Analytical characterization of laser-generated copper nanoparticles for antibacterial composite food packaging

MMP-3 mediates copper oxide nanoparticle-induced pulmonary inflammation and fibrosis

BACKGROUND

The increasing production and usage of copper oxide nanoparticles (Nano-CuO) raise human health concerns. Previous studies have demonstrated that exposure to Nano-CuO could induce lung inflammation, injury, and fibrosis. However, the potential underlying mechanisms are still unclear. Here, we proposed that matrix metalloproteinase-3 (MMP-3) might play an important role in Nano-CuO-induced lung inflammation, injury, and fibrosis.

RESULTS

Exposure of mice to Nano-CuO caused acute lung inflammation and injury in a dose-dependent manner, which was reflected by increased total cell number, neutrophil count, macrophage count, lactate dehydrogenase (LDH) activity, and CXCL1/KC level in bronchoalveolar lavage fluid (BALF) obtained on day 3 post-exposure. The time-response study showed that Nano-CuO-induced acute lung inflammation and injury appeared as early as day 1 after exposure, peaked on day 3, and ameliorated over time. However, even on day 42 post-exposure, the LDH activity and macrophage count were still higher than those in the control group, suggesting that Nano-CuO caused chronic lung inflammation. The Nano-CuO-induced pulmonary inflammation was further confirmed by H&E staining of lung sections. Trichrome staining showed that Nano-CuO exposure caused pulmonary fibrosis from day 14 to day 42 post-exposure with an increasing tendency over time. Increased hydroxyproline content and expression levels of fibrosis-associated proteins in mouse lungs were also observed. In addition, Nano-CuO exposure induced MMP-3 overexpression and increased MMP-3 secretion in mouse lungs. Knocking down MMP-3 in mouse lungs significantly attenuated Nano-CuO-induced acute and chronic lung inflammation and fibrosis. Moreover, Nano-CuO exposure caused sustained production of cleaved osteopontin (OPN) in mouse lungs, which was also significantly decreased by knocking down MMP-3.

CONCLUSIONS

Our results demonstrated that short-term Nano-CuO exposure caused acute lung inflammation and injury, while long-term exposure induced chronic pulmonary inflammation and fibrosis. Knocking down MMP-3 significantly ameliorated Nano-CuO-induced pulmonary inflammation, injury, and fibrosis, and also attenuated Nano-CuO-induced cleaved OPN level. Our study suggests that MMP-3 may play important roles in Nano-CuO-induced pulmonary inflammation and fibrosis via cleavage of OPN and may provide a further understanding of the mechanisms underlying Nano-CuO-induced pulmonary toxicity.

Evaluation of PLA-Based Composite Films Filled with Cu2(OH)3NO3 Nanoparticles as an Active Material for the Food Industry: Biocidal Properties and Environmental Sustainability

The globalization of markets has diversified the food supply, but it has also made the distribution chain more difficult, increasing the risk of microbial contamination. One strategy to obtain safer food and extend its shelf life is to develop active packaging with antimicrobial properties that prevent the growth of pathogenic microorganisms or spoilage in food products. In this context, and in line with the growing social awareness about the environmental impact generated by plastic waste, this work evaluated the effectiveness of polylactic acid (PLA) films loaded with different concentrations of copper (II) hydroxynitrate nanoparticles (CuHS) against the microbiota of fresh foods (chicken, fish and cheese). The results showed that the developed films containing 1, 3 and 5% w/w of CuHS in the polymeric matrix caused a decrease in the microbial abundance equal to or higher than 3 logarithmic units in all foods tested. Moreover, the mechanical and thermal properties of the formulated composites showed that the added CuHS concentrations did not substantially modify these properties compared to the PLA films. Taking into account the results obtained for antimicrobial activity, Cu (II) migration levels and the cytotoxicity of the films formulated, the PLA composite loaded with 1% CuHS (w/w) was the most suitable for its potential use as food packaging material. In addition, the biodegradation of this composite film was studied under conditions simulating intensive aerobic composting, demonstrating that almost 100% disintegration after 14 days of testing was achieved. Therefore, the innovative PLA-based films developed represent a promising strategy for the fabrication of packaging and active surfaces to increase food shelf life while maintaining food safety. Moreover, their biodegradable character will contribute to efficient waste management, turning plastic residues into a valuable resource.

Promising biomedical systems based on copper nanoparticles: Synthesis, characterization, and applications

Copper and copper oxide nanoparticles (CuNPs) have unique physicochemical properties that make them highly promising for biomedical applications. This review discusses the application of CuNPs in biomedicine, including diagnosis, therapy, and theranostics. Recent synthesis methods, with an emphasis on green approaches, are described, and the latest techniques for nanoparticle characterization are critically analyzed. CuNPs, including Cu2O, CuO, and Cu, have significant potential as anti-cancer agents, drug delivery systems, and photodynamic therapy enhancers, among other applications. While challenges such as ensuring biocompatibility and stability must be addressed, the state-of-the-art research reviewed here provides strong evidence for the efficacy and versatility of CuNPs. These multifunctional properties have been extensively researched and documented, showcasing the immense potential of CuNPs in biomedicine. Overall, the evidence suggests that CuNPs are a promising avenue for future research and development in biomedicine. We strongly support further progress in the development of synthesis and application strategies to enhance the effectiveness and safety of CuNPs for clinical purposes.

Copper oxide nanoparticles: In vitro and in vivo toxicity, mechanisms of action and factors influencing their toxicology

Copper oxide nanoparticles (CuO NPs) have received increasing interest due to their distinctive properties, including small particle size, high surface area, and reactivity. Due to these properties, their applications have been expanded rapidly in various areas such as biomedical properties, industrial catalysts, gas sensors, electronic materials, and environmental remediation. However, because of these widespread uses, there is now an increased risk of human exposure, which could lead to short- and long-term toxicity. This review addresses the underlying toxicity mechanisms of CuO NPs in cells which include reactive oxygen species generation, leaching of Cu ion, coordination effects, non-homeostasis effect, autophagy, and inflammation. In addition, different key factors responsible for toxicity, characterization, surface modification, dissolution, NPs dose, exposure pathways and environment are discussed to understand the toxicological impact of CuO NPs. In vitro and in vivo studies have shown that CuO NPs cause oxidative stress, cytotoxicity, genotoxicity, immunotoxicity, neurotoxicity, and inflammation in bacterial, algal, fish, rodents, and human cell lines. Therefore, to make CuO NPs a more suitable candidate for various applications, it is essential to address their potential toxic effects, and hence, more studies should be done on the long-term and chronic impacts of CuO NPs at different concentrations to assure the safe usage of CuO NPs.

MMP-3-mediated cleavage of OPN is involved in copper oxide nanoparticle-induced activation of fibroblasts

BACKGROUND

Copper oxide nanoparticles (Nano-CuO) are one of the most produced and used nanomaterials. Previous studies have shown that exposure to Nano-CuO caused acute lung injury, inflammation, and fibrosis. However, the mechanisms underlying Nano-CuO-induced lung fibrosis are still unclear. Here, we hypothesized that exposure of human lung epithelial cells and macrophages to Nano-CuO would upregulate MMP-3, which cleaved osteopontin (OPN), resulting in fibroblast activation and lung fibrosis.

