Many studies have demonstrated that the mechanical properties of the extracellular matrix can significantly influence the morphology, strength and lifetime of focal adhesions. However, how the morphology of the contact surface affects the pattern formation of the molecular bonds still remains largely unknown. Here, by simplifying the cell and extracellular matrix to two opposing elastic bodies and considering the lateral diffusion as well as the bonding/debonding of molecular bonds, we study the clustering behavior of receptor-ligand bonds between curved surfaces and the phase diagrams of cluster patterns. We reveal the important role of surface morphology and bond kinetics in regulating the patterns of bond clusters. We further investigate the segregation dynamics of the interfacial bonds under various loading speeds, and we show that the average interfacial stress is rate-dependent while the rupture stress is rate-independent. Finally, we demonstrate that programmable patterning of bond clusters can be achieved through the designed surface morphology.

Adhesive contact of soft materials plays an essential role in flexible electronics, soft robots, and biological systems. Classical contact mechanics theories assume that the contact region between a spherical indenter and a flat surface is circular. In this paper, however, we show that fingering instability and inner cavitation may appear and disappear during the loading−unloading process when a soft thin elastic film is indented with a spherical indenter. We further demonstrate that this adhesion-induced instability can enhance the resistance to deformation and thus significantly increase contact force. Finally, we find an important dimensionless number, defined as the ratio of adhesion energy to elastic energy, and thus reveal that the competition between adhesion energy and elastic energy yields the critical condition for adhesion-induced instability. Thus, our findings bridge the gap between contact mechanics and interfacial instabilities of soft materials and may have many important implications for the applications of soft materials.