Cell adhesion strength increases linearly with adsorbed fibronectin surface density

Cell adhesion is involved in numerous physiological processes and is important to biotechnological applications, including tissue engineering and development of artificial organs. The relationship between cell adhesion strength and fibronectin (Fn) surface density was analyzed using a spinning disk device that applied a linear range of forces to attached cells under uniform surface chemical conditions. ROS 17/2.8 cells were seeded onto Fn-coated glass substrates for 15 min. Cells were then subjected to detachment forces for 10 min and adherent cells were counted at different radial distances. The fraction of adherent cells decreased non-linearly with applied force, and the resulting detachment profile was accurately described by a sigmoidal curve, Analysis of detachment profiles for different Fn concentrations and quantitative Fn adsorption measurements revealed that, for short attachment times, cell adhesion strength increased linearly with Fn surface density. This linear dependence of attachment strength on adsorbed Fn was observed for two different glasses, a non-reactive substrate and a surface-active glass, suggesting that this relationship is not substrate specific. The increases in adhesion strength were effectively blocked by a monoclonal antibody directed against the RGD cell binding domain. The linear relationship between attachment strength and ligand density is consistent with theoretical models for initial receptor-mediated adhesion and suggests the absence of cooperative receptor-ligand binding during the initial phases of cell adhesion.