Fig. 2. Chondrocytes were subjected to differential adhesion to fibronectin as described in the Materials and Methods, and colonies consisting of more than 32 cells were counted at 6 and 10 days and the results expressed as colony forming efficiency as described in the Materials and Methods. (A,B) Colonies initially appeared at 6 days in samples derived from the surface zone subjected to differential adhesion to fibronectin for 20 minutes and the CFE of this cohort had increased by 10 days. Using 4 cells as being indicative of a colony the same trend was apparent, with surface zone cells subjected to differential adhesion to fibronectin for 20 minutes showing enhanced CFE at both 6 and 10 days (C,D). Colony size of surface (S), middle (M) and deep (D) zone chondrocytes was also assessed at 6 (E) and 10 (F) days. Cells were plated and the number of cells per colony was counted at 6 and 10 days. Surface zone chondrocytes formed bigger colonies when plated onto fibronectin for 20 minutes (SFN 20) at both 6 (E) and 10 (F) days than any other sample. There was no difference in colony size within any other cohort at either time point. In addition, the colony size of surface zone cells plated on fibronectin for 20 minutes was increased at 10 days compared with 6 days and there was no increase within any of the other cohorts. *P<0.01 compared with 6 days; **P<0.01 compared with all other cohorts at the same time point; ***P<0.001 compared with all other cohorts at the same time point. Abbreviations as in Table 1.