Molecular NMR T₂ values can predict cartilage stress-relaxation parameters

Articular cartilage lines synovial joints and functions as a low-friction deformable tissue to enable smooth and stable joint articulation. The objective of this study was to determine the relationships between cartilage stress-relaxation properties and the collagen and GAG NMR transverse relaxation times (T₂) toward understanding mechanisms of cartilage viscoelasticity. Stress-relaxation tests were performed on both cultured and enzymatically digested bovine cartilage, followed by measurements of both the collagen and GAG T₂ using the Call-Purcell-Meiboom-Gill pulse sequence. The peak and equilibrium stresses were correlated with the GAG T₂, and the stress-relaxation time constant was correlated with the collagen T₂. Multiple linear regression models were successful in using the specific T₂ values to predict the stress-relaxation properties. As a model of osteoarthritis, enzymatic digestion with collagenase and testicular hyaluronidase had weak effects on T₂ values. These data present a complex picture of cartilage mechanical behavior, with cartilage stiffness associated with the GAG T₂ values and the stress-relaxation time constant associated with the collagen T₂.