Cytotoxic effects of nanosilver are highly dependent on the chloride concentration and the presence of organic compounds in the cell culture media

Respiration and growth of Paracoccus denitrificans R-1 with nitrous oxide as an electron acceptor

In the nitrogen biogeochemical cycle, the reduction of nitrous oxide (N2O) to N2 by N2O reductase, which is encoded by nosZ gene, is the only biological pathway for N2O consumption. In this study, we successfully isolated a strain of denitrifying Paracoccus denitrificans R-1 from sewage treatment plant sludge. This strain has strong N2O reduction capability, and the average N2O reduction rate was 5.10 ± 0.11 × 10-9 µmol·h-1·cell-1 under anaerobic condition in a defined medium. This reduction was accompanied by the stoichiometric consumption of acetate over time when N2O served as the sole electron acceptor and the reduction can yield energy to support microbial growth, suggesting that microbial N2O reduction is related to the energy generation process. Genomic analysis showed that the gene cluster encoding N2O reductase of P. denitrificans R-1 was composed of nosR, nosZ, nosD, nosF, nosY, nosL, and nosZ, which was identified as that in other strains in clade I. Respiratory inhibitors test indicated that the pathway of electron transport for N2O reduction was different from that of the traditional electron transport chain for aerobic respiration. Cu2+, silver nanoparticles, O2, and acidic conditions can strongly inhibit the reduction, whereas NO3- or NH4+ can promote it. These findings suggest that modular N2O reduction of P. denitrificans R-1 is linked to the electron transport and energy conservation, and dissimilatory N2O reduction is a form of microbial anaerobic respiration.

IMPORTANCE

Nitrous oxide (N2O) is a potent greenhouse gas and contributor to ozone layer destruction, and atmospheric N2O has increased steadily over the past century due to human activities. The release of N2O from fixed N is almost entirely controlled by microbial N2O reductase activities. Here, we investigated the ability to obtain energy for the growth of Paracoccus denitrificans R-1 by coupling the oxidation of various electron donors to N2O reduction. The modular N2O reduction process of denitrifying microorganism not only can consume N2O produced by itself but also can consume the external N2O generated from biological or abiotic pathways under suitable condition, which should be critical for controlling the release of N2O from ecosystems into the atmosphere.

Organic Electronic Platform for Real-Time Phenotypic Screening of Extracellular-Vesicle-Driven Breast Cancer Metastasis

Tumor-derived extracellular vesicles (TEVs) induce the epithelial-to-mesenchymal transition (EMT) in nonmalignant cells to promote invasion and cancer metastasis, representing a novel therapeutic target in a field severely lacking in efficacious antimetastasis treatments. However, scalable technologies that allow continuous, multiparametric monitoring for identifying metastasis inhibitors are absent. Here, the development of a functional phenotypic screening platform based on organic electrochemical transistors (OECTs) for real-time, noninvasive monitoring of TEV-induced EMT and screening of antimetastatic drugs is reported. TEVs derived from the triple-negative breast cancer cell line MDA-MB-231 induce EMT in nonmalignant breast epithelial cells (MCF10A) over a nine-day period, recapitulating a model of invasive ductal carcinoma metastasis. Immunoblot analysis and immunofluorescence imaging confirm the EMT status of TEV-treated cells, while dual optical and electrical readouts of cell phenotype are obtained using OECTs. Further, heparin, a competitive inhibitor of cell surface receptors, is identified as an effective blocker of TEV-induced EMT. Together, these results demonstrate the utility of the platform for TEV-targeted drug discovery, allowing for facile modeling of the transient drug response using electrical measurements, and provide proof of concept that inhibitors of TEV function have potential as antimetastatic drug candidates.

Comparative in vivo toxicokinetics of silver powder, nanosilver and soluble silver compounds after oral administration to rats

