Force-dependent bond lifetime: Bell model vs Dembo catch-slip model
—Mean lifetime (s)
—Peak force (pN)
—Avg bonds at t=0
Slip bond (Bell 1978): k_off(F) = k₀ · exp(Fδ/kT) — force always accelerates unbinding. Catch bond (Dembo 1988): force can decrease off-rate over a range, creating a lifetime peak. Observed in selectins, integrins, FimH adhesins. Two-state model: bonds switch between weak (high k_off) and strong (low k_off) states; force shifts equilibrium toward strong state up to a peak force, then overwhelms it.
Cluster dynamics: rebinding (k_on) competes with breakage; cooperative effects create bistability.