. Carbon dioxide (CO2) is built in sac-charides molecules, which are subsequently used as a source of energy or

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as building blocks for forming complicated molecules like polysaccharides and glycosides. The photosynthesis process depends on external factors like light, carbon dioxide concentration in the air, temperature, and water. The amount of chlorophylls, age of leaves, and mineral nutrition are inter-nal factors in the photosynthesis process. Light affects the photosynthesis by its spectral distribution depending on the sun’s position and radiance intensity. An increasing intensity can influence the photosynthesis only to a certain level. Carbon dioxide from air is the main source of carbon for the photosynthesis process. Photosynthesis is terminated when the carbon dioxide concentration is higher than up to 5% in the air. Photosynthesis depends on temperature too, but this is a very complicated description due to the influence of temperature on other physiological processes.

Generally it is possible to state that the photosynthesis rate increases up to temperature optimum only depending on the climatic band of the selected plant. The influence of water on photosynthesis is essential but really complicated. Water actively participates in all biochemical reactions, hydrates assimilatory tissues, influences the growth of assimilatory surface, distributes ions of elements and assimilates, and it regulates the stoma size and transpiration itself. The water deficiency influences the composition of photosynthesis products. In this case the production of macromolecular matters is lower and simple matters are produced (Campbell & Reece, 2008). The slow exchange of carbon dioxide and oxide takes place in the photosynthesis process in the case that leaves surfaces are covered by water film. The diffusion of carbon dioxide through the water film on leaves surfaces is 10,000 times lower in comparison with the direct transpiration (Brewer, Smith, & Vogelmann, 1991).

Characteristic surface structures on plants protect leaves, assimilatory surfaces against the creation of a water film that would cause the photo-synthesis process to be radically inhibited. Specific structures create hydro-phobic and superhydrophobic surfaces used for removing water from the leaves, making the process of leaves, surface self-cleaning easier; there are clean impurities from different sources which would restrain not only photosynthesis as pollination and reproduction (Koch & Barthlott, 2009).

Surface structures often take part in the other no less important func-tions. By their surface character and chemical composition, they protect the plants against fungi or pathogenic germs, increase resistance to climate changes, and create barriers against both excessive water evaporation and herbivores too. Protective surface structures and barriers create in ani-mals not only barriers to water and ultraviolet radiation but they can also

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influence the velocity of their movement in water (Neethirajan, Gordon, & Wang, 2009).

Composite systems are another no less interesting group of structures which are used in the case of beetle cases also low density materials of butter-fly wings designed for long-term dynamic loading, high strength, and tough inorganic–organic systems forming tooth enamel, perfect inorganic–organic package materials used by birds for millions of years, protection surfaces with excellent hydrodynamic properties and, e.g., compound eyes enabling quick movement and immaculate orientation in space (Raab, 1999).

Samples of plants and animal objects were selected for monitoring such objects by SEM with respect to covering not only a basic concep-tion about the structures that are commonly present in natural plant and animal objects but also conception of structures important for specific functions too.

2. SAMPLE PREPARATION AND ELECTRON MICROSCOPY

Fully developed samples of plant and animal objects were selected for the investigation. All samples were air-dried and subsequently sputter-coated with several nanometer thin layers of Au–Pd alloy. Air-dried process means complications connected with the cell shape change of plant surfaces due to water loss which results in their shape collapsing. The specimens were examined with a scanning electron microscope VEGA\\TESCAN at magnification from 200× up to 140,000×, accelerating voltage 10 kV, and JEOL at magnification from 200× up to 120,000× and accelerating voltage 0.80 kV.

3. MICROSTRUCTURES AND NANOSTRUCTURES OF SELECTED NATURAL OBJECTS

Pansy (Viola x wittrockiana) is an annual herb that is a hybrid initially planted in Great Britain (Slavík, 2000). The surface of flower leaves (petals) appears velvet by unaided vision. In water one can already see that water drops are reflected by petals surface to every direction and the petals are still dry and clear. It is possible to observe very fine approximately from 20 up to 50 μm wide remaining tiny tongue shapes during the investigation using a scanning electron microscope. These shapes, thickness ranges from 2 up to 3 μm and whose growth is perpendicular to the parent base.


