In-situ observation of collective bubble collapse dynamics in a quasi-two-dimensional foam

Abstract The stability of foams is an important subject not only for fundamental science, but for applications in daily life. The most destructive phenomenon underpinning foam collapse is a collective bubble collapse, yet the mechanism behind this is unclear. In this study, we clarify the dynamics of the collective bubble collapse in a quasi-two-dimensional foam by in-situ observation with a high speed camera. We find two modes for collective bubble collapse: one is the propagation of liquid film breakage via impact with the stream of another broken liquid film. The other is breakage of a distant liquid film due to penetration by a liquid droplet, emitted by impact with the flow of a broken liquid film. As the liquid fraction increases, the velocity of liquid droplets decreases. Instead of penetration, the liquid droplet bounces like a billiard ball or it is absorbed into other films

Statistical Features of Collective Cell Migration

We discuss recent advances in interpreting the collective dynamics of cellular assemblies using ideas and tools coming from the statistical physics of materials. Experimental observations suggest analogies between the collective motion of cell monolayers and the jamming of soft materials. Granular media, emulsions and other soft materials display transitions between fluid-like and solid-like behavior as control parameters, such as temperature, density and stress, are changed. A similar jamming transition has been observed in the relaxation of epithelial cell monolayers. In this case, the associated unjamming transition, in which cells migrate collectively, is linked to a variety of biochemical and biophysical factors. In this framework, recent works show that wound healing induce monolayer fluidization with collective migration fronts moving in an avalanche-like behavior reminiscent of intermittent front propagation in materials such as domain walls in magnets, cracks in disordered media or flux lines in superconductors. Finally, we review the ability of discrete models of cell migration, from interacting active particles to vertex and Voronoi models, to simulate the statistical properties observed experimentally