Modulation of the mechanical properties of tissue engineered cartilage

Cartilaginous constructs have been grown in vitro using chondrocytes, biode gradable polymer scaffolds, and tissue culture bioreactors. In the present work, we studied how the composition and mechanical properties of engineere d cartilage can be modulated by the conditions and duration of in vitro cul tivation, using three different environments: static flasks, mixed flasks, and rotating vessels. After 4-6 weeks, static culture yielded small and fra gile constructs, while turbulent flow in mixed flasks induced the formation of an outer fibrous capsule; both environments resulted in constructs with poor mechanical properties. The constructs that were cultured freely suspe nded in a dynamic laminar flow field in rotating vessels had the highest fr actions of glycosaminoglycans and collagen (respectively 75% and 39% of lev els measured in native cartilage), and the best mechanical properties (equi librium modulus, hydraulic permeability, dynamic stiffness, and streaming p otential were all about 20% of values measured in native cartilage). Chondr ocytes in cartilaginous constructs remained metabolically active and phenot ypically stable over prolonged cultivation in rotating bioreactors. The wet weight fraction of glycosaminoglycans and equilibrium modulus of 7 month c onstructs reached or exceeded the corresponding values measured from freshl y explanted native cartilage. Taken together, these findings suggest that f unctional equivalents of native cartilage can be engineered by optimizing t he hydrodynamic conditions in tissue culture bioreactors and the duration o f tissue cultivation.