  We study the nucleation of blebs, i.e., protrusions arising from a local
detachment of the membrane from the cortex of a cell. Based on a simple model
of elastic linkers with force-dependent kinetics, we show that bleb nucleation
is governed by membrane peeling. By this mechanism, the growth or shrinkage of
a detached membrane patch is completely determined by the linker kinetics,
regardless of the energetic cost of the detachment. We predict the critical
nucleation radius for membrane peeling and the corresponding effective energy
barrier. These may be typically smaller than those predicted by classical
nucleation theory, implying a much faster nucleation. We also perform
simulations of a continuum stochastic model of membrane-cortex adhesion to
obtain the statistics of bleb nucleation times as a function of the stress on
the membrane. The determinant role of membrane peeling changes our
understanding of bleb nucleation and opens new directions in the study of
blebs.
