Increased matrix stiffness contributes to increased force generation.

<p>Net traction force (|<i>F</i>|) increases with increasing substrate stiffness (E = 1–10 kPa) for (A) MCF10A non-metastatic mammary epithelial cells and MDAMB231 metastatic cancer cells, (B) PrEC non-metastatic primary prostate epithelial cells and PC3 metastatic prostate cancer cells, and (C) BEAS2B non-metastatic bronchial epithelial cells and A549 metastatic lung cancer cells. Ligand density is maintained at 0.1 mg/mL collagen I. 5 kPa data is from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032572#pone-0032572-g001" target="_blank">Figure 1</a>. Note also that the metastatic cancer cells (black) exert greater forces than non-metastatic cells (white) at all matrix stiffness levels studied. Mean+SEM; * indicates p<0.05; *** indicates p<0.001.