Short versus long silver nanowires: a comparison of in vivo pulmonary effects post instillation

Metallic Engineered Nanomaterials and Ocular Toxicity: A Current Perspective

The ocular surface, comprised of the transparent cornea, conjunctiva, and protective tear film, forms a protective barrier defending deeper structures of the eye from particulate matter and mechanical trauma. This barrier is routinely exposed to a multitude of naturally occurring and engineered nanomaterials (ENM). Metallic ENMs are particularly ubiquitous in commercial products with a high risk of ocular exposure, such as cosmetics and sunscreens. Additionally, there are several therapeutic uses for metallic ENMs owing to their attractive magnetic, antimicrobial, and functionalization properties. The increasing commercial and therapeutic applications of metallic ENMs come with a high risk of ocular exposure with poorly understood consequences to the health of the eye. While the toxicity of metallic ENMs exposure has been rigorously studied in other tissues and organs, further studies are necessary to understand the potential for adverse effects and inform product usage for individuals whose ocular health may be compromised by injury, disease, or surgical intervention. This review provides an update of current literature on the ocular toxicity of metallic ENMs in vitro and in vivo, as well as the risks and benefits of therapeutic applications of metallic ENMs in ophthalmology.

Patterned Sandwich-Type Silver Nanowire-Based Flexible Electrode by Photolithography

Silver nanowires (AgNWs) are one of the important flexible electrode material candidates that can replace brittle indium tin oxide (ITO). In this work, we demonstrated novel patterned sandwich-type AgNW-based transparent electrodes easily prepared using the photolithography method for application in flexible devices. A cross-linked underlayer was introduced to increase the adhesion properties between a poly(ethylene terephthalate) substrate and AgNWs, and as a result, a uniform AgNW layer was easily deposited. Finally, the AgNW layer could be easily patterned by introducing a photocross-linkable upper layer without lift-off, dry transfer, and removal methods. A mixture of poly(sodium-4-styrene sulfonate) (PSS^-Na⁺) and 2,4-hexadiyne-1,6-diol (HDD), which is a component of the upper layer, exhibited good cross-linking properties as well as excellent adhesion to the AgNW layer. Through the above method, it was possible to easily fabricate a patterned electrode with smooth surface morphology. Moreover, AgNW-based patterned electrodes exhibit good optical and electrical properties (R_s = 29.8 Ω/□, T_550 nm = 94.6%), making them suitable for optoelectronic devices. Flexible polymer solar cells (PSCs) using patterned AgNW electrodes showed a high power conversion efficiency of over 10%, which is comparable to that of PSCs using rigid ITO electrodes. In addition, the high mechanical stability of AgNW-based PSCs was confirmed by bending experiments.

Small Airway Susceptibility to Chemical and Particle Injury

Small airways (SA) in humans are commonly defined as those conducting airways <2 mm in diameter. They are susceptible to particle- and chemical-induced injury and play a major role in the development of airway disease such as COPD and asthma. Susceptibility to injury can be attributed in part to structural features including airflow dynamics and tissue architecture, but recent evidence may indicate a more prominent role for cellular composition in directing toxicological responses. Animal studies support the hypothesis that inherent cellular differences across the tracheobronchial tree, including metabolic CYP450 expression in the distal conducting airways, can influence SA susceptibility to injury. Currently, there is insufficient information in humans to make similar conclusions, prompting further necessary work in this area. An understanding of why the SA are more susceptible to certain chemical and particle exposures than other airway regions is fundamental to our ability to identify hazardous materials, their properties, and accompanying exposure scenarios that compromise lung function. It is also important for the ability to develop appropriate models for toxicity testing. Moreover, it is central to our understanding of SA disease aetiology and how interventional strategies for treatment may be developed. In this review, we will document the structural and cellular airway regional differences that are likely to influence airway susceptibility to injury, including the role of secretory club cells. We will also describe recent advances in single-cell sequencing of human airways, which have provided unprecedented details of cell phenotype, likely to impact airway chemical and particle injury.

