Cartilaginous constructs have been grown in v i f m with use of isolated cells, biodegradable polymer scaffolds, and bioreactors. In the present work, the relationships between the composition and mechanical properties of engineered 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, mixed flasks. and rotating vessels. After 6 weeks of cultivation, the composition, morphology, and mechanical function of the constructs in radially confined static and dynamic compression all depended on the conditions of in vitro cultivation. Static culture yielded small and fragile constructs, while turbulent flow in mixed flasks yielded constructs with fibrous outer capsules: both environments resulted in constructs with poor mechanical properties. The constructs that were cultured freely suspended in a dynamic laminar flow field in rotating vessels were the largest, contained continuous cartilage-like extracellular matrices with the highest fractions of glycosarninoglycan and collagen, and had the best mechanical properties. The equilibrium modulus, hydraulic permeability, dynamic stiffness, and streaming potential correlated with the wet-weight fractions of glycosaminoglycan, collagen, and water. These findings suggest that the hydrodynamic conditions in tissue-culture bioreactors can modulate the composition. morphology, mechanical properties, and electromechanical function of engineered cartilage.
Articular cartilage derives its form and mechanical function from its matrix. which consists of tissue fluid and a framework of structural macromolecules (collagens, proteoglycans, and noncollagenous proteins and glycoproteins). During the development, maintenance, and remodeling of cartilage, chondrocytes synthesize appropriate types and amounts of macromolecules and assemble thcm into a highly organized matrix (4). Adult articular cartilage has a limited capacity to repair damage resulting from injury or disease, and there have been many different approaches to restore tissue composition, structure, and function. including the development of engineered cartilage for potential implantation (5.27). Cartilaginous constructs have been grown in vitro with use of isolated chondrocytes. biodegradable polymer scaffolds, and bioreactors and implanted in vivo to form subcutaneous cartilage or to promote joint repair (16). Fibrous polyglycolic acid scaffolds permitted chondrocytes to