Surface modification for controlled studies of cell–ligand interactions

This work describes a method for coupling cell adhesion peptides to hydrophobic materials for the purpose of controlling surface peptide density while simultaneously preventing nonspecific protein adsorption. PEO/PPO/PEO triblock copolymers (PluronicTM F108) were equipped with terminal pyridyl disulfide functionalities and used to tether RGD containing peptides to polystyrene (PS). The density of F108 on PS was 1.4 E5±2.12 E1 molecules/μm2. XPS and ToF SIMS indicated that the F108 coating was homogeneous and that the unmodified and activated F108 distributed evenly on PS. By mixing unmodified F108 with PDS-activated F108 prior to adsorption, it was possible to vary peptide density between 0 and 8.7 E4±2.66 E3 peptides/μm2, while otherwise, maintaining consistent surface properties. GRGDSY grafted PS supported cell attachment, spreading, and development of cytoskeletal structure, all of which were found to increase with increasing peptide density. Cell proliferation followed this same trend, however, maximal growth occurred at a submaximal peptide density. Cell aspect ratio varied in a biphasic manner with GRGDSY density. F108 coated PS and GRGESY grafted PS were inert to cell adhesion. Cells released from GRGDSY grafted PS upon addition of either a reducing agent or free GRGDSY, which indicates that cell–substrate interactions were mediated solely by the tethered peptides.