Direct Observations of Silver Nanowire-Induced Frustrated Phagocytosis among NR8383 Lung Alveolar Macrophages

The interaction of long nanowires and living cells is directly related to nanowires' nanotoxicity and health impacts. Interactions of silver nanowires (AgNWs) and macrophage cell lines (NR8383) were investigated using laser scanning confocal microscopy and single cell compression (SCC). With high-resolution imaging and mechanics measurement of individual cells, AgNW-induced frustrated phagocytosis was clearly captured in conjunction with structural and property changes of cells. While frustrated phagocytosis is known for long microwires and long carbon nanotubes, this work reports first direct observations of frustrated phagocytosis of AgNWs among living cells in situ. In the case of partial penetration of AgNWs into NR8383 cells, confocal imaging revealed actin participation at the entry sites, whose behavior differs from microwire-induced frustrated phagocytosis. The impacts of frustrated phagocytosis on the cellular membrane and cytoskeleton were also quantified by measuring the mechanical properties using SCC. Taken collectively, this study reveals the structural and property characteristics of nanowire-induced frustrated phagocytosis, which deepens our understanding of nanowire-cell interactions and nanocytotoxicity.

A review on nanotoxicity and nanogenotoxicity of different shapes of nanomaterials

Nanomaterials (NMs) generally display fascinating physical and chemical properties that are not always present in bulk materials; therefore, any modification to their size, shape, or coating tends to cause significant changes in their chemical/physical and biological characteristics. The dramatic increase in efforts to use NMs renders the risk assessment of their toxicity highly crucial due to the possible health perils of this relatively uncharted territory. The different sizes and shapes of the nanoparticles are known to have an impact on organisms and an important place in clinical applications. The shape of nanoparticles, namely, whether they are rods, wires, or spheres, is a particularly critical parameter to affect cell uptake and site-specific drug delivery, representing a significant factor in determining the potency and magnitude of the effect. This review, therefore, intends to offer a picture of research into the toxicity of different shapes (nanorods, nanowires, and nanospheres) of NMs to in vitro and in vivo models, presenting an in-depth analysis of health risks associated with exposure to such nanostructures and benefits achieved by using certain model organisms in genotoxicity testing. Nanotoxicity experiments use various models and tests, such as cell cultures, cores, shells, and coating materials. This review article also attempts to raise awareness about practical applications of NMs in different shapes in biology, to evaluate their potential genotoxicity, and to suggest approaches to explain underlying mechanisms of their toxicity and genotoxicity depending on nanoparticle shape.

How Reversible Are the Effects of Fumed Silica on Macrophages? A Proteomics-Informed View

Synthetic amorphous silica is one of the most used nanomaterials, and numerous toxicological studies have studied its effects. Most of these studies have used an acute exposure mode to investigate the effects immediately after exposure. However, this exposure modality does not allow the investigation of the persistence of the effects, which is a crucial aspect of silica toxicology, as exemplified by crystalline silica. In this paper, we extended the investigations by studying not only the responses immediately after exposure but also after a 72 h post-exposure recovery phase. We used a pyrolytic silica as the test nanomaterial, as this variant of synthetic amorphous silica has been shown to induce a more persistent inflammation in vivo than precipitated silica. To investigate macrophage responses to pyrolytic silica, we used a combination of proteomics and targeted experiments, which allowed us to show that most of the cellular functions that were altered immediately after exposure to pyrolytic silica at a subtoxic dose, such as energy metabolism and cell morphology, returned to normal at the end of the recovery period. However, some alterations, such as the inflammatory responses and some aldehyde detoxification proteins, were persistent. At the proteomic level, other alterations, such as proteins implicated in the endosomal/lysosomal pathway, were also persistent but resulted in normal function, thus suggesting cellular adaptation.