METHODS

A triple co-culture model was established to explore the mechanisms underlying Nano-CuO-induced fibroblast activation. Cytotoxicity of Nano-CuO on BEAS-2B, U937* macrophages, and MRC-5 fibroblasts were determined by alamarBlue and MTS assays. The expression or activity of MMP-3, OPN, and fibrosis-associated proteins was determined by Western blot or zymography assay. Migration of MRC-5 fibroblasts was evaluated by wound healing assay. MMP-3 siRNA and an RGD-containing peptide, GRGDSP, were used to explore the role of MMP-3 and cleaved OPN in fibroblast activation.

RESULTS

Exposure to non-cytotoxic doses of Nano-CuO (0.5 and 1 µg/mL) caused increased expression and activity of MMP-3 in the conditioned media of BEAS-2B and U937* cells, but not MRC-5 fibroblasts. Nano-CuO exposure also caused increased production of cleaved OPN fragments, which was abolished by MMP-3 siRNA transfection. Conditioned media from Nano-CuO-exposed BEAS-2B, U937*, or the co-culture of BEAS-2B and U937* caused activation of unexposed MRC-5 fibroblasts. However, direct exposure of MRC-5 fibroblasts to Nano-CuO did not induce their activation. In a triple co-culture system, exposure of BEAS-2B and U937* cells to Nano-CuO caused activation of unexposed MRC-5 fibroblasts, while transfection of MMP-3 siRNA in BEAS-2B and U937* cells significantly inhibited the activation and migration of MRC-5 fibroblasts. In addition, pretreatment with GRGDSP peptide inhibited Nano-CuO-induced activation and migration of MRC-5 fibroblasts in the triple co-culture system.

CONCLUSIONS

Our results demonstrated that Nano-CuO exposure caused increased production of MMP-3 from lung epithelial BEAS-2B cells and U937* macrophages, which cleaved OPN, resulting in the activation of lung fibroblasts MRC-5. These results suggest that MMP-3-cleaved OPN may play a key role in Nano-CuO-induced activation of lung fibroblasts. More investigations are needed to confirm whether these effects are due to the nanoparticles themselves and/or Cu ions.

Capability of Copper Hydroxy Nitrate (Cu2(OH)3NO3) as an Additive to Develop Antibacterial Polymer Contact Surfaces: Potential for Food Packaging Applications

The globalization of the market, as well as the increasing world population, which require a higher demand for food products, pose a great challenge to ensure food safety and prevent food loss and waste. In this sense, active materials with antibacterial properties are an important alternative in the prolongation of shelf life and ensuring food safety. In this work, the ability of copper(II) hydroxy nitrate (CuHS) to obtain antibacterial films based on low density polyethylene (LDPE) and polylactic acid (PLA), was evaluated. The thermal properties of the composites, evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), showed that the concentrations of added CuHS do not particularly change these characteristics with respect to the neat polymer matrix films. The mechanical properties, determined using dynamic mechanical analysis (DMTA), indicate a small increase in the brittleness of the material in PLA-based composites. The antibacterial properties against Listeria monocytogenes and Salmonella enterica were evaluated using a surface contact test, and a bacterial reduction of at least 8 to 9 logarithmic units for the composites with 0.3% CuHS, both in LDPE and PLA and against both bacteria, were achieved. The reusability of the composite films after their first use demonstrated a higher stability against Listeria monocytogenes. The migration and cytotoxicity of the composites loaded with 0.3% CuHS was evaluated, demonstrating the safety of these materials, which reinforces their potential use in food packaging applications.

Copper-based nanoparticles for biopolymer-based functional films in food packaging applications

This review summarizes the latest developments in the design, fabrication, and application of various Cu-based nanofillers to prepare biopolymer-based functional packaging films, focusing on the effects of inorganic nanoparticles on the optical, mechanical, gas barrier properties, moisture sensitivity, and functional properties of the films. In addition, the potential application of Cu-based nanoparticle-added biopolymer films for fresh food preservation and the effect of nanoparticle migration on food safety were discussed. The incorporation of Cu-based nanoparticles improved the film properties with enhanced functional performance. Cu-based nanoparticles such as copper oxide, copper sulfide, copper ions, and copper alloys affect biopolymer-based films differently. The properties of composite films containing Cu-based nanoparticles depend on the concentration of the filler, the state of dispersion, and the interaction of the nanoparticles with the biopolymer matrix in the film. The composite film filled with Cu-based nanoparticles effectively extended the shelf life by maintaining the quality of various fresh foods and securing safety. However, studies on the migration characteristics and safety of copper-based nanoparticle food packaging films are currently being conducted on plastic-based films such as polyethylene, and research on bio-based films is limited.

Antimicrobial Poly (Lactic Acid)/Copper Nanocomposites for Food Packaging Materials

Composites based on polylactic acid (PLA) and copper for food packaging applications were obtained. Copper clusters were synthesized in polyethylene glycols 400 and 600, respectively, using ascorbic acid as a reducing agent, by reactive milling. Copper clusters were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR), and Ultraviolet-Visible (UV-VIS) spectroscopy. Copper/PLA composites containing Proviplast as plasticizer were characterized by FT-IR spectroscopy, mechanical tests, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), absorption of the saline solution, contact angle, and antibacterial properties. It was observed that the concentration of Copper/PEG influenced the investigated properties. The mechanical properties of the samples decreased with the increasing of Copper/PEG concentration. We recorded the phase transformation temperatures and identified the exothermic or endothermic processes. The lowest absorption values were recorded in the case of the sample containing 1% Cu. The contact angle decreases with the increase in the concentration of the PEG 600-Cu mixture in the recipes. The increase in the content of Cu clusters favors the decrease in the temperature, taking place 15% wt mass losses. The obtained composites showed antibacterial properties for all tested strains. These materials could be used as alternative materials for obtaining biodegradable food packaging.

Functional insights to the development of bioactive material for combating bacterial infections

The emergence of antibiotic-resistant "superbugs" poses a serious threat to human health. Nanomaterials and cationic polymers have shown unprecedented advantages as effective antimicrobial therapies due to their flexibility and ability to interact with biological macromolecules. They can incorporate a variety of antimicrobial substances, achieving multifunctional effects without easily developing drug resistance. Herein, this article discusses recent advances in cationic polymers and nano-antibacterial materials, including material options, fabrication techniques, structural characteristics, and activity performance, with a focus on their fundamental active elements.

