Collagen pre-strain discontinuity at the bone—Cartilage interface

Abstract

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.

A coarse-grained molecular dynamics investigation of the role of mineral arrangement on the mechanical properties of mineralized collagen fibrils

“…With this in mind, our results provide novel insight into the mechanical response of this fundamental tissue unit, considering it as an isolated system. One of the primary reasons for higher fracture strains of the MCFs with increasing mineral content was the higher residual strains in the system caused by presence of these minerals, which is a feature that has also been observed experimentally [67]. Eliminating the residual strain, our simulations showed that the fracture strain actually remained unchanged for different mineral contents.…”

3D-printed PCL scaffolds with anatomy-inspired bionic stratified structures for the treatment of growth plate injuries

“…4 G and I. It is well known that COL Ⅱ is associated with chondrocyte proliferation and cartilage phenotype maintenance [ 53 ]. Therefore, the small- and medium-pore regions were beneficial to chondrocyte proliferation and retain their differentiation capacity.…”

Denoising an X-ray image by exploring the power of its physical symmetry

“…SMAE allows us to efficiently recover physical information of spatially and temporally resolved data. For spatially resolved data, the strain gradient and orientation distribution information related to bone collagen fibers and minerals, which is essential for determining the nanoscale physiological status of bone health (Xi et al, 2018;Badar et al, 2022;Inamdar et al, 2021) but severely deteriorated due to constituent decrease, can be efficiently retrieved under shorter X-ray exposure times. For temporally resolved data, the SNR of an X-ray pattern with 2 s exposure time under SMAE zeroshot mode is comparable to an unoptimized pattern with 120 s exposure time, giving the Beijing Synchrotron Radiation Facility (a first-generation synchrotron light source) the ability to carry out time-resolved PDF experiments at the second timescale without instrumentation upgrades.…”