Performance of Graphene/Polydimethylsiloxane Surfaces against S. aureus and P. aeruginosa Single- and Dual-Species Biofilms

Abstract

The increasing incidence of implant-associated infections has prompted the development of effective strategies to prevent biofilm formation on these devices. In this work, pristine graphene nanoplatelet/polydimethylsiloxane (GNP/PDMS) surfaces containing different GNP loadings (1, 2, 3, 4, and 5 wt%) were produced and evaluated on their ability to mitigate biofilm development. After GNP loading optimization, the most promising surface was tested against single- and dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa. The antibiofilm activity of GNP/PDMS surfaces was determined by the quantification of total, viable, culturable, and viable but nonculturable (VBNC) cells, as well as by confocal laser scanning microscopy (CLSM). Results showed that 5 wt% GNP loading reduced the number of total (57%), viable (69%), culturable (55%), and VBNC cells (85%) of S. aureus biofilms compared to PDMS. A decrease of 25% in total cells and about 52% in viable, culturable, and VBNC cells was observed for P. aeruginosa biofilms. Dual-species biofilms demonstrated higher resistance to the antimicrobial activity of GNP surfaces, with lower biofilm cell reductions (of up to 29% when compared to single-species biofilms). Still, the effectiveness of these surfaces in suppressing single- and dual-species biofilm formation was confirmed by CLSM analysis, where a decrease in biofilm biovolume (83% for S. aureus biofilms and 42% for P. aeruginosa and dual-species biofilms) and thickness (on average 72%) was obtained. Overall, these results showed that pristine GNPs dispersed into the PDMS matrix were able to inhibit biofilm growth, being a starting point for the fabrication of novel surface coatings based on functionalized GNP/PDMS composites.

Graphene-Based Coating to Mitigate Biofilm Development in Marine Environments

“…PDMS stood out as more homogeneous and smoother than the G5/PDMS composite, which displayed a rough appearance, with the presence of uniformly dispersed graphene agglomerates forming small elevations on the surface of the coating ( Figure 3 b). These results corroborate the AFM analysis, as well as those reported by Oliveira et al [ 51 ]. As a result of the van der Waals forces and strong π–π interactions between individual GNP sheets, the dispersion of GNP is often challenging, leading to the formation of graphene agglomerates [ 51 , 74 ].…”

“…These results corroborate the AFM analysis, as well as those reported by Oliveira et al [ 51 ]. As a result of the van der Waals forces and strong π–π interactions between individual GNP sheets, the dispersion of GNP is often challenging, leading to the formation of graphene agglomerates [ 51 , 74 ]. In these clusters, the carbon material is more exposed, promoting its direct contact with bacteria, which, in turn, potentiates graphene’s antimicrobial activity [ 68 , 75 ].…”

“…It is hypothesized that the first layer of adhered cells is particularly affected by this dart-like effect, impairing the subsequent adhesion of cell layers, and, therefore, curbing long-term biofilm formation. Overall, these results corroborate the previously reported antibacterial and antifouling properties of graphene materials [ 32 , 51 , 75 , 76 ].…”

“…Additionally, epifluorescence microscopy and SEM analysis further demonstrated the cell membrane damage caused by GNP exposure ( Figures S3 and S4 ). This finding is consistent with the proposed GNP mechanism of action which postulates that the direct contact between the bacterial membranes and the sharp edges of graphene sheets or wrapping and trapping of bacterial membranes by the nanosheets induce cell membrane damage [ 38 , 51 ]. In addition, the analysis of non-treated C. marina cells versus those treated with GNP 5% and stained with 5-CFDA ( Figure 1 c,d) suggested that cells exposed to GNP displayed higher metabolic activity (approximately 1.5-fold) than non-treated cells (control).…”

“…The curing agent (Sylgard 184 Part B, Dow Corning) was then gently added to the base-polymer/GNP combination (in a 10:1 A:B ratio) and carefully mixed. Spin coating (Spin150 PolosTM, Caribbean, The Netherlands) for 1 min with a 500 rpm ramp to 6000 rpm was used to apply the GNP/PDMS composites as a thin layer on top of the glass coupons [ 51 ]. Finally, to induce the curing process, coated coupons were incubated overnight in an oven at 80 °C [ 52 ].…”