Silver (Ag; massive, powder and nanoform) and Ag compounds are used in industrial, medical and consumer applications, with potential for human exposure. Uncertainties exist about their comparative mammalian toxicokinetic ('TK') profiles, including their relative oral route bioavailability, especially for Ag massive and powder forms. This knowledge gap impedes concluding on the grouping of Ag and Ag compounds for hazard assessment purposes. Therefore, an in vivo TK study was performed in a rat model. Sprague-Dawley rats were exposed via oral gavage for up to 28 days to silver acetate (AgAc; 5, 55, 175 mg/kg(bw)/d), silver nitrate (AgNO3; 5, 55, 125 mg/kg(bw)/d), nanosilver (AgNP; 15 nm diameter; 3.6, 36, 360 mg/kg(bw)/d) or silver powder (AgMP; 0.35 µm diameter; 36, 180, 1000 mg/kg(bw)/d). Total Ag concentrations were determined in blood and tissues to provide data on comparative systemic exposure to Ag and differentials in achieved tissue Ag levels. AgAc and AgNO3 were the most bioavailable forms with comparable and linear TK profiles (achieved systemic exposures and tissue concentrations). AgMP administration led to systemic exposures of about an order of magnitude less, with tissue Ag concentrations 2-3 orders of magnitude lower and demonstrating non-linear kinetics. The apparent oral bioavailability of AgNP was intermediate between AgAc/AgNO3 and AgMP. For all test items, highest tissue Ag concentrations were in the gastrointestinal tract and reticuloendothelial organs, whereas brain and testis were minor sites of distribution. It was concluded that the oral bioavailability of AgMP was very limited. These findings provide hazard assessment context for various Ag test items and support the prediction that Ag in massive and powder forms exhibit low toxicity potential.

Physicochemical Transformations of Silver Nanoparticles in the Oro-Gastrointestinal Tract Mildly Affect Their Toxicity to Intestinal Cells In Vitro: An AOP-Oriented Testing Approach

The widespread use of silver nanoparticles (Ag NPs) in food and consumer products suggests the relevance of human oral exposure to these nanomaterials (NMs) and raises the possibility of adverse effects in the gastrointestinal tract. The aim of this study was to investigate the toxicity of Ag NPs in a human intestinal cell line, either uncoated or coated with polyvinylpyrrolidone (Ag PVP) or hydroxyethylcellulose (Ag HEC) and digested in simulated gastrointestinal fluids. Physicochemical transformations of Ag NPs during the different stages of in vitro digestion were identified prior to toxicity assessment. The strategy for evaluating toxicity was constructed on the basis of adverse outcome pathways (AOPs) showing Ag NPs as stressors. It consisted of assessing Ag NP cytotoxicity, oxidative stress, genotoxicity, perturbation of the cell cycle and apoptosis. Ag NPs caused a concentration-dependent loss of cell viability and increased the intracellular level of reactive oxygen species as well as DNA damage and perturbation of the cell cycle. In vitro digestion of Ag NPs did not significantly modulate their toxicological impact, except for their genotoxicity. Taken together, these results indicate the potential toxicity of ingested Ag NPs, which varied depending on their coating but did not differ from that of non-digested NPs.

Enhanced antibacterial effect and biodegradation of coating via dual-in-situ growth based on carboxymethyl cellulose

The lack of antimicrobial effect of commercial paper coating for food packaging makes it difficult to prevent food spoilage and harms the environment by non-biodegradation. Herein, carboxymethyl cellulose (CMC) provides negatively charged sites for anchoring Ag⁺ and Zn²⁺ to grow AgNPs and ZIF-8 in situ on its molecular chains. The ZIF-8/AgNPs@CMC paper coating has excellent synergistic antibacterial activity to prolong the shelf-life of food. It not only has good thermal stability but binds closely to the paper and its adhesion force reaches 628.9 nN. Besides, the ZIF-8/AgNPs@CMC coated paper has better mechanical properties, water vapor barrier, and resists water solubility. Interestingly, due to the confinement effect of ZIF-8, the cumulative release of AgNPs after 168 h is only 2.66 % to avoid possible food safety risks. Especially, the coating can be almost biodegraded in the soil after 30 days, which provides the possibility to replace the non-biodegradable coatings in food packaging.

Biofilm Inhibitory Activity of Actinomycete-Synthesized AgNPs with Low Cytotoxic Effect: Experimental and In Silico Study

The emergence of resistance by biofilm-forming bacteria has reached alarming and dangerous levels that threaten human civilization. The current study sought to investigate the antibiofilm potential of green-synthesized silver nanoparticles, mediated by a new Streptomyces strain. Zeta potential, transmission electron microscopy (TEM), and UV-Vis spectroscopy were used to analyze the biosynthesized AgNPs. Results revealed that silver nanoparticles had a size of (5.55 and 45.00 nm) nm and a spherical shape, with surface plasmon resonance (SPR) absorption at 400-460 nm in the UV-vis spectra establishing the formation of Streptomyces-Ag-NPs. The biosynthesized AgNPs showed a pronounced antibacterial efficacy against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus. Moreover, the obtained Streptomyces-AgNPs exerted biofilm inhibition activity against nosocomial hospital-resistant bacteria, including Bacillus subtilis, Staphylococcus aureus, and Escherichia coli. The mechanism of biogenic AgNPs antibacterial action was visualized using TEM, which indicated the AgNPs accumulation and disruption of bacterial cell membrane function. Additionally, a molecular docking study was conducted to evaluate the binding mode of AgNPs with an Escherichia coli outer membrane. Furthermore, the cytotoxic profile of the AgNPs was evaluated toward three cell lines (MCF-7, HepG2 & HCT 116), and the low cytotoxic effects of the obtained nanoparticles indicated their possible medical application with low risks to human health.

