Protein interactions with poly(ethylene glycol) self-assembled monolayers on glass substrates: Diffusion and adsorption

Hydrophilic polymer chains, poly(ethylene glycol) (PEG), are attached to glass surfaces by silylation of the silanol groups on glass surfaces with (omega-methoxy-terminated PEG)trimethoxysilanes. We consider these tethered polymer chains to resemble self-assembled monolayers (SAMs) of PEG since the grafting process is entirely spontaneous. They are shown to exhibit excellent biocompatibility and represent a model system for studying the interactions of proteins with polymer surfaces. The PEG SAMs are prepared with two different molecular weight polymers (MW = 750 and 5000) and characterized with the techniques of angular-dependent X-ray photoelectron spectroscopy and atomic force microscopy. For the low molecular weight sample, the polymer chains tend to extend, forming a brush-like monolayer, whereas for the large molecular weight sample, the longer polymer chains tend to interpenetrate each other, forming a mushroom-like PEG monolayer on the surface. Interactions between a plasma protein, bovine serum albumin, and the PEG SAMs are investigated in terms of protein adsorption and diffusion on the surfaces by the technique of fluorescence recovery after photobleaching. The diffusion and aggregation behaviors of the protein on the two monolayers are found to be quite different despite the similarities in adsorption and desorption behaviors. The results are analyzed with a hypothesis of the hydrated surface dynamics.