Meeting Abstract

39.5  Monday, Jan. 5  Cartilaginous vertebral columns: mechanical responses to external loads and internal joint pressurization PORTER, ME*; LONG, JH; Vassar College; Vassar College meporter@vassar.edu

While we have shown that vertebral number and centra shape are important predictors of body curvature in cartilaginous fishes during powered turns, morphological correlates predict only about 50% of body curvature among five species. We are interested in determining what other, non-morphological and non-muscular features may be correlated with body curvature during swimming. Based on previous biomechanical work on axial skeletons, we predicted that variation in mechanical properties of the intervertebral joints correlates with variation in body curvature. To test this prediction, we tested motion segments (vertebra-joint-vertebra) from shark vertebral columns. Using a MTS Tytron 250 one-axis testing machine, we designed a rig that allowed us to measure storage and loss moduli of the segment loaded in shear, compression, and bending. Following initial characterization of the intact motion segment, we then punctured the external and internal intervertebral ligaments to eliminate the internal pressure within the capsule of the joint. Motion segments were cycled 50 times to remove the fluid components of the joint. We again tested the viscoelastic mechanics of the motion segment without internal fluid compartments. This procedure measured the effects of joint pressurization on mechanical properties, and we thus used this proxy for pressure as one of the mechanical properties compared across species. These data contribute to the growing understanding of how cartilaginous skeletons respond to loads, and how those responses are correlated with morphology and swimming performance. This work was supported by NSF DBI-0442269.