Associations of human femoral condyle cartilage structure and composition with viscoelastic and constituent-specific material properties at different stages of osteoarthritis

Abstract

The relationships between structure and function in human knee femoral cartilage are not well-known at different stages of osteoarthritis. Thus, we characterized the depth-dependent composition and structure of normal and osteoarthritic human femoral condyle cartilage (n = 47) and related them to their viscoelastic and constituent-specific mechanical properties. We observed that, in superficial cartilage, the collagen network disorganization and proteoglycan loss were associated with the smaller initial fibril network modulus (collagen pretension). Furthermore, the proteoglycan loss was associated with the greater strain-dependent fibril network modulus (a measure of nonlinear mechanical behavior). The proteoglycan loss was also associated with greater cartilage viscosity at a low loading frequency (0.005 Hz), while the disorganization of the collagen network was associated with greater cartilage viscosity at a high loading frequency (1 Hz). Our results suggest that proteoglycan degradation and collagen disorganization reduce the pretension of the collagen network while proteoglycan degradation also increases the nonlinear mechanical response of the collagen network. Further, the results also highlight that proteoglycan degradation and collagen disorganization increase the viscosity of cartilage, but their contribution to increased viscosity occurs in completely different loading frequencies.