Pulmonary toxicity of silver vapours, nanoparticles and fine dusts: A review

Silver is used in a wide range of products, and during their production and use, humans may be exposed through inhalation. Therefore, it is critical to know the concentration levels at which adverse effects may occur. In rodents, inhalation of silver nanoparticles has resulted in increased silver in the lungs, lymph nodes, liver, kidney, spleen, ovaries, and testes. Reported excretion pathways of pulmonary silver are urinary and faecal excretion. Acute effects in humans of the inhalation of silver include lung failure that involved increased heart rate and decreased arterial blood oxygen pressure. Argyria-a blue-grey discoloration of skin due to deposited silver-was observed after pulmonary exposure in 3 individuals; however, the presence of silver in the discolorations was not tested. Argyria after inhalation seems to be less likely than after oral or dermal exposure. Repeated inhalation findings in rodents have shown effects on lung function, pulmonary inflammation, bile duct hyperplasia, and genotoxicity. In our evaluation, the range of NOAEC values was 0.11-0.75 mg/m³. Silver in the ionic form is likely more toxic than in the nanoparticle form but that difference could reflect their different biokinetics. However, silver nanoparticles and ions have a similar pattern of toxicity, probably reflecting that the effect of silver nanoparticles is primarily mediated by released ions. Concerning genotoxicity studies, we evaluated silver to be positive based on studies in mammalian cells in vitro and in vivo when considering various exposure routes. Carcinogenicity data are absent; therefore, no conclusion can be provided on this endpoint.

Evaluation of Antibacterial and Cytotoxicity Properties of Silver Nanowires and Their Composites with Carbon Nanotubes for Biomedical Applications

In this work, we prepared silver nanowires (AgNWs) via the polyol method in the presence or absence of single wall carbon nanotubes (CNTs) and tested their physicochemical, antibacterial and cytotoxic properties. Results showed that the introduction of CNTs lead to the formation of AgNWs at lower temperature, but the final product characteristics of AgNWs and AgNWs-CNT were not significantly different. AgNWs exhibited antibacterial properties against all the studied bacterial species via the formation of oxygen reactive species (ROS) and membrane damage. Furthermore, AgNWs exhibited a dose-dependent and time-dependent toxicity at concentrations ≥ 10 µg/mL. Fibroblasts appeared to be more resistant than human colorectal adenocarcinoma (Caco-2) and osteoblasts to the toxicity of AgNWs. The cytotoxicity of AgNWs was found to be related to the formation of ROS, but not to membrane damage. Overall, these results suggest that AgNWs are potential antibacterial agents against E. coli, S. aureus, MRSA and S. saprophyticus, but their dosage needs to be adjusted according to the route of administration.

Ultralong AgNWs-induced toxicity in A549 cells and the important roles of ROS and autophagy

Safety concerns have been raised with regard to silver nanowires (AgNWs) because of their extensive applications. Recently, ultralong AgNWs have shown physical properties superior to those of short AgNWs. However, little is known about their toxicity and potential risks. In this study, we demonstrated a series of ultralong AgNWs-induced biological effects in human lung cancer epithelial cells (A549). Ultralong AgNWs treatments induced ROS generation, mitochondria-mediated apoptosis, and self-protective autophagy at nonlethal concentrations. In contrast to some previous reports, apoptosis was found not to correlate with the reduction of intracellular ROS. Measuring the processing of ROS generation, apoptosis and autophagy, we demonstrated that ROS not only enhance mitochondrial damage, but also raise protective autophagic flux in ultralong AgNW-treated cells. Moreover, ultralong AgNWs were found to be internalized into the cytoplasm of the epithelial cells. This study not only investigates ultralong AgNWs-induced cytotoxicity but also pinpoints ROS as a key signal in mechanisms of their toxicity.

Length and diameter-dependent phagocytosis and cytotoxicity of long silver nanowires in macrophages

Long silver nanowires (AgNWs, >5 μm) have shown promising applications in next generation biomaterials. However, the toxicity of long AgNWs is not well characterized in terms of their size. In this study, five AgNWs types, including SAgNW30 (length: 5-10 μm; diameter: 30 nm), MAgNW30 (length: 20-30 μm; diameter: 30 nm), LAgNW30 (length: ∼100 μm; diameter: 30 nm), LAgNW50 (length: ∼100 μm; diameter: 50 nm), and LAgNW100 (length: ∼100 μm; diameter: 100 nm), were used to investigate the size-dependent phagocytosis and cytotoxicity in macrophage. It showed that SAgNW30, MAgNW30, LAgNW30 can be fully phagocytosed by macrophages, but LAgNW50 and LAgNW100 frustrated the phagocytosis. It demonstrated that LAgNW30 can be internalized into macrophage in a curly manner. The size-dependent cytotoxicity was observed in cell viability, apoptosis, mitochondrial damage, phenotypic transition, and inflammatory response in AgNWs-treated macrophage. The AgNWs-induced cytotoxicity was depended on their length and diameter, increased gradually in the order of SAgNW30 > MAgNW30 > LAgNW30 > LAgNW50 > LAgNW100. The findings presented here will assist in the evaluation of the size-dependent cytotoxicity mediated by long AgNWs.

