Modulating cell adhesion and spreading by control of FnIII_7-10 orientation on charged self-assembled monolayers (SAMs) of alkanethiolates

In this work, we demonstrate that surface charge can be used to modulate cell adhesion/spreading through the control of the orientation of adsorbed FnIII_7-10, which is a cell-adhesive protein containing RGD residues. Carboxylic acid (COOH) and amine (NH₂)-terminated self-assembled monolayers (SAMs) of alkanethiolates were used as model negatively and positively charged surfaces, respectively. The adsorbed amount of FnIII _7-10 is controlled to be equivalent on both SAMs as confirmed by the adsorption isotherms determined using I¹²⁵-radiolabeled FnIII _7-10 The binding of a monoclonal antibody specific for the cell-binding domain of FnIII_7-10 was measured by surface plasmon resonance (SPR) to evaluate FnIII_7-10 orientations on different SAMs. Results indicate that adsorbed FnIII_7-10 on NH₂-SAM has an orientation with more cell-binding domains accessible than on COOH-SAM, confirming our predictions from Monte Carlo simulations. Both phase contrast images and Vybrant® MTT cell proliferation assays show that the adhesion/spreading of bovine aortic endothelial cells (BAECs) on the NH ₂-SAM is significantly better than that on the COOH-SAM coated with an equivalent amount of FnIII_7-10. These results indicate that surface charge can be used to specifically orient cell adhesive proteins such as FnIII_7-10, thus providing a promising strategy to increase the activity of materials incorporating biological moieties.