Multifunctional Fe3O4 Nanoparticles Filled Polydopamine Hollow Rods for Antibacterial Biofilm Treatment

Abstract

This work reports the use of mesoporous silica rods as templates for the step-wise preparation of multifunctional Fe₃O₄ NPs filled polydopamine hollow rods (Fe₃O₄@PDA HR). The capacity of as-synthesized Fe₃O₄@PDA HR as a new drug carrier platform was assessed by its loading and the triggered release of fosfomycin under various stimulations. It was found that the release of fosfomycin was pH dependent with ~89% of fosfomycin being released in pH 5 after 24 h, which was 2-fold higher than that in pH 7. The magnetic properties of Fe₃O₄ NPs and the photothermal properties of PDA enabled the triggered release of fosfomycin upon the exposure to rotational magnetic field, or NIR laser irradiation. Additionally, the capability of using multifunctional Fe₃O₄@PDA HR to eliminate preformed bacterial biofilm was demonstrated. Upon exposure to the rotational magnetic field, the biomass of a preformed biofilm was significantly reduced by 65.3% after a 20 min treatment with Fe₃O₄@PDA HR. Again, due to the excellent photothermal properties of PDA, a dramatic biomass decline (72.5%) was achieved after 10 min of laser exposure. This study offers an alternative approach of using drug carrier platform as a physical mean to kill pathogenic bacteria along with its traditional use for drug delivery.

Keywords: Fe3O4 nanoparticles; drug delivery system; fosfomycin; polydopamine.

Figure 1

Schematic illustration for the preparation of Fe₃O₄ NPs filled PDA HR.

Figure 2

SEM image of synthesized MSR and its size distribution (A) and TEM image of monodisperse Fe₃O₄ NPs and its size distribution (B).

Figure 3

XRD pattern of monodisperse Fe₃O₄ NPs, MSR-COOH and Fe₃O₄ grafted MSR.

Figure 4

SEM (A), TEM (B) images and EDX analysis (C) of Fe₃O₄ filled PDA HR.

Figure 5

Release profile of fosfomycin from Fe₃O₄@PDA HR at different pH and upon the exposure to a rotational magnetic field (A) and upon NIR laser irradiation (B).

Figure 6

Inhibitory effect on biofilm formation of fosfomycin loaded Fe₃O₄@PDA HR and free fosfomycin drug molecules.

Figure 7

Reduction of pre-formed biofilm biomass upon exposure to rotational magnetic field (A), and SEM images of pre-formed biofilm upon exposure to rotational magnetic field (B): biofilm only (i), biofilm with added Fe₃O₄ NPs (ii) and biofilm with added Fe₃O₄@PDA HR (iii).

Figure 8

Live/dead cell staining of S. aureus biofilms under different treatment: control preformed biofilm (A), preformed biofilm treated with bare Fe₃O₄ NPs (B) and preformed biofilm treated with Fe₃O₄ @PDA HR (C) under rotational magnetic field (Scale bar = 10 µm).

Figure 9

Photothermal conversion performance of bare Fe₃O₄ and Fe₃O₄@PDA HR (A) and photostability of Fe₃O₄@PDA HR (B); Reduction of preformed biofilm biomass upon laser irradiation (C) and live/dead cell staining of biofilm treated with Fe₃O₄@PDA HR upon exposure to NIR laser (Scale bar = 10 µm) (D).