One can observe the characteristic surface structure on both sides of these shapes at higher magnification. This structure is created by the tiny submicroscopic parallel rows (cuticular folding) growing from the parent cell base and reminding us of the textile material marked like trademark cor-duroy. Due to this specific structure, the water drops can be easily removed from the petals and it seems to be like a velvet surface (see Figures 1–3).

Designation rose (Rosa) belongs to the genus bush plant with more than 100 species that occurs in temperate and cold climate band of the northern hemisphere (Slavík, 2000). There are mixtures of aromatic essential

Figure 1 Flower leaves (petals) of pansy.

Figure 2 SEM micrographs—pansy flower leaves (petals) surface.

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oils in the rose flower leaves. Their volume varies according to their type, weather, and daytime. The basic aromatic component is alcohol geraniol and 1-citronellol. The velvet-like surface of rose flowers is created by a fine struc-ture which differs according to the upper or lower side of the flower leaves. This structure is created by fine additionally structured shapes with size in the range from 10 up to 15 μm. Structure shapes look like grooved peaks with the height of about tens of micrometers. The width of the individual groove is about on average 1 μm. This structure provides the hydrophobic surface and the characteristic velvet-like appearance of rose petals (see Figures 4–7).

Figure 3 SEM micrograph—pansy petals surface covered by tiny shapes (left), detailed SEM micrograph of structured petals—cuticular folding (right).

Figure 4 Rose flower.


Orchids (Orchidaceae) growth is spread in the areas with different cli-mate conditions from tundra up to tropical forest. Some types of orchids that grow on trees get carbon dioxide from the air, required nutrients from the decomposed part of plants, and absorb water by the aerial roots due to high air humidity in a tropical forest (Dušek & Krístek, 1986;

Figure 5 SEM micrographs—upper rose flower leaves, velvet surface with characteris-tic structure.

Figure 6 SEM micrographs—upper part of rose petals surface creating their velvet-like appearance and ensuring hydrophobic behavior, surface cells reveal deformed shapes due to the air-drying process, non-dried cells reveal regular cone shapes (Koch et al., 2009).

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Slavík, 2000). Excessive air humidity could be very deleterious for plants however. Flowers surface is perceived by naked eye to be glossy and glitter-ing. Such a surface is created by the special structure reminding us of tiny tongues which grow perpendicular to the cell base and is formed by obvi-ous strongly grooved protrusions. The height of these protrusions is from 25 up to 40 μm, width is in the range from 25 up to 30 μm. The regular surface grooves covering the cells have a thickness of about 1 μm and a depth of few micrometers. This hierarchical structure ensures the hydro-phobic character of flower surface in the case of plants (see Figures 8–10).

White snowberry (Symphoricarpos) is an undemanding bush that can grow on any type of soil and is tolerant to any moisture and light

Figure 8 Orchid petals.

Figure 7 SEM micrographs—lower part of rose petals surface.


conditions. This bush is, from the botanical point of view, interesting for its heterophyllous leaf structure (different shapes of leaves) (Attenborough, 1996; Kremer, 1995). Some leaves are entire, while others are deeply lobed. The character of leaves surface is specific from the technical point of view too. Water droplets falling on these leaves cannot hold on their surfaces and

Figure 9 SEM micrographs—part of orchid flower surface with characteristic surface structure (regularly grooved surface peaks).

Figure 10 SEM micrographs—structured orchid flower surface peaks with evident surface grooves.

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roll away immediately. That is due to the characteristic surface structure that is created by a tangle of submicroscopic protrusions growing almost perpendicularly to the leaves surface. The diameter of every protrusion is in the range from 100 up to 200 nm, while height range of every protrusion is from 200 up to 500 nm. The SEM micrograph of leaf surface reveals the regular arrangement of this substructure with the hundreds of micrometers place of value (see Figures 11–14).

Figure 11 White snowberry leaf.

Figure 12 SEM micrographs—upper surface of white snowberry leaf. There is evident a structure which consists of rhomb-like appearance (left). Individual formations reveal their own surface structure (right).


Nasturtium (Tropaeolum) comes from the northern tropical parts of the South America. This is an annual fleshy herb that has been used in natural medicine due to its bacteriostatic and insecticidal effects (Slavík, 2000). During the microscope observation, one can see the community of its sur-face with the white snowberry surface leaves character. Individual cells of

Figure 13 SEM micrographs—detail of white snowberry leaf surface structure. Peaks creating the leaf surface are additionally covered by fine-structured protrusions with submicron size.

