Adhesion differentials control the rheology of biomimetic emulsions

Animal morphogenesis involves complex tissue deformation processes, which require tight control over tissue rheology. Yet, it remains insufficiently understood how tissue rheology results from the interplay between cellular packing and forces, such as cortical tension or cell-cell adhesion. We follow a biomimetic approach to study this interplay, using oil droplets with tunable adhesion strength to mimic adhesive cells. We expose emulsions to cyclic shear and use a geometric method to quantify their rheology using only imaging data. We find that emulsions made of two droplet types change yielding behavior across subsequent shear cycles. Combining this with vertex model simulations, we show that this shift is due to a progressive compaction, which only occurs with a high adhesion differential and only under oscillatory shear. Our work thus demonstrates how gradients observed during development can lead to gradients in tissue rheology. Moreover, progressive compaction suggests the emergence of a pumping mechanism, which potentially acts in many cellular materials, from foams to tissues.