Cytotoxicity of degrading and cross-linking agents. The relative cytotoxicity of (a) degrading and (b) cross-linking agents was determined using the resazurin assay (expressed as relative fluorescence units). Cartilage blocks were treated with the respective reagents for either one or two hours. The controls were incubated in PBS. P values are from Tukey test for pairwise comparisons. EDC, 1-ethyl-3-diaminopropyl-carbodiimide; NHS, N-hydroxysuccinimide.