Surface Oxidation of Cu2O Nanoparticles by Adsorbed Ammonia

Copper-based nanoparticles have been intensively studied owing to their superior antibacterial activity. In this study, cuprous oxide (Cu₂O) nanoparticles were synthesized using two different methods. In particular, two methods for synthesizing copper oxide from NaOH, namely, with and without the addition of NH₃, were used to adjust the morphology of the nanoparticles. The nanoparticles from the NH₃ and NaOH samples possessed an octahedral morphology. The crystal structure of the samples was confirmed by X-ray diffraction. The size distribution of the NH₃ sample was narrower than that of the NaOH sample. Furthermore, the average size of the NH₃ sample was smaller than that of the NaOH sample. Unexpectedly, the antibacterial activity of the NH₃ sample was found to be lower than that of the NaOH sample. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy revealed that the adsorbed NH₃ caused the surface oxidation of Cu₂O nanoparticles with azide (N₃) formation on surface.

Hepatic and renal toxicity following the injection of copper oxide nanoparticles (CuO NPs) in mature male Westar rats: histochemical and caspase 3 immunohistochemical reactivities

Copper nanoparticles are widely utilized in a variety of applications, including metal catalysts, semiconductors, heat transfer fluids in machine tools, and even in antibacterial medications. Forty mature healthy Westar rats were utilized in the current investigation and grouped randomly into four groups (n = 10 rats/group). Group I (G1) was kept as a control group, but G2, G3, and G4 were intraperitoneally injected with CuO NPs with a dose (5 mg, 10 mg, 25 mg/kg body weight/day) respectively for 9 days. Rats were sacrificed; then, the livers and kidneys were dissected and subjected to histopathological and immunohistochemical examination. Our findings of G2 and G3 revealed mild to moderate degenerative changes within the hepatic parenchyma, moderate blood vessel congestions, glycogen depletion, hemosiderosis, and microvesicular steatosis (fatty changes within the hepatocytes). In addition, at the level of kidney, our examination clarified moderate degenerations of the renal corpuscles and renal tubules with moderate swelling and congestions of the glomerulus with moderate vacuolations in the renal tubules lining epithelium. On the other hand, increasing the dose of CuO NPs, the toxicity became more obvious, where the liver of G4 revealed severe necrosis of hepatocytes with completely disorganizations of the hepatic rays, loss of the hepatic architectures, severe steatosis, severe hemosiderosis, sinusoidal dilatations with congestions, as well as severe fibrous tissue proliferation with anti-inflammatory cell infiltrations specially around portal triad with hyperplasia of bile duct. Meanwhile in kidney, G4 clarified severe necrosis and atrophy of the renal corpuscles with severe damage of Bowman's capsule leading to completely disorganization and loss of normal renal cortex architectures, severe congestion of the glomerulus, severe necrosis of the renal tubules with damage and sloughing for its lining epithelium, and severe hemorrhage between renal tubules. In addition, severe and diffuse caspase 3 immunoreactivity were observed within the hepatic and renal tissues of G4. The present investigation was concluded that the CuO NPs have a potential toxicological effect on the hepatic and renal tissues that may affect their functions.-->.

Zn and Zn-Fe Nanostructures with Multifunctional Properties as Components for Food Packaging Materials

Metallic and bimetallic nanostructures have shown interesting chromatic and antibacterial properties, and they can be used in various applications. In this work, zinc (Zn) and iron (Fe) nanostructures were produced with different morphologies: (i) pure Zn; (ii) Zn-Fe nanoalloys; (iii) Zn-Fe nanolayers (Zn-Fe NLs); and (iv) Zn nanolayers combined with Fe nanoparticles (Zn NLs + Fe NPs). The aim was to produce components for food packaging materials with active and intelligent properties, including oxygen absorption capacity, chromatic properties, and antibacterial properties. Thus, the morphology, structure, and chemical composition of the samples were characterized and correlated with their oxidation, chromatic, and antibacterial properties. The results revealed a relevant reduction in the coating’s opacity after oxidation varying from 100 to 10% depending on the morphology of the system. All coatings exhibited significant antibacterial activity against S. aureus, revealing a direct correlation with Zn content. The incorporation of Fe for all atomic arrangements showed a negative impact on the antibacterial effect against E. coli, decreasing to less than half the zone of inhibition for Zn-Fe NLs and Zn NLs + Fe NPs and suppressing the antibacterial effect for Zn-Fe alloy when compared with the pure Zn system.

Development of Functional Composite Cu(II)-Polyoxometalate/PLA with Antimicrobial Properties

Novel composite self-disinfecting films of polylactic acid (PLA) filled with nanosized particles of double sodium–copper(II) paratungstate B Na₂Cu₃(CuOH)₂[W₁₂O₄₀(OH)₂]·32H₂O (POM) were developed. The solvent casting (POM/PLA film) and solvent-free melt extrusion methods (Extr. POM/PLA film) were applied for film preparation. The copper (II) ion release to water from both types of the films after 10 days at different temperatures demonstrated that the PLA matrix acts as a diffusion barrier, and the resulting concentration of released copper in water at room temperature remained low, at 0.79% for POM/PLA film and 0.51% for Extr. POM/PLA film. The POM-containing films reveals a significant inhibitory effect against E. coli ATCC 25922 in the agar diffusion test. The numbers of CFUs in washes of the films after incubation for 24 h were found to be 3.6 log CFU mL^–1 (POM/PLA film) and 4.1 log CFU mL^–1 (Extr. POM/PLA film). The films combine the antibacterial properties of POM and a bio-based polymer matrix, which makes them a prospective coating material for applications in hospital indoor environments. Excellent thermal stability of POM gives a technological advantage for industrial manufacturing to allow the processing of novel composite material in the solvent free (molten) state.

Artificial Digestion of Polydisperse Copper Oxide Nanoparticles: Investigation of Effects on the Human In Vitro Intestinal Co-Culture Model Caco-2/HT29-MTX

Copper oxide nanoparticles (CuO-NP) are increasingly used in consumer-related products, which may result in increased oral ingestion. Digestion of particles can change their physicochemical properties and toxicity. Therefore, our aim was to simulate the gastrointestinal tract using a static in vitro digestion model. Toxic properties of digested and undigested CuO-NP were compared using an epithelial mono-culture (Caco-2) and a mucus-secreting co-culture model (Caco-2/HT29-MTX). Effects on intestinal barrier integrity, permeability, cell viability and apoptosis were analyzed. CuO-NP concentrations of 1, 10 and 100 µg mL−1 were used. Particle characterization by dynamic light scattering and transmission electron microscopy showed similar mean particle sizes before and after digestion, resulting in comparable delivered particle doses in vitro. Only slight effects on barrier integrity and cell viability were detected for 100 µg mL−1 CuO-NP, while the ion control CuCl2 always caused significantly higher adverse effects. The utilized cell models were not significantly different. In summary, undigested and digested CuO-NP show comparable effects on the mono-/co-cultures, which are weaker than those of copper ions. Only in the highest concentration, CuO-NP showed weak effects on barrier integrity and cell viability. Nevertheless, a slightly increased apoptosis rate indicates existing cellular stress, which gives reason for further investigations.

