Oxygen-dependent matrix production in healthy and osteoarthritic chondrocytes. The DNA content per pellet (A), hydroxyproline/DNA (B), sulfated glycosaminoglycans (sGAGs)/DNA (C) and percentage of total sGAGs retained in the pellet matrix (D) were quantified for papain-digested pellets following 2 wk of redifferentiation in either 20% oxygen (gray bars) or 2% oxygen (white bars). All values are the means ± 1 SD for chondrocyte pellets from n = 5 donors. Statistical significance was determined by performing independent t-tests or Mann-Whitney U test (between disease conditions) and paired t-test or Wilcoxon tests as appropriate (between oxygen levels). *P < 0.05.