Figure 14 SEM micrographs—regular arrangement of structured protrusions covering the leaf surface.

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the leaf surface are covered by the specific tangle of perpendicularly grow-ing protrusions, whose diameter is around 200 nm and the height range is from 500 nm up to 1 μm. The nasturtium flowers and leaves reveal the hierarchical structure and the water-repellent surface character similarly like how the snowberry leaves do (see Figures 15–18).

Figure 15 Nasturtium flowers and leaves.

Figure 16 SEM micrographs—upper surface of nasturtium leaf—overview (left) and detail (right).


White clover (Trifolium repens) is a widespread plant which can be found on all continents, except the Antarctica. A white clover is unique because it can be found both in the lowlands and in the above-lying areas (mountains). It grows up to 2300 m above sea level in the Alps, but was also already found above the snow line at 2760 m above sea level (Slavík, 2000).

Figure 17 SEM micrographs—upper surface of nasturtium leaf (left), the leaf surface is covered by a tangle of nanostructured protrusions (right).

Figure 18 SEM micrographs—lower surface of nasturtium leaf (left), detailed micro-graph of a leaf surface with specific structure (right).

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The white clover leaf surface reveals the special structure resembling a crumpled gossamer forming the regular circular folds at microscopic observation. The diameter of these units is within the range from 20 up to 30 μm. Very fine plates form a kind of quasi-secondary structure that grows almost perpendicularly to the surface. These platelets with lengths ranging from 300 up to 600 nm and a thickness from 50 up to 150 nm are arranged stochastically; nevertheless at lower magnification, one can get the impres-sion of the homogeneous structure. This hierarchical structure together with the chemical composition of plant leaves platelets provides plants the hydrophobic character within the desired range (see Figures 19–22).

Historically, the banana tree (Musa) has been apparently cultivated in the Southeast Asia, where it grows in its original botanical species. According

Figure 19 White clover flowers and leaves.

Figure 20 SEM micrographs—upper part of white clover leaves surface (left), detailed micrograph of leaf surface (right).


Figure 21 SEM micrographs—white clover leaf submicron size homogeneous surface waxy structure (left), waxy platelets (right).

Figure 22 SEM micrographs—lower part of white clover leaf surface without specific submicroscopic layer.

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to archeological findings, this tree was probably planted at the current territory of Papua New Guinea from 8000 to 5000 years BC (Nowak & Schultz, 2002; Rohwer, 2002; Valícek et al., 2002). The banana tree origi-nally came from areas with a higher-than-average rainfall. The leaves surface is properly adapted to these conditions thus to be hydrophobic and will not be permanently wet, which would restrict the photosynthesis process. The hydrophobic banana tree leaves surface layer reveals the characteristic struc-ture created from the column units growing up more or less perpendicular to the leaf surface. Diameters of single columns are within the range from 80 up to 150 nm, while the height range is from 300 up to 500 nm. In some cases, it is seen that the columns are very close to each other, or are directly fused. One can see the specific leaf row surface structure at a low microscope magnification or just by naked eye. This row structure ensures droplets running-down to the plant stem (see Figures 23–26).

European olive (Olea europium) is a slow-growing evergreen tree spe-cies found mainly in the Mediterranean. Narrow lanceolate leaves with the characteristic gray-green coloration which have the typical silver tint on the bottom leaf side grow up on the thorny branches of olive trees (Sterry, 2006; Vetvicka, 2005; Zelený, 2005). However, this silver tint of leaves visible by naked eye is not color to all intents and purposes in the true sense, but only the impression generated by light reflection and refraction on the leaf structure. Especially bottom leaves side is continuously covered by the waxy-like character cells with specific shape. Also, the upper side of the leaves is thus protected, but because the stomata are located mainly on

Figure 23 Banana tree. Banana tree leaf row surface.


Figure 24 SEM micrographs—banana leaf surface with characteristic row surface structure.

Figure 25 SEM micrographs—upper part (surface) of banana leaf with specific structure.

Figure 26 SEM micrographs—detailed micrograph of the structure observed among individual rows on the banana leaf upper surface.

