Description
Articular cartilage is a fibrillar load-bearing tissue whose exceptional mechanical properties arise from coupled biomechanical and biochemical processes. In osteoarthritis (OA), this coupling progressively deteriorates, leading to irreversible tissue degeneration. OA has no cure, making early diagnosis and understanding of degeneration critical. We hypothesise that mechanical loading reveals biomechanical and biochemical signatures that distinguish healthy from degenerate cartilage before overt structural failure.
To validate the hypothesis, we developed the first real-time multimodal mechanical testing platform integrating polarisation-sensitive optical coherence tomography (PS-OCT) and Raman spectroscopy. PS-OCT measures tissue birefringence, reflecting collagen fibrillar organisation, a key component of cartilage. Raman spectroscopy probes biochemical composition simultaneously. Twenty-five bovine cartilage samples spanning multiple degeneration grades were compressed at 1.2MPa for two hours using a transparent indenter, capturing both fast initial (<3min) and slow long-term fibrillar and biochemical dynamics, with simultaneous periodic acquisition of PS-OCT images and Raman spectra.
The PS-OCT images revealed degeneration-dependent structural differences in cartilage after sustained compression (>20min), reflecting long-timescale morphological changes under load. The standard deviation of the whole tissue birefringence, a proxy for collagen fibrillar network heterogeneity, exhibited even earlier divergence between grades, within the first 3 min of loading. The rate of change of standard deviation decreased with degeneration before increasing again at advanced stages, revealing a previously unknown non-monotonic dependence of fast initial cartilage dynamics on degeneration state. Raman spectroscopy provided complementary insight. Non-negative matrix factorisation and two-dimensional correlation analysis revealed degeneration-dependent differences in spectral dynamics.
Overall, the multimodal platform enables the discovery of new degeneration-dependent biomarkers under mechanical loading by revealing rapid early biomechanical and biochemical responses, providing a powerful tool for assessing disease progression and therapeutics. Further, we established a novel multimodal mechanical testing framework as a new approach for probing the dynamics of soft tissues under load, enabling the identification of previously inaccessible phenomenon.
| I am the presenting author | Yes |
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