Protein-Resistant Poly(ethylene oxide)-Grafted Surfaces:  Chain Density-Dependent Multiple Mechanisms of Action

Abstract

A clear understanding of the mechanisms responsible for the protein-resistant nature of end-tethered poly(ethylene oxide) (PEO) surfaces remains elusive. A barrier to improved understanding is the fact that many of the factors involved (chain length, chain density, hydration, conformation, and distal chemistry) are inherently correlated. We hypothesize that, by comparing systems of variable but precisely known chain density, it should be possible to gain additional insight into the effects of the other factors. To evaluate this hypothesis, chain-end-thiolated PEOs were chemisorbed to gold-coated silicon wafers such that a range of chain densities was obtained. Three different PEOs were investigated: hydroxy-terminated chains of molecular weight 600 (600-OH), methoxy-terminated chains of molecular weight 750 (750-OCH3), and methoxy-terminated chains of molecular weight 2000 (2000-OCH3). In situ null ellipsometry was used to determine PEO chemisorption kinetics, ultimate PEO chain densities, protein adsorption kinetics, and ultimate protein adsorbed quantities. With this approach, it was possible to ascertain the effects of PEO distal chemistry (-OH, -OCH3), chain length, and layer hydration on protein adsorption. The data obtained suggested that properties related to chain density (conformational freedom, hydration) were the main determinants of protein resistance at chain densities up to a critical value of approximately 0.5 chain/nm2; at this value, protein adsorption was a minimum for the methoxy-terminated PEOs. For the hydroxyl-terminated PEO, adsorption leveled off at the critical value. Thus distal chemistry appears to be a major determinant of protein resistance at chain densities greater than the critical value.

Stimuli-sensitive intrinsically disordered protein brushes

“…This dynamic range is comparable to many existing synthetic polymer brush systems and suggests that these materials may serve as an attractive complement or alternative to synthetic systems in specific settings 24,39 . It is also conceivable that this dynamic range could be shifted, widened, or narrowed in interesting ways by exerting more control over the grafting density, such as by using cloud point grafting to achieve very dense brushes 40,41 . Furthermore, we have demonstrated that we can use proteases to reduce the height of the brush in situ by cleaving the constituent chains at well-defined points.…”

An X-ray and neutron reflectometry study of ‘PEG-like’ plasma polymer films

“…It is becoming clear that chain density and, thus, conformation are critical factors in the successful lowprotein-fouling properties of PEG and PEG-like films [19,[35][36][37]. In a study by Fick et al [17], PEG self-assembled monolayers were reported to be highly protein resistant when they contain a solvated densely grafted brush of only 40 Å thick, which correlates to a chain length of only 11 ethylene glycol units.…”

Mixed poly (ethylene glycol) and oligo (ethylene glycol) layers on gold as nonfouling surfaces created by backfilling

“…4 The ability for a given PEG functionalized surface to resist fouling is thought to be mainly dependent on the graft density and molecular weight (M W ) of PEG used, both of which are key properties that decide the conformation of PEG chains on surfaces. [5][6][7] For example. in the case of high or low graft density, PEG chains are arranged in either the "brush" or "mushroom" conformation, respectively.…”