Antibacterial and Cytocompatible: Combining Silver Nitrate with Strontium Acetate Increases the Therapeutic Window

Microbial infection and insufficient tissue formation are considered to be the two main causes of dental implant failure. Novel studies have focused on designing dual-functional strategies to promote antibacterial properties and improve tissue cell response simultaneously. In this study, we investigated the antibacterial properties and cytocompatibility of silver nitrate (AgNO₃) and strontium acetate (SrAc) in a mono-culture setup for dental application. Additionally, we defined the therapeutic window between the minimum inhibitory concentration against pathogenic bacteria and maximum cytocompatible dose in the case of combined applications in a co-culture setup. Antibacterial properties were screened using Aggregatibacter actinomycetemcomitans and cell response experiments were performed with osteoblastic cells (MC3T3) and fibroblastic cells (NIH3T3). The osteoinductive behavior was investigated separately on MC3T3 cells using alizarin red staining. A therapeutic window for AgNO₃ as well as SrAc applications could be defined in the case of MC3T3 cells while the cytocompatibility of NIH3T3 cells was compromised for all concentrations with an antibacterial effect. However, the combined application of AgNO₃/SrAc caused an enhanced antibacterial effect and opened a therapeutic window for both cell lines. Enhanced mineralization rates could be observed in cultures containing SrAc. In conclusion, we were able to demonstrate that adding SrAc to AgNO₃ not only intensifies antibacterial properties but also exhibits bone inductive characteristics, thereby offering a promising strategy to combat peri-implantitis and at the same time improve osseointegration in implant therapy.

U.S. Federal Agency interests and key considerations for new approach methodologies for nanomaterials

Engineered nanomaterials (ENMs) come in a wide array of shapes, sizes, surface coatings, and compositions, and often possess novel or enhanced properties compared to larger sized particles of the same elemental composition. To ensure the safe commercialization of products containing ENMs, it is important to thoroughly understand their potential risks. Given that ENMs can be created in an almost infinite number of variations, it is not feasible to conduct in vivo testing on each type of ENM. Instead, new approach methodologies (NAMs) such as in vitro or in chemico test methods may be needed, given their capacity for higher throughput testing, lower cost, and ability to provide information on toxicological mechanisms. However, the different behaviors of ENMs compared to dissolved chemicals may challenge safety testing of ENMs using NAMs. In this study, member agencies within the Interagency Coordinating Committee on the Validation of Alternative Methods were queried about what types of ENMs are of agency interest and whether there is agency-specific guidance for ENM toxicity testing. To support the ability of NAMs to provide robust results in ENM testing, two key issues in the usage of NAMs, namely dosimetry and interference/bias controls, are thoroughly discussed.

Use of an in silico knowledge discovery approach to determine mechanistic studies of silver nanoparticles-induced toxicity from in vitro to in vivo

Background

Silver nanoparticles (AgNPs) are considered a double-edged sword that demonstrates beneficial and harmful effects depending on their dimensions and surface coating types. However, mechanistic understanding of the size- and coating-dependent effects of AgNPs in vitro and in vivo remains elusive. We adopted an in silico decision tree-based knowledge-discovery-in-databases process to prioritize the factors affecting the toxic potential of AgNPs, which included exposure dose, cell type and AgNP type (i.e., size and surface coating), and exposure time. This approach also contributed to effective knowledge integration between cell-based phenomenological observations and in vitro/in vivo mechanistic explorations.

