Lifetime of ligand-receptor clusters under external force.

We present a theory for the lifetime T(N,f) of a ligand-receptor cluster with N bonds under constant external force F=fN , where f is force per bond. We show that there exists a critical force per bond f(c) such that at large N when f>f(c) the lifetime T(N,f) is independent of cluster size N ; when f>f(c) the lifetime scales as ln[T(N,f)] approximately N due to a free energy barrier with height approximately N along the dissociation path; when f=f(c), the lifetime scales as T(N,f) approximately N(1/3) due to strong fluctuation of a number of closed bonds. Our study shows that adhesion clusters with more bonds are more stable at small f but respond to external force as fast as smaller adhesion clusters at large f .