Influence of enzymatic degeneration and mechanical damage on cartilage tissue mechanics: an in vitro biomechanical study.

Abstract

Articular cartilage degeneration arising from the complex interplay of focal defect and enzymatic degradation compromises its morpho-mechanical integrity. The lack of comprehensive characterization of this combined pathology limits our mechanistic understanding of osteoarthritis (OA) initiation and progression. Cylindrical osteochondral explants were harvested from six bovine knee joints and allocated into five experimental groups (n = 12 per group): intact healthy cartilage (Control), focal defect alone (Def), enzymatic degradation alone (Enz), enzymatic degradation followed by focal defect (Enz+Def), and focal defect followed by enzymatic degradation (Def+Enz). In vitro mechanical characterization was performed under three loading configurations-ramp compression, multi-step stress-relaxation, and dynamic sinusoidal loading conditions-to characterize the elastic and viscoelastic properties of each group. Semi-quantitative compositional and histological analyses were conducted using Fourier transform infrared (FTIR) spectroscopy, light, and polarized light microscopy. Enzymatic degradation plays a dominant role in compromising cartilage mechanical integrity, with enzymatically degraded cartilage exhibiting substantially greater mechanical deterioration than cartilage with a focal defect alone. FTIR analysis revealed greater zone-wise collagen loss than proteoglycan depletion in Enz group. While the combined insults compromised mechanical response across all loading conditions, Enz+Def group produced the most severe reduction in compressive 79.7%p<0.001,95%CI:[58.1%,90.1%] and equilibrium 97.7%p<0.001,[95.1%,98.9%] moduli and dynamic loading capacity relative to Control. To the best of our knowledge, this is the first study to systematically combine and sequence enzymatic degradation and a focal cartilage defect, providing mechanistic insight into their isolated and combined effects on cartilage morpho-mechanics with relevance to OA pathomechanics and early intervention strategies.