Results

The consolidated cell viability assessment results were used to create a tree model for generalizing cytotoxic behavior of the four AgNP types: SCS, LCS, SAS, and LAS. The model ranked the toxicity-related parameters in the following order of importance: exposure dose > cell type > particle size > exposure time ≥ surface coating. Mechanistically, larger AgNPs appeared to provoke greater levels of autophagy in vitro, which occurred during the earlier phase of both subcytotoxic and cytotoxic exposures. Furthermore, apoptosis rather than necrosis majorly accounted for compromised cell survival over the above dosage range. Intriguingly, exposure to non-cytotoxic doses of AgNPs induced G2/M cell cycle arrest and senescence instead. At the organismal level, SCS following a single intraperitoneal injection was found more toxic to BALB/c mice as compared to SAS. Both particles could be deposited in various target organs (e.g., spleen, liver, and kidneys). Morphological observation, along with serum biochemical and histological analyses, indicated that AgNPs could produce pancreatic toxicity, apart from leading to hepatic inflammation.

Conclusions

Our integrated in vitro, in silico, and in vivo study revealed that AgNPs exerted toxicity in dose-, cell/organ type- and particle type-dependent manners. More importantly, a single injection of lethal-dose AgNPs (i.e., SCS and SAS) could incur severe damage to pancreas and raise blood glucose levels at the early phase of exposure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00447-0.

Monitoring of Lactate in Interstitial Fluid, Saliva and Sweat by Electrochemical Biosensor: The Uncertainties of Biological Interpretation

Lactate electrochemical biosensors were fabricated using Pediococcus sp lactate oxidase (E.C. 1.1.3.2), an external polyurethane membrane laminate diffusion barrier and an internal ionomeric polymer barrier (sulphonated polyether ether sulphone polyether sulphone, SPEES PES). In a needle embodiment, a Pt wire working electrode was retained within stainless steel tubing serving as pseudoreference. The construct gave linearity to at least 25 mM lactate with 0.17 nA/mM lactate sensitivity. A low permeability inner membrane was also unexpectedly able to increase linearity. Responses were oxygen dependent at pO2 < 70 mmHg, irrespective of the inclusion of an external diffusion barrier membrane. Subcutaneous tissue was monitored in Sprague Dawley rats, and saliva and sweat during exercise in human subjects. The tissue sensors registered no response to intravenous Na lactate, indicating a blood-tissue lactate barrier. Salivary lactate allowed tracking of blood lactate during exercise, but lactate levels were substantially lower than those in blood (0–3.5 mM vs. 1.6–12.1 mM), with variable degrees of lactate partitioning from blood, evident both between subjects and at different exercise time points. Sweat lactate during exercise measured up to 23 mM but showed highly inconsistent change as exercise progressed. We conclude that neither tissue interstitial fluid nor sweat are usable as surrogates for blood lactate, and that major reappraisal of lactate sensor use is indicated for any extravascular monitoring strategy for lactate.

Characterization, bio-uptake and toxicity of polymer-coated silver nanoparticles and their interaction with human peripheral blood mononuclear cells

Silver nanoparticles (AgNPs) are widely used in medical applications due to their antibacterial and antiviral properties. Despite the extensive study of AgNPs, their toxicity and their effect on human health is poorly understood, as a result of issues such as poor control of NP properties and lack of proper characterization. The aim of this study was to investigate the combined characterization, bio-uptake, and toxicity of well-characterized polyvinylpyrrolidone (PVP)-coated AgNPs in exposure media during exposure time using primary human cells (peripheral blood mononuclear cells (PBMCs)). AgNPs were synthesized in-house and characterized using a multimethod approach. Results indicated the transformation of NPs in RPMI medium with a change in size and polydispersity over 24 h of exposure due to dissolution and reprecipitation. No aggregation of NPs was observed in the RPMI medium over the exposure time (24 h). A dose-dependent relationship between PBMC uptake and Ag concentration was detected for both AgNP and AgNO₃ treatment. There was approximately a two-fold increase in cellular Ag uptake in the AgNO₃ vs the NP treatment. Cytotoxicity, using LDH and MTS assays and based on exposure concentrations was not significantly different when comparing NPs and Ag ions. Based on differential uptake, AgNPs were more toxic after normalizing toxicity to the amount of cellular Ag uptake. Our data highlights the importance of correct synthesis, characterization, and study of transformations to obtain a better understanding of NP uptake and toxicity. Statistical analysis indicated that there might be an individual variability in response to NPs, although more research is required.

