  Bistability is a major mechanism for cellular decision making and usually
results from positive feedback in biochemical control systems. Here we show
theoretically that bistability between unbound and bound states of adhesion
clusters results from positive feedback mediated by structural rather than
biochemical processes, namely by receptor-ligand dissociation and association
dynamics which depend non-linearly on mechanical force and receptor-ligand
separation. For small cell-matrix adhesions, we find rapid switching between
unbound and bound states, which in the initial stages of adhesion allows the
cell to explore its environment through many transient adhesions.
