Antibacterial Activity of Inverse Vulcanized Polymers

Abstract

Inverse vulcanization is a bulk polymerization method for synthesizing high sulfur content polymers from elemental sulfur, a byproduct of the petrochemical industry, with vinylic comonomers. There is growing interest in polysulfides as novel antimicrobial agents due to the antimicrobial activity of natural polysulfides found in garlic and onions (Tsao et al. J. Antimicrob. Chemother. 2001, 47, 665-670). Herein, we report the antibacterial properties of several inverse vulcanized polymers against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa, two common causes of nosocomial infection and pathogens identified by the World Health Organization as priorities for antimicrobial development. High sulfur content polymers were synthesized with different divinyl comonomers and at different sulfur/comonomer ratios, to determine the effect of such variables on the antibacterial properties of the resulting materials. Furthermore, polymers were tested for their potential as antibacterial materials at different temperatures. It was found that the test temperature influenced the antibacterial efficacy of the polymers and could be related to the glass transition temperature of the polymer. These findings provide further understanding of the antibacterial properties of inverse vulcanized polymers and show that such polymers have the potential to be used as antibacterial surfaces.

Figure 1. A general scheme for the inverse vulcanization of sulfur with a vinylic comonomer.

Figure 1

The structures of the comonomers used in the study: 1,3-diisopropenylbenzene (DIB), perillyl alcohol, dicyclopentadiene (DCPD), divinylbenzene (DVB) and an example of triglyceride which is a major component of vegetable oils such as linseed oil.

Figure 2

A summary of the % reduction in viable S. aureus cells extracted from the surface and from solution compared to polypropylene for A) S-PA and B) S-DIB at varying test temperature and sulfur:comonomer ratio. * p<0.05 relative to polypropylene, ** p<0.01 relative to polypropylene, *** p<0.001, # p<0.05 relative to polypropylene, ## p<0.01 for 50 wt.% sulfur compared to 70 wt.% sulfur polymers at the same test conditions.

Figure 4

A summary of the % reduction in viable P. aeruginosa cells extracted from the surface and from solution compared to polypropylene for A) S50-PA and S70-PA and B) S50-DIB and S70-DIB. *p<0.05 relative to polypropylene ##p<0.01 for 50 wt% sulfur compared to 70 wt% sulfur polymer.

Figure 5

Absorbance at 600 nm for A) S-PA and B) S-DCPD, after staining with crystal violet at 2, 24 and 48 h incubation times with S. aureus. Where PP: polypropylene, S50: 50 wt.% sulfur polymer and S70: 70 wt.% sulfur polymer.

Figure 6. SEM images of A) polypropylene B) S50-DCPD and C) S50-PA after incubation with S. aureus.