  Cell-cell contacts in tissues are continuously subject to mechanical forces
due to homeostatic pressure and active cytoskeleton dynamics. While much is
known about the molecular pathways of adhesion, the role of mechanics is less
well understood. To isolate the role of pressure we present a dense packing of
functionalized emulsion droplets in which surface interactions are tuned to
mimic those of real cells. By visualizing the microstructure in 3D we find that
a threshold compression force is necessary to overcome electrostatic repulsion
and surface elasticity and establish protein-mediated adhesion. Varying the
droplet interaction potential maps out a phase diagram for adhesion as a
function of force and salt concentration. Remarkably, fitting the data with our
theoretical model predicts binder concentrations in the adhesion areas that are
similar to those found in real cells. Moreover, we quantify the adhesion size
dependence on the applied force and thus reveal adhesion strengthening with
increasing homeostatic pressure even in the absence of active cellular
processes. This biomimetic approach reveals the physical origin of
pressure-sensitive adhesion and its strength across cell-cell junctions.
