Bioreactor cultivation conditions modulate the composition and mechanical properties of tissue-engineered cartilage

Cartilaginous constructs have been grown in vitro with use of isolated cell s, biodegradable polymer scaffolds, and bioreactors. In the present work, t he relationships between the composition and mechanical properties of engin eered cartilage constructs were studied by culturing bovine calf articular chondrocytes on fibrous polyglycolic acid scaffolds (5 mm in diameter, 2-mm thick, and 97% porous) in three different environments: static flasks, mix ed flasks, and rotating vessels. After 6 weeks of cultivation, the composit ion, morphology, and mechanical function of the constructs in radially conf ined static and dynamic compression all depended on the conditions of in vi tro cultivation. Static culture yielded small and fragile constructs, while turbulent flow in mixed flasks yielded constructs with fibrous outer capsu les; both environments resulted in constructs with poor mechanical properti es. The constructs that were cultured freely suspended in a dynamic laminar flow field in rotating vessels were the largest, contained continuous cart ilage-like extracellular matrices with the highest fractions of glycosamino glycan and collagen, and had the best mechanical properties. The equilibriu m modulus, hydraulic permeability, dynamic stiffness, and streaming potenti al correlated with the wet-weight fractions of glycosaminoglycan, collagen, and water. These findings suggest that the hydrodynamic conditions in tiss ue-culture bioreactors can modulate the composition, morphology, mechanical properties, and electromechanical function of engineered cartilage.