405
the developing embryos from displacement, and to some extent from predation. The
corners of the capsules produced by many oviparous dogfi sh (e.g., Scyliorhinus
canicula ) extend into dense tendrils that are much longer than the body of the capsule. These tendrils may be heavily spiralled or coiled, and are believed to help
anchor the capsules (Knight et al. 1996 ). The capsules of Heterodontus phillipi and
Heterodontus galeatus resemble a screw, and are literally screwed into narrow crevices in the substrate following oviposition,” (Heiden et al. 2005 ). This both protects
and supports the capsule (Smith 1942 ; McLaughlin and O’Gower 1971 ). Roland
Brown characterized the egg capsules of living Chimaeroid species as consisting of
two parts, dartlike to elliptic structures with characteristic morphological features.
The part with leathery, centrally located embryo case possesses bilateral symmetry.
The other part extends outward from the case in the horizontal plane, and is of membraneous nature (Brown 1946 ).
From biomaterials point of view, not only the form of egg capsules, but also their
chemistry, composition, and mechanical properties are of special importance.
Interestingly, besides teeth, scales and fi n, spines are the only mineralized skeletal
remains of fossil sharks. Their egg capsules are being increasingly reported from
Paleozoic and Mesozoic brackish to fl uvio-lacustrine deposits (Böttcher 2010 ;
Fischer et al. 2010a , b ). Studies on the chemical composition of these structures
started at the beginning of the twentieth century. For example, the paper published
in Journal of Biological Chemistry in 1908 was entitled “ Notes on the chemical
nature of egg cases of two species of sharks ” (Hussakof and Welker 1908 ). Later egg
capsule proteins were studied by Brown ( 1955 ) as well as by Cox et al. ( 1987 ).
Today, very specifi c egg capsule collagens, as well as polyphenol-containing proteins, are the “prime examples” for the biomaterials community.
12.1 Collagen
Collagenous composite material of the egg capsule of selachian fi sh is known as
“a sophisticated collagenous material ” (Hepworth et al. 1994 ). Why? As reviewed by
Knight and Vollrath ( 2001 ), “the Selachian egg case serves mainly as a shock absorber
to protect the embryo. The wall of the case is a highly cross-linked collagenous
composite material with a complex, multilamellate, highly hierarchical construction,”
(Knight and Vollrath 2001 ; see also Knight and Feng 1992 , 1994a , b ; Knight and
Hunt 1974 , 1976 , 1986 ; Rusaouën et al. 1976 ; Hunt 1985 ; Knight et al. 1993 ;
Gathercole et al. 1993 ; Knupp et al. 1996 , 1998 ). Evidence for the collagenous nature
of the dogfi sh egg case came from X-ray diffraction studies that indicated the
existence of a 2.9 A° meridional arc typical of collagens, the thermal shrinkage
characteristic curve (S-shaped with a mean half shrinkage temperature of 78 °C), and
amino acid composition analysis showing that glycines accounted for about 16 % of
the amino acid residues (Knight and Hunt 1974 ; Rusaouën et al. 1976 ).
In small-spotted catshark ( Scyliorhinus canicula ) the case wall is formed from
about 20 lamellae. According detailed description made by Knight and Vollrath
( 2001 ), “each lamella is built up from a single layer of fl attened collagenous
12.1 Collagen
the developing embryos from displacement, and to some extent from predation. The
corners of the capsules produced by many oviparous dogfi sh (e.g., Scyliorhinus
canicula ) extend into dense tendrils that are much longer than the body of the capsule. These tendrils may be heavily spiralled or coiled, and are believed to help
anchor the capsules (Knight et al. 1996 ). The capsules of Heterodontus phillipi and
Heterodontus galeatus resemble a screw, and are literally screwed into narrow crevices in the substrate following oviposition,” (Heiden et al. 2005 ). This both protects
and supports the capsule (Smith 1942 ; McLaughlin and O’Gower 1971 ). Roland
Brown characterized the egg capsules of living Chimaeroid species as consisting of
two parts, dartlike to elliptic structures with characteristic morphological features.
The part with leathery, centrally located embryo case possesses bilateral symmetry.
The other part extends outward from the case in the horizontal plane, and is of membraneous nature (Brown 1946 ).
From biomaterials point of view, not only the form of egg capsules, but also their
chemistry, composition, and mechanical properties are of special importance.
Interestingly, besides teeth, scales and fi n, spines are the only mineralized skeletal
remains of fossil sharks. Their egg capsules are being increasingly reported from
Paleozoic and Mesozoic brackish to fl uvio-lacustrine deposits (Böttcher 2010 ;
Fischer et al. 2010a , b ). Studies on the chemical composition of these structures
started at the beginning of the twentieth century. For example, the paper published
in Journal of Biological Chemistry in 1908 was entitled “ Notes on the chemical
nature of egg cases of two species of sharks ” (Hussakof and Welker 1908 ). Later egg
capsule proteins were studied by Brown ( 1955 ) as well as by Cox et al. ( 1987 ).
Today, very specifi c egg capsule collagens, as well as polyphenol-containing proteins, are the “prime examples” for the biomaterials community.
12.1 Collagen
Collagenous composite material of the egg capsule of selachian fi sh is known as
“a sophisticated collagenous material ” (Hepworth et al. 1994 ). Why? As reviewed by
Knight and Vollrath ( 2001 ), “the Selachian egg case serves mainly as a shock absorber
to protect the embryo. The wall of the case is a highly cross-linked collagenous
composite material with a complex, multilamellate, highly hierarchical construction,”
(Knight and Vollrath 2001 ; see also Knight and Feng 1992 , 1994a , b ; Knight and
Hunt 1974 , 1976 , 1986 ; Rusaouën et al. 1976 ; Hunt 1985 ; Knight et al. 1993 ;
Gathercole et al. 1993 ; Knupp et al. 1996 , 1998 ). Evidence for the collagenous nature
of the dogfi sh egg case came from X-ray diffraction studies that indicated the
existence of a 2.9 A° meridional arc typical of collagens, the thermal shrinkage
characteristic curve (S-shaped with a mean half shrinkage temperature of 78 °C), and
amino acid composition analysis showing that glycines accounted for about 16 % of
the amino acid residues (Knight and Hunt 1974 ; Rusaouën et al. 1976 ).
In small-spotted catshark ( Scyliorhinus canicula ) the case wall is formed from
about 20 lamellae. According detailed description made by Knight and Vollrath
( 2001 ), “each lamella is built up from a single layer of fl attened collagenous
12.1 Collagen