Meeting Abstract

25.7  Jan. 5  Structural properties of shark vertebrae: the functional contribution of mineral in mineralized cartilage PORTER, ME*; KOOB, TJ; Univ. of California, Irvine; Univ. of South Florida porterm@uci.edu

Mineral content is an important predictor of material properties in bone. Altering mineral content of bone can have dramatic effects on stiffness (the material�s ability to resist compression) and strength (the maximum stress the material can withstand before failing). The mineral content of elasmobranch vertebral cartilage varies across species and this variation significantly impacts both stiffness and strength. We reported that relatively high mineral fractions were found in cartilaginous vertebrae with stiffness and strength values nearing those of trabecular bone. In this study, we manipulated mineral content in elasmobranch cartilage from a single species to determine the functional contribution of the mineral phase to the material properties of the vertebrae in compression. We examined the compressive properties of vertebrae with their full mineral component and those in various states of demineralization. Also, vertebrae were compressed using 4 different strain rates (1%, 5%, 10%, and 20% per second) to determine viscoelastic effects. We tested vertebrae from five Mustelus californicus (Carcharhiniformes: Triakidae), the grey smooth-hound. All animals were male and approximately 80 cm total length to control for potential ontogenetic changes in the pattern of vertebral mineralization. Mineral was removed from vertebrae using EDTA. After material tests were performed the mineral content was measured by ashing each vertebra. Completely removing the mineral from the cartilage decreased the stiffness from 500MPa to 50MPa and strength from 40MPa to 8MPa. Strain rate had a significant effect by increasing strength but not stiffness. These observations establish that mineral content governs both strength and stiffness of mineralized vertebral cartilage in this shark, and is ultimately responsible for the differing material properties in other shark species.