Catherine M. Santos

Antimicrobial graphene polymer (PVK-GO) nanocomposite films

The first report on the fabrication and application of a nanocomposite containing poly-N-vinyl carbazole (PVK) polymer and graphene oxide (GO) as an antimicrobial film was demonstrated. The antimicrobial film was 90% more effective in preventing bacterial colonization relative to the unmodified surface. More importantly, the nanocomposite thin film showed higher bacterial toxicity than pure GO-modified surface.

Graphene nanocomposite for biomedical applications: fabrication, antimicrobial and cytotoxic investigations

Materials possessing excellent bacterial toxicity, while presenting low cytotoxicity to human cells, are strong candidates for biomaterials applications. In this study, we present the fabrication of a nanocomposite containing poly(N-vinylcarbazole) (PVK) and graphene (G) in solutions and thin films. Highly dispersed PVK-G (97-3 w/w%) solutions in various organic and aqueous solvents were prepared by solution mixing and sonication methods. The thermal properties and morphology of the new composite were analyzed using thermal gravimetry analysis (TGA) and atomic force microscopy (AFM), respectively. PVK-G films were immobilized onto indium tin oxide (ITO) substrates via electrodeposition. AFM was used to characterize the resulting topography of the nanocomposite thin films, while cyclic voltammetry and UV-vis were used to monitor their successful electrodeposition. The antimicrobial properties of the electrodeposited PVK-G films and solution-based PVK-G were investigated against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). Microbial growth after exposure to the nanocomposite, metabolic assay and live-dead assay of the bacterial solutions exposed to PVK-G presented fewer viable and active bacteria than those exposed to pure PVK or pure graphene solutions. The PVK-G film inhibited about 80% of biofilm surface coverage whereas the PVK- and G-modified surfaces allowed biofilm formation over almost the whole coated surface (i.e. > 80%). The biocompatibility of the prepared PVK-G solutions on NIH 3T3 cells was evaluated using the MTS cell proliferation assay. A 24 h exposure of the PVK-G nanocomposite to the NIH 3T3 cells presented ~80% cell survival.

Improved removal of lead(II) from water using a polymer-based graphene oxide nanocomposite

Poly(N-vinylcarbazole) (PVK) was blended with graphene oxide (GO) to form a PVK–GO polymer nanocomposite capable of adsorbing heavy metal from aqueous solutions. The homogenous distribution of GO in the PVK–GO nanocomposite was determined by X-ray photoelectron microscopy (XPS) and attenuated total reflectance – infrared spectroscopy (ATR-IR). The results show that the adsorption capacity of Pb2+ by the nanocomposite increased with increasing amount of GO. This phenomenon was attributed to the increasing concentration of oxygen-containing functional groups available in the nanocomposite. Furthermore, the adsorption of Pb2+ onto PVK–GO nanocomposite was influenced by pH changes. Higher pHs had a better adsorption capacity than lower pHs, due to changes in the nanocomposite surface properties. The highest adsorption capacity of the PVK–GO nanocomposite for Pb2+ was 887.98 mg g−1 and fits well the Langmuir model. This adsorption capacity was achieved using a 10 : 90 wt% ratio of PVK : GO at pH 7 ± 0.5 with a 90 min contact time. The high removal efficiency of this nanocomposite suggests that PVK–GO is effective and can be applied to remove heavy metals from water.

Antimicrobial applications of electroactive PVK-SWNT nanocomposites.

The antibacterial properties of a nanocomposite containing an electroactive polymer, polyvinyl-N-carbazole (PVK) (97 wt %), and single-walled carbon nanotubes (SWNT) (3 wt %) was investigated as suspensions in water and as thin film coatings. The toxic effects of four different PVK-SWNT (97:3 wt %) nanocomposite concentrations (1, 0.5, 0.05, and 0.01 mg/mL) containing 0.03, 0.015, 0.0015, and 0.0003 mg/mL of SWNT, respectively, were determined for planktonic cells and biofilms of Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). The results showed that the nanocomposite PVK-SWNT had antibacterial activity on planktonic cells and biofilms at all concentration levels. Higher bacterial inactivation (94% for E. coli and 90% for B. subtilis) were achieved in planktonic cells at a PVK-SWNT concentration of 1 mg/mL. Atomic force microscopy (AFM) imaging showed significant reduction of biofilm growth on PVK-SWNT coated surfaces. This study established for the first time that the improved dispersion of SWNTs in aqueous solutions in the presence of PVK enhances the antimicrobial effects of SWNTs at very low concentrations. Furthermore, PVK-SWNT can be used as an effective thin film coating material to resist biofilm formation.

Antimicrobial PVK:SWNT nanocomposite coated membrane for water purification: Performance and toxicity testing

This study demonstrated that coated nitrocellulose membranes with a nanocomposite containing 97% (wt%) of polyvinyl-N-carbazole (PVK) and 3% (wt%) of single-walled carbon nanotubes (SWNTs) (97:3 wt% ratio PVK:SWNT) achieve similar or improved removal of bacteria when compared with 100% SWNTs coated membranes. Membranes coated with the nanocomposite exhibited significant antimicrobial activity toward Gram-positive and Gram-negative bacteria (≈ 80-90%); and presented a virus removal efficiency of ≈ 2.5 logs. Bacterial cell membrane damage was considered a possible mechanism of cellular inactivation since higher efflux of intracellular material (Deoxyribonucleic acid, DNA) was quantified in the filtrate of PVK-SWNT and SWNT membranes than in the filtrate of control membranes. To evaluate possible application of these membrane filters for drinking water treatment, toxicity of PVK-SWNT was tested against fibroblast cells. The results demonstrated that PVK-SWNT was non toxic to fibroblast cells as opposed to pure SWNT (100%). These results suggest that it is possible to synthesize antimicrobial nitrocellulose membranes coated with SWNT based nanocomposites for drinking water treatment. Furthermore, membrane filters coated with the nanocomposite PVK-SWNT (97:3 wt% ratio PVK:SWNT) will produce more suitable coated membranes for drinking water than pure SWNTs coated membranes (100%), since the reduced load of SWNT in the nanocomposite will reduce the use of costly and toxic SWNT nanomaterial on the membranes.

CHAPTER 12:Carbon-Based Polymer Nanocomposites: From Material Preparation to Antimicrobial Applications

The development of new methods to control or prevent bacterial contamination in medical devices is essential to the improvement of the quality of life. The discovery of new carbon-based nanomaterials (CBNs) (i.e. graphene, carbon nanotubes, and graphene oxide) with unique optical, thermal, and mechanical properties did not only provide avenues in the creation of new technologies for energy, sensing, electronics, and mechanical applications; but also enabled new routes towards addressing the emerging problems of bacterial contamination due to their recently reported biocidal properties. However, even with the many desirable properties that CBNs possess, their practical uses as an antimicrobial material have not been fully explored due to issues related to their dispersibility, difficulty for scalability, and relatively high cost. To circumvent these issues, the addition of polymers to fabricate carbon-based polymer nanocomposites (CBPNs) was explored. Various polymers have been incorporated with CBNs. These polymers were utilized as dispersing agents, linkers for antimicrobial compounds, and matrices for fibers and membranes. This chapter reviews the current investigations related to biocidal properties of CBPNs, outlines the different methods that are used for their preparation as films or solutions, and assesses their contribution for antimicrobial applications.