Relaxation capacity of cartilage is a critical factor in rate- and integrity-dependent fracture

Abstract

Articular cartilage heals poorly but experiences mechanically induced damage across a broad range of loading rates and matrix integrity. Because loading rates and matrix integrity affect cartilage mechanical responses due to poroviscoelastic relaxation mechanisms, their effects on cartilage failure are important for assessing and preventing failure. This paper investigated rate- and integrity-dependent crack nucleation in cartilage from pre- to post-relaxation timescales. Rate-dependent crack nucleation and relaxation responses were obtained as a function of matrix integrity through microindentation. Total work for crack nucleation increased with decreased matrix integrity, and with decreased loading rates. Critical energy release rate of intact cartilage was estimated as 2.39 ± 1.39 to 2.48 ± 1.26 kJ m−2 in a pre-relaxation timescale. These findings showed that crack nucleation is delayed when cartilage can accommodate localized loading through poroviscoelastic relaxation mechanisms before fracture at a given loading rate and integrity state.

Microindentation Technique to Create Localized Cartilage Microfractures

“…Typical load, displacement, and time‐series raw data are obtained from microfracture experiments through the microindentation at slow and fast loading rates (Fig. 3B and 3C), which is consistent with a wider range of loading rates reported earlier by the authors (Han et al., 2021). Load‐versus‐displacement plots are obtained from the raw data and indicate the sudden drop in the load representing the first major point of fracture (Fig.…”

“…Analysis of microfracture experiments has shown that less energy is required to nucleate microcracks under fast than under slow loading because of a shift from pre‐relaxation scale to post‐relaxation timescale (Han et al., 2019). Microfracture data can also be used to estimate cartilage toughness as a function of cartilage matrix integrity (Han et al., 2021). Under fatigue loading, load and displacement time‐series data can be analyzed (Fig.…”

“…Our extended protocol will enable the research community to understand crack propagation at different loading combinations, such as fatigue loading, that have not been studied in detail. Previous studies of our group on the rate‐dependent crack nucleation (Han et al., 2019) and integrity and rate dependent fracture (Han et al., 2021) have used the standard protocols (Basic Protocols 1 and 3) described above.…”

High-frame-rate analysis of knee cartilage deformation by spiral dualMRI and relaxation mapping

“…Such measurements are connected with cartilage damage and PG content. 10,[41][42][43] Considering the fact that spiral DENSE MRI has a high penetration depth, it becomes an optimal method to measure viscoelastic behavior while easily tranferable to a clinical setting.…”

“…This is because viscoelastic measurements need data acquisition with time which may require special methods not suitable for rapid physiolocal movements or in a clinical setting. On the other hand, spiral DENSE MRI captures high temporal resolution images that can measure not only creep behavoir but also other viscoelastic responses of the tissue including time-dependent deformation 10,41 and relaxation time 42,43 . Such measurements are connected with cartilage damage and PG content.…”