Risk assessment on-a-chip: a cell-based microfluidic device for immunotoxicity screening

Nanomaterials are widely used in industrial and clinical settings due to their unique physical and chemical properties. However, public health and environmental concerns have emerged owing to their undesired toxicity and ability to trigger immune responses. This paper presents the development of a microfluidic-based cell biochip device that enables the administration of nanoparticles under laminar flow to cells of the immune system to assess their cytotoxicity. The exposure of human B lymphocytes to 10 nm silver nanoparticles under fluid flow led to a 3-fold increase in toxicity compared to static conditions, possibly indicating enhanced cell-nanoparticle interactions. To investigate whether the administration under flow was the main contributing factor, we compared and validated the cytotoxicity of the same nanoparticles in different platforms, including the conventional well plate format and in-house fabricated microfluidic devices under both static and dynamic flow conditions. Our results suggest that commonly employed static platforms might not be well-suited to perform toxicological screening of nanomaterials and may lead to an underestimation of cytotoxic responses. The simplicity of the developed flow system makes this setup a valuable tool to preliminary screen nanomaterials.

L-Cysteine/AgNO2 low molecular weight gelators: self-assembly and suppression of MCF-7 breast cancer cells

We report a new supramolecular hydrogel based on simple amino acids and silver salt compounds with low molecular weights. The in situ formation of silver nanoparticles during the self-assembly process endows the hydrogel with high cytotoxicity towards adenocarcinoma breast cells but no toxic effects towards embryonic fibroblasts.

Carboxymethyl cellulose/cellulose nanocrystals immobilized silver nanoparticles as an effective coating to improve barrier and antibacterial properties of paper for food packaging applications

A new natural formulation composed of CMC and various contents of CNC immobilized AgNPs (CNC@AgNPs) was developed for paper coating. The mechanical strength, water vapor and air barrier properties, and antibacterial activities of CMC/CNC@AgNPs coated paper improved with the increasing content of CNC@AgNPs. CMC/CNC@AgNPs7 % coated paper exhibited 1.26 times increase in tensile strength, 45.4 % decrease in WVP, 93.3 % reduction in air permeability as well as the best antibacterial activities against E.coli and S.aureus compared with uncoated paper. Moreover, the cumulative release rate of AgNPs from coated paper significantly reduced due to the immobilization effect of CNC on AgNPs. Furthermore, CMC/CNC@AgNPs coated paper was used to package strawberries under ambient conditions. The results showed that coated paper could maintain better strawberries quality compared with unpackaged strawberries and extend the shelf-life of strawberries to 7 days. Therefore, the prepared CMC/CNC@AgNPs coated paper will have a great application prospect in the food packaging.

Hepato(Geno)Toxicity Assessment of Nanoparticles in a HepG2 Liver Spheroid Model

(1) In compliance with the 3Rs policy to reduce, refine and replace animal experiments, the development of advanced in vitro models is needed for nanotoxicity assessment. Cells cultivated in 3D resemble organ structures better than 2D cultures. This study aims to compare cytotoxic and genotoxic responses induced by titanium dioxide (TiO₂), silver (Ag) and zinc oxide (ZnO) nanoparticles (NPs) in 2D monolayer and 3D spheroid cultures of HepG2 human liver cells. (2) NPs were characterized by electron microscopy, dynamic light scattering, laser Doppler anemometry, UV-vis spectroscopy and mass spectrometry. Cytotoxicity was investigated by the alamarBlue assay and confocal microscopy in HepG2 monolayer and spheroid cultures after 24 h of NP exposure. DNA damage (strand breaks and oxidized base lesions) was measured by the comet assay. (3) Ag-NPs were aggregated at 24 h, and a substantial part of the ZnO-NPs was dissolved in culture medium. Ag-NPs induced stronger cytotoxicity in 2D cultures (EC₅₀ 3.8 µg/cm²) than in 3D cultures (EC₅₀ > 30 µg/cm²), and ZnO-NPs induced cytotoxicity to a similar extent in both models (EC₅₀ 10.1-16.2 µg/cm²). Ag- and ZnO-NPs showed a concentration-dependent genotoxic effect, but the effect was not statistically significant. TiO₂-NPs showed no toxicity (EC₅₀ > 75 µg/cm²). (4) This study shows that the HepG2 spheroid model is a promising advanced in vitro model for toxicity assessment of NPs.

