Nisin adsorption to PEO-PPO-PEO tri-block copolymer layers and its resistance to elution by fibrinogen Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s1784q92f

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  • While hydrophobic surfaces coated with the poly[ethylene oxide]-poly[propylene oxide]-poly[ethylene oxide] (PEO-PPO-PEO) surfactant Pluronic® F108 are highly resistant to plasma protein adsorption, the antimicrobial peptide nisin has been observed to adsorb in multilayer quantities at such surfaces, and the PEO chains themselves suggested to inhibit nisin exchange by blood proteins. But this had been investigated only with F108 bound by physical association between the hydrophobic surface and its apolar PPO block. In this work, nisin adsorption at hydrophobic, silanized silica surfaces coated with F108, and in separate experiments, coated with F108 that had been end-activated with nitrilotriacetic acid groups (EGAP-NTA), was detected in situ, by zeta potential measurements. The triblocks were covalently immobilized prior to the introduction of protein in each case. Zeta potential measurements were also used to evaluate fibrinogen adsorption, and the sequential adsorption behavior of nisin and fibrinogen, at bare hydrophobic and triblock-coated surfaces. Silica microspheres (1 µm diameter) were silanized with either allyldimethylchlorosilane (ADCS) or trichlorovinylsilane (TCVS). Silanized microspheres were incubated overnight in a solution of F108 or EGAP-NTA to allow for self assembly of a PEO layer. Coated microspheres were then subjected to γ-irradiation under water or in the presence of the triblock coating solution. Layer stability was quantified by its resistance to elution by SDS. Zeta potential changes indicated that pretreatment with TCVS, and γ-irradiation performed in the presence of the triblock coating solution, produced more stable triblock layers than were produced with ADCS. For this reason silanization only with TCVS was used in protein adsorption experiments. Introduction of fibrinogen to triblock-coated microspheres showed little change in zeta potential, indicating the presence of a steric repulsive barrier to fibrinogen adsorption. Introduction of nisin to triblock-coated microspheres showed a significant increase in zeta potential, a result of adsorption of the cationic nisin. In sequential adsorption experiments, the introduction of fibrinogen to "nisin-loaded" triblock layers caused a decrease in the zeta potential, consistent with the net negative charge of fibrinogen. This decrease was substantially more pronounced for TCVS-modified silica in the absence of triblock coatings, suggesting an enhanced resistance to nisin elution owing to its location in the PEO layer.
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