Using Mixed Self-Assembled Monolayers Presenting RGD and (EG)₃OH Groups To Characterize Long-Term Attachment of Bovine Capillary Endothelial Cells to Surfaces

This paper describes surfaces that promote the ligand-directed binding of cells and resist the cellular deposition of adhesive proteins. These surfaces are based on self-assembled monolayers (SAMs) of alkanethiolates on gold that present mixtures of arginine-glycine-aspartate (RGD), a tripeptide that promotes cell adhesion by binding to cell surface integrin receptors, and oligo(ethyleneglycol) moieties, groups that resist nonbiospecific adsorption of proteins and cells. Surface plasmon resonance (SPR) spectroscopy was used to measure the adsorption of carbonic anhydrase and fibrinogen to mixed SAMs comprising RGD groups ((EG)6OGRGD) and tri(ethylene glycol) groups ((EG)3OH); SAMs having values of the mole fraction of RGD (χRGD) ≤ 0.05 adsorbed nearly undetectable levels of carbonic anhydrase or fibrinogen. Bovine capillary endothelial cells attached and spread on SAMs at χRGD ≥ 0.00001, with spreading of cells reaching a maximum at χRGD ≥ 0.001. These mixed SAMs reduced the deposition of proteins by attached cells relative to both fibronectin adsorbed on SAMs of hexadecanethiolate on gold and RGD peptide coated on glass. After allowing cells to attach for 2 or 4 h to any of these surfaces presenting RGD groups, addition of soluble GRGDSP to the medium contacting the adherent cells rapidly released them from the surfaces. However, if cells were allowed to attach to surfaces for 24 h, only those cells attached to the mixed SAM presenting (EG)6OGRGD and (EG)3OH groups could be released using the soluble GRGDSP at a rate comparable to cells attached to fibronectin for 2 h. These results demonstrate that RGD alone is sufficient for adhesion and survival of cells over 24 h.