Protein and bacterial fouling characteristics of peptide and antibody decorated surfaces of PEG-poly(acrylic acid) co-polymers

Abstract

The potential for base poly(ethylene glycol) graft poly(acrylic acid) PEG-g-PA copolymers and surface-modified PEG-g-PA materials to inhibit random protein fouling and bacterial adhesion are investigated. PEG-g-PA co-polymers were synthesized that inhibited non-specific protein and cellular adhesion. PEG-g-PA co-polymers were then covalently modified with either cell adhesion peptides (YRGDS, YEILDV) or fragments of antibodies to monocyte/macrophage integrin receptors (Anti-VLA4, Anti- β 1, Anti- β 2, and Anti-CD64) known to enhance macrophage adhesion and, perhaps, modulate their activation. Materials produced in this work were characterized using: hydrophobicity by contact angle; angle-resolved X-ray Photoelectron Spectroscopy to confirm the presence of PEG in the bulk material and the surface; degree of hydration; differential scanning calorimetry; and thermal gravimetric analysis. To evaluate the non-fouling efficacy of the various modified surfaces, three proteins, human serum albumin, human fibronectin (Fraction I) and human immunoglobulin were 125I labeled. Samples of base PEG-g-PA and PEG-g-PA, modified with various peptides, were exposed to solutions containing either 2 or 200 μg/ml of one of the labeled proteins at 37°C for 24 h. PEG-g-PA substrata modified with directly bound peptides exhibited protein adsorption that varied depending upon the surface bounded peptide. PEG-g-PA modified with peptides linked by linear PEG tethers reduced protein adsorption at 24 h by ∼45% in comparison to PEG-g-PA. Peptides linked by way of StarPEO and StarlikePEO tethers further decreased protein adsorption in comparison to PEG-g-PA. The ability of peptide:PEOtethers to inhibit protein adsorption appeared to be a function of type and surface coverage of the PEO tether and not influenced by the amount or molecular structure the tethered peptide. Peptides directly coupled to the PEG-g-PA increased the amount of protein fouling relative to controls and there appeared to be some dependency of the amount of protein adsorption on which peptide was tethered. Two 14C-labeled pathogens, Staphylococcus epidermidis and Pseudomonas aeruginosa, were used to quantify the degree of bacterial adhesion using two types of laminar flow cell chambers; one that provided invasive sampling of the target substrata and one that provided non-invasive microscopic surveillance of adhering bacterial cells. Attachment of both species to PEG-g-PA and peptide-modified PEG-g-PA was reduced compared to the basic poly(acrylic acid). Presence of peptides on the surface, whether directly bound or bound by the PEO tether did not influence adhesion of P. aeruginosa relative to controls. S. epidermidis adhesion rates increased slightly for those materials where peptides were directly bound to the surface but were reduced relative to base PEG-g-PA when peptides were bound by PEO tethers. All PEG-g-PA surfaces modified with fragments of monoclonal antibodies dramatically enhanced bacterial initial adhesion rates and maximum extent of attachment.