The antimicrobial peptide nisin shows potent activity against Gram-positive bacteria including the most prevalent implant-associated pathogens. Its mechanism of action minimizes the opportunity for the rise of resistant bacteria and it does not appear to be toxic to humans, suggesting good potential for its use in antibacterial coatings for selected medical devices. A more quantitative understanding of nisin loading and release from polyethylene oxide (PEO) brush layers will inform new strategies for drug storage and delivery, and in this work optical waveguide lightmode spectroscopy was used to record changes in adsorbed mass during cyclic adsorption-elution experiments with nisin, at uncoated and PEO-coated surfaces. PEO layers were prepared by radiolytic grafting of Pluronic® surfactant F108 or F68 to silanized silica surfaces, producing long- or short-chain PEO layers, respectively. Kinetic patterns were interpreted with reference to a model accounting for history-dependent adsorption, in order to evaluate rate constants for nisin adsorption and desorption, as well as the effect of pendant PEO on the lateral clustering behavior of nisin. Nisin adsorption was observed at the uncoated and F108-coated surfaces, but not at the F68-coated surfaces. Nisin showed greater resistance to elution by peptide-free buffer at the uncoated surface, and lateral rearrangement and clustering of adsorbed nisin was apparent only at the uncoated surface. We conclude peptide entrapment at the F108-coated surface is governed by a hydrophobic inner region of the PEO brush layer that is not sufficient for nisin entrapment in the case of the shorter PEO chains of the F68-coated surface.

A number of sufficiently small peptides have been shown to integrate into polyethylene oxide (PEO) brush layers in accordance with their amphiphilicity and ordered structure. Those results have suggested that responsive drug delivery systems based on peptide-loaded PEO layers can be controlled by modulation of solution conditions and peptide amphiphilicity. However, the presence of entrapped peptide may compromise the protein repulsive character of the PEO layer, and in this way reduce the viability of a medical device coating based on such an approach. Nisin is a cationic, amphiphilic, and antimicrobial peptide that has been shown to integrate into PEO brush layers. In this work, the preferential location of fibrinogen at PEO-coated, nisin-loaded layers was investigated in nisin-fibrinogen sequential adsorption experiments using detection of fluorescein isothiocyanate labeled fibrinogen, detection of changes in zeta potential, and measurement of adsorption and elution kinetics by optical waveguide lightmode spectroscopy. Results from each technique indicate that the presence of entrapped nisin does not affect fibrinogen interaction with the PEO layer. In addition, entrapment of blood solutes within PEO layers contacted with 25% equine plasma in phosphate-buffered saline was reduced by the prior entrapment of nisin within the layer.