249
apatite containing a small amount of sodium and magnesium ions, as well as
carbonate anions in phosphate sites of the apatite lattice,” (Ikom et al. 2003 ). The
tensile strength of this fi sh scale reaches 90 MPa. This value is high because of the
hierarchically ordered structure of “mineralized collagen fi bers, in association with
long, narrow platelike apatite crystals that are aligned along the crystallographic
c-axis parallel to the collagen fi bers,” (Ikom et al. 2003 ). Functional advantages
based on mechanical anisotropy of collagen-mineral-containing composite matrices
are well known (Bigi et al. 1996 ). The tensile stress–strain curve obtained by Ikom
et al. ( 2003 ) was initially linear with a corresponding Youngs modulus (stress/
strain) of 2.2 GPa. In comparison with data reported for red deer (50 %, 6.1 GPa)
and axis deer (80 %, 31.6 GPa) (Currey and Brear 1990 ; Mann 2001 ), this value
confi rms the relatively low stiffness of the fi sh scales due to their small mineral
content (46 %). As reported in the discussed work, “at high stress values, the tensile
stress–strain curve showed considerable plastic yielding before fracture.
Corresponding SEM images of the fracture surface indicated that sliding of the
collagen lamellae and pulling out of individual collagen fi bers, 2–3 μm in thickness,
were responsible for the plasticity close to the yield point (Fig. 5.12 ). Demineralization
of the fi sh scales considerably reduced the average tensile strength and Young’s
modulus to values of 36 MPa and 0.53 GPa, respectively, although the fracture
behavior was essentially the same as for the mineralized tissue,” (Ikom et al. 2003 ).
Defi nitively, model presented by Vernerey and Barthelat ( 2010 ) is very much
idealized and can, probably, be used to assess general trends in the mechanics of fi sh
scale structures, probably only with respect to elasmoid scales. The situation with,
for example, multi-layered ganoid scale seems to be more complex. Thus, in ganoid
Polypterus seneglus scale, “each material layer was found to have signifi cantly
different mechanical properties compared to others (except for bone), as compared
to the isopedine layer,” (Bruet 2008 ). These nanocomposite structured layers are of
different thickness (from outer to inner): ganoine (ca. 10 μm), dentin (ca. 46 μm),
isopedine (ca. 45 μm) and the basal bone plate (ca 300 μm). The plastic and elastic
properties through the four layers were investigated spatially using high resolution
nanomechanical methods. The obtained data showed that both “indentation modulus and hardness decrease with distance from the outer to the inner surfaces of the
scale, from 62 to 17 GPa and 4.5 to 0.54 GPa, respectively,” (Bruet 2008 ).
The study on the ganoid armor scales of P. senegalus has elucidated the biomechanical advantages of ganoine–dentin–isopedine–bone- based multilayers in penetration resistance (Bruet et al. 2008 ), but at the added weight of the higher density
external layers (Song et al. 2010 ) as well as at the energetic “cost” of additional
biomineralization (Vermeij 2006 ). Recently, it was reported by Wang et al. ( 2009 )
that “the elastic-plastic anisotropy of the outmost ganoine layer of P. senegalus scale
enhances the load-dependent penetration resistance of the multilayered armor
compared with the isotropic ganoine layer by (i) retaining the effective indentation
modulus and hardness properties, (ii) enhancing the transmission of stress and dissipation to the underlying dentin layer, (iii) lowering the ganoine/dentin interfacial
stresses and hence reducing any propensity toward delamination, (iv) retaining the
5.1 Biomechanics of Fish Scales
apatite containing a small amount of sodium and magnesium ions, as well as
carbonate anions in phosphate sites of the apatite lattice,” (Ikom et al. 2003 ). The
tensile strength of this fi sh scale reaches 90 MPa. This value is high because of the
hierarchically ordered structure of “mineralized collagen fi bers, in association with
long, narrow platelike apatite crystals that are aligned along the crystallographic
c-axis parallel to the collagen fi bers,” (Ikom et al. 2003 ). Functional advantages
based on mechanical anisotropy of collagen-mineral-containing composite matrices
are well known (Bigi et al. 1996 ). The tensile stress–strain curve obtained by Ikom
et al. ( 2003 ) was initially linear with a corresponding Youngs modulus (stress/
strain) of 2.2 GPa. In comparison with data reported for red deer (50 %, 6.1 GPa)
and axis deer (80 %, 31.6 GPa) (Currey and Brear 1990 ; Mann 2001 ), this value
confi rms the relatively low stiffness of the fi sh scales due to their small mineral
content (46 %). As reported in the discussed work, “at high stress values, the tensile
stress–strain curve showed considerable plastic yielding before fracture.
Corresponding SEM images of the fracture surface indicated that sliding of the
collagen lamellae and pulling out of individual collagen fi bers, 2–3 μm in thickness,
were responsible for the plasticity close to the yield point (Fig. 5.12 ). Demineralization
of the fi sh scales considerably reduced the average tensile strength and Young’s
modulus to values of 36 MPa and 0.53 GPa, respectively, although the fracture
behavior was essentially the same as for the mineralized tissue,” (Ikom et al. 2003 ).
Defi nitively, model presented by Vernerey and Barthelat ( 2010 ) is very much
idealized and can, probably, be used to assess general trends in the mechanics of fi sh
scale structures, probably only with respect to elasmoid scales. The situation with,
for example, multi-layered ganoid scale seems to be more complex. Thus, in ganoid
Polypterus seneglus scale, “each material layer was found to have signifi cantly
different mechanical properties compared to others (except for bone), as compared
to the isopedine layer,” (Bruet 2008 ). These nanocomposite structured layers are of
different thickness (from outer to inner): ganoine (ca. 10 μm), dentin (ca. 46 μm),
isopedine (ca. 45 μm) and the basal bone plate (ca 300 μm). The plastic and elastic
properties through the four layers were investigated spatially using high resolution
nanomechanical methods. The obtained data showed that both “indentation modulus and hardness decrease with distance from the outer to the inner surfaces of the
scale, from 62 to 17 GPa and 4.5 to 0.54 GPa, respectively,” (Bruet 2008 ).
The study on the ganoid armor scales of P. senegalus has elucidated the biomechanical advantages of ganoine–dentin–isopedine–bone- based multilayers in penetration resistance (Bruet et al. 2008 ), but at the added weight of the higher density
external layers (Song et al. 2010 ) as well as at the energetic “cost” of additional
biomineralization (Vermeij 2006 ). Recently, it was reported by Wang et al. ( 2009 )
that “the elastic-plastic anisotropy of the outmost ganoine layer of P. senegalus scale
enhances the load-dependent penetration resistance of the multilayered armor
compared with the isotropic ganoine layer by (i) retaining the effective indentation
modulus and hardness properties, (ii) enhancing the transmission of stress and dissipation to the underlying dentin layer, (iii) lowering the ganoine/dentin interfacial
stresses and hence reducing any propensity toward delamination, (iv) retaining the
5.1 Biomechanics of Fish Scales