MMP-3 activation is involved in copper oxide nanoparticle-induced epithelial-mesenchymal transition in human lung epithelial cells

Copper oxide nanoparticles (Nano-CuO) are widely used in medical and industrial fields and our daily necessities. However, the biosafety assessment of Nano-CuO is far behind their rapid development. Here, we investigated the adverse effects of Nano-CuO on normal human bronchial epithelial BEAS-2B cells, especially determined whether Nano-CuO exposure would cause dysregulation of MMP-3, an important mediator in pulmonary fibrosis, and its potential role in epithelial-mesenchymal transition (EMT). Our results showed that exposure to Nano-CuO, but not Nano-TiO₂, caused increased ROS generation, MAPKs activation, and MMP-3 upregulation. Nano-CuO-induced ROS generation was not observed in mitochondrial DNA-depleted BEAS-2B ρ⁰ cells, indicating that mitochondria may be the main source of Nano-CuO-induced ROS generation. Pretreatment of the cells with ROS scavengers or inhibitors or depleting mitochondrial DNA significantly attenuated Nano-CuO-induced MAPKs activation and MMP-3 upregulation, and pretreatment of cells with MAPKs inhibitors abolished Nano-CuO-induced MMP-3 upregulation, suggesting Nano-CuO-induced MMP-3 upregulation is through Nano-CuO-induced ROS generation and MAPKs activation. In addition, exposure of the cells to Nano-CuO for 48 h resulted in decreased E-cadherin expression and increased expression of vimentin, α-SMA, and fibronectin, which was ameliorated by MMP-3 siRNA transfection, suggesting an important role of MMP-3 in Nano-CuO-induced EMT. Taken together, our study demonstrated that Nano-CuO exposure caused mitochondrial ROS generation, MAPKs activation, and MMP-3 upregulation. Nano-CuO exposure also caused cells to undergo EMT, which was through Nano-CuO-induced dysregulation of ROS/MAPKs/MMP-3 pathway. Our findings will provide further understanding of the potential mechanisms involved in metal nanoparticle-induced various toxic effects including EMT and pulmonary fibrosis.

Composite Films of Thermoplastic Starch and CaCl2 Extracted from Eggshells for Extending Food Shelf-Life

Calcium chloride (CaCl2) has been widely used to maintain the quality of fresh-cut fruits and vegetables because it stabilizes and strengthens the membrane system against fungal attacks. It is mainly applied via spray coating and dip coating techniques. This study explored a method of incorporating calcium chloride extracted from eggshells in a packaging material, thermoplastic starch (TPS), via a hot-melt extrusion process. The composites were characterized by FTIR, DSC, SEM-EDX and tensile testing. FTIR confirmed the chemical reactions between CaCl2 and TPS. DSC results showed a significant decrease in the heat of fusion by adding 20 wt% of CaCl2 content in TPS, indicating a drop in the degree of crystallinity. The Young’s modulus of TPS was not significantly affected by the incorporation of 10 wt% CaCl2 (P = 0.968), but reduced notably with the addition of 20 wt% CaCl2 (P = 0.05), indicating the plasticizer effect of the CaCl2. Physiochemical analysis of fresh-cut apple slices was assessed. Samples placed on the surface of the TPS/CaCl2 composites displayed less pH reduction, reduced antioxidant activity, more weight loss and increased reducing sugar compared to the samples placed on the surface of virgin TPS films. CaCl2 released from the TPS/CaCl2 films was measured and their antimicrobial activity was confirmed by bacterial inhibitory growth assessment. Fungal growth was observed on apple slices placed on virgin TPS film by day 21 while apple slices placed on TPS/CaCl2 20 wt% composites did not support any fungal growth for 28 days. In summary, TPS and eggshell-extracted CaCl2 showed the ability to maintain the quality of fresh-cut apples, and TPS/CaCl2 10 wt% composite could be a good option as a packaging material for fresh-cut fruits due to active antimicrobial activity and maintained Young’s modulus.

In Situ Collection of Nanoparticles during Femtosecond Laser Machining in Air

Nanoparticles generated during laser material processing are often seen as annoying side products, yet they might find useful application upon proper collection. We present a parametric study to identify the dominant factors in nanoparticle removal and collection with the goal of establishing an in situ removal method during femtosecond laser machining. Several target materials of different electrical resistivity, such as Cu, Ti, and Si were laser machined at a relatively high laser fluence. Machining was performed under three different charge conditions, i.e., machining without an externally applied charge (alike atmospheric pulsed laser deposition (PLD)) was compared to machining with a floating potential and with an applied field. Thereby, we investigated the influence of three different charge conditions on the behavior of laser-generated nanoparticles, in particular considering plume deflection, nanoparticle accumulation on a collector plate and their redeposition onto the target. We found that both strategies, machining under a floating potential or under an applied field, were effective for collecting laser-generated nanoparticles. The applied field condition led to the strongest confinement of the nanoparticle plume and tightest resulting nanoparticle collection pattern. Raster-scanning direction was found to influence the nanoparticle collection pattern and ablation depth. However, the laser-processed target surface remained unaffected by the chosen nanoparticle collection strategy. We conclude that machining under a floating potential or an applied field is a promising setup for removing and collecting nanoparticles during the machining process, and thus provides an outlook to circular waste-free laser process design.

Antimicrobial Properties of Food Nanopackaging: A New Focus on Foodborne Pathogens

Food products contaminated by foodborne pathogens (bacteria, parasites, and viruses) cause foodborne diseases. Today, great efforts are being allocated to the development of novel and effective agents against food pathogenic microorganisms. These efforts even might have a possible future effect in coronavirus disease 2019 (COVID-19) pandemic. Nanotechnology introduces a novel food packaging technology that creates and uses nanomaterials with novel physiochemical and antimicrobial properties. It could utilize preservatives and antimicrobials to extend the food shelf life within the package. Utilizing the antimicrobial nanomaterials into food packaging compounds typically involves incorporation of antimicrobial inorganic nanoparticles such as metals [Silver (Ag), Copper (Cu), Gold (Au)], and metal oxides [Titanium dioxide (TiO2), Silicon oxide (SiO2), Zinc oxide (ZnO)]. Alternatively, intelligent food packaging has been explored for recognition of spoilage and pathogenic microorganisms. This review paper focused on antimicrobial aspects of nanopackaging and presented an overview of antibacterial properties of inorganic nanoparticles. This article also provides information on food safety during COVID-19 pandemic.

Simulated Gastric Digestion and In Vivo Intestinal Uptake of Orally Administered CuO Nanoparticles and TiO2 E171 in Male and Female Rat Pups

Oral exposure to nanoparticles (NPs) during early life is an understudied area. The goals of this study were to evaluate the effect of pre-weaned rat gastric fluids on 50 nm CuO NPs and TiO2 E171 in vitro, and to evaluate uptake in vivo. The NP uptake was studied in vivo in male and female Sprague-Dawley rat pups following oral administration of four consecutive daily doses of 10 mg/kg CuO NPs, TiO2 E171, or vehicle control (water) between postnatal day (PND) 7-10. Rat pups were sacrificed on either PND10 or PND21. Simulated digestion led to dissolution of CuO NPs at the later ages tested (PND14 and PND21, but not PND7). In vivo intestinal uptake of CuO NPs and TiO2 E171 was observed by hyperspectral imaging of intestinal cross sections. Brightfield microscopy showed that the number of immune cells increased in the intestinal tissue following NP administration. Orally administered NPs led to low intestinal uptake of NPs and an increase in immune cells in the small and large intestine, suggesting that oral exposure to NPs during early life may lead to irritation or a low-grade inflammation. The long-term impact of increased immune cells in the intestinal tract during early life is unknown.

