Pellet culture elicits superior chondrogenic redifferentiation than alginate‐based systems

Although pellet culture and encapsulation of chondrocytes into gel‐like biomaterials have lead to major advances in cartilage tissue engineering, a quantitative comparative characterization of cellular differentiation behavior during those cultivation procedures has not yet been performed. Our study therefore aimed at answering the following question: is the redifferentiation pathway of chondrocytes altered by slight changes in the type of alginate biomaterial (pure alginate, alginate‐fibrin, alginate‐chitosan) and how do the cells behave in comparison to biomaterial‐free (pellet) three‐dimensional culturing? Monolayer‐expanded chondrocytes from healthy adult porcine knee joints were cultivated in alginate, alginate‐chitosan, alginate‐fibrin beads and as pellets up to 4 weeks. Quantitative PCR and Immunohistology were used to assess chondrogenic markers. Alginate‐fibrin—encapsulated chondrocytes behaved almost like monolayer chondrocytes. Alginate‐ and alginate‐chitosan encapsulation lead to a low chondrogenic marker gene expression. Although all 3D‐cultured chondrocytes showed a considerable amount of Sox9 expression, only pellet cultivation lead to a sufficient Collagen II expression. This puts the usage of alginate‐cultivated cartilage tissue engineering constructs under question. Fibrin addition is not beneficial for chondrogenic differentiation. Sox9 and Collagen II behave differently, depending upon the surrounding 3D‐environment. © 2009 American Institute of Chemical Engineers AIChE J, 2009