CPM (Graner-Glazier 1992): generalized Ising
σ=0: medium, σ≥1: cell identity
J(type_a, type_b): contact energy matrix
Steinberg DAH (1962): cells sort by adhesion
High J_diff: types segregate (like oil+water)
Low J_diff: types mix freely
Effective surface tension γ = J − λ·∂A/∂P
Tissue surface tension measurable in vitro