Proteoglycan incorporation and release during culture of cartilage explants (mean +/- SD). (a) Proteoglycan release during culture of cartilage explants. A similar amount of proteoglycans were released into the culture medium by explants cultured with unstimulated (n = 24) or conditioned serum (CS; n = 24). (b) PG incorporation rate on Days 4, 8 and 12 of the culture, measured using 35SO42- incorporation (n = 8 per timepoint). Results are representative of three separate experiments with different OA cartilage donor - serum donor combinations.