Differentiation of chondrocytes and sorted sub-populations. Expression of mRNA in primary expanded human chondroyctes after MACS separation (P0), and subsequent passage in monolayer (P1 ML) or in hydrogel culture (P1 Gel). The P1 ML cells were cultured in chondrocyte medium (CM) until they had reached approx. 80% confluence (about 1 week), hydrogels were maintained in CM for 6 weeks. The expression of collagen type I (COL1), type II (COL2), and aggrecan (ACAN) was analyzed and the ratio of COL2/COL1 was calculated as a measure to describe the chondrogenic phenotype of the cells as indicated. Box plots represent 25% / 75% percentiles, mean values (dotted lines) and median values (hairlines). Lower right: the cumulated glycosaminoglycan production from cells in hydrogel culture was determined. GAG content was measured in the hydrogel and in the combined medium supernatant of the six-week cultures and normalized to the corresponding DNA content in the hydrogel. Mean values and standard deviation are shown (n = 3 cultures).