Silver nanoparticles inhibit denitrification by altering the viability and metabolic activity of Pseudomonas stutzeri

The environmental toxicity of silver nanoparticles (AgNPs) is currently the focus of intensive research. However, the mechanisms underlying the cytotoxic effects of AgNPs on denitrifying microbes have yet to be explicitly demonstrated. Herein, Pseudomonas stutzeri was used to explore the effects of AgNPs on denitrification and cytotoxicity. The denitrification efficiency decreased from 94.91% in the AgNP-free treatment to 87.66%, 60.51% and 36.10% with treatments of 3.125, 6.25 and 12.5 mg/L AgNPs, respectively. The inhibition and delay in the denitrification process from treatment with AgNPs likely occurred through alteration of the viability and metabolic activity of P. stutzeri. Flow cytometry analysis indicated that the early apoptotic rates of P. stutzeri were 8.72%, 30.60%, and 48.60% with treatments of 3.125, 6.25, and 12.5 mg/L AgNPs, respectively. Results for scanning electron microscope (SEM) imaging, ζ-potential analysis, lactate dehydrogenase (LDH) release and malondialdehyde (MDA) production assays demonstrated adsorption of AgNPs on the cell surface, which altered membrane potential and mediated lipid peroxidation; these events eventually resulted in the aberration of cell morphology. Transmission electron microscopy (TEM) images and measurements of Ag content distribution by ICP-MS indicated that AgNPs were easily internalized by P. stutzeri, which increased the accumulation of reactive oxygen species (ROS). Furthermore, the presence of AgNPs also greatly inhibited expression of genes napA, nirS, cnorB, and nosZ, thereby reducing the activities of nitrate reductase (NAR) and nitrite reductase (NIR). These findings will help further our understanding of the mechanism underlying AgNPs cytotoxicity, and provide the means to evaluate the negative effect of nanoparticles in the environment.

Silver-Containing Titanium Dioxide Nanocapsules for Combating Multidrug-Resistant Bacteria

BACKGROUND

Joint arthroplasty has improved the quality of life of patients worldwide, but infections of the prosthesis are frequent and cause significant morbidity. Antimicrobial coatings for implants promise to prevent these infections.

METHODS

We have synthesized nanocapsules of titanium dioxide in amorphous or anatase form containing silver as antibacterial agent and tested their impact on bacterial growth. Furthermore, we explored the possible effect of the nanocapsules on the immune system. First, we studied their uptake into macrophages using a combination of electron microscopy and energy-dispersive spectroscopy. Second, we exposed immune cells to the nanocapsules and checked their activation state by flow cytometry and enzyme-linked immunosorbent assay.

RESULTS

Silver-containing titanium dioxide nanocapsules show strong antimicrobial activity against both E. coli and S. aureus and even against a multidrug-resistant strain of S. aureus. We could demonstrate the presence of the nanocapsules in macrophages, but, importantly, the nanocapsules did not affect cell viability and did not activate proinflammatory responses at doses up to 20 μg/mL.

CONCLUSION

Our bactericidal silver-containing titanium dioxide nanocapsules fulfill important prerequisites for biomedical use and represent a promising material for the coating of artificial implants.

Competitive Surface Colonization of Antibacterial and Bioactive Materials Doped with Strontium and/or Silver Ions

Nowadays, there is a large amount of research aimed at improving the multifunctional behavior of the biomaterials for bone contact, including the concomitant ability to induce apatite formation (bioactivity), fast and effective osteoblasts colonization, and antibacterial activity. The aim of this study is to develop antibacterial and bioactive surfaces (Ti6Al4V alloy and a silica-based bioactive glass) by chemical doping with strontium and/or silver ions. The surfaces were characterized by Scanning Electron Microscopy equipped with Energy Dispersive X ray Spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Transmission Electron Microscopy (TEM). To better focus on the cells-bacteria competition for the implant surface, in addition to the standard assays for the evaluation of the bacteria adhesion (ISO22196) and for single-cell cultures or biofilm formation, an innovative set of co-cultures of cells and bacteria is here proposed to simulate a competitive surface colonization. The results suggest that all the bioactive tested materials were cytocompatible toward the bone progenitor cells representative for the self-healing process, and that the doped ones were effective in reducing the surface colonization from a pathogenic drug-resistant strain of Staphylococcus aureus. The co-cultures experiments demonstrated that the doped surfaces were able to protect the adhered osteoblasts from the bacteria colonization as well as prevent the infection prior to the surface colonization by the osteoblasts.

