Emulsions: from jamming to tissue mechanics

Emulsions are metastable systems that consist of droplets of a given phase that are dispersed in anoter immiscible continuous phase. Anyone uses them in their day to day life, from mayonnaise to beauty lotions. But despite their apparent mundanity, they have been used to study a wide range of topics in physics. For instance, packings of oil droplets in water are a great tool to explore the structure of jammed matter. Indeed, contrary to classical granular systems, emulsions can be made transparent by matching the indices of the oil and water phases, allowing to image their 3D structure through classical microscopy techniques. It is then possible to study straightforwardly how the packing structure depends on parameters such as the size distribution of the droplets, their interactions, or an applied pressure.

Emulsions can also be tuned to exhibit properties that resemble those of biological tissues, with the general goal to understand the physical basis of collective remodeling during development. These biomimetic emulsions are designed to mimic the minimal mechanical and adhesive properties of cells in biological tissues. Such a biomimetic approach allows to study the mechanical properties of tissues in a simplified framework, i.e. a framework in which the inherent biological complexity due to intracellular regulations is bypassed. In particular, we focus on the ways in which the interplay between adhesion and mechanical forces is able to control the emergence of tissue architecture during morphogenesis. To do so, we first showed that our biomimetic emulsions did exhibit properties that were close to those of soft tissues. We then used these emulsions to study their elasto-plasticity as a function of interdroplet adhesion and showed that adhesion alone was leading to emerging structuration in biomimetic emulsions.

Finally, because the properties of these emulsions are close to the ones of tissues, droplets can be used to probe cellular forces inside biological environments. In other words, droplets can be made soft enough to probe forces exerted by cells or tissues: knowing their surface tension, it is possible to quantify the local exerted stress from their observed deformation. We are currently using droplets to unravel the role of the extracellular matrix in the mechanical coupling of cells and tissues during morphogenesis.