Stirred flow bioreactor modulates chondrocyte growth and extracellular matrix biosynthesis in chitosan scaffolds

The aim of this study is to show the favorable effect of simple dynamic culture conditions on chondrogenesis of previously expanded human chondrocytes seeded in a macroporous scaffold with week cell-pore walls adhesion. We obtained enhanced chondrogenesis by the combination of chitosan porous supports with a double micro- and macro-pore structure and cell culture in a stirring bioreactor. Cell-scaffold constructs were cultured under static or mechanically stimulated conditions using an intermittent stirred flow bioreactor during 28 days. In static culture, the chondrocytes were homogeneously distributed throughout the scaffold pores; cells adhered to the scaffold pore walls, showed extended morphology and were able to proliferate. Immunofluorescense and biochemical assays showed abundant type I collagen deposition at day 28. However, the behavior of chondrocytes submitted to mechanical stimuli in the bioreactor was completely different. Mechanical loading influenced cell morphology and extracellular matrix composition. Under dynamic conditions, chondrocytes kept their characteristic phenotype and tended to form cell aggregates surrounded by a layer of the main components of the hyaline cartilage extracellular matrix, type II collagen, and aggrecan. An enhanced aggrecan and collagen type II production was observed in engineered cartilage constructs cultured under stirred flow compared with those cultured under static conditions.