Abstract

Abstract. The initial stages of spreading of a suspended cell onto a substrate under the effect of (specific or nonspecific) adhesion exhibit a universal behaviour, which is cell-type independent. We show that this behaviour is governed by cell-scale phenomena only. This can be understood if the main retarding force that opposes cell adhesion is of mechanical origin, that is, dissipation occuring during the spreading. By comparing several naive models that generate different patterns of dissipation, we show by numerical simulation that only dissipation due to the deformation of the actin cortex is compatible with the experimental observations. This viscous-like dissipation corresponds to the energetic cost of rearranging the cytoskeleton, and is the trace of all dissipative events occuring in the cell cortex during the early spreading, such as the binding and unbinding of cross-linkers and molecular friction.