Figure 3.

Measurements of Compressive Stresses Due to Monolayer Proliferation and Folding

(A) Schematic of capsule thinning during epithelium proliferation.

(B) Confocal equatorial plane of thinning alginate capsule. Red contours correspond to the capsule inner perimeter at T = 0 h.

(C) Superimposed contours of inner and outer boundaries corresponding to different time points.

(D) Normalized mean capsule thickness as a function of time for different alginate concentrations.

(E) Young’s modulus (kPa) as a function of the alginate concentration measured by AFM. Respective Young moduli are: 1%, 7.1 ± 0.3 kPa (n = 25), 1.5%, 11.5 ± 0.4 kPa (n = 52), 2%, 20.7 ± 0.7 kPa (n = 46) and 2.5%, 19.5 ± 0.7 kPa (n = 29). Difference between 2% and 2.5% alginate is not statistically significant (ns) with two-tailed p value 0.7042.

(F) Evolution of pressure (Pa) within capsules over time during epithelium proliferation and for different alginate concentrations (see STAR Methods).

(G) Mean buckling pressure (Pa) for different alginate concentration. For (D), (F), and (G): 1% alginate, n = 22; for 1.5%, n = 35; for 2%, n = 25; for 2.5%, n = 53; error bars are SEM. Difference between 1.5% and 2% alginate, and between 2.5% and 1.5% are not statistically significant (ns) with two-tailed p values 0.1119 and 0.4909, respectively.

(H) Schematic of capsule invagination following epithelium folding.

(I) Confocal equatorial planes showing capsule invagination for 1% alginate capsule.

(J) Left, schematic of an indentation experiment with the FemtoTools indenter (see also Figure S5). Right, a representative plot of force with indentation depth.

(K) Box plot of spring constant for 1% alginate.

(L) Box plot of pressure at buckling (Pa) for 1% alginate capsule calculated from capsule deformation (see STAR Methods). Scale bars, 100 μm.