Adhesion has long been described through empirical models invoking van der Waals forces and surface energy. Here we derive adhesion as a direct consequence of F=∇(1/N), the unified force law based on layer density gradients. At any interface between two materials of differing layer density N, a density gradient ∇(1/N) is generated — this gradient constitutes the adhesive force. The model predicts adhesion strength proportional to ΔN across the interface, unifies adhesion, cohesion, and interfacial failure under a single equation, and directly informs the KHDS v1.0 cardiac tissue interface design parameters.