Fig. 4: The surface tension of fibroblast spheroid is higher than cancer cells.

a Measurement of surface tension using the micropipette aspiration assay. First row: Phase contrast and epifluorescent image showing micropipette aspiration of HT29 cancer cell side; second row: Phase contrast and epifluorescent image showing micropipette aspiration of GFP expressing NIH3T3 fibroblasts side. Scale bar, 50 μm. b Individual (dots) surface tension measurements on cancer cell spheroids (red) and fibroblast spheroids (green) growing without confinement and co-cultures after the onset of fibroblast spreading. N = 3 runs of encapsulation, n = 82 capsules. One-way ANOVA test was performed (***p < 0.001). Three independent experiments were performed. n = 82 capsules. c Measurement of a spheroid using microplates assay. Scale bars: 25 μm. d Evolution of force as a function of time in a microplate assay. e Individual (dots) surface tension measurements on cancer cell spheroids (red) and fibroblast spheroids (green) growing without confinement. One-way ANOVA test (***p < 0.001). n = 40 spheroids from three independent experiments. f Western blot showing myosin IIA expression level in control HT29 cancer cells (Ctrl, transfected with scrambled shRNA) and myosin II-depleted cancer cells (shMyosinIIa). GAPDH is used as a loading control. g Individual (dots) surface tension measurements on cancer cell spheroids made of control and myosin IIa-depleted cancer cells growing without confinement. One-way ANOVA test was performed (**p < 0.01). Three independent experiments were performed. n = 59 capsules, from N = 3 experiments. h Frequency of capsules in which fibroblasts enveloped cancer cells. Capsules contain fibroblasts and control or myosin IIa-depleted cancer cells. t = 0 corresponds to the confluent stage. n ≥ 40 capsules per condition.