Crumpling of silver nanowires by endolysosomes strongly reduces toxicity

Fibrous particles interact with cells and organisms in complex ways that can lead to cellular dysfunction, cell death, inflammation, and disease. The development of conductive transparent networks (CTNs) composed of metallic silver nanowires (AgNWs) for flexible touchscreen displays raises new possibilities for the intimate contact between novel fibers and human skin. Here, we report that a material property, nanowire-bending stiffness that is a function of diameter, controls the cytotoxicity of AgNWs to nonimmune cells from humans, mice, and fish without deterioration of critical CTN performance parameters: electrical conductivity and optical transparency. Both 30- and 90-nm-diameter AgNWs are readily internalized by cells, but thinner NWs are mechanically crumpled by the forces imposed during or after endocytosis, while thicker nanowires puncture the enclosing membrane and release silver ions and lysosomal contents to the cytoplasm, thereby initiating oxidative stress. This finding extends the fiber pathology paradigm and will enable the manufacture of safer products incorporating AgNWs.

In vitro exposure of a 3D-tetraculture representative for the alveolar barrier at the air-liquid interface to silver particles and nanowires

BACKGROUND

The present study aimed to evaluate the potential differences in the biological effects of two types of spherical silver particles of 20 and 200 nm (Ag20 and Ag200), and of PVP-coated silver nanowires (AgNWs) with a diameter of 50 nm and length up to 50 μm, using a complex 3D model representative for the alveolar barrier cultured at air-liquid interface (ALI). The alveolar model was exposed to 0.05, 0.5 and 5 μg/cm2 of test compounds at ALI using a state-of-the-art exposure system (Vitrocell™Cloud System). Endpoints related to the oxidative stress induction, anti-oxidant defence mechanisms, pro-inflammatory responses and cellular death were selected to evaluate the biocompatibility of silver particles and nanowires (AgNMs) and to further ascribe particular biological effects to the different morphologic properties between the three types of AgNMs evaluated.

RESULTS

Significant cytotoxic effect was observed for all three types of AgNMs at the highest tested doses. The increased mRNA levels of the pro-apoptotic gene CASP7 suggests that apoptosis may occur after exposure to AgNWs. All three types of AgNMs increased the mRNA level of the anti-oxidant enzyme HMOX-1 and of the metal-binding anti-oxidant metallothioneins (MTs), with AgNWs being the most potent inducer. Even though all types of AgNMs induced the nuclear translocation of NF-kB, only AgNWs increased the mRNA level of pro-inflammatory mediators. The pro-inflammatory response elicited by AgNWs was further confirmed by the increased secretion of the 10 evaluated interleukins.

CONCLUSION

In the current study, we demonstrated that the direct exposure of a complex tetra-culture alveolar model to different types of AgNMs at ALI induces shape- and size-specific biological responses. From the three AgNMs tested, AgNWs were the most potent in inducing biological alterations. Starting from 50 ng/cm2, a dose representative for an acute exposure in a high exposure occupational setting, AgNWs induced prominent changes indicative for a pro-inflammatory response. Even though the acute responses towards a dose representative for a full-lifetime exposure were also evaluated, chronic exposure scenarios at low dose are still unquestionably needed to reveal the human health impact of AgNMs during realistic conditions.

