Covalent Attachment of Poly(ethylene glycol) to Surfaces, Critical for Reducing Bacterial Adhesion

Abstract

The effects of different poly(ethylene glycol) (PEG) attachment strategies upon the adhesion of a Gramnegative bacteria (Pseudomonas sp.) was tested. PEG was covalently immobilized, at the lower critical solution temperature of PEG, to a layer of branched poly(ethylenimine) (PEI). PEI was both physically adsorbed to a stainless-steel (SS) substrate and covalently immobilized to a carboxylated poly(ethylene terephthalate) (PET-COOH) surface. On both substrates, the PEI and PEG grafting conditions were optimized so that the levels of surface coverage after each step were maximized and were the same on both substrates, as judged by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Also, ToF-SIMS imaging showed that both substrates were chemically uniform after each surface modification step. Thus, the two surfaces differ only in the mode of attachment of PEI to the substrate. In bacterial adhesion experiments, the optimal SS-PEG surface was not capable of reducing the number of adherent Pseudomonas sp. when compared to the controls. However, the PET-PEG surface reduced the level of adhesion by between 2 and 4 orders of magnitude for up to 5 h. ToF-SIMS analysis showed that both PEG surfaces adsorbed low but comparable levels of proteinaceous growth medium components (tryptic soy broth), as indicated by the addition of unique amino acid fragment ions in the spectra, most likely small peptides. Thus, bacterial adhesion was strongly dependent on the PEG immobilization strategy and not on the extent of peptide/protein adsorption. However, for the best PEG surfaces the residual bacterial adhesion is most likely from recognition of the small amount of adsorbed peptides. This highlights the necessity for preventing the adsorption of small biological species that can even penetrate PEG layers of high graft density, in the quest for the ultimate "nonfouling" surface.

Surface-Bound Proteins with Preserved Functionality

“…37,40,56 The second approach allows for considerably better control of the thickness and functionality of the formed coatings.…”

“…Covalent attachment of layers of poly-and oligoethylene glycols to various solid substrates, indeed, presents a broadly chosen approach for engineering of nonfouling interfaces. 3,37,40,43,48,67 PEGylated surfaces demonstrate some of the highest protein resistance; they are relatively durable; and chemically, PEGs are relatively easy to manipulate. 40,52,58 Utilizing self-assembled monolayers (SAMs) of alkylthiols on gold surfaces for engineering of bioactive interfaces has gained significant popularity due to the simplicity of the used chemistry 45,74 and to the availability of high-resolution structural information for such SAMs.…”

Inhibition of bacterial adhesion and biofilm formation on zwitterionic surfaces

“…on PEG-grafted surfaces by Kingshott et al [5], S. aureus on oligo(ethylene glycol) (OEG) self-assembled monolayers (SAMs) by Cooper and Tegoulia [6], and for S. aureus and S. epidermidis on OEG SAMs by Ostuni et al [7]. Recently, various factors influencing microbial adhesion to PEG brushes (i.e., PEG chain length and adsorbed protein) were systematically studied.…”

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

“…7 Studies have shown that covalently immobilized PEG coatings provide superior antifouling properties, probably since they cannot easily be displaced by biomolecules or conditioning layer molecules. 9 PEG functionalization techniques can be broadly classified into "grafting to" and "grafting from" approaches. The grafting from technique generally gives higher graft density since the limiting factor is diffusion of monomer onto the reactive ends of growing chains, whereas in the case of the grafting to technique the limitation is diffusion of entire polymer chains to the reactive substrate.…”