  We present a theory of unbinding transitions for membranes that interact via
short and long receptor/ligand bonds. The detail of unbinding behavior of the
membranes is governed by the binding energies and concentrations of receptors
and ligands. We investigate the unbinding behavior of these membranes with
Monte Carlo simulations and via a comparison with strings. We derive the
scaling laws for strings analytically. The exact analytic results provide
scaling estimate for membranes in the vicinity of the critical point.
