Development of a post-traumatic osteoarthritis model to evaluate the effects of impact velocity and maximum strain on articular cartilage cell viability, matrix biomarkers, and material properties
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Post-traumatic osteoarthritis (PTOA) is a very painful and debilitating disease that is associated with mechanical injury to articular cartilage, yet the severity of trauma required to induce it is unknown. The objective of this thesis work was to develop a clinically-relevant ex vivo PTOA model with repeatable single impact having constant velocity and maximum strain (i.e. severity categories normalized to thickness of cartilage explant) to study their effect on cartilage PTOA biomarkers: cell viability, extracellular matrix, and material properties. A 25 kN servo-hydraulic test machine was used to measure thickness and subsequently deliver an impact load at velocity (V) of 1 or 100 mm/sec to a maximum strain (S) of 10, 30, or 50% (six velocity: strain test groups) to cartilage explants. Non-impact (0V:0S) and sham controls were included. Thereafter, explants were cultured in supplemented media for twelve days. Cell viability was analyzed post-injury at day 0 and 12 as was cartilage extracellular matrix for collagen (specifically hydroxyproline) and glycosaminoglycan (GAG) content. Media was changed after day 1, 2, 3, 6, 9, and 12 and tested for GAG, collagen II synthesis, nitric oxide, and prostaglandin E₂ (PGE₂). Material testing measuring the elastic, equilibrium, and dynamic moduli of cartilage explants was performed at day 0 (pre-injury) and days 6 and 12. Cell death, GAG and PGE₂ release to media (at day 1) were strain dependent with 50% strain groups being significantly different than others, and high velocity prolonging release of PGE₂ up to day 6. These results indicate key biomarkers involved in early PTOA.