FIGURE 7.

State diagrams for the shear threshold effect in the space of selected catch-slip bond parameters. Other parameters are base case. In region (i), cells travel at <90% V_h at low shear rates. In region (ii), cells do not achieve a minimum in velocity. (A) State-wise off rate parameter space. When k_1rup is too small, cells bind and roll even at very low shear rates. When k_1rup is too large, cells do not reach a minimum in velocity. The smaller is, however, the larger k_1rup can be and still achieve the minimum in velocity. The shear threshold effect can never occur when is too large because cells will not bind well enough to achieve a minimum in velocity. (B) Average velocity as a function of shear rate. An example from each region of the state diagram is shown, with parameters given by the corresponding symbols in A. (C) Transition parameter space. When f₁₂ is too small, cells roll at low shear rates since the system quickly switches to the slow pathway. When f₁₂ is too large, on the other hand, the switch to the slow pathway occurs at too high a force, so that cells cannot roll slowly enough to achieve a minimum in velocity. (D) Average velocity as a function of shear rate. An example from each region of the state diagram is shown with parameters given by the corresponding symbols in C.