In Vitro Dermal Safety Assessment of Silver Nanowires after Acute Exposure: Tissue vs. Cell Models

Silver nanowires (AgNW) are attractive materials that are anticipated to be incorporated into numerous consumer products such as textiles, touchscreen display, and medical devices that could be in direct contact with skin. There are very few studies on the cellular toxicity of AgNW and no studies that have specifically evaluated the potential toxicity from dermal exposure. To address this question, we investigated the dermal toxicity after acute exposure of polymer-coated AgNW with two sizes using two models, human primary keratinocytes and human reconstructed epidermis. In keratinocytes, AgNW are rapidly and massively internalized inside cells leading to dose-dependent cytotoxicity that was not due to Ag⁺ release. Analysing our data with different dose metrics, we propose that the number of NW is the most appropriate dose-metric for studies of AgNW toxicity. In reconstructed epidermis, the results of a standard in vitro skin irritation assay classified AgNW as non-irritant to skin and we found no evidence of penetration into the deeper layer of the epidermis. The findings show that healthy and intact epidermis provides an effective barrier for AgNW, although the study does not address potential transport through follicles or injured skin. The combined cell and tissue model approach used here is likely to provide an important methodology for assessing the risks for skin exposure to AgNW from consumer products.

Silver Nanowire Particle Reactivity with Human Monocyte-Derived Macrophage Cells: Intracellular Availability of Silver Governs Their Cytotoxicity

Silver nanowires (AgNWs) are increasingly being used in the production of optoelectronic devices, with manufacturing processes posing a risk for occupational exposures via inhalation. Although some studies have explored the environmental effects of AgNWs, few data exist on human health effects. Alveolar macrophages are central in the clearance of inhaled fibers from the lungs, with frustrated phagocytosis often stated as a key determinant for the onset of inflammatory reactions. However, the mechanisms through which fully ingested AgNWs interact with, degrade, and transform within primary macrophages over time, and whether the reactivity of the AgNWs arises due to ionic or particulate effects, or both, are poorly understood. Here, a combination of elemental quantification, 3D tomography, analytical transmission electron microscopy (TEM), and confocal microscopy were employed to monitor the uptake, intracellular Ag⁺ availability, and processing of AgNWs of two different lengths (1 and 10 μm) inside human monocyte-derived macrophages (HMMs). Using AgNO₃ and spherical silver nanoparticles (AgNPs) as a comparison, the amount of total bioavailable/intracellular Ag highly correlated to the cytotoxicity of AgNWs. The 10 μm AgNWs were completely internalized in HMMs, with numerous lysosomal vesicles observed in close vicinity to the AgNWs. Following cellular uptake, AgNWs dissolved and transformed intracellularly, with precipitation of AgCl as well as Ag₂S. These transformation processes were likely due to AgNW degradation in the acidic environment of lysosomes, leading to the release of Ag⁺ ions that rapidly react with Cl^- and SH^- species of the cell microenvironment. Our data suggest that, in HMMs, not only frustrated phagocytosis but also the extent of intracellular uptake and dissolution of AgNWs dictates their cytotoxicity.

Inactivation, Clearance, and Functional Effects of Lung-Instilled Short and Long Silver Nanowires in Rats

There is a potential for silver nanowires (AgNWs) to be inhaled, but there is little information on their health effects and their chemical transformation inside the lungs in vivo. We studied the effects of short (S-AgNWs; 1.5 μm) and long (L-AgNWs; 10 μm) nanowires instilled into the lungs of Sprague-Dawley rats. S- and L-AgNWs were phagocytosed and degraded by macrophages; there was no frustrated phagocytosis. Interestingly, both AgNWs were internalized in alveolar epithelial cells, with precipitation of Ag₂S on their surface as secondary Ag₂S nanoparticles. Quantitative serial block face three-dimensional scanning electron microscopy showed a small, but significant, reduction of NW lengths inside alveolar epithelial cells. AgNWs were also present in the lung subpleural space where L-AgNWs exposure resulted in more Ag+ve macrophages situated within the pleura and subpleural alveoli, compared with the S-AgNWs exposure. For both AgNWs, there was lung inflammation at day 1, disappearing by day 21, but in bronchoalveolar lavage fluid (BALF), L-AgNWs caused a delayed neutrophilic and macrophagic inflammation, while S-AgNWs caused only acute transient neutrophilia. Surfactant protein D (SP-D) levels in BALF increased after S- and L-AgNWs exposure at day 7. L-AgNWs induced MIP-1α and S-AgNWs induced IL-18 at day 1. Large airway bronchial responsiveness to acetylcholine increased following L-AgNWs, but not S-AgNWs, exposure. The attenuated response to AgNW instillation may be due to silver inactivation after precipitation of Ag₂S with limited dissolution. Our findings have important consequences for the safety of silver-based technologies to human health.

