The contribution of mineral to the material properties of vertebral cartilage from the smooth-hound shark Mustelus californicus.

Elasmobranch vertebral cartilage has a substantial mineral fraction (39-55%) and the arrangement of mineral varies among species. We examined vertebrae from one shark species, Mustelus californicus, to determine mineral content, the effect of mineral on material properties and the viscoelastic response of vertebral cartilage. We serially demineralized vertebrae and compressively tested them to failure at varying strain rates. Mineral in vertebral cartilage varies within individuals, intraspecifically and interspecifically; this is in contrast to bone, in which significant variation in mineral content is pathological or an interspecific effect. Within Mustelus, vertebrae with larger mineral fractions were significantly stiffer and stronger; however when variation is assessed across species, the structure has a larger effect. Shark vertebral cartilage did not show a substantial viscoelastic response at biologically relevant strain rates, validating the use of quasistatic testing for this material.