Meeting Abstract
The epidermis and dermal layers of shark skin have characteristics that increase hydrodynamic efficiency. The denticles are superficial dentin-rich projections embedded in the epidermis that reduce friction drag during locomotion and inhibit algal growth. The stratum compactum, an interior layer of the dermis, is composed of layers of collagen fibers wound in two distinct orientations. Both the denticles and the angle of collagen fibers have been found to vary significantly in respect to anatomical location. The goal of this study was to quantify differences in fiber angle and denticle density (denticles/mm^-2) around the circumference of the shark and among species, and to correlate those values with the Ultimate Tensile Strength(MPa), Strain at Maximum Load(%), Toughness(MPa), and Young’s Modulus(MPa) of the skin in two directions of uniaxial stress: longitudinal and circumferential. The skin used for these experiments was located between the two dorsal fins, and came from two species, the great hammerhead,Sphyrna mokarran, and the tiger shark, Galeocerdo cuvier. The skin section was divided into a grid of 9 rows and 3 columns, with each square having the dimensions of 5cmx5cm. Denticle density and fiber angle were assessed under a microscope and quantified using ImageJ. Each square was then divided into 4 dog-bone shaped sections, two at each orientation, and used in tensile testing on an Instron E1000. We found significant differences among species and also by testing orientation. For example, G cuvier was stronger than S. mokarran in both orientations, and both species were stronger when skin was tested in the circumferential orientation. Finally, skin strength decreased with increasing denticle density in both species.