Antimicrobial Polymeric Structures Assembled on Surfaces

Pathogenic microbes are the main cause of various undesired infections in living organisms, including humans. Most of these infections are favored in hospital environments where humans are being treated with antibiotics and where some microbes succeed in developing resistance to such drugs. As a consequence, our society is currently researching for alternative, yet more efficient antimicrobial solutions. Certain natural and synthetic polymers are versatile materials that have already proved themselves to be highly suitable for the development of the next-generation of antimicrobial systems that can efficiently prevent and kill microbes in various environments. Here, we discuss the latest developments of polymeric structures, exhibiting (reinforced) antimicrobial attributes that can be assembled on surfaces and coatings either from synthetic polymers displaying antiadhesive and/or antimicrobial properties or from blends and nanocomposites based on such polymers.

Recent developments in antimicrobial and antifouling coatings to reduce or prevent contamination and cross-contamination of food contact surfaces by bacteria

Illness as the result of ingesting bacterially contaminated foodstuffs represents a significant annual loss of human quality of life and economic impact globally. Significant research investment has recently been made in developing new materials that can be used to construct food contacting tools and surfaces that might minimize the risk of cross-contamination of bacteria from one food item to another. This is done to mitigate the spread of bacterial contamination and resultant foodborne illness. Internet-based literature search tools such as Web of Science, Google Scholar, and Scopus were utilized to investigate publishing trends within the last 10 years related to the development of antimicrobial and antifouling surfaces with potential use in food processing applications. Technologies investigated were categorized into four major groups: antimicrobial agent-releasing coatings, contact-based antimicrobial coatings, superhydrophobic antifouling coatings, and repulsion-based antifouling coatings. The advantages for each group and technical challenges remaining before wide-scale implementation were compared. A diverse array of emerging antimicrobial and antifouling technologies were identified, designed to suit a wide range of food contact applications. Although each poses distinct and promising advantages, significant further research investment will likely be required to reliably produce effective materials economically and safely enough to equip large-scale operations such as farms, food processing facilities, and kitchens.

Employing Nanosilver, Nanocopper, and Nanoclays in Food Packaging Production: A Systematic Review

Over the past decade, there has been an increasing demand for “ready-to-cook” and “ready-to-eat” foods, encouraging food producers, food suppliers, and food scientists to package foods with minimal processing and loss of nutrients during food processing. Following the increasing trend in the customer’s demands for minimally processed foodstuffs, this underscores the importance of promising interests toward industrial applications of novel and practical approaches in food. Along with substantial progress in the emergence of “nanoscience”, which has turned into the call of the century, the efficacy of conventional packaging has faded away. Accordingly, there is a wide range of new types of packaging, including electronic packaging machines, flexible packaging, sterile packaging, metal containers, aluminum foil, and flexographic printing. Hence, it has been demonstrated that these novel approaches can economically improve food safety and quality, decrease the microbial load of foodborne pathogens, and reduce food spoilage. This review study provides a comprehensive overview of the most common chemical or natural nanocomposites used in food packaging that can extend food shelf life, safety and quality. Finally, we discuss applying materials in the production of active and intelligent food packaging nanocomposite, synthesis of nanomaterial, and their effects on human health.

Poly Lactic Acid (PLA) Nanocomposites: Effect of Inorganic Nanoparticles Reinforcement on Its Performance and Food Packaging Applications

Poly lactic acid (PLA) is a compostable, as well as recyclable, sustainable, versatile and environmentally friendly alternative, because the monomer of PLA-lactide (LA) is extracted from natural sources. PLA's techno-functional properties are fairly similar to fossil-based polymers; however, in pristine state, its brittleness and delicacy during processing pose challenges to its potential exploitation in diverse food packaging applications. PLA is, therefore, re-engineered to improve its thermal, rheological, barrier and mechanical properties through nanoparticle (NP) reinforcement. This review summarises the studies on PLA-based nanocomposites (PLA NCs) developed by reinforcing inorganic metal/metallic oxide, graphite and silica-based nanoparticles (NPs) that exhibit remarkable improvement in terms of storage modulus, tensile strength, crystallinity, glass transition temperature (Tg) value, antimicrobial property and a decrease in water vapour and oxygen permeability when compared with the pristine PLA films. This review has also discussed the regulations around the use of metal oxide-based NPs in food packaging, PLA NC biodegradability and their applications in food systems. The industrial acceptance of NCs shows highly promising perspectives for the replacement of traditional petrochemical-based polymers currently being used for food packaging.

Synthesis of Air-Stable Cu Nanoparticles Using Laser Reduction in Liquid

We report the synthesis of air-stable Cu nanoparticles (NPs) using the bottom-up laser reduction in liquid method. Precursor solutions of copper acetlyacetonate in a mixture of methanol and isopropyl alcohol were irradiated with femtosecond laser pulses to produce Cu NPs. The Cu NPs were left at ambient conditions and analyzed at different ages up to seven days. TEM analysis indicates a broad size distribution of spherical NPs surrounded by a carbon matrix, with the majority of the NPs less than 10 nm and small numbers of large particles up to ∼100 nm in diameter. XRD collected over seven days confirmed the presence of fcc-Cu NPs, with some amorphous Cu₂O, indicating the stability of the zero-valent Cu phase. Raman, FTIR, and XPS data for oxygen and carbon regions put together indicated the presence of a graphite oxide-like carbon matrix with oxygen functional groups that developed within the first 24 h after synthesis. The Cu NPs were highly active towards the model catalytic reaction of para-nitrophenol reduction in the presence of NaBH₄.

Improved antioxidative performance of a water-soluble copper nanoparticle@fullerenol composite formed via photochemical reduction

We synthesized a water-soluble nanocomposite consisting of ultrasmall copper nanoparticles and fullerenol, which showed excellent radical scavenging ability (IC50 = 14.5 μg mL−1).

In vitro copper oxide nanoparticle toxicity on intestinal barrier

The use of CuO nanoparticles (NPs) has increased greatly and their potential effects on human health need to be investigated. Differentiated Caco-2 cells were treated from the apical (Ap) and the basolateral (Bl) compartment with different concentrations (0, 10, 50 and 100 μg/mL) of commercial or sonochemically synthesized (sono) CuO NPs. Sono NPs were prepared in ethanol (CuOe) or in water (CuOw), obtaining CuO NPs differing in size and shape. The effects on the Caco-2 cell barrier were assessed via transepithelial electrical resistance (TEER) evaluation just before and after 1, 2 and 24 hours of exposure and through the analysis of cytokine release and biomarkers of oxidative damage to proteins after 24 hours. Sono CuOe and CuOw NPs induced a TEER decrease with a dose-dependent pattern after Bl exposure. Conversely, TEER values were not affected by the Ap exposure to commercial CuO NPs and, concerning the Bl exposure, only the lowest concentration tested (10 μg/mL) caused a TEER decrease after 24 hours of exposure. An increased release of interleukin-8 was induced by sono CuO NPs after the Ap exposure to 100 μg/mL and by sono and commercial CuO after the Bl exposure to all the concentrations. No effects of commercial and sono CuO NPs on interleukin-6 (with the only exception of 100 μg/mL Bl commercial CuO) and tumor necrosis factor-α release were observed. Ap treatment with commercial and CuOw NPs was able to induce significant alterations on specific biomarkers of protein oxidative damage (protein sulfhydryl group oxidation and protein carbonylation).

