Fig. (2) Cell proliferation assays: Comparison of the overall proliferative capacity of fresh and frozen cells related to the superficial or deep origin of the articular cartilage biopsy. Fresh or frozen human knee superficial and deep articular cartilage chondrocytes were stimulated by culturing with Dulbecco's Modified Eagle's Medium (DMEM) with 10% fetal bovine serum (FBS). Following staining with toluidine blue, the cells were solubilized and the absorbance was determined. The results represent the differences in absorbance for stimulated cells relative to the control culture in DMEM without FBS at the same time point. * p<0.05.