Fig. 1: Fibroblasts envelop cancer cells under confinement.

a Schematic representation of the encapsulation. Cells are encapsulated into hollow alginate spheres using a three-way injector consisting of the outermost phase containing alginate, the intermediate phase containing sorbitol and the innermost phase containing cells. Gelation of alginate occurs upon the fall of droplets into the gelation bath containing calcium chloride hexahydrate. Capsules were then filtered and transferred to the appropriate culture medium within less than 5 min. b Schematic representation of possible outcomes after encapsulation of cancer cells and fibroblasts as single cells into alginate capsules. c Evolution of co-culture of HT29 cancer cells and GFP expressing NIH3T3 fibroblasts over time in alginate capsules. Time t = 0 corresponds to the encapsulation of cells. Time represented in days, d First row: Phase contrast image showing cancer cell and fibroblast spheroids; second row: epifluorescent image of fibroblasts expressing GFP (green); last row: Merge. Scale bar, 100 μm. d Percentage of capsules in which fibroblasts envelop spheroids of cancer cells over time. t = 0 corresponds to the confluent stage. n = 79 capsules. e Confocal image of a fixed spheroid. All cells were visualized by staining F-actin (phalloidin, red) and DNA (DAPI, blue). Fibroblasts were discriminated as cells expressing GFP (green). Left, equatorial slices. Bottom right, maximal projection. Scale bar, 50 μm. f Evolution of co-culture of HT29 cancer cells and GFP expressing NIH3T3 fibroblasts over time on agarose-coated individual wells. Time t = 0 corresponds seeding of cells. Time represented in days, d First row: Phase contrast image showing cancer cell and fibroblast spheroids; second row: epifluorescent image of fibroblasts expressing GFP (green); last row: Merge. Scale bar, 100 μm. g Evolution of cancer cells spheroids enwrapped with GFP expressing NIH3T3 fibroblasts over time after removal of alginate capsules. Time t = 0 corresponds to capsule dissolution, thus the release of the confinement. Time represented in hours, h Scale bar, 100 μm.