Fig. 6. Ligand-clustering-dependent model for adhesion reinforcement. In the top panel, the blue solid line depicts the physical response of objects undergoing detachment. No peak is observed in this purely physical process; more objects are removed as detaching force is increased. However, on an RGD-clustered substrate, a living cell may be able to transduce the mechanical stimulus into intracellular signals (pink solid line) that result in the strengthening of ligand-receptor and/or receptor-cytoskeleton linkages. The outcome of combining physical detachment with signaling-mediated adhesion reinforcement is a characteristic peak in the resultant adhesion profile (red line, region A). At a higher threshold of mechanical stimulus (region B), the primary signal (pink solid line) is itself reinforced by a secondary signal (pink dotted line), resulting in a non-zero plateau in the observed adhesion profile (red line, region B).