## 3 Biomechanics of Articular Cartilage
### Mechanical Properties of Articular Cartilage
Its use makes it possible to analyse the elastic and viscoelastic properties of a material [51]. Using this method, [PERSON] et al. [175] evaluated the effect of enzymatic removal of glycosaminoglycans (GAG) on the viscoelastic properties of AC. Dynamic tests were used to examine the AC response before and after enzymatic digestion, making it possible to determine the contribution of extracellular matrix components to shear deformation resistance. Glycosaminoglycans have been shown to play an important role in suppressing mechanical forces, as a significant reduction in stiffness was observed, as well as an increase in energy loss after GAG removal. [PERSON] et al. [156] focused on studying the effect of ACL transection on the mechanical properties of the knee AC. Specimens were tested in dynamic shear using variable loads at different frequencies to assess the reduction in stiffness after injury. It was demonstrated that ACL transection affected the deterioration of the AC shear properties. Dynamic shear testing was also used in the work of [PERSON] et al. [176] to investigate alginate gels as potential scaffolds for tissue engineering. Dynamic tests were performed as a function of the alginate concentration and the presence of sodium ions, assessing the effect of these parameters on the mechanical properties of the gel. The obtained results indicate that the chemical composition and structure of the gel network have a significant effect on the dynamic properties. [PERSON] et al. [179] used this measurement method, among others, to assess the influence of pore geometry and architecture of scaffolds produced by direct fibre deposition. The material behaviour under variable loading was characterised, and the optimal structural parameters influencing the mechanical properties of the biomaterial, which can be intended for applications in bone and cartilage tissue engineering, were determined. The last of the mentioned measurement methods is the equilibrium shear test, which is used to determine the mechanical properties of AC by applying a constant shear strain and measuring the stress after reaching the equilibrium state [176; 183]. The use of this method makes it possible to isolate the elastic properties of the solid matrix, excluding the influence of time-dependent phenomena. [PERSON] et al. [183] investigated the nonlinear viscoelastic properties of AC using this method. Samples were subjected to gradually increasing shear strains and then held in a steady state of displacement to determine the variation of the shear modulus with strain. The obtained results indicated a nonlinear nature of the AC response in the equilibrium state. It was also shown that the shear angle has a significant effect on the steady-state stress, which indicates the complexity of this tissue's behaviour and its ability to adapt to different loading conditions. In the work of [PERSON] et al. [176], the use of this measurement method made it possible to determine the static shear modulus. It showed a significant dependence on the alginate concentration and the presence of sodium ions, which indicates that ionic interactions are crucial in controlling mechanical properties. Table 3 provides a comparative summary of selected measurement methods used to assess the mechanical properties of AC, including parameters, advantages and limitations.