Viscoelastic properties of the human medial collateral ligament

摘要: 10 Ligament viscoelasticity controls viscous dissipation of energy and thus the potential for injury or catastrophic failure. Visco-11 elasticity under different loading conditions is likely related to the organization and anisotropy of the tissue. The objective of this 12 study was to quantify the strain-and frequency-dependent viscoelastic behavior of the human medial collateral ligament (MCL) in 13 tension along its longitudinal and transverse directions, and under shear loading. The overall hypothesis was that human MCL 14 would exhibit direction-dependent viscoelastic behavior, reflecting the composite structural organization of the tissue. Incremental 15 stress relaxation testing was performed, followed by the application of small sinusoidal strain oscillations at three different equi-16 librium strain levels. The peak and equilibrium stress–strain curves for the longitudinal, transverse and shear tests demonstrate that 17 the instantaneous and long-time stress–strain response of the tissue differs significantly between loading conditions of along-fiber 18 stretch, cross-fiber stretch and along-fiber shear. The reduced relaxation curves demonstrated at least two relaxation times for all 19 three test modes. Relaxation resulted in stresses that were 60–80% of the initial stress after 1000 s. Incremental stress relaxation 20 proceeded faster at the lowest strain level for all three test configurations. Dynamic stiffness varied greatly with test mode and 21 equilibrium strain level, and showed a modest but significant increase with frequency of applied strain oscillations for longitudinal 22 and shear tests. Phase angle was unaffected by strain level (with exception of …