Comparison between protein repulsions by diblock PLA-PEO and albumin nanocoatings using OWLS

A previous investigation suggested that a surface bearing a rinsing-resistant depot (nanocoating) of albumin is more protein-repulsive than the same surface physically pegylated by a poly(D,L-lactic acid)-poly(ethylene oxide) diblock copolymer. To complement the study, Optical Waveguide Lightmode Spectroscopy was used to compare the mass and the thickness of protein depots from different systems, namely albumin alone at different concentrations, a mixture of albumin + fibrinogen + γ-globulin at their physiological concentrations, and sheep serum. The same standard OWLS protocol was applied to compare data for bare sensor chips, for chips covered by an albumin nanocoating, and for chips physically pegylated using poly(D,L-lactic acid)-poly(ethylene oxide) diblock copolymers with different compositions and block lengths. The strategy and the conditions being rather different from those generally used to study pegylation-related antifouling properties; the literature was first reviewed critically. Then full coverage of sensor chips by albumin was demonstrated. The comparative study confirmed that albumin was more protein-repulsive than any of the diblock copolymers, irrespective of the protein system. Furthermore, it was found that pegylated surfaces were albumin-repulsive only when the concentration of the protein solution flowing over the surface was very low (0.1 g/L). It was not possible to correlate the copolymer data to PEO chain density, chain length and existence of brush. The in vitro repulsive activity of albumin was not affected by drying and rehydration, a feature of interest for storage of albumin-coated surfaces. All these observations confirmed our preliminary findings and showed that considering model proteins individually or in mixtures at concentrations far from physiological concentrations are not suitable to reflect the reality of full blood-surface interactions.