Oral Presentation ANZBMS-MEPSA-ANZORS 2022

Linking the Ultrastructure and Micromechanics of Articular Cartilage (#125)

Jingrui Hu 1 , Keke Zheng 1 , Eve Nebbiolo 1 , Jessica Mansfield 1 , Ellen Green 1 , Peter Winlove 1 , Ben Sherlock 1 , Junning Chen 1
  1. University of Exeter, Exeter, DEVON, United Kingdom

Articular cartilage, as the connective tissue of diarthrodial joints, plays a crucial role in load-bearing and mobility. Its extracellular matrix (ECM), consisting of a collagenous network interacting with interstitial fluid rich in proteoglycans, largely determines the biomechanical properties [1]. Polarisation-resolved second-harmonic generation (pSHG) is a recently developed optical technique, which could investigate the intrafibrillar organisation of fresh, unlabelled, and thick collagenous tissues at sub-diffraction length scales [2, 3]. The fast-scanning speed also provided the ability to visualise the dynamic response to external loads. However, a quantitative correlation between collagen organisation and its mechanical function still lacking. Cartilage in the anterior and posterior regions of the joint found more shear force than the apex, which is subjected to the compression force [4]. Therefore, we hypothesise that the collagen organisation is tailored to its local biomechanical environment at different anatomical locations, and such organisational variation is also manifested in their susceptibility to injury and degenerative disease.

The overarching aim of our study is to establish a framework quantitative of the relationship between the ultrastructure of articular cartilage and its biomechanics. Four bovine metacarpophalangeal (MCP) joints were acquired from a local abattoir, and 48 explants in cuboid shapes were harvested from the anterior, apex and posterior regions of trochlear surfaces and condyles. We first mapped the longitudinal cross-section of the explants with pSHG and evaluated the structural variations among three zones quantifying the principal angles and degrees of dispersion of collagen. Next, the same specimens were loaded on a custom-built rig integrated with our pSHG microscope, to visualise structural responses under two levels of tissue strains applied at 8% and 16%. These two strain levels present a medium and an extreme case in normal activities, respectively. The structural responses were evaluated in terms of the re-orientation and re-alignment of the collagen fibrils.

  1. Inamdar, S.R., et al., The secret life of collagen: temporal changes in nanoscale fibrillar pre-strain and molecular organization during physiological loading of cartilage. ACS nano, 2017. 11(10): p. 9728-9737.
  2. Mansfield, J.C., J.S. Bell, and C.P. Winlove, The micromechanics of the superficial zone of articular cartilage. Osteoarthritis and cartilage, 2015. 23(10): p. 1806-1816.
  3. Mansfield, J.C., et al., Collagen reorganization in cartilage under strain probed by polarization sensitive second harmonic generation microscopy. Journal of the Royal Society Interface, 2019. 16(150): p. 20180611.
  4. Moger, C., et al., Regional variations of collagen orientation in normal and diseased articular cartilage and subchondral bone determined using small angle X-ray scattering (SAXS). Osteoarthritis and cartilage, 2007. 15(6): p. 682-687.