Dual-Functioning Antibacterial Eugenol-Derived Plasticizers for Polylactide

Dual-functioning additives with plasticizing and antibacterial functions were designed by exploiting the natural aromatic compound eugenol and green platform chemical levulinic acid or valeric acid that can be produced from biobased resources. One-pot synthesis methodology was utilized to create three ester-rich plasticizers. The plasticizers were thoroughly characterized by several nuclear magnetic resonance techniques (¹H NMR, ¹³C NMR, ³¹P NMR, HSQC, COSY, HMBC) and by electrospray ionization-mass spectrometry (ESI-MS) and their performances, as plasticizers for polylactide (PLA), were evaluated. The eugenyl valerate was equipped with a strong capability to depress the glass transition temperature (T_g) of PLA. Incorporating 30 wt% plasticizer led to a reduction of the T_g by 43 °C. This was also reflected by a remarkable change in mechanical properties, illustrated by a strain at break of 560%, almost 110 times the strain for the breaking of neat PLA. The two eugenyl levulinates also led to PLA with significantly increased strain at breaking. The eugenyl levulinates portrayed higher thermal stabilities than eugenyl valerate, both neat and in PLA blends. The different concentrations of phenol, carboxyl and alcohol functional groups in the three plasticizers caused different bactericidal activities. The eugenyl levulinate with the highest phenol-, carboxyl- and alcohol group content significantly inhibited the growth of Staphylococcus aureus and Escherichia coli, while the other two plasticizers could only inhibit the growth of Staphylococcus aureus. Thus, the utilization of eugenol as a building block in plasticizer design for PLA illustrated an interesting potential for production of additives with dual functions, being both plasticizers and antibacterial agents.

Controlled Release of Thymol from Poly(Lactic Acid)-Based Silver Nanocomposite Films with Antibacterial and Antioxidant Activity

Thymol and silver nanoparticles (Ag-NPs) were used to develop poly(lactic acid) (PLA)-based films with antioxidant and antibacterial performance. Different amounts of thymol (6 and 8 wt%) and 1 wt% Ag-NPs were added to PLA to produce the active films. Ag-NPs and thymol were successfully identified in the nanocomposite structures using spectroscopic techniques. A kinetic study was performed to evaluate the release of thymol and Ag-NPs from the nanocomposites to an aqueous food simulant (ethanol 10%, v/v) at 40 °C. The diffusion of thymol from the polymer matrix was affected by the presence of non-migrating Ag-NPs, which showed non-Fickian release behavior. The ternary system including 1 wt% Ag-NPs and 8 wt% thymol showed clear antibacterial performance by reducing the cell viability of Escherichia coli and Staphylococcus aureus by around 40% after 3 and 24 h of storage at 4, 25, and 37 °C compared to neat PLA. Significant antioxidant behavior of all active films was also confirmed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. The obtained nanocomposite films based on PLA and the addition of Ag-NPs and thymol were proven to have combined antioxidant and antibacterial performance, with controlled release of thymol. These formulations have potential applications in the development of innovative and customized active packaging systems to increase the shelf-life of food products.

Mechanical properties and antibacterial activities of novel starch-based composite films incorporated with salicylic acid

To control food contamination and meet the growing demand for high quality food, a novel and excellent starch composite film as packing material with optimized physical, mechanical properties and antimicrobial activity was produced in this paper. Starch-based composite films incorporated with salicylic acid (SA) and waxy maize starch nanoparticles/κ-carrageenan (WMSNs/KC) were used to achieve antimicrobial activity and improve the mechanical properties. WMSNs were fabricated through enzymolysis and recrystallisation method, followed by individually adding KC to form WMSNs/KC by self-assembly, and used as a nanofiller and stabilizer to be incorporated into hydroxypropyl tapioca starch-based films at a concentration of 0-9%. Characterization of macromorphology and scanning electron microscope indicated the starch composite films with WMSNs/KC were smooth, uniform, and transparent. X-ray diffraction pattern and Thermogravimetric analysis also showed strong interactions such as hydrogen bond formation among films, WMSNs/KC and SA. Compared with the pure starch-based films, the composite films reinforced by the addition of WMSNs/KC significantly increased the tensile strength, water vapor barrier and thermal stability, while the transparency and elongation at break decreased slightly. Moreover, the starch composite films showed excellent antimicrobial activity for three typical undesired microorganisms in foods, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis.

Robust Antibacterial Activity of Tungsten Oxide (WO3-x) Nanodots

Antibacterial agents are an important tool in the prevention of bacterial infections. Inorganic materials are attractive due to their high stability under a variety of conditions compared to organic antibacterial agents. Herein tungsten oxide nanodots (WO_3-x), synthesized by a simple one-pot synthetic approach, were found to exhibit strong antibacterial capabilities. The analyses with colony-forming units (CFU) showed an excellent antibacterial activity of WO_3-x against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) strains. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed clear damages to the bacterial cell membranes, which was further confirmed by molecular dynamics simulations. Additionally, exposure to simulated sunlight was found to further increase the germicidal activity of WO_3-x nanodots, a 30 min exposure to sunlight combined with 50 μg/mL WO_3-x nanodots showed a 70% decrease in E. coli viability compared to without exposure. Electron spin resonance spectroscopy (ESR) was used to elucidate the underlying mechanism of this photocatalytic activity through the generation of hydroxyl radical species. The cell counting kit-8 (CCK-8) and the live/dead assay were further employed to evaluate the cytotoxicity of WO_3-x nanodots on eukaryotic cells, which demonstrated their general biocompatibility. In summary, our results suggest WO_3-x nanodots have considerable potential in antibacterial applications, while also being biocompatible at large.

Fabrication of nano CuAl2O4 spinel for copper stabilization and antibacterial application

With widely reported antibacterial potential, the copper-containing nanoparticles have become attractive antibacterial agents to prohibit the undesirable bacterial adhesion and growth. However, after applying the copper-containing agents in the environment, the potential leaching and bioaccumulation of copper ions may cause severe environmental contamination and irreversible health problems. Therefore, the nano CuAl₂O₄ spinel was fabricated as a novel copper-stabilized antibacterial agent with much minimized copper leachability. Results show the successful fabrication of nano CuAl₂O₄ spinel as well-shaped polyhedral particles with maximum length of ˜100 nm and width of ˜50 nm. The optimal parameters for the synthesis of CuAl₂O₄ include pH value of 11.0, sintering temperature of 1000 °C, dwelling time of 3 h, and the heating rate of 5 °C/min. The leaching test also confirmed the superiority of the nano CuAl₂O₄ in copper stabilization. The beneficial antibacterial activity of the nano CuAl₂O₄ was further testified by an obvious decrease in the amount of Escherichia coli in a medium with addition of the CuAl₂O₄ spinel. Besides the growth mechanisms of the nano-particles, this work has also innovatively demonstrated a strategy to replace the traditional antibacterial agents by a novel, long-lasting nano CuAl₂O₄ with little copper leachability.

