FIG. 1. Substrate stiffness and aggregate size determine wetting dynamics.

(A) Diagram of an aggregate spreading on a fibronectin-coated polyacrylamide gel. (B) z-profile of F-actin stained aggregate adhered to glass. (C) DIC image of an aggregate spreading on glass. $A_0$ is the projected area of an un-deformed aggregate, and A is the instantaneous contact area over which the monolayer has spread. (D) Normalized spread area $\left(A/A_0\right)$ as a function of time and stiffness. (E) Difference in fitting $R^2$ values as a function of stiffness. (F) Spreading rate $\frac{1}{A_0}\frac{dA}{dt}$ measured between $A=A_0$ and $A=2A_0(\mathrm{n}=13$ for 0.7 kPa and $\mathrm{n}=10$ for 40 kPa). (G) Spreading rate as a function of aggregate size for 0.7 kPa substrate (red, $\mathrm{n}=27),$ 40 kPa substrate (blue, $\mathrm{n}=18$), and glass (black, $\mathrm{n}=8$). Scale bars are $50\mu m$. *P < 0.05, **P < 0.01, ***P < 0.001. ns is non-significant. Error bars are mean ± standard deviation.