Fig. 1

Flow chart of the ex vivo potency study. Schematic overview and work flow of the ex vivo experiments performed to establish a potency assay for the matrix-associated autologous chondrocyte implant chondrosphere. Human knee joints were used to generate both chondrocyte spheroids and the cartilage condyle chips used as cartilage defect model. Spheroids were analysed before implantation by means of histology, immunohistochemistry, GAG production and expression of chondrogenic marker genes. Spheroids derived from the same batch as characterised before implantation, were used to implant into subchondral cartilage defects set into the condyle cartilage chips, reflecting cartilage defects as treated in the clinic with chondrosphere. After co-cultivation of spheroids with the cartilage condyle chips, the level of tissue regeneration was quantified by histomorphometry. The regenerated tissue was furthermore analysed for hyaline cartilage specific protein expression. A correlation between the spheroid characteristics before implantation and the amount of regenerated tissue formed after 12 weeks of co-cultivation was statistically tested by calculating the Spearman’s correlation coefficient (r)