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Journal Article

Collagen pre-strain discontinuity at the bone—cartilage interface


Fratzl,  Peter
Peter Fratzl, Biomaterialien, Max Planck Institute of Colloids and Interfaces, Max Planck Society;

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Badar, W., Ali, H., Brooker, O. N., Newham, E., Snow, T., Terrill, N. J., et al. (2022). Collagen pre-strain discontinuity at the bone—cartilage interface. PLoS One, 17(9): e0273832. doi:10.1371/journal.pone.0273832.

Cite as: https://hdl.handle.net/21.11116/0000-000B-1C80-5
The bone-cartilage unit (BCU) is a universal feature in diarthrodial joints, which is mechanically-graded and subjected to shear and compressive strains. Changes in the BCU have been linked to osteoarthritis (OA) progression. Here we report existence of a physiological internal strain gradient (pre-strain) across the BCU at the ultrastructural scale of the extracellular matrix (ECM) constituents, specifically the collagen fibril. We use X-ray scattering that probes changes in the axial periodicity of fibril-level D-stagger of tropocollagen molecules in the matrix fibrils, as a measure of microscopic pre-strain. We find that mineralized collagen nanofibrils in the calcified plate are in tensile pre-strain relative to the underlying trabecular bone. This behaviour contrasts with the previously accepted notion that fibrillar pre-strain (or D-stagger) in collagenous tissues always reduces with mineralization, via reduced hydration and associated swelling pressure. Within the calcified part of the BCU, a finer-scale gradient in pre-strain (0.6% increase over ~50μm) is observed. The increased fibrillar pre-strain is linked to prior research reporting large tissue-level residual strains under compression. The findings may have biomechanical adaptative significance: higher in-built molecular level resilience/damage resistance to physiological compression, and disruption of the molecular-level pre-strains during remodelling of the bone-cartilage interface may be potential factors in osteoarthritis-based degeneration.