Application of antimicrobial active packaging film made of semolina flour, nano zinc oxide and nano-kaolin to maintain the quality of low-moisture mozzarella cheese during low-temperature storage

BACKGROUND

Active food packaging films with improved properties and strong antimicrobial activity were prepared by blending mixed nanomaterials with different ratio [1:4 (40 mg:160 mg), 3:2 (120 mg: 80 mg), 0:5 (0 mg: 200 mg) and 5:0 (200 mg:0 mg)] of ZnO and kaolin with semolina using a solvent casting method and used for the packaging of low moisture mozzarella cheese to test the effect of packaging on the quality change of the cheese for long-term (up to 72 days) refrigerated storage.

RESULTS

Compared with the neat semolina film, mechanical strength (TS) of the nanocomposite films increased significantly (increase in 21-65%) and water vapor barrier (WVP) and O₂ gas barrier (OP) properties decreased significantly (decrease in 43-50% and 60-65%, respectively) depending on the blending ratio of ZnO and kaolin nanoclay. The nanocomposite films also exhibited strong antimicrobial activity against bacteria (E. coli and S. aureus), yeast (C. albicans), and mold (A. niger). The nanocomposite packaging films were effectively prevented the growth of microorganisms (coliforms, total microbial, and fungi) of the cheese during storage at low-temperature and showed microbial growth of less than 2.5 log CFU/g after 72 days of storage compared to the control group, and the quality of the packaged cheese was still acceptable.

CONCLUSION

The semolina-based nanocomposite films, especially Sem/Z₃ K₂ film, were effective for packaging of low moisture mozzarella cheese to maintain the physicochemical properties (pH, moisture, and fat content) and quality (color, taste, texture, and overall acceptability) of the cheese as well as preventing microbial growth (coliforms, total microbial, and fungi). © 2018 Society of Chemical Industry.

Carbon Fibers Encapsulated with Nano-Copper: A Core‒Shell Structured Composite for Antibacterial and Electromagnetic Interference Shielding Applications

A facile and scalable two-step method (including pyrolysis and magnetron sputtering) is created to prepare a core–shell structured composite consisting of cotton-derived carbon fibers (CDCFs) and nano-copper. Excellent hydrophobicity (water contact angle = 144°) and outstanding antibacterial activity against Escherichia coli and Staphylococcus aureus (antibacterial ratios of >92%) are achieved for the composite owing to the composition transformation from cellulose to carbon and nano-size effects as well as strong oxidizing ability of oxygen reactive radicals from interactions of nano-Cu with sulfhydryl groups of enzymes. Moreover, the core–shell material with high electrical conductivity induces the interfacial polarization loss and conduction loss, contributing to a high electromagnetic interference (EMI) shielding effectiveness of 29.3 dB. Consequently, this flexible and multi-purpose hybrid of nano-copper/CDCFs may be useful for numerous applications like self-cleaning wall cladding, EMI shielding layer and antibacterial products.

Sustainable control strategies for plant protection and food packaging sectors by natural substances and novel nanotechnological approaches

An overview is provided of the current technological strategies (also at the nanoscale level) recently involved in plant and/or food protection. In addition, the potential use of natural and sustainable substances, instead of traditional synthesized molecules or chemical-based compounds, is addressed both with respect to packaging systems and novel pesticide formulations. In this context, nanotechnological approaches represent promising strategies for the entire agriculture industry chain, from the field to consumers. Traditional plant protection strategies are often insufficient and the application of chemical-based pesticides has negative effects on animals, humans and the environment. Novel greener tools could represent efficient alternatives for the management of plant diseases using promising strategies; the use of nanotechnologies allows the promotion of the more efficient assembly and subsequent release of environmentally sustainable active principles, limiting the use of chemicals in terms of economic losses. At the same time, new sustainable, antimicrobial and antioxidant systems have been rapidly promoted and investigated in the food packaging sector as a valid eco-friendly possibility for improving the safety and quality of food products and reducing and/or limiting the environmental impact with respect to traditional materials. Together, the scientific community and the growing interest of consumers have promoted the development of new edible and eco-friendly packaging that reduces waste and any environmental impact. In this context, the aim is to provide evidence of the usefulness of strategies aiming to limit agrochemicals, as well as the potential of nanomaterials, in sustainable plant and food protection for agriculture management and the packaging sector. © 2018 Society of Chemical Industry.

Mechanisms of toxic action of copper and copper nanoparticles in two Amazon fish species: Dwarf cichlid (Apistogramma agassizii) and cardinal tetra (Paracheirodon axelrodi)

Copper oxide nanoparticles (nCuO) are widely used in boat antifouling paints and are released into the environment, potentially inducing toxicity to aquatic organisms. The present study aimed to understand the effects of nCuO and dissolved copper (Cu) on two ornamental Amazon fish species: dwarf cichlid (Apistogramma agassizii) and cardinal tetra (Paracheirodon axelrodi). Fish were exposed to 50% of the LC₅₀ for nCuO (dwarf cichlid 58.31μgL^-1 and cardinal tetra 69.6μgL^-1) and Cu (dwarf cichlid 20μgL^-1 and cardinal tetra 22.9μgL^-1) for 24, 48, 72 and 96h. Following exposure, aerobic metabolic rate (ṀO₂), gill osmoregulatory physiology and mitochondrial function, oxidative stress markers, and morphological damage were evaluated. Our results revealed species specificity in metabolic stress responses. An increase of ṀO₂ was noted in cardinal tetra exposed to Cu, but not nCuO, whereas ṀO₂ in dwarf cichlid showed little change with either treatment. In contrast, mitochondria from dwarf cichlid exhibited increased proton leak and a resulting decrease in respiratory control ratios in response to nCuO and Cu exposure. This uncoupling was directly related to an increase in reactive oxygen species (ROS) levels. Our findings reveal different metabolic responses between these two species in response to nCuO and Cu, which are probably caused by the differences between species natural histories, indicating that different mechanisms of toxic action of the contaminants are associated to differential osmoregulatory strategies among species.

