Meeting Abstract
The surface of shark skin is covered with dermal denticles that reduce drag and are hypothesized to increase swimming speeds. Denticle morphology and skin material properties have been shown to vary regionally along the body and denticle density has been correlated with skin material properties like stiffness and toughness. The stratum compactum, an interior layer of the dermis, is composed of sheets of collagen fibers wound in two distinct orientations that vary regionally and between species. Our goal was to assess the anisotropic mechanical and structural properties of shark skin among species. We determined the following mechanical properties in two directions of uniaxial stress (longitudinal and circumferential): ultimate tensile strength (MPa), strain at maximum load (%), toughness (MPa), and Young’s Modulus (MPa). From each shark, we dissected a section of skin from between the two dorsal fins, and we divided this section into a grid. For each cell of the grid, denticle density and fiber angle were assessed under a microscope and quantified using NIH ImageJ. Four dog-bone shaped samples, 2 at each orientation, were tested in tension until failure at a 2 mm/s strain rate on an Instron E1000. A stress-strain curve was generated for each sample and tensile properties were calculated. We found significant differences among species and testing orientation; skin is strongest in the circumferential orientation. Skin mechanical properties also correlated with denticle density. These data support the hypothesis that shark skin may act as an exotendon modulating body stiffness during swimming.