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the lower leaf side, there are much less cells, which are associated with own leaf coloration. Cells are embedded in the leaf base. They have a star-like shape and the diameter is within the range from 100 up to 150 μm. During dry weather which is characteristic for the Mediterranean region, the cells aggregate thus forming the protective barrier against the excessive water evaporation from leaves (see Figures 27–29).

Figure 27 European olive tree.

Figure 28 SEM micrographs—olive tree leaf surface, upper part of leaf with lower number of cells (left), lower part of leaf with cells close to each other (right).


Horsetail (Equisetum arvense) belongs to the oldest plants of the Earth. This type of horsetail can be found both in the lowlands and in mountain-ous areas (Slavík, 2000). The horsetail surface is also created hierarchically. The precipitated spiral formations of silicon dioxide are clearly visible under the electron microscope. Dimensions of the individual plant surface silica particles are within the range from 2 up to 20 μm. Very fine plate-like formations are clearly evident at higher magnification. These tiny plate-lets are similar to structures that have been identified for the white clover surface. The length of platelets changes within the range from 200 up to 500 nm and their thickness is from 50 up to 100 nm. Platelets are growing almost perpendicularly to the surface and are stochastically arranged as in the case of white clover leaves surface. It is possible to perceive this stochas-tic orderliness as the homogeneous structure at lower magnification. There is certain interest about these tiny platelets because they cover the surface of the precipitated silica particles too, thereby it seems that they are created secondarily on the silicon dioxide surface. As was noted in previous stud-ies (Neethirajan et al., 2009) the horsetail belongs to a plant group where their cells are able to convert inorganic substances, especially silica. In this way, precipitated silica is used for functions associated with own growth and reproduction. Silica strengthens the construction of the plant body, helps the own thermoregulation of plant, reveals the bacteriostatic effect, and last but not least discourages herbivores from eating plants, as it negatively affects their tooth enamel (Neethirajan et al., 2009) (see Figures 30–33).

Figure 29 SEM micrographs—characteristic shape of barrier waxy cells (left—detail of leaf fracture surface) and waxy cells embedded in leaf surface (right).

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Benjamina ficus (Ficus benjamina) is a well-known home decorative plant that comes from the Southeast Asia region and Australia (Sterry, 2006). The trees reach a height of 30 m at natural conditions. The leaves are oval, pointed at the end, and noticeably shiny. Although leaves of this plant seem to be glossy, their surface reveals a very interesting structure. Larger or smaller thin platelets growing up perpendicularly from the leaf base are

Figure 30 Horsetail.

Figure 31 SEM micrographs—horsetail stem surface (left), part of stem surface struc-ture (right).


regularly arranged around stomata and are clearly visible from micrographs. Length of larger platelets is from 4 up to 8 μm, while their thickness is less than 1 μm. Smaller plates surrounding them are in submicron size. Leaves of these plants are characterized by the water-repellent surface (see Figures 34 and 35).

Figure 32 SEM micrographs—horsetail stem surface structure—overview (left) and spiral formation created by precipitated silicon dioxide (right).

Figure 33 SEM micrographs—horsetail stem surface—tiny waxy platelets covering both leaves and precipitated silicon dioxide particles surface (left), nanostructured waxy platelets (right).

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Lady’s mantle (Alchemilla vulgaris) is a perennial herb growing from lowlands to mountains. Alchemilla got its name from era of the medieval alchemists, researches, who in search of gold and the Philosopher’s Stone used the “heavenly dews”—drops of water noticeably glittering on the lady’s mantle leaves (Slavík, 2000). The creation of “heavenly dews” can be easily explained by studying the plant surface. A large number of fine hairs covering the leaves surface are clearly visible by naked eye. The hairs have a length of up to 1 mm, the diameter is within the range from 20 up to 40 μm, depending on whether it is at the end of the hair or its base. Although hairs on leaf surface appear as dense, the distance between the

Figure 34 Benjamina ficus.

Figure 35 SEM micrographs—upper part of benjamina ficus leaf surface. Detailed micrograph with evident regular distribution of stomata (left), two waxy platelets types covering leaf surface (right).


individual hairs is about 1 mm on average. Hairs grow up from the leaf base that at first sight reminds us of a wrinkled cloth. One can get another idea about the hierarchical structure, by which this common herb is equipped, at closer look. About a micron surface protrusions grow up from the leaf surface revealing interconnection. The hierarchical structure is responsible for leaf surface water-repellent character, respectively for the excellent technology, which provides water outflow from the leaf stem surface to the plant roots (see Figures 36–38).

