Mechanisms for Tendon Viscoelasticity Determined through Qlv Analysis of Transverseand Fiber-aligned Samples

INTRODUCTION: Tendon viscoelastic behaviors are due to frictional losses that may arise from several sources: fluid flow, internal friction between aligned collagen fibers, intrinsic friction in extrafibrillar matrix components (e.g., proteoglycans and glycosaminoglycans), or interactions between the fibers and extrafibrillar matrix (1-4). While it is generally accepted that these are the potential mechanisms, their relative contribution to viscoelasticity is not known. By testing tendon samples oriented transverse and parallel to the fiber direction, it is possible to separate viscoelastic behaviors that are primarily extrafibrillar-related from those that are primarily fiber-related. Our objective was therefore to study the effect of fiber alignment on the viscoelastic properties of tendon using quasi-linear viscoelastic (QLV) modeling. We hypothesized that relaxation in transverse samples will be slower and smaller compared to fiber-aligned samples (i.e., τ1, τ2 will be larger and C will be smaller), due to fluid permeability differences. We further hypothesized that the elastic properties (A and B) will be larger for fiber-aligned samples, due to the stiffness of the fibers in tension.