Fig 2. Schematic of the model.

A) Filopodia are modeled as a set of molecular clutches that reversibly bind to an F-actin filament undergoing retrograde flow. These clutches allow force transduction and deformation of the substrate. Each cell is modeled as a circle of radius R_c. The forces of all filopodia, F_fi, are summed to a net force F_filopodia (green), which is balanced by resistive forces F_friction (orange) and F_fluid (purple) to produce a velocity v_cell (light blue). Also note position of the “front” and “back” of cell. B) Cells are simulated in linear, time-invariant gradients, each with a slope -ε_i and a maximum concentration C_i. Each gradient is oriented at an angle θ_gi for the i^th gradient.