Collagen pre-strain discontinuity at the bone—Cartilage interface

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-...

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Bibliographic Details
Published in:PloS one 2022-09, Vol.17 (9), p.e0273832-e0273832
Main Authors: Badar, Waqas, Ali, Husna, Brooker, Olivia N, Newham, Elis, Snow, Tim, Terrill, Nicholas J, Tozzi, Gianluca, Fratzl, Peter, Knight, Martin M, Gupta, Himadri S
Format: Article
Language:English
Subjects:
Analysis
Biology and Life Sciences
Biomechanics
Bone remodeling
Calcification
Cancellous bone
Care and treatment
Cartilage
Cartilage diseases
Collagen
Compression
Compressive properties
Degeneration
Diagnosis
Extracellular matrix
Fibrils
Health aspects
Interfaces
Mechanical properties
Medicine and Health Sciences
Microscopy
Mineralization
Osteoarthritis
Periodicity
Physical Sciences
Physiology
Research and Analysis Methods
Swelling pressure
X-ray scattering
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Summary: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.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0273832