Antibiofilm surface functionalization of catheters by magnesium fluoride nanoparticles

Abstract

The ability of bacteria to colonize catheters is a major cause of infection. In the current study, catheters were surface-modified with MgF₂ nanoparticles (NPs) using a sonochemical synthesis protocol described previously. The one-step synthesis and coating procedure yielded a homogenous MgF₂ NP layer on both the inside and outside of the catheter, as analyzed by high resolution scanning electron microscopy and energy dispersive spectroscopy. The coating thickness varied from approximately 750 nm to 1000 nm on the inner walls and from approximately 450 nm to approximately 580 nm for the outer wall. The coating consisted of spherical MgF₂ NPs with an average diameter of approximately 25 nm. These MgF₂ NP-modified catheters were investigated for their ability to restrict bacterial biofilm formation. Two bacterial strains most commonly associated with catheter infections, Escherichia coli and Staphylococcus aureus, were cultured in tryptic soy broth, artificial urine and human plasma on the modified catheters. The MgF₂ NP-coated catheters were able to significantly reduce bacterial colonization for a period of 1 week compared to the uncoated control. Finally, the potential cytotoxicity of MgF₂ NPs was also evaluated using human and mammalian cell lines and no significant reduction in the mitochondrial metabolism was observed. Taken together, our results indicate that the surface modification of catheters with MgF₂ NPs can be effective in preventing bacterial colonization and can provide catheters with long-lasting self-sterilizing properties.

Keywords:

• MgF₂ NP coating
• modified surfaces
• bacterial colonization
• human plasma
• artificial urine
• biocompatibility

Acknowledgments

We thank Dr Gal Yerushalmi for her helpful discussion and critical review of the manuscript. This research was carried out as part of the activities of the KAMIN project financed by the Israeli Ministry of Industry. This research is part of the requirements for a PhD thesis for Jonathan Lellouche at Bar Ilan University. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship that are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us.

Disclosure

We confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.

Supplementary data

MgF₂ NP characterization

The NP morphology and its crystalline characterization are depicted in Figure S1. The powder XRD analysis of the NPs showed a clear crystalline pattern (Figure S1A). The XRD pattern matched the reflection peaks of the tetragonal MgF₂ phase (Joint Committee on Powder Diffraction Standards card No 00-041-1443) characterized by diffraction planes (110), (101), (111), (210), (211), (220), (002), (310), (301), (311), and (222). No additional diffraction peaks of any impurity were detected, demonstrating the high purity of the product. In addition, the average diameter of crystallites calculated by the Debye–Scherrer equation afforded a value of 24.8 nm, which is similar to the average size measured by HR SEM (Figure S1B and C). The fabricated MgF₂ NPs showed spherical, well-shaped nanostructure morphology. Figure S1D also disclosed characteristic lattice fringes of the crystalline phase. The measured inter-fringe distance of 3.32 Å matches perfectly the (110) interplanar distance (Joint Committee on Powder Diffraction Standards card No 00-041-1443).

Figure S1 MgF₂ NP characterization. (A) XRD patterns of MgF₂ NPs with the Miller indices of the respective atomic planes; (B) HR SEM image; (C) size distribution; and (D) HR TEM micrograph of MgF₂ NPs and the 110 plane.

Abbreviations: HR SEM, high resolution scanning electron microscope; HR TEM, high resolution transmission electron microscope; NP, nanoparticle; XRD, X-ray diffraction.

Table S1 Influence of Mg⁺² and F⁻ on the Escherichia coli biofilm formation on the catheter walls

Table S2 Influence of Mg⁺² and F⁻ on the Staphylococcus aureus biofilm formation on the catheter walls