Figure 36 Lady’s mantle.

Figure 37 SEM micrographs—upper part of lady’s mantle leaf surface with characteris-tic long fibers (hair—left), leaf surface specific structure (right).

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The leaves of some grass types have a very rough surface when you touch them or you can even be cut (Slavík, 2000; Steinbach et al., 1998). Leaves of these grasses are truly equipped with teeth, which noticeably remind us of the saw teeth. However, it is revealed only under microscope scale. They are built upwards, so it is possible to move the hand upward grass leaf, but moving the hand in the opposite direction is practically impos-sible. Protrusions longitudinally covering the grass leaves were identified by the electron microscope observation. Protrusions have a height within the range from 60 up to 80 μm and length of about 100 μm. They occur not only at the edges of the leaves but at all leaves surface area. The other fine structure created by tiny platelets growing perpendicularly to the leave base was found out at higher magnification. Similar structures were identified for other plant surfaces too. This tiny structure is responsible for the water-repellent character of the leaf surface (see Figures 39 and 40).

Small tortoiseshell (Aglais urticae) belongs to the butterfly order that after the beetles creates the largest order of insects. They are spread all over the world, except the Antarctica (Kovarík, 2000; Novák & Severa, 1990; Zahradník, 2009). The creation of the butterfly’s wings is possible to consider as a nature miracle in comparison with the current knowledge of technological processes and reality that these processes consume a large number of raw materials and energy. Caterpillars hatched from the egg

Figure 38 SEM micrographs—upper part of lady’s mantle leaf surface structure with characteristic submicron net covering surface structure (left), connecting waxy struc-ture of leaf surface (right).


feed on the leaves of herbs and shrubs. There is the technological miracle resulting in the formation of wings when caterpillar changes to the chrysalis at certain evolution stage after the relatively short time at normal temperature, air moisture, and air pressure. From both sides are butterfly wings fitted with tiny superimposed scales that create rows. Individual scales are placed into formations resembling joints. The scales movement

Figure 39 SEM micrographs—grass fibrous structure with clearly visible “teeth” on the surface edges.

Figure 40 SEM micrographs—grass surface structure (left), tiny platelets waxy surface structure (right).

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and the rotation under the dynamic loading during the flight of butterfly is the reason for this technological innovation. There would be the danger of scales breaking when embedded stationary. The structure of the scales reveals a row character and the basic rows are far away from each other by about 2 μm and are connected by finer joints. The distance between the fine joints is in hundreds of nanometers, their own thickness being even smaller. It is possible to observe another structural level with nanometric dimensions at higher magnification. Chitin scales do not usually con-tain any pigments except melanin or pterins. Butterfly wings coloration that one perceives is mainly due to the individual scales structuring (see Figures 41–43).

It is well known that butterfly olfactory apparatus is one of the best developed in the animal kingdom (Feltwell, 1995; Zahradník, 2009). The micrographs show the butterfly antennae surface at two different magnifi-cations (see Figure 44).

Ground beetle (Carabus arcensis) belongs to the order of beetles which is one of the most common spread insects in this class and includes about 400,000 described species that can be found all over the world except the polar regions. Most of the beetles are closely bound to a particular habitat type, react to its changes, and during the evolution they have been able to perfectly adapt to many environments. Beetle wing cases ensuring the protection of their bodies usually protect membranous wings too (Kovarík,

Figure 41 Small tortoiseshell.


Figure 42 SEM micrographs—chitin scales regular distribution on butterfly wing base-ment (left), arrangement of chitin scales embedded in “joints” (right).

Figure 43 SEM micrograph—butterfly wing structure with tiny row structure of scales.

