Time course of 3D fibrocartilage formation by expanded human meniscus fibrochondrocytes in hypoxia

Abstract

Adult human meniscus fibrocartilage is avascular and nonhealing after injury. Meniscus tissue engineering aims to replace injured meniscus with lab-grown fibrocartilage. Dynamic culture systems may be necessary to generate fibrocartilage of sufficient mechanical properties for implantation; however, the optimal static preculture conditions before initiation of dynamic culture are unknown. This study thus investigated the time course of fibrocartilage formation by human meniscus fibrochondrocytes on a three-dimensional biomaterial scaffold under various static conditions. Human meniscus fibrochondrocytes from partial meniscectomy were expanded to passage 1 (P1) or P2 (3.0 ± 0.4 and 6.5 ± 0.6 population doublings), seeded onto type I collagen scaffolds, and grown in hypoxia (HYP, 3% O2) or normoxia (NRX, 20% O2) for 3, 6, and 9 weeks. Mechanical properties were not different between P1 and P2 cell-based constructs. Mechanical properties were lower in HYP, increased continually in NRX only, and were positively correlated with glycosaminoglycan content and accumulation of hyaline cartilage-like matrix components. The most mechanically competent tissues (NRX/9 weeks) reached 1/5 of the native meniscus instantaneous compression modulus but had an increasingly hypertrophic matrix-forming phenotype. HYP consistently suppressed the hypertrophic phenotype. The results provide baselines of engineered meniscus fibrocartilage properties under static conditions, which can be used to select a preculture strategy for dynamic culture depending on the desired combination of mechanical properties, hyaline cartilage-like matrix abundance, and hypertrophic phenotype.