Anodically Grown Titania Nanotube Induced Cytotoxicity has Genotoxic Origins

Nanoarchitectures of titania (TiO₂) have been widely investigated for a number of medical applications including implants and drug delivery. Although titania is extensively used in the food, drug and cosmetic industries, biocompatibility of nanoscale titania is still under careful scrutiny due to the conflicting reports on its interaction with cellular matter. For an accurate insight, we performed in vitro studies on the response of human dermal fibroblast cells toward pristine titania nanotubes fabricated by anodic oxidation. The nanotubes at low concentrations were seen to induce toxicity to the cells, whereas at higher concentrations the cell vitality remained on par with controls. Further investigations revealed an increase in the G₀ phase cell population depicting that majority of cells were in the resting rather than active phase. Though the mitochondrial set-up did not exhibit any signs of stress, significantly enhanced reactive oxygen species production in the nuclear compartment was noted. The TiO₂ nanotubes were believed to have gained access to the nuclear machinery and caused increased stress leading to genotoxicity. This interesting property of the nanotubes could be utilized to kill cancer cells, especially if the nanotubes are functionalized for a specific target, thus eliminating the need for any chemotherapeutic agents.

Assessment of Human Exposure to ENMs

Human exposure assessment of engineered nanomaterials (ENMs) is hampered, among other factors, by the difficulty to differentiate ENM from other nanomaterials (incidental to processes or naturally occurring) and the lack of a single metric that can be used for health risk assessment. It is important that the exposure assessment is carried out throughout the entire life-cycle as releases can occur at the different stages of the product life-cycle, from the synthesis, manufacture of the nano-enable product (occupational exposure) to the professional and consumer use of nano-enabled product (consumer exposure) and at the end of life.Occupational exposure surveys should follow a tiered approach, increasing in complexity in terms of instruments used and sampling strategy applied with higher tiers in order tailor the exposure assessment to the specific materials used and workplace exposure scenarios and to reduce uncertainty in assessment of exposure. Assessment of consumer exposure and of releases from end-of-life processes currently relies on release testing of nano-enabled products in laboratory settings.

Metallic Nanowire-Based Transparent Electrodes for Next Generation Flexible Devices: a Review

Transparent electrodes attract intense attention in many technological fields, including optoelectronic devices, transparent film heaters and electromagnetic applications. New generation transparent electrodes are expected to have three main physical properties: high electrical conductivity, high transparency and mechanical flexibility. The most efficient and widely used transparent conducting material is currently indium tin oxide (ITO). However the scarcity of indium associated with ITO's lack of flexibility and the relatively high manufacturing costs have a prompted search into alternative materials. With their outstanding physical properties, metallic nanowire (MNW)-based percolating networks appear to be one of the most promising alternatives to ITO. They also have several other advantages, such as solution-based processing, and are compatible with large area deposition techniques. Estimations of cost of the technology are lower, in particular thanks to the small quantities of nanomaterials needed to reach industrial performance criteria. The present review investigates recent progress on the main applications reported for MNW networks of any sort (silver, copper, gold, core-shell nanowires) and points out some of the most impressive outcomes. Insights into processing MNW into high-performance transparent conducting thin films are also discussed according to each specific application. Finally, strategies for improving both their stability and integration into real devices are presented.

