CORRELATION OF ULTRASTRUCTURE AND TENSILE PROPERTIES OF A COLLAGENOUSCOMPOSITE-MATERIAL, THE EGG CAPSULE OF THE DOGFISH, SCYLIORHINUS SPP,A SOPHISTICATED COLLAGENOUS MATERIAL

The egg capsules of dogfish are largely constructed from laminae of pa rallel orientated collagenous fibrils arranged longitudinally, near-di agonally, and near-transversely. The fibrils show an axial (D) period of about 40 nm. These characteristics facilitated the observation of f ibril rotation and strain and the construction of an exploratory model of the mechanical behaviour based on composite theory. Low angle X-ra y diffraction demonstrated reversible changes in material strained up to 24%; the D period extended by 5% with a loss in transverse order. E lectron microscopy confirmed this fibril strain and demonstrated that failure of the interfibrillar matrix at moderate global strains was co nspicuous in the near-transverse laminae and less marked in the near-d iagonal ones. Light microscopy demonstrated that rotation of the near- diagonal fibrils occurred during global strain. The results of mechani cal testing are described. The model helps to explain the double S-sha ped stress/strain and unrecoverable deformation plots. The tensile beh aviour up to strains of 10% appeared dominated by failure of the inter fibrillar matrix in the near-transverse laminae. The behaviour of the material at strains in excess of this was thought to result from a com bination of rotation and straining of matrix and fibrils in the near-l ongitudinal and near-diagonal laminae. The egg capsule is thought to f unction as an efficient shock absorber reducing the likelihood of inju ry from both wave action and attempted predation by fish. (C) 1994 Aca demic Press, Inc.