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2000; Rich, 1997). We can easily identify the beetle wing cases’s, hierarchi-cal structure during the microscopy research. Own wing case is protected by the surface layer that is generally resistant to water and ultraviolet radia-tion. Layers differ by species of beetles, their surface is often equipped with tiny hairs, and the surfaces usually have the water-repellent character. Layers thicknesses are about 20 μm. Below this layer there is by the evolution per-fectly developed composite system embedded in a protein matrix and con-sisting of the reinforcing chitin fibers of rectangular or square cross-section shape. The advantage of a rectangular cross-section shape of reinforcing fibers is improved by the fibers arrangement in the matrix thus minimizing its volume. The lengths of the fibers edges are within the range from 1 up to 5 μm depending on the location of the fibers in wing case. The fibers are composed into layers, with layers alternating with each other at an angle of 90° (Raab, 1999) (see Figures 45–48).

Moths (Lepidoptera) belong to the class of insects and are closely related to butterflies. An active night life is the fundamental difference between moths and butterflies, although there are moths that can fly dur-ing days too. The moth eyes are composed (facets) and each single eye (ommatidium) can see only certain part of the image. The complete mosaic image is created due to the connection between all nerve fibers from all eye parts into the single optic nerve. The moth eye is created from many individual arched loop eyes forming the ordered structure. Each eye reveals a hexagonal shape thus reaching the optimal arrangement. The diameter of each eye is within the range from 22 up to 25 μm. One can see the tiny

Figure 44 SEM micrographs—butterfly antennae surface.


hairs with more or less regular intervals in the hollows between individual eyes. This arrangement is important for the reflection and refraction of the wavelengths as incident light on the moth compound eye. Each eye (ommatidium) is further composed of the already smaller units, whose diameter is about 100 nm. The ability to perceive a large field of view is the main advantage of the insect compound eyes. Insect can see backward that

Figure 45 Ground beetle.

Figure 46 SEM micrograph—wing case protective surface. From the micrograph, more or less regular hexagonal structure that nature structures quite often reveal is evident.

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is associated with the need for quick orientation in space. The number of eyes varies and depends on the insect types or its kind of life and especially flight capability. The common number of eyes is around 5000 but some dragonflies reveal up to 28,000 eyes. Insect can perceive the ultraviolet light

Figure 48 SEM micrograph—regularly alternating chitin fibers layers.

Figure 47 SEM micrographs—wing case composite systems concur on the wing case protective layer. It is created by chitin fibers with visible oblong or square cross-section shape which can change depending on fibers position in wing case.


that is essential for the food provision from plants and the polarized light important for the navigation due to compound eyes (Macek, 2008; Rich, 1997) (see Figures 49 and 50).

One can realize during the study of egg shell (as the perfect natural shell) that perhaps no other evolution innovation did affect the land life in such a fundamental way. Due to the protective cover, the first reptile

Figure 49 SEM micrographs—moth compound eyes (left) with the specific structure (right).

Figure 50 SEM micrographs—individual compound eyes (ommatidia). There is evident slight camber and regular hexagonal shape (left), the internal nanostructure (rodlets) of compound eye one part (right).

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predecessors could breed their descendants far away from water thus finally dominating the land (Walters, 2007). The calcareous shell of a bird pro-tects the embryo from the drying out and mechanical influences, the shell reflects ultraviolet and infrared radiation and prevents the entry of bacteria. The hard eggshell is composed of the microscopic column crystals (mainly calcite). The composition of the crystals is as follows: 89–97% calcium carbonate and 2% magnesium carbonate, 0.5–5% calcium phosphate and magnesium phosphate, and 2–5% organic matter—glycoproteins. Inorganic crystals grow up in larger or smaller clusters on the base protein membrane. The protein membrane protects the fetus from bacteria (Hunton, 2005). The individual columns of crystals are formed by even finer crystals grow-ing up in a circular arrangement. There is free space—the pores between individual columns. The pores allow gas exchange between the external environment and the internal space—or more precisely the developing organism. During hatching by these pores, the embryo receives oxygen and eliminates carbon dioxide and water vapor (see Figures 51–53).

Sharks (Selachimorpha) belong to the oldest animals from the present fauna point of view. The first sharks were found out in Ordovician layers from the era 450 to 420 million years ago. It was before both the first ter-restrial vertebrates were discovered on the Earth and the plant colonization of continents. Ordovician sharks, however, differed from the current spe-cies. Most of the current sharks can be identified back to the days before 100 million years ago (Maniguet, 1994). Sharks are perfectly adapted to move in water not just because of the body shape, but also due to its

Figure 51 Egg shell.


surface. The shark skin surface layer is covered with the placoid scales. The scales have a characteristic chemical composition and their shape resembles a hexagon. The special shape and arrangement of scales is used in order to reducing drag and reducing turbulences. The above-mentioned behav-ior can reduce frontal resistance when the shark moves in water and its speed can be increased with lower energy consuming. Own saddle-shaped

Figure 52 SEM micrographs—protein protective membrane (left) against bacteria, the column crystals of calcium carbonate abutting on the protective membrane (right).

