Size-Selective Protein Adsorption to Polystyrene Surfaces by Self-Assembled Grafted Poly(ethylene Glycols) with Varied Chain Lengths

Abstract

We report about the surface modification of polystyrene (PSt) with photoreactive alpha-4-azidobenzoyl-omega-methoxy poly(ethylene glycol)s (ABMPEG) of three different molecular weights (MWs of approximately 2, approximately 5, and approximately 10 kg/mol) and with two poly(ethylene glycol)/poly(propylene glycol) triblock copolymers (PEG-PPG-PEG) of about identical PEG/PPG ratio (80/20, w/w) and MW(PEG) of approximately 3 and approximately 6 kg/mol, all via adsorption from aqueous solutions. For ABMPEGs, an additional UV irradiation was used for photografting to the PSt. Contact angle (CA) and atomic force microscopy data revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surfaces as a function of PEG type and concentration used for the modification. In all cases, an incomplete coverage of the PSt was observed even after modification at the highest solution concentrations (10 g/L). However, clear differences were seen between PEG-PPG-PEGs and ABMPEGs; only for the latter was a nanoscale-ordered interphase structure with an influence of MW(PEG) on the PEG density observed; after modification at the same solution concentrations, the density was significantly higher for lower MW(PEG). The adsorption of three proteins, myoglobin (Mgb), bovine serum albumin (BSA), and fibrinogen to the various surfaces was analyzed by surface plasmon resonance. Pronounced differences between the two PEG types with respect to the reduction of protein adsorption were found. At high, but still incomplete, surface coverage and similar CA, the shielding of ABMPEG layers toward the adsorption of Mgb and BSA was much more efficient; e.g., the adsorbed Mgb mass relative to that of unmodified PSt was reduced to 10% for ABMPEG 2 kg/mol while for both PEG-PPG-PEGs the Mgb mass was still around 100%. In addition, for the ABMPEG layers an effect of MW(PEG) on adsorbed protein mass-decrease with decreasing MW-could be confirmed; and the highest Mgb/BSA selectivities were also observed. A "two-dimensional molecular sieving", based on PEG molecules having a nanoscale order at the hydrophobic substrate polymer surface has been proposed, and the main prerequisites were the use of PEG conjugates which are suitable for an "end-on" grafting (e.g., ABMPEGs), the use of suitable (not too high) concentrations for the surface modification via adsorption/self-assembly, optionally the photografting on the substrate (possible only for ABMPEG), and presumably, a washing step to remove the excess of unbound PEGs. The results of this study also strongly support the hypothesis that the biocompatibility of hydrophobic materials can be very much improved by PEG modifications at surface coverages that are incomplete but have an ordered layer structure controlled by the size and steric interactions of surface-bound PEGs.

Poly(ether imide) Membranes Modified with Poly(ethylene imine) as Potential Carriers for Epidermal Substitutes

“…Similar observations were made with polysulphone membranes or polystyrene on which hydrophilic, non-charged poly(ethylene glycol) was covalently immobilised. [36,37] Since the quantities of polar (charged) amine functionalities were higher on PETIM_60, the lower water CAs can be explained.…”

Poly(l-lysine)-grafted-poly(ethylene glycol)-based surface-chemical gradients. Preparation, characterization, and first applications

“…The protein resistance of PEG modified surfaces is attributed mainly to entropic repulsion and the high water content of the PEG chains. Among other methods, PEG chains may be immobilized on surfaces via covalent coupling, either by "grafting to" [16][17][18][19] or "grafting from," 20 via the adsorption of PEG-containing block copolymers, 18,[21][22][23] graft copolymers, 24,25 and interpenetrating polymer networks 26,27 and via functionalization with ethylene glycol-terminated alkanethiols 7,[28][29][30][31] or silanes. 32,33 For the platforms dealing with PEG in a brushlike conformation, it was found that the most important parameter determining the protein resistance is the ethylene glycol monomer density on the surface n EG expressed as EG units/surface unit.…”

Designing nanostructured block copolymer surfaces to control protein adhesion

“…Two of the most common bulk techniques are: making the surface more hydrophilic through a variety of processes such as plasma etching [6,[20][21][22][23]; or modifying the surface with a hydrophilic polymer such as polyethylene glycol [24][25][26][27][28][29][30]. Other methodologies have used smallscale modifications at the micro-and nanolevels to create patterned surfaces that can regulate protein and cellular behaviour [31][32][33][34][35][36].…”