Figure 1.

Substrates were produced by mixing various ratios of Sylgard 184 (S184) and Sylgard 527 (S527), and their stiffnesses were characterized. (A) These stiffnesses show a logarithmic trend as the percentage of S184 was increased. Pure S527 was shown to have a similar stiffness to in vivo kidney tissue (∼6 kPa). Tissue culture plastic (TCP) was also plotted for comparison. From top to bottom, the dotted lines denote substrate moduli for substrates of TCP (112.8 MPa), S184 (1123.2 kPa), 1:1 blend of S184 and S527 (450.7 kPa), and S527 (3.2 kPa). (B) Phase contrast images of confluent MDCK layers, five days postseeding, grown on TCP and S527 show no significant morphological change despite the five orders magnitude difference in the stiffness. Scale bar represents 30 μm. Volcano plots of log2 ratio versus p value compare genes expressed by cells grown on TCP and S527 for confluent (C) and nonconfluent, 24 h postseeding (D) conditions. For confluent culture, the substrate stiffness induced virtually no differences in gene expression. In contrast, nonconfluent cells grown on the soft substrate show upregulation of genes related to EMT, epithelial phenotype, cell adhesion, and solute transporters. The vast differences between confluence conditions suggest that intercellular contact may be a factor in determining cell phenotype. For (C)–(D), n = 6.