Dependence of crack shape in loaded articular cartilage on the collagenous structure

ABSTRACT

Cartilage cracks disrupt tissue mechanics, alter cell mechanobiology, and often trigger tissue degeneration. Yet, some tissue cracks heal spontaneously. A primary factor determining the fate of tissue cracks is the compression-induced mechanics, specifically whether a crack opens or closes when loaded. Crack deformation is thought to be affected by tissue structure, which can be probed by quantitative polarized light microscopy (PLM). It is unclear how the PLM measures are related to deformed crack morphology. Here, we investigated the relationship between PLM-derived cartilage structure and mechanical behavior of tissue cracks by testing if PLM-derived structural measures correlated with crack morphology in mechanically indented cartilages. Methods: Knee joint cartilages harvested from mature and immature animals were used for their distinct collagenous fibrous structure and composition. The cartilages were cut through thickness, indented over the cracked region, and processed histologically. Sample-specific birefringence was quantified as two-dimensional (2D) maps of azimuth and retardance, two measures related to local orientation and degree of alignment of the collagen fibers, respectively. The shape of mechanically indented tissue cracks, measured as depth-dependent crack opening, were compared with azimuth, retardance, or “PLM index,” a new parameter derived by combining azimuth and retardance. Results: Of the three parameters, only the PLM index consistently correlated with the crack shape in immature and mature tissues. Conclusion: In conclusion, we identified the relative roles of azimuth and retardance on the deformation of tissue cracks, with azimuth playing the dominant role. The applicability of the PLM index should be tested in future studies using naturally-occurring tissue cracks.

KEYWORDS:

• collagen fibers
• polarized light microscopy
• anisotropy
• skeletal maturity;
• osteoarthritis

Acknowledgements

We would like to express our gratitude to Ruth A. Seerattan for handling the histological processing, Dr. Tak-Shing Fung for guidance in statistical analysis and Tina Le for organising the histological sections.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

All data used in this study are available from the corresponding author upon request. https://cmailcarletonca-my.sharepoint.com/:f:/r/personal/engkuanmoo_cunet_carleton_ca/Documents/Data_AL-Saffar_Moo_ConnectiveTissueResearch_2023?csf=1&web=1&e=WnVqFU

Additional information

Funding

This study was supported by the Marie Skłodowska-Curie Actions postdoctoral fellowship (project number: 890936), Academy of Finland (grant 324529), the Canadian Institutes for Health Research, the Killam Foundation and the Canada Research Chair Programme.