Secondary caries are considered the main cause of dental restoration failure. In this context, anti-biofilm and bactericidal properties are desired in dental materials against pathogens such as Streptococcus mutans. To this purpose, graphene based materials can be used as fillers of polymer dental adhesives. In this work, we investigated the possibility to use as filler of dental adhesives, graphene nanoplatelets (GNP), a non toxic hydrophobic nanomaterial with antimicrobial and anti-biofilm properties. Graphene nanoplatelets have been produced starting from graphite intercalated compounds through a process consisting of thermal expansion and liquid exfoliation. Then, a dental adhesive filled with GNPs at different volume fractions has been produced through a solvent evaporation method. The rheological properties of the new experimental adhesives have been assessed experimentally. The adhesive properties have been tested using microtensile bond strength measurements (µ-TBS). Biocidal activity has been studied using the colony forming units count (CFU) method. The anti-biofilm properties have been demonstrated through FE-SEM imaging of the biofilm development after 3 and 24 h of growth. A significantly lower vitality of S. mutans cells has been demonstrated when in contact with the GNP filled dental adhesives. Biofilm growth on adhesive-covered dentine tissues demonstrated anti-adhesion properties of the produced materials. µ-TBS results demonstrated no significant difference in µ-TBS between the experimental and the control adhesive. The rheology tests highlighted the necessity to avoid low shear rate regimes during adhesive processing and application in clinical protocol, and confirmed that the adhesive containing the 0.2%wt of GNPs possess mechanical properties comparable with the ones of the control adhesive.

Nanotechnologies are currently revolutionizing the world around us, improving the quality of our lives thanks to a multitude of applications in several areas including the environmental preservation, with the biodeterioration phenomenon representing one of the major concerns. In this study, an innovative nanomaterial consisting of graphene nanoplatelets decorated by zinc oxide nanorods (ZNGs) was tested for the ability to inhibit two different pathogens belonging to bacterial genera frequently associated with nosocomial infections as well as biodeterioration phenomenon: the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa. A time- and dose-dependent bactericidal effect in cell viability was highlighted against both bacteria, demonstrating a strong antimicrobial potential of ZNGs. Furthermore, the analysis of bacterial surfaces through Field emission scanning electron microscopy (FESEM) revealed ZNGs mechanical interaction at cell wall level. ZNGs induced in those bacteria deep physical damages not compatible with life as a result of nanoneedle-like action of this nanomaterial together with its nanoblade effect. Cell injuries were confirmed by Fourier transform infrared spectroscopy, revealing that ZNGs antimicrobial effect was related to protein and phospholipid changes as well as a decrease in extracellular polymeric substances; this was also supported by a reduction in biofilm formation of both bacteria. The antibacterial properties of ZNGs applied on building-related materials make them a promising tool for the conservation of indoor/outdoor surfaces. Finally, ZNGs nanotoxicity was assessed in vivo by exploiting the soil free living nematode Caenorhabditis elegans. Notably, no harmful effects of ZNGs on larval development, lifespan, fertility as well as neuromuscular functionality were highlighted in this excellent model for environmental nanotoxicology. Overall, ZNGs represent a promising candidate for developing biocompatible materials that can be exploitable in antimicrobial applications without releasing toxic compounds, harmful to the environment.

In recent years, several studies have demonstrated the strong cytotoxicity toward bacteria of graphene-based materials, suggesting their use as antimicrobial agents. The objective of this study was to evaluate the antibacterial activity against Streptococcus mutans, the principal microbiological agent in the etiology of dental caries, of two types of graphene nanoplatelets (GNPs), characterized by different thickness and lateral dimensions of the flakes. The antimicrobial properties of GNPs were valued on some plaque and saliva samples extracted from children with dental caries. Our results show that the killing effect of GNPs on S. mutans cells is both lateral size and thickness dependent. In fact, lower thickness and smaller size GNPs exhibit stronger antibacterial activity than larger and thicker ones. Scanning electron microscopy analysis revealed that GNPs interact strongly with cells. This study suggests that GNPs may be highly effective against S. mutans and therefore caries.

Recently, graphene-polymer composites gained a central role in advanced stress and strain sensing. A fundamental step in the production of epoxy-composites filled with graphene nanoplatelets (GNPs) consists in the exfoliation and dispersion of expanded graphite in a proper solvent, in the mixing of the resulting GNP suspension with the polymer matrix, and in the final removal of the solvent from the composite before curing through evaporation. The effects of traces of residual solvent on polymer curing process are usually overlooked, even if it has been found that even a small amount of residual solvent can affect the mechanical properties of the final composite. In this paper, we show that residual traces of N,N′-Dimethylformamide (DMF) in vinylester epoxy composites can induce relevant variations of the electrical, mechanical and electromechanical properties of the cured GNP-composite. To this purpose, a complete analysis of the morphological and structural characteristics of the composite samples produced using different solvent mixtures (combining acetone and DMF) is performed. Moreover, electrical, mechanical and electromechanical properties of the produced composites are assessed. In particular, the effect on the piezoresistive response of the use of DMF in the solvent mixture is analyzed using an experimental strain dependent percolation law to fit the measured electromechanical data. It is shown that the composites realized using a higher amount of DMF are characterized by a higher electrical conductivity and by a strong reduction of Young’s Modulus.

Poly(vinylidene fluoride) (PVDF) is a biocompatible polymer commonly used for biomedical applications, food packaging and hygiene products. Within these contexts, the polymer surface is typically exposed to microorganisms and bacteria, with consequent biofilm formation. In this paper, self-standing flexible composite poly(vinylidene fluoride)(PVDF) films with antimicrobial properties were prepared by simple solution casting method. We investigated the effect of three different types of nanofillers, namely graphene nanoplatelets (GNPs), zinc oxide nanorods (ZnO-NRs) and ZnO-NR-decorated GNPs (ZNGs), on the antimicrobial activity of PVDF composite films against Pseudomonas aeruginosa. ZnO-NRs were also grown directly over the surface of PVDF composite films filled with ZnO nanoparticles, acting as nucleation seeds. In all cases, vitality tests performed in static conditions demonstrated a strong antimicrobial property of the produced specimens. This effect can be mainly ascribed to the bacteria/nanomaterials strong surface interaction, which results in the biofilm integrity disruption.

Graphene and its derivatives are nowadays gaining an ever increasing attention for diverse applications, such as supercapacitors, flexible screens and nanocomposites. One of the main challenges still limiting the wide spreading use of graphene-based nanomaterials in electrical and electromagnetic applications consists in the capability of controlling their morphological properties and electrical conductivity through the proper setting of the synthesis route and production process. In this paper graphene nanoplatelets (GNPs) are produced via thermochemical exfoliation of graphite intercalated compound (GIC). The crucial phase of the exfoliation process consists in the tip sonication of the solution containing thermally reduced GIC. The study presented here aims at evaluating the effect of several synthesis parameters, such as the sonication duty cycle and suspension temperature, on the DC conductivity of GNP thick films and on the morphological properties of GNPs.