Effect of Degeneration on the Dynamic Viscoelastic Properties of Human Annulus Fibrosus in Tension

Physiological cyclic loading of the intervertebral disc generally occurs between 1 and 5 Hz [1]. However, most mechanical assessments of disc AF tissue have relied on uniaxial tensile tests under quasi-static conditions [2]. Furthermore, the few studies that have addressed AF viscoelasticity have reported only static viscoelastic properties such as creep or stress-relaxation [3]. As such, there exists almost no data characterizing the dynamic viscoelastic properties of AF tissue in tension. Such data would be critical for several applications: to elucidate the mechanical progression of intervertebral disc degeneration, to develop and validate structural finite element models, and to provide native tissue benchmarks for regenerative approaches that aim to restore mechanical function to diseased or degenerate tissue. Therefore, the objectives of this study are to: (1) quantify human AF tissue frequency-dependent and strain-dependent viscoelastic properties of human AF tissue in circumferential tension, and (2) determine the effects of disc degeneration on these properties.