Figure 53 SEM micrographs—lower part of calcium carbonate column crystals base (left) by which they abut on the protective membrane, the detail of crystals base (right).

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structure of surface scales is placed on stalk connecting scale with the skin base. The scale is composed of hydroxyapatite particles that are embedded in a protein matrix. That is a composite particle system. The width of scales is within the range from 150 up to 200 μm, while the distance between the longitudinal grooves is about 40 μm. The depth between the longitudinal grooves is within the range from 10 up to 20 μm. The transverse scale structure is clearly visible at the scale surface from the micrograph that can be related to their growth during the shark life (see Figures 54 and 55).

Teeth (dens) generally reveal a high stiffness and a high compressive strength. Especially the dental enamel is an extremely interesting material. It is hard, abrasion resistant, but yet tough. Its thickness reaches a maximum of 2.5 mm (Vigné, 2008). A combination of material properties such as strength, hardness, and toughness is practically unapproachable by synthetic materials. The secret of the dental enamel rests in its special structure. It is created by the hydroxyapatite fibrous crystals with only a few micrometers in diameter and of several hundred micrometers in length oriented perpen-dicularly to the tooth surface (Raab, 1999). These fibrous crystals further consist of the submicron longitudinal formations that are created by more or less spherical hydroxyapatite particles. There are tiny pores filled with water among the closely arranged mineral formations. The mechanical energy is absorbed during biting due to these submicroscopic pores filled with water

Figure 54 SEM micrographs—regular and symmetric placoid scales distribution on the shark skin.


which serve as microscopic liquid absorbers. Dental enamel is composed of 96% mineral phase, the rest being water and the organic phase. Proteins—amelogenin and enamelin-can be found in such an organic phase. The importance of these proteins is not yet fully understood, but it is thought that they manage the development of the tooth enamel (see Figures 56–58).

Figure 55 SEM micrographs—placoid scales surface with clearly visible longitudinal grooves and attachment into skin basis.

Figure 56 SEM micrographs—the tooth fracture surface (left), the dental enamel fibrous structure (right).

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4. DISCUSSION

The plant object surface structures reveal the hierarchical arrange-ment ranging from macrosize to microsize and very often up to nanosize.

Figure 57 SEM micrographs—the dental enamel fibrous structure.

Figure 58 SEM micrographs—detail of the one fibrous crystal created by finer sub-microscopic structure formations (left), dental enamel hierarchical structure primarily created by hydroxyapatite nanoparticles (right).


Garden violet (pansy), rose, and orchid exhibit analogous surface structure, consisting of the convex (say about dome-shaped) surface cells that are further surface structured. The common feature of these objects is the specific surface, which is visible by naked eye as a velvet-like sur-face. The hydrophobic behavior is a truly important behavior of these surfaces.

On observation of white snowberry and nasturtium leaves the surface was found to show that their protection against wetting is ensured in the same way or more precisely by the same surface structure consisting of the waxy rodlets formations with nanometers size.

White clover and the F. benjamina (weeping fig) have surface cells cov-ered with waxy platelets growing up perpendicularly to the surface cells base. The platelets length is from micron to submicron size, thicknesses reaching from tens to hundreds of nanometers. In the case of white clover, platelets are arranged stochastically on the surface but this arrangement nevertheless forms a homogeneous structure. F. benjamina shows a similar waxy platelets size but they are not arranged stochastically but circularly around the stoma.

Horsetail reveals the typical hierarchical surface structure that is com-posed by both the inorganic micrometer silica particles forming the simple point or the spiral formations and waxy platelets that provide hydrophobic behavior. It seems that the primarily precipitated inorganic shapes are sub-sequently superimposed by the waxy platelets.

Similarly excluded very soft waxy structural units were identified on the lady’s mantle surface and selected grasses.

