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Arthropod
cuticle is a composite material made up of two constituents: chitin fibers
and protein matrix. The cuticle is subdivided into two main layers epicuticle
and procuticle. Also keratin-containing materials, such as snake skin, gecko setae, bird feathers are studied (figure: SEM picture of the fracture of insect cuticle)
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The
plant materials are organised into several hierarchical layers.Plant actuators and wax layers are the most interesting systems under considerartion (figure: phase-contrast image of
a frozen section of plant material) |
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Detailed
information about the correlation of the mechanical properties and the
structure of biological materials may aid in understanding the relationship
between structure and function (figure: SEM picture of beetle terminal
elements attaching to surface irregularities. This visualises contact
behaviour of adhesive setae) |
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Surface
profile and chemistry of biological materials may be part of a particular
function. Understanding of the correlation between surface characteristics
of contacting surfaces and their biological function is an important goal
of our studies (figure: SEM picture of the surface of dragonfly head arresting system) |
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Knowledge about
the structure
and mechanical properties of biological materials
may
aid in understanding the relationship between structure and function. Arthropod
cuticle, reptile keratin and plant materials are three main groups of materials under study.
Arthropod
cuticle serves many functions. It limits body dimensions
and is a basis for muscle insertions (mechanical function and function
of locomotion). It is an important element in organism protection against
a variety of external factors, such as mechanical stress, dry, wet, cold
or hot environments. It takes part in the transport of diverse epidermal
secretions, and serves as a chemical reservoir for the storage of metabolic
waste products. A variety of cuticular structures are parts of mechano-
and chemoreceptors. The cuticle, its coloration pattern, and chemical
components are important for thermoregulation, and are often involved
in diverse communication systems. Specialised cuticular protuberances
may serve a variety of functions, such as oxygen retention, food grinding,
body cleaning (grooming), etc..
Snake locomotion relies on the frictional properties of the skin, which can demonstrate friction maximisation, minimisation and frictional anisotropy. Wear reduction of the snake skin is related to the gradient of material properties.
Insect
attachment pads evolved mainly as adaptations for efficient locomotion
on plant surfaces. However, plant surfaces have a wide range of textures.
They may be smooth, hairy, or covered with waxes or moist secretions.
As with any integument, plant cuticle, with related structures, is a functional
organ reflecting a number of environmental pressures. These pressures
resulted in the particular design, ultrastructure, and chemistry of the
plant surface. During the long period of co-evolution between flowering
plants and insects, plants have developed not only structures attracting
pollinators, but also a wide variety of structural and chemical attributes
of their surface related to defence against herbivores.
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