Interaction Forces and Morphology of a Protein-Resistant Poly(ethylene glycol) Layer

INTRODUCTION

Poly(ethylene glycol) (PEG) surface grafts have gained considerable attention as being stable films that provide resistance to nonspecific protein adsorption (Elbert and Hubbell, 1996; Harris and Zalipsky, 1997). This protein resistance is of practical importance for a number of surface-engineering applications including biomaterials, drug delivery, or biosensors.

The molecular mechanisms underlying protein resistance of grafted PEG have not yet been fully identified. Two different aspects of the problem are usually considered: first, the brush-induced "steric" repulsion that is thought to prevent direct contact between proteins and the underlying surface (Szleifer, 1997); and second, hydration shells, which energetically suppress adsorption of proteins onto the PEG layer. Recently, it has been argued that the protein resistance also observed on well-ordered model systems of self-assembled monolayers of oligo(emylene glycol) may alternatively be due to charging effects (Chan et al., 2003; Herrwerth et al.,2003; Kreuzer et al., 2003).