Spontaneous migration of cellular aggregates from giant keratocytes to running spheroids

Despite extensive knowledge on the mechanisms that drive singlecell migration, those governing the migration of cell clusters, as occurring during embryonic development and cancer metastasis,remain poorly understood. Here, we investigate the collective migration of cell on adhesive gels with variable rigidity, using 3D cellular aggregates as a model system. After initial adhesion to the substrate, aggregates spread by expanding outward a cell monolayer, whose dynamics is optimal in a narrowrange of rigidities. Fast expansion gives rise to the accumulation of mechanical tension that leads to the rupture of cell–cell contacts and the nucleation of holes within the monolayer, which becomes unstable and undergoes dewetting like a liquid film. This leads to a symmetry breaking and causes the entire aggregate to move as a single entity. Varying the substrate rigidity modulates the extent of dewetting and induces different modes of aggregate motion: “giant keratocytes,” where the lamellipodium is a cell monolayer that expands at the front and retracts at the back; “penguins,” characterized by bipedal locomotion; and “running spheroids,” for nonspreading aggregates. We characterize these diverse modes of collectivemigration by quantifying the flows and forces that drive them, andwe unveil the fundamental physical principles that govern these behaviors, which underscore the biological predisposition of living material to migrate, independent of length scale

Spreading dynamics of cellular aggregates confined to adhesive bands

We examine the spreading of cellular aggregates deposited on adhesive striated glass surfaces consisting of 100μm large bands alternatively coated with fibronectin and with PolyEthyleneGlycol-Poly-L-lysine (PEG-PLL). The aggregates spread confined to the adhesive fibronectin bands. A front of cells expands from the aggregate at constant velocity. In comparison, the radial spreading of an aggregate on the uniform fibronectin coated glass surface obeys a diffusive law. We develop a common theoretical model in agreement with our experimental observations to describe the apparently disparate spreading kinetics of cellular aggregates. These results demonstrate the dominant role of the permeation in the expansion of the precursor film of cells around the aggregate

Curling instability induced by swelling

We study the spontaneous curving observed when a strip of tracing paper is deposited on a water surface. The differential swelling across the ribbon thickness leads to a curling of the sheet, with the curvature increasing to a maximum and then relaxing as the sheet becomes completely wet. We develop a theoretical model, in good agreement with our experimental observations and relevant to the understanding of curling instabilities induced by asymmetric swelling of natural or synthetic shells. © 2011 The Royal Society of Chemistry