Towards tissue engineering of meniscus substitutes: selection of cell source and culture environment

With the ultimate goal to engineer a meniscus substitute based on autologous cells, we aimed this work at identifying (i) a human cell source capable of generating fibrocartilaginous tissues and (ii) a culture environment promoting the development of bi-zonal constructs, resembling the complex structure and function of a meniscus. The post-expansion differentiation capacity of different chondrogenic cells readily available by knee arthroscopy, namely inner meniscus, fat pad, synovial membrane cells and articular chondrocytes (AC), was assessed within hyaluronan based non-woven meshes. Under our experimental conditions, only expanded AC generated tissues containing relevant amounts of glycosaminoglycans (GAG) and with cell phenotypes compatible with those of the inner and outer meniscus regions. Physical conditioning of constructs generated by expanded AC was applied using mixed flasks. The hydrodynamic environment of mixed flasks was instrumental to promote the formation of bi-zonal tissues, with an inner region rich in GAG and stiffer in compression and an outer rim rich in collagen and stiffer in tension. Therefore, the use of AC cultured within porous scaffolds in mixed flasks allowed engineering of constructs resembling some aspects of the phenotype and function of meniscus tissue.