Correlation analysis of cartilage wear with biochemical composition, viscoelastic properties and friction

Abstract

Healthy articular cartilage exhibits remarkable resistance to wear, sustaining mechanical loads and relative motion for decades. However, tissues that replace or repair cartilage defects are much less long lasting. Better information on the compositional and material characteristics that contribute to the wear resistance of healthy cartilage could help guide strategies to replace and repair degenerated tissue. The main objective of this study was to assess the relationship between wear of healthy articular cartilage, its biochemical composition, and its viscoelastic material properties. The correlation of these factors with the coefficient of friction during the wear test was also evaluated. Viscoelastic properties of healthy bovine cartilage were determined via stress relaxation indentation. The same specimens underwent an accelerated, in vitro wear test, and the amount of glycosaminoglycans (GAGs) and collagen released during the wear test were considered measures of wear. The frictional response during the wear test was also recorded. The GAG, collagen and water content and the concentration of the enzymatic collagen crosslink pyridinoline were quantified in tissue that was adjacent to each wear test specimen. Finally, correlation analysis was performed to identify potential relationships between wear characteristics of healthy articular cartilage with its composition, viscoelastic material properties and friction. The findings suggest that stiffer cartilage with higher GAG, collagen and water content has a higher wear resistance. Enzymatic collagen crosslinks also enhance the wear resistance of the collagen network. The parameters of wear, composition, and mechanical stiffness of cartilage were all correlated with one another, suggesting that they are interrelated. However, friction was largely independent of these in this study. The results identify characteristics of healthy articular cartilage that contribute to its remarkable wear resistance. These data may be useful for guiding techniques to restore, regenerate, and stabilize cartilage tissue.

Keywords: Cartilage; Collagen; Crosslinks; Friction; Glycosaminoglycans; Pyridinoline; Viscoelastic; Wear.

Figure 1.

Wear test set-up. Osteochondral specimens underwent reciprocating motion while loaded against a polished T316 stainless-steel plate. The wear test was performed in PBS containing protease inhibitors. Friction and normal forces were collected from the two-axis load cells and the coefficient of friction was calculated. Adapted from Hossain et al., 2020.

Figure 2.

Positive correlations between A) the GAG and HYP released in the wear of articular cartilage; B) HYP and GAG content of cartilage, each normalized to tissue wet weight (WW).

Figure 3.

Negative correlations between matrix constituents and cartilage wear. HYP content normalized to tissue wet weight (WW) (A, B); GAG content normalized to tissue WW (C, D); PYD density (E, F); water content (G, H); HYP released due to wear (A, C, E, G); GAG released due to wear (B,D, F, H).

Figure 4.

Relationships between viscoelastic material properties and cartilage wear. HYP released due to wear (A – C); GAG released due to wear (D-F); instantaneous modulus, E_inst (A, D); equilibrium modulus, E_eq (B, E); time constant, τ (C, F).

Figure 5.

Relationship between cartilage composition and viscoelastic material properties. HYP content normalized to tissue wet weight (WW) (A – C); GAG content normalized to tissue WW (D-F); PYD density (G-I); instantaneous modulus, E_inst (A, D, G); equilibrium modulus, E_eq (B, E, H); time constant, τ (C, F, I).

Figure 6.

Representative mean coefficient of friction (COF) value calculated for each reciprocating cycle of the wear test.

Figure 7.

Relationship between cartilage composition and coefficient of friction. HYP content normalized to wet weight (WW) (A, B); GAG content normalized to WW (C, D); PYD density (E, F); water content (G, H); initial coefficient of friction (A, C, E, F); equilibrium coefficient of friction (B, D, F, H).

Figure 8.

Relationship between coefficient of friction and viscoelastic material properties in cartilage. Initial coefficient of friction (A – C); Equilibrium coefficient of friction (D-F); Instantaneous modulus, E_inst (A, D); Equilibrium modulus, E_eq (B, E); Time constant, τ (C, F).

Figure 9.

Relationship between cartilage wear and coefficient of friction. Initial coefficient of friction (A, C); Equilibrium coefficient of friction (B, D); HYP released due to wear (A, B); GAG released due to wear (C, D).