The specific structure providing the hydrophobic surface behavior has been identified on the banana leaves surface. The structure consists of the individual or joined column formations with diameter in the range from 80 up to 150 nm and height in the range from 300 up to 500 nm. These submicron-size units are arranged into the smaller and subsequently larger longitudinal lines thus enabling running down of the water to the plant stem and also providing the perfect water management.

European olive tree reveals the perfectly managed water management too. Its leaves are covered by the specific shaped cells that are at high temp-eratures approaching each other and thus form a surface waxy barrier to prevent excessive transpiration.

The representatives of insect are equipped with very interesting struc-tures. Wings of small tortoiseshell as well as other species of butterflies are characterized by mutually superimposing chitin scales thereby forming a

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large and a light enough wings area. Butterfly wings are the typical example of the hierarchical structure that includes structures in the macro-, micro-, and nano-scale but also the example of the perfectly managed technologi-cal process.

Some insect species are adapted to dynamic loading to which they are exposed during their flight. The wing cases of such species are formed in a similar way as synthetic composite systems prepared by human to withstand long-term loading reveal. More or less square cross-section chitin fibers embedded in the protein matrix act as the wing cases reinforcing elements. The perfect distribution of a protein matrix is subjected by the specific fibers cross-section, which is technologically entirely inimitable by human being.

The structure of insect eyes reveals a hierarchical micro- and nano-structure also with a characteristic hexagonal arrangement so typical of natural objects. Inorganic–organic micro- and nanostructures observed and described for an egg shell, shark skin, and tooth enamel are the perfect examples of the chemical composition, shape, and design. The inorganic phase providing systems their strength, hardness, toughness, resistance to pressure, or abrasion is surrounded by an organic phase, which assumes the function of binder that ensures toughness. The egg shell structure is also passable for gases and water vapor and completely impassable for bacteria that could endanger the life of the developing embryo. The organic phase respectively different types of proteins control arrangement of the inorganic particles into the upper structural units, as for example in the case of dental enamel. These structures can be considered as perfect from the point of view of technological processes which have not been reached by human beings until nowadays.

However, it should be noted that many successes have already been achieved in the imitation of natural structures. It is possible to mention the following examples: the technology utilized in the manufacture of swimming needs by which (upon the base of the shark skin) a hydrody-namic resistance during swimming was minimized, special foils for reduc-tion in airflow resistance, the self-cleaning coatings using the principle of the so-called lotus effect that is based on the chemical composition and the structure hierarchy simulating hierarchy of superhydrophobic plant surfaces, the colorless textile fibers manufactured according to the butterfly wing scales pattern changing colors in dependence on the light reflection.


5. CONCLUSION

The following conclusions based on the study of selected structures for plant and animal objects were formulated:• thestructurehierarchieswerefoundoutatmostoftheselectednatural

objects structures; these structure hierarchies are generally related to the functions that parts of given objects have to fulfill and are modified by the different natural conditions where the object has been evolved and where it is situated,

• microstructureandnanostructureplantssurfacesformationsaregener-ally of the organic waxy origin and their shape is related to the natural conditions in which the objects are situated, but there are formations consisting of the inorganic compounds too,

• microstructureandnanostructureobjectsoccurringintheanimalking-dom are of the organic origin but often there are composite systems consisting of inorganic particles embedded in an organic phase, where the inorganic particles provide a system hardness, strength, and abrasion resistance, while the organic phase allows their mutual connection and ensures toughness of the system as a whole, the organic phase in the form of different proteins types controls arrangement of the inorganic phase into the different shapes crystallic structures,

• thesameorverysimilarsurfacestructuresthatrevealsimilarbehaviorassociated with hydrophobic surface properties were found out at different plants types,

• theinternalstructuresofthestudiedobjectsaredesignedforthespecificmechanical loading and also reveal the hierarchical orderliness,

• nanostructures,microstructures,andmacrostructuresareinnaturecreatedso as to fulfill the vitality and reproduction both for plant and animal world.

ACKNOWLEDGMENTSI would like to express thanks to my colleague Pavel Kejzlar for making all scanning elect ron micrographs and Rudolf Krois for making plant and animal photographs. The work was car-ried out under the Projects MSM 4674788501 and CxI CZ.1.05/2.1.00/01.0005.

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