Real-time PCR of matrix protein aggrecan expression (A, B), type II collagen (C, D), and link protein (E, F) transcripts were quantified by using SYBR green fluorescence after 21 day of culture. Expression levels were normalized to levels of β-actin and relative amounts of mRNA were normalized to respective cartilage sub-populations in PEGDA hydrogels. SZC: Superficial zone chondrocytes, DZP: Deep zone chondrocytes. * P<0.05; ** P<0.01