Translocation of 40 nm diameter nanowires through the intestinal epithelium of Daphnia magna

Nanowires (NWs) have unique electrical and optical properties of value for many applications including lighting, sensing, and energy harnessing. Consumer products containing NWs increase the risk of NWs being released in the environment, especially into aquatic ecosystems through sewage systems. Daphnia magna is a common, cosmopolitan freshwater organism sensitive to toxicity tests and represents a likely entry point for nanoparticles into food webs of aquatic ecosystems. Here we have evaluated the effect of NW diameter on the gut penetrance of NWs in Daphnia magna. The animals were exposed to NWs of two diameters (40 and 80 nm) and similar length (3.6 and 3.8 μm, respectively) suspended in water. In order to locate the NWs in Daphnia, the NWs were designed to comprise one inherently fluorescent segment of gallium indium phosphide (GaInP) flanked by a gallium phosphide (GaP) segment. Daphnia mortality was assessed directly after 24 h of exposure and 7 days after exposure. Translocation of NWs across the intestinal epithelium was investigated using confocal fluorescence microscopy directly after 24 h of exposure and was observed in 89% of Daphnia exposed to 40 nm NWs and in 11% of Daphnia exposed to 80 nm NWs. A high degree of fragmentation was observed for NWs of both diameters after ingestion by the Daphnia, although 40 nm NWs were fragmented to a greater extent, which could possibly facilitate translocation across the intestinal epithelium. Our results show that the feeding behavior of animals may enhance the ability of NWs to penetrate biological barriers and that penetrance is governed by the NW diameter.

Static and Dynamic Microscopy of the Chemical Stability and Aggregation State of Silver Nanowires in Components of Murine Pulmonary Surfactant

The increase of production volumes of silver nanowires (AgNWs) and of consumer products incorporating them may lead to increased health risks from occupational and public exposures. There is currently limited information about the putative toxicity of AgNWs upon inhalation and incomplete understanding of the properties that control their bioreactivity. The lung lining fluid (LLF), which contains phospholipids and surfactant proteins, represents a first contact site with the respiratory system. In this work, the impact of dipalmitoylphosphatidylcholine (DPPC), Curosurf, and murine LLF on the stability of AgNWs was examined. Both the phospholipid and protein components of the LLF modified the dissolution kinetics of AgNWs, due to the formation of a lipid corona or aggregation of the AgNWs. Moreover, the hydrophilic proteins, but neither the hydrophobic surfactant proteins nor the phospholipids, induced agglomeration of the AgNWs. Finally, the generation of a secondary population of nanosilver was observed and attributed to the reduction of Ag(+) ions by the surface capping of the AgNWs. Our findings highlight that combinations of spatially resolved dynamic and static techniques are required to develop a holistic understanding of which parameters govern AgNW behavior at the point of exposure and to accurately predict their risks on human health and the environment.

Response-metrics for acute lung inflammation pattern by cobalt-based nanoparticles

Background

Although the surface area metric has been proposed as a possible dose-metric for nanoparticles (NPs), it is limited to low-solubility NPs and the dose-metric for high-solubility NPs is poorly understood. In this study, we aimed to assess the appropriate dose-metric or response-metric for NPs using two cobalt (Co)-based NPs, cobalt monoxide (CoO) and cobalt oxide (Co₃O₄), which both show distinctive solubility, and determine the role of their soluble Co ions in inflammation.

Methods

We evaluated the physicochemical properties of NPs, including solubility in artificial lysosomal fluid (ALF, pH 5.5). Acute lung inflammogenicity was evaluated by bronchoalveolar lavage fluid analysis using the rat intratracheal instillation model. The appropriate response-metric was then determined by plotting several dose-metrics against parameters for lung inflammation. To investigate the effect of the soluble fraction of CoO NPs, the equivalent doses of Co ions from CoCl₂ were instilled.

Results

The Co₃O₄ and CoO NPs showed about 11.46 % and 92.65 % solubility in ALF, respectively. Instillation of Co₃O₄ NPs produced neutrophilic inflammation, but CoO NPs induced eosinophilic inflammation. The number of eosinophils showed good correlation with the soluble Co ions dose from NPs (r² = 0.987, p <0.001), while the number of neutrophils showed good correlation with the surface area dose of the biopersistent NPs (r² = 0.876, p <0.001). Instillation of CoCl₂ showed a similar type and magnitude of inflammation as CoO NPs.

Conclusions

In the Co-based NPs, the eosinophilic inflammation was produced by Co ions based on the ion metric, while the neutrophilic inflammation was developed based on the surface area metric of the biopersistent NPs.