Meeting Abstract

14.4  Monday, Jan. 4  Non-linear Viscoelastic Properties of Squalus acanthias Vertebral Columns Bending Dynamically PORTER, M.E.*; EWOLDT, R.H.; LONG, J.H; Vassar College; University of Minnesota; Vassar College meporter@vassar.edu

In engineering, any system is expected to behave linearly if the mechanical inputs are sufficiently small, even if the individual elements are non-linear. The properties of linear systems are the same at both largest and minimum strains within each testing cycle but may vary among cycles. In non-linear systems, properties vary within cycles. However, we often describe biological systems in terms of linear viscoelastic properties even when we are working with large inputs that may produce non-linear viscoelasticity. Our goal was to analyze the non-linear viscoelastic properties of vertebral column segments (ten centra) of Squalus acanthias, the spiny dogfish. Segments were dynamically bent on a MTS Tytron 250 at cycle frequencies ranging from 0.25 to 2.0 Hz and at various curvatures. We hypothesized that columns would stiffen at higher frequencies and curvatures and that during those high-input tests the system would become increasingly non-linear. We found that the linear elastic modulus (MPa) increased significantly with increasing frequency and curvature, as did the non-linear modulus at largest strain. However, the non-linear minimum elastic modulus was frequency-independent and curvature-dependent. The linear and non-linear viscous moduli (Pa s) are all significantly frequency- and curvature-dependent. These data contribute to the growing understanding of how cartilaginous skeletons respond to loads, and how those responses are correlated with swimming performance. This work was supported by NSF DBI-0442269 and IOS-0922605.