Critical physiological factors influencing the outcome of antimicrobial testing according to ISO 22196 / JIS Z 2801

Bactericidal materials gained interest in the health care sector as they are capable of preventing material surfaces from microbial colonization and subsequent spread of infections. However, commercialization of antimicrobial materials requires proof of their efficacy, which is usually done using in vitro methods. The ISO 22196 standard (Japanese test method JIS Z 2801) is a method for measuring the antibacterial activity of daily goods. As it was found reliable for testing the biocidal activity of antimicrobially active materials and surface coatings most of the laboratories participating in this study used this protocol. Therefore, a round robin test for evaluating antimicrobially active biomaterials had to be established. To our knowledge, this is the first report on inaugurating a round robin test for the ISO 22196 / JIS Z 2801. The first round of testing showed that analyses in the different laboratories yielded different results, especially for materials with intermediate antibacterial effects distinctly different efficacies were noted. Scrutinizing the protocols used by the different participants and identifying the factors influencing the test outcomes the approach was unified. Four critical factors influencing the outcome of antibacterial testing were identified in a series of experiments: (1) incubation time, (2) bacteria starting concentration, (3) physiological state of bacteria (stationary or exponential phase of growth), and (4) nutrient concentration. To our knowledge, this is the first time these parameters have been analyzed for their effect on the outcome of testing according to ISO 22196 / JIS Z 2801. In conclusion, to enable assessment of the results obtained it is necessary to evaluate these single parameters in the test protocol carefully. Furthermore, uniform and robust definitions of the terms antibacterial efficacy / activity, bacteriostatic effects, and bactericidal action need to be agreed upon to simplify communication of results and also regulate expectations regarding antimicrobial tests, outcomes, and materials.

Influence of the stabilizers on the toxicity of metallic nanomaterials in aquatic organisms and human cell lines

In this study, following a systematic approach, we used aquatic species (bacteria Vibrio fischeri and microalgae Raphidocelis subcapitata) and different human cell lines (Caco-2, HepG2, SV-80 and HaCaT) representing different tissues and exposure pathways, to investigate how two organic stabilizers (PVA and DMSO) used for NMs dispersion influence their physicochemical properties, the persistence of metals in suspension and the toxicity/ecotoxicity of two metallic NMs (nano-Ag and nano-Cu). Although the stabilizers are expected to contribute to improve the dispersion and stability of NMs, the results obtained clearly showed that no similar changes in toxicity and morphological properties of the nano-Ag can be expected after its stabilization with PVA. Thus, regarding human cell lines, the reduction in the average size of the PVA-nano-Ag was followed by a reduction or maintenance of its toxicity, but the opposite was observed for the aquatic species tested since an increase in the average size enhanced its toxicity. As far as nano-Cu is considered DMSO contributed for a better dispersion of this nanomaterial, however this was not translated in a similar toxicity/ecotoxicity modification. In summary, even for nano-Cu, for which few or no data exists regarding its toxicity after stabilization with organic compounds, it was confirmed with consistent data, that the toxicity of metallic NMs is a complex combination of average size, chemical composition, solubilization or persistence in suspension of the metallic forms, interaction with test medium components and sensitivity of test species and cell lines. The combination of all of these factors makes the toxicity of metallic NMs unpredictable and points for the need of an extensive evaluation of each new formulation.

Impact of copper oxide nanomaterials on differentiated and undifferentiated Caco-2 intestinal epithelial cells; assessment of cytotoxicity, barrier integrity, cytokine production and nanomaterial penetration

BACKGROUND

Copper oxide nanomaterials (CuO NMs) are exploited in a diverse array of products including antimicrobials, inks, cosmetics, textiles and food contact materials. There is therefore a need to assess the toxicity of CuO NMs to the gastrointestinal (GI) tract since exposure could occur via direct oral ingestion, mucocillary clearance (following inhalation) or hand to mouth contact.

METHODS

Undifferentiated Caco-2 intestinal cells were exposed to CuO NMs (10 nm) at concentrations ranging from 0.37 to 78.13 μg/cm2 Cu (equivalent to 1.95 to 250 μg/ml) and cell viability assessed 24 h post exposure using the alamar blue assay. The benchmark dose (BMD 20), determined using PROAST software, was identified as 4.44 μg/cm2 for CuO NMs, and 4.25 μg/cm2 for copper sulphate (CuSO4), which informed the selection of concentrations for further studies. The differentiation status of cells and the impact of CuO NMs and CuSO4 on the integrity of the differentiated Caco-2 cell monolayer were assessed by measurement of trans-epithelial electrical resistance (TEER), staining for Zonula occludens-1 (ZO-1) and imaging of cell morphology using scanning electron microscopy (SEM). The impact of CuO NMs and CuSO4 on the viability of differentiated cells was performed via assessment of cell number (DAPI staining), and visualisation of cell morphology (light microscopy). Interleukin-8 (IL-8) production by undifferentiated and differentiated Caco-2 cells following exposure to CuO NMs and CuSO4 was determined using an ELISA. The copper concentration in the cell lysate, apical and basolateral compartments were measured with Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES) and used to calculate the apparent permeability coefficient (Papp); a measure of barrier permeability to CuO NMs. For all experiments, CuSO4 was used as an ionic control.

RESULTS

CuO NMs and CuSO4 caused a concentration dependent decrease in cell viability in undifferentiated cells. CuO NMs and CuSO4 translocated across the differentiated Caco-2 cell monolayer. CuO NM mediated IL-8 production was over 2-fold higher in undifferentiated cells. A reduction in cell viability in differentiated cells was not responsible for the lower level of cytokine production observed. Both CuO NMs and CuSO4 decreased TEER values to a similar extent, and caused tight junction dysfunction (ZO-1 staining), suggesting that barrier integrity was disrupted.

CONCLUSIONS

CuO NMs and CuSO4 stimulated IL-8 production by Caco-2 cells, decreased barrier integrity and thereby increased the Papp and translocation of Cu. There was no significant enhancement in potency of the CuO NMs compared to CuSO4. Differentiated Caco-2 cells were identified as a powerful model to assess the impacts of ingested NMs on the GI tract.

Biogenic fabrication of CuNPs, Cu bioconjugates and in vitro assessment of antimicrobial and antioxidant activity

In the present study, the authors synthesised copper nanoparticles (CuNPs) by using extract of Zingiber officinale (ginger) and later the NPs were bioconjugated with nisin, which shows antimicrobial activity against food spoilage microorganisms. CuNPs and its bioconjugate were characterised by ultraviolet-vis spectroscopy, NP tracking analysis, Zetasizer, transmission electron microscopy analysis, X-ray diffraction and Fourier transform infra-red (FTIR) spectroscopy. Zeta potential of CuNPs and its bioconjugate were found to be very stable. They evaluated in vitro efficacy of CuNPs and its bioconjugate against selected food spoilage bacteria: namely, Staphylococcus aureus, Pseudomonas fluorescens, Listeria monocytogenes and fungi including Fusarium moniliforme and Aspergillus niger. Antimicrobial activity of CuNPs was found to be maximum against F. moniliforme (18 mm) and the least activity was noted against L. monocytogenes (13 mm). Antioxidant activity of CuNPs and ginger extract was performed by various methods such as total antioxidant capacity reducing power assay, 1-1-diphenyl-2-picryl-hydrazyl free radical scavenging assay and hydrogen peroxide assay. Antioxidant activity of CuNPs was higher as compared with ginger extract. Hence, CuNPs and its bioconjugate can be used against food spoilage microorganisms.