New Look on Antifungal Activity of Silver Nanoparticles (AgNPs)

The progress of research on silver nanoparticles (AgNPs) has led to their inclusion in many consumer products (chemicals, cosmetics, clothing, water filters, and medical devices) as a biocide. Despite the widespread use of AgNPs, their biocidal activity is not yet fully understood and is usually associated with various factors (size, composition, surface, red-ox potential, and concentration) and, obviously, specific features of microorganisms. There are merely a few studies concerning the interaction of molds with AgNPs. Therefore, the determination of the minimal AgNPs concentration required for effective growth suppression of five fungal species (Paecilomyces variotii, Penicillium pinophilum, Chaetomium globosum, Trichoderma virens, and Aspergillus brasiliensis), involved in the deterioration of construction materials, was particularly important. Inhibition of bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli) and yeasts (Candida albicans and Yarrowia lipolytica) was also assessed as the control of AgNPs effectiveness. AgNPs at the concentrations of 9–10.7 ppm displayed high inhibitory activity against moulds, yeast, and bacteria. The TEM images revealed that 20 nm AgNPs migrated into bacterial, yeast, and fungal cells but aggregated in larger particles (50–100 nm) exclusively inside eukaryotic cells. The aggregation of 20 nm AgNPs and particularly their accumulation in the cell wall, observed for A. brasiliensis cells, are described here for the first time.

Revealing the Importance of Aging, Environment, Size and Stabilization Mechanisms on the Stability of Metal Nanoparticles: A Case Study for Silver Nanoparticles in a Minimally Defined and Complex Undefined Bacterial Growth Medium

Although the production and stabilization of metal nanoparticles (MNPs) is well understood, the behavior of these MNPs (possible aggregation or disaggregation) when they are intentionally or unintentionally exposed to different environments is a factor that continues to be underrated or overlooked. A case study is performed to analyze the stability of silver nanoparticles (AgNPs)-one of the most frequently used MNPs with excellent antibacterial properties-within two bacterial growth media: a minimally defined medium (IDL) and an undefined complex medium (LB). Moreover, the effect of aging, size and stabilization mechanisms is considered. Results clearly indicate a strong aggregation when AgNPs are dispersed in IDL. Regarding LB, the 100 nm electrosterically stabilized AgNPs remain stable while all others aggregate. Moreover, a serious aging effect is observed for the 10 nm electrostatically stabilized AgNPs when added to LB: after aggregation a restabilization effect occurs over time. Generally, this study demonstrates that the aging, medium composition (environment), size and stabilization mechanism-rarely acknowledged as important factors in nanotoxicity studies-have a profound impact on the AgNPs stabilization and should gain more attention in scientific research.

Enhanced antibacterial performance of ultrathin silver/platinum nanopatches by a sacrificial anode mechanism

The development of antibacterial implant surfaces is a challenging task in biomaterial research. We fabricated a highly antibacterial bimetallic platinum (Pt)/silver(Ag) nanopatch surface by short time sputtering of Pt and Ag on titanium. The sputter process led to a patch-like distribution with crystalline areas in the nanometer-size range (1.3-3.9 nm thickness, 3-60 nm extension). Structural analyses of Pt/Ag samples showed Ag- and Pt-rich areas containing nanoparticle-like Pt deposits of 1-2 nm. The adhesion and proliferation properties of S. aureus on the nanopatch samples were analyzed. Consecutively sputtered Ag/Pt nanopatches (Pt followed by Ag) induced enhanced antimicrobial activity compared to co-sputtered Pt/Ag samples or pure Ag patches of similar Ag amounts. The underlying sacrificial anode mechanism was proved by linear sweep voltammetry. The advantages of this nanopatch coating are the enhanced antimicrobial activity despite a reduced total amount of Ag/Pt and a self-limited effect due the rapid Ag dissolution.

Size-dependent cytotoxicity of silver nanoparticles to Azotobacter vinelandii: Growth inhibition, cell injury, oxidative stress and internalization

The influence of nanomaterials on the ecological environment is becoming an increasingly hot research field, and many researchers are exploring the mechanisms of nanomaterial toxicity on microorganisms. Herein, we studied the effect of two different sizes of nanosilver (10 nm and 50 nm) on the soil nitrogen fixation by the model bacteria Azotobacter vinelandii. Smaller size AgNPs correlated with higher toxicity, which was evident from reduced cell numbers. Flow cytometry analysis further confirmed this finding, which was carried out with the same concentration of 10 mg/L for 12 h, the apoptotic rates were20.23% and 3.14% for 10 nm and 50 nm AgNPs, respectively. Structural damage to cells were obvious under scanning electron microscopy. Nitrogenase activity and gene expression assays revealed that AgNPs could inhibit the nitrogen fixation of A. vinelandii. The presence of AgNPs caused intracellular reactive oxygen species (ROS) production and electron spin resonance further demonstrated that AgNPs generated hydroxyl radicals, and that AgNPs could cause oxidative damage to bacteria. A combination of Ag content distribution assays and transmission electron microscopy indicated that AgNPs were internalized in A. vinelandii cells. Overall, this study suggested that the toxicity of AgNPs was size and concentration dependent, and the mechanism of antibacterial effects was determined to involve damage to cell membranes and production of reactive oxygen species leading to enzyme inactivation, gene down-regulation and death by apoptosis.

