Effects of surface functional groups on protein adsorption and subsequent cell adhesion using self-assembled monolayers

We investigated initial cell adhesion on self-assembled monolayers (SAMs) of alkanethiols carrying different functional groups including methyl (CH3), hydroxyl ( OH), carboxylic acid ( COOH), and amine (NH2). The combination of a surface plasmon resonance (SPR) instrument and a total internal reflection fluorescence microscope (TIRFM) allowed us to examine the kinetics of protein adsorption and correlating cell adhesion. Upon exposure of the SAM surface to a serum-containing medium, serum proteins rapidly adsorbed, and cells subsequently approached the surface. Adhesion of human umbilical vein endothelial cells (HUVECs) was greatly affected by surface functional groups; HUVECs adhered well to COOH- and NH2- SAMs, whereas poorly to CH3- and OH-SAMs. The amount of adsorbed protein from the serum-containing medium varied slightly with the terminal groups of the SAMs. On COOH- and NH2-SAMs, HUVECs adhered to bovine serum albumin (BSA)-preadsorbed surfaces with a few minutes delay, suggesting that displacement of preadsorbed BSA with cell-adhesive proteins, such as fibronectin or vitronectin, supports cell adhesion to these surfaces. Since the concentration of cell-adhesive proteins is much less than that of non-adhesive proteins such as BSA, displacement of adsorbed proteins with cell-adhesive proteins plays an important role in initial cell adhesion.