(656b) Decoupling Contributions to Cell Adhesion in the Context of Laterally Mobile Ligands

Cells employ a set of subcellular structures including integrin receptors and focal adhesions (FAs) in order to transmit, sense, and respond the properties of their extracellular environment. Previous works attempted to understand the role of ligand mobility on cell adhesion by using receptor-bearing vesicles as a model system. Their findings show that ligand mobility enhances force-induced cell adhesion, interpreted as being due to the energy of vesicle membrane deformation. However, these model systems obviously neglect the roles of FAs, the cytoskeletal network, and receptor diversity in living cells. To improve upon these early descriptions of receptor-ligand adhesion, we have studied cell (receptor) interactions on polymer films presenting laterally mobile ligands. The polymer films were created by an interfacial self-assembly process, whereby a fraction of the polymer chains bear RGD ligands to allow for integrin-specific adhesion. We find that NIH 3T3 fibroblasts seeded on our polymer films exhibit biphasic responses in spreading and adhesion strength as a function of the ligand mobility, with a minimal response for intermediate mobility values. These results highlight ligand mobility as a key property of biologically active materials, and may also point to pathophysiological roles. Towards decoupling the contributions of cellular components such as FAs and actin cytoskeleton, we independently administer pharmacological agents (e.g., Y-27632, cytochalasin, and trypsin) to cells seeded on films with different ligand mobility. This method has previously been used to estimate the mechanical properties of adherent cells, with the rate of cell de-adhesion corresponding to cellular viscoelasticity (i.e., storage and loss moduli). Our work will give experimental insight into the contributions of both cell and substrate mechanical properties on cell adhesion in the context of mobile ligands. Furthermore, our results will assist the development of more complete theoretical representations of cell adhesion.