Figure 3.

Initial model conditions. (a) Initial cell distribution. A- and M-cells are placed at random along the left border of a rectangular lattice. Periodic boundary conditions are applied along the S ₁ axis. At S ₂ = 1 reflecting boundary conditions are imposed. (b) Chemotactic gradient field defined by equation (1). The color code indicates the chemotactic gradient concentration function, where blue corresponds to low, red is related to high concentrations. The arrows illustrate the local gradient direction. (c–e) Initial ECM resistance distribution of differently structured ECM: (c) homogeneous, moderate ECM resistance distribution, modeled by a constant value μ(r ₁,r ₂) = 0.5; (d) heterogeneous, weakly structured ECM resistance distribution, defined by equation (2) with heterogeneity parameter θ = 0.1; (e) heterogeneous, highly structured ECM resistance distribution, defined by equation (2) with heterogeneity parameter θ = 0.5. The gray scale in (c–e) indicates the level of matrix resistance on cell migration: low (white) to high (black).