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.

This paper describes a technique that uses mixed self-assembled monolayers of two alkanethiolates ( -S(CH2)11(OCH2CH2)6OR, R ) a hydrophobic group, and -S(CH2)11(OCH2CH2)nOH, n ) 3, 6, EGnOH), in combination with surface plasmon resonance spectroscopy, to study the influence of the size and shape of R, and its density at the surface, on the hydrophobic adsorption of proteins at solid-liquid interfaces. Detailed results were obtained for β-galactosidase, carbonic anhydrase, lysozyme, and RNase A using R ) C(C6H5)3, CH(C6H5)2, and CH2(C6H5). A hard-sphere model is used to rationalize the adsorption; this model, although very approximate, helps to interpret qualitative trends in the data. Using this model, the extent to which adsorbed proteins undergo conformational rearrangements appears to depend on the density of the hydrophobic groups at the surface and on the concentration of protein in solution. This paper describes the first step toward the development of a system that will allow the study of hydrophobic interactions of proteins with surfaces presenting organic groups of well-defined shape.

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