Silver nanoparticles in complex media: an easy procedure to discriminate between metallic silver nanoparticles, reprecipitated silver chloride, and dissolved silver species

Silver nanoparticles undergo oxidative dissolution in water upon storage. This occurs in pure water as well as in more complex media, including natural environments, biological tissues, and cell culture media. However, the dissolution leads to the reprecipitation of silver chloride as chloride is present in almost all relevant environments. The discrimination between dissolved silver species (ions and silver complexes) and dispersed (solid) species does not take this into account because all solid species (metallic silver and silver chloride) are isolated together. By applying a chemical separation procedure, we show that it is possible to quantify silver, silver chloride, and dissolved silver species after immersion into a typical cell culture medium (DMEM + 10% FCS). During the dissolution of metallic silver nanoparticles, about half of the dissolved silver is reprecipitated as solid silver chloride, i.e. the mere analysis of the soluble silver species does not reflect the true situation. The separation protocol is suitable for all chloride-containing media in the presence or in the absence of biomolecules.

A reversible fluorescent probe for monitoring Ag(I) ions

Silver-containing nanomaterials are of interest for their antibiotic properties, for a wide range of applications from medicine to consumer products. However, much remains to be learnt about the degradation of such materials and their effects on human health. While most analyses involve measurement of total silver levels, it is important also to be able to measure concentrations of active free Ag(I) ions. We report here the preparation of a coumarin-based probe, thiocoumarin silver sensor 1 (TcAg1), that responds reversibly to the addition of silver ions through the appearance of a new fluorescence emission peak at 565 nm. Importantly, this peak is not observed in the presence of Hg(II), a common interferent in Ag(I) sensing. To establish the utility of this sensor, we prepared silver-doped phosphate glasses with demonstrated bactericidal properties, and observed the Ag(I) release from these glasses in solutions of different ionic strength. TcAg1 is therefore a useful tool for the study of the environmental and medical effects of silver-containing materials.

Synthesis and biological characterization of alloyed silver–platinum nanoparticles: from compact core–shell nanoparticles to hollow nanoalloys

Bimetallic nanoparticles consisting of silver and platinum were prepared by a modified seeded-growth process in water in the full composition range in steps of 10 mol%. The particles had diameters between 15–25 nm as determined by disc centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). Whereas particles with high platinum content were mostly spherical with a solid silver core/platinum shell structure, mostly hollow alloyed nanoparticles were observed with increasing silver content. The internal structure and the elemental distribution within the particles were elucidated by high-resolution transmission electron microscopy (HRTEM) in combination with energy-dispersive X-ray spectroscopy (EDX). The particles were cytotoxic for human mesenchymal stem cells (hMSC) above 50 mol% silver. This was explained by dissolution experiments where silver was only released at and above 50 mol% silver. In contrast, platinum-rich particles (less than 50 mol% silver) did not release any silver ions. This indicates that the presence of platinum inhibits the oxidative dissolution of silver.

Bimetallic nanoparticles consisting of silver and platinum were prepared by a modified seeded-growth process in water in the full composition range in steps of 10 mol%.

Silver nanoparticles as a medical device in healthcare settings: a five-step approach for candidate screening of coating agents

Silver nanoparticle-based antimicrobials can promote a long lasting bactericidal effect without detrimental toxic side effects. However, there is not a clear and complete protocol to define and relate the properties of the particles (size, shape, surface charge, ionic content) with their specific activity. In this paper, we propose an effective multi-step approach for the identification of a 'purpose-specific active applicability window' to maximize the antimicrobial activity of medical devices containing silver nanoparticles (Ag NPs) (such as surface coaters), minimizing any consequent risk for human health (safety by design strategy). The antimicrobial activity and the cellular toxicity of four types of Ag NPs, differing in their coating composition and concentration have been quantified. Through the implementation of flow-field flow fractionation, Ag NPs have been characterized in terms of metal release, size and shape. The particles are fractionated in the process while being left unmodified, allowing for the identification of biological particle-specific contribution. Toxicity and inflammatory response in vitro have been assessed on human skin models, while antimicrobial activity has been monitored with both non-pathogenic and pathogenic Escherichia coli. The main benefit associated with such approach is the comprehensive assessment of the maximal effectiveness of candidate nanomaterials, while simultaneously indexing their properties against their safety.