Effects of flow-dependent and flow-independent viscoelastic mechanisms on the stress relaxation of articular cartilage

St. Stoytchev, S. Nikolov

Abstract: Articular cartilage is a bearing material that lines the ends of the bones of synovial joints. The solid phase of articular cartilage is chiefly composed of complex macromolecules including collagen and proteoglycans. The fluid phase is presented by interstitial fluid filling in the solid phase’s pores. The rheological behavior of articular cartilage depends upon the intrinsic interaction between the solid matrix's deformation and the interstitial fluid's motion. Thus, the viscoelastic properties of articular cartilage arise from (1) the diffusional drag of relative velocity between the interstitial fluid and the solid matrix, or flow-dependent mechanism, and (2) the intrinsic viscoelastic properties of the solid matrix, or flow-independent mechanism. This study aimed to assess both mechanisms' contribution to the stress relaxation of articular cartilage.
The mathematical model of confined compression of articular cartilage was developed using the linear biphasic theory of Mow et al. [1]. The stress-time curves were computed using the quasi-linear viscoelastic model of Fung. The assessment procedure was considered based on the experimental data of Soltz and Ateshian [2].
Our findings envisage that the linear biphasic theory of Mow et al. failed in predicting stress relaxation, that is, the flow-dependent viscoelastic mechanism is not able solely (coincidence 41.4 % of the theoretical and experimental data) to cover the stress relaxation mechanism after stepwise loading. The interrelation between the intrinsic viscoelasticity and the permeability of the solid matrix is discussed.

Series on Biomechanics, Vol.37, No.1 (2023), 43-50
DOI: 10.7546/SB.07.01.2023

Keywords: Articular cartilage; stress relaxation; viscoelastic mechanisms

Date published: 2023-02-02