Surface coatings that resist non-specific protein adsorption and bacterial adhesion are important for a number of applications including biosensors, biomaterials, and marine coatings. Recent efforts have shown that surface coatings composed of a mixture of charged groups with an overall charge neutrality result in surfaces that are highly resistant to non-specific protein adsorption. Examples of polymers that show these super-low fouling characteristics include zwitterionic materials such as poly(sulfobetaine methacrylate) (pSBMA) and co-polymers formed from a mixture of charged monomers. It has been shown that low-fouling surface coatings composed of poly(oligo(ethylene glycol) (pOEG) reduce bacterial adhesion as well. In this work we show that these mixed-charge, super-low fouling polymer brush coatings present an excellent approach for preventing bacterial adhesion and biofilm formation.

In this study polymer brushes were grafted to gold coated glass slides using atom transfer radical polymerization (ATRP). The composition of the polymer brushes were characterized using electron spectroscopy for chemical analysis (ESCA), to determine reaction conditions that resulted in a statistical copolymer. The thickness of the polymer brush was characterized by atomic force microscopy (AFM) and the brushes were shown to be 25-35 nm in thickness. The non-specific adsorption of proteins to polymer brush coated surfaces was quantified using a surface plasmon resonance (SPR) biosensor. Solutions of 1 mg/mL of fibrinogen (FBG), lysozyme (LYZ), and bovine serum albumin (BSA) were used to confirm the super-low fouling characteristics of the polymer brushes. It was seen that there is no non-specific protein binding to these polymer brush surfaces following 10 minutes of adsorption. Bacterial adhesion of both S. epidermidis and P. aeruginosa was quantified after both 2 hours and 24 hours with fluorescent microscopy using a live/dead stain. In this study, it was seen that the pSBMA surface coating significantly decreased the bacterial adhesion as compared to the control glass surface. Additionally, it was shown that the pSBMA brushes reduced the bacterial adhesion to the same extent as pOEG brushes. Finally, the biofilm formation was characterized on the polymer brush coated surfaces after 24 hours. It was seen that the mixed charge surface coatings greatly reduced the biofilm formation as compared to the control surfaces. Additionally, the biofilm formation was reduced to a similar level as that seen for pOEG surface coatings. This indicates that mixed charge polymer brushes composed of either zwitterionic or mixed charge co-polymers represent a very promising surface coating for the next generation of non-fouling materials.

This work has shown that super-low fouling polymer brush coatings can be prepared from both zwitterionic and mixed charge co-polymers. These surface coatings greatly reduce non-specific protein binding as well as the adhesion and accumulation of bacteria. Due to the susceptibility of pOEG to oxidation damage, these mixed charge materials represent a promising new approach for the development of bacteria resistant coatings.