  We use a coarse grained molecular model of supported lipid bilayers to study
the formation of adhesion domains. We find that this process is a first order
phase transition, triggered by a combination of pairwise short range attractive
interactions between the adhesion bonds and many-body Casimir-like
interactions, mediated by the membrane thermal undulations. The simulation
results display an excellent agreement with the recently proposed Weil-Farago
2D lattice model, in which the occupied and empty sites represent,
respectively, the adhesion bonds and unbound segments of the membrane. A second
phase transition, into a hexatic phase, is observed when the attraction between
the adhesion bonds is further strengthened.
