Material extrusion 3D printing has been widely used in industrial, educational and residential environments, while its exposure health impacts have not been well understood. High levels of ultrafine particles are found being emitted from 3D printing and could pose a hazard when inhaled. However, metals that potentially transfer from filament additives to emitted particles could also add to the exposure hazard, which have not been well characterized for their emissions. This study analyzed metal (and metalloid) compositions of raw filaments and in the emitted particles during printing; studied filaments included pure polymer filaments with metal additives and composite filaments with and without metal powder. Our chamber study found that crustal metals tended to have higher partitioning factors from filaments to emitted particles; silicon was the most abundant element in emitted particles and had the highest yield per filament mass. However, bronze and stainless-steel powder added in composite filaments were less likely to transfer from filament to particle. For some cases, boron, arsenic, manganese, and lead were only detected in particles, which indicated external sources, such as the printers themselves. Heavy metals with health concerns were also detected in emitted particles, while their estimated exposure concentrations in indoor air were below air quality standards and occupational regulations. However, total particle exposure concentrations estimated for indoor environments could exceed ambient air fine particulate standards.

Manufacturing advancements in polymer printing now allow for the addition of metal additives to thermoplastic feedstock up to 80-90 % by weight and subsequent printing on low-cost desktop 3D printers. Particles associated with metal additives are not chemically bound to the plastic polymer, meaning these particles can potentially migrate and become bioavailable. This study investigated the degree to which two human exposure pathways, oral (ingestion) and dermal (skin contact), are important exposure pathways for metals (copper, chromium, and tin) from metal-fill thermoplastics used in consumer fused filament fabrication (FFF). We found that dermal exposure to copper and bronze filaments presents the highest exposure risk due to chloride (Cl-) in synthetic sweat driving copper (Cu2+) release and dissolution. Chromium and tin were released as micron-sized particles < 24 μm in diameter with low bioaccessibility during simulated oral and dermal exposure scenarios, with potential to undergo dissolution in the gastrointestinal tract based on testing using synthetic stomach fluids. The rate of metal particle release increased by one to two orders of magnitude when thermoplastics were degraded under 1 year of simulated UV weathering. This calls into question the long-term suitability of biodegradable polymers such as PLA for use in metal-fill thermoplastics if they are designed not to be sintered. The greatest exposure risk appears to be from the raw filaments rather than the printed forms, with the former having higher metal release rates in water and synthetic body fluids for all but one filament type. For brittle feedstock that requires greater handling, as metal-fill thermoplastics can be, practices common in metal powder 3D printing such as wearing gloves and washing hands may adequately reduce metal exposure risks.

Surface coatings, including paints, stains, and sealants, have recently become a focus of “nano-enabled” consumer product engineering. Specifically, zinc oxide (ZnO) nanoparticles (NPs) have been introduced to surface coatings to increase UV resistance. As more “nano-enabled” products are made available for purchase, questions arise regarding their long-term environmental and human health effects. This study tracked the transformation of NP additives commonly added to consumer paints and stains using ZnO NPs as a model system. During product application and use, there is a risk of inhalation of aerosolized ZnO NPs. To investigate the potential chemical interactions and transformations that would occur after inhalation, ZnO NPs were incubated in two synthetic lung fluids (SLFs). Initial studies utilized ZnO NPs dispersed in Milli-Q water (control), or a commercially available deck stain. Additionally, two commercially available products advertising the inclusion of ZnO NP additives were evaluated. Subsamples were taken throughout incubation and analyzed via atomic absorption spectroscopy to determine both the total (including particulate) zinc concentration and dissolved (non-particulate) zinc concentration. Results indicate that the vast majority of ZnO transformation takes place within the first 24 h of incubation and is primarily driven by SLF pH and composition complexity. Significant dissolution of ZnO NPs was observed when incubated in Gamble’s solution (between 25 and 68% depending on the matrix. Additionally, all ZnO solutions saw near immediate dissolution (~ 98–100%) within 3 h of incubation in artificial lysosomal fluid. Results illustrate potential for NPs in consumer products to undergo significant transformation during use and exposure over short time periods.

Complexes consisting of earth-abundant main group metals such as silicon with polypyridine ligands are of interest for a variety of optical and electronic applications including as electrochromic colorants. Previous spectroelectrochemical studies with tris(2,2′-bipyridyl)silicon(IV) hexafluorophosphate, [Si(bpy)3](PF6)4, demonstrated an ability to control the color saturation of the potential electrochromic dye, with the intensity of the dye’s green color increasing as the charge state sequentially reduces from 4+ to 1+. In this study, the synthesis of bis(4′-(4-tolyl)-2,2′:6′,2″-terpyridine)silicon(IV) hexafluorophosphate, [Si(ttpy)2](PF6)4, is reported along with electrochemical and spectroelectrochemical analyses. Computational modeling (density functional theory) is used to further elucidate the electrochromic properties of previously reported Si(bpy)3n+ species and the new Si(ttpy)2n+ species. While the homoleptic tris(bidentate)silicon(IV) complexes are attractive as electrochromic dyes for tunable color saturation, the bis(tridentate)silicon(IV) complexes are attractive as polychromatic electrochromic dyes.

Fused filament fabrication is a 3D printing technique that has gained widespread use from homes to schools to workplaces. Thermoplastic filaments, such as acrylonitrile-butadiene-styrene (ABS) and polylactic acid (PLA), are extruded at temperatures near their respective glass transition temperature or melting point, respectively. Little has been reported on the inorganic elemental composition and concentrations present in these materials or the methods available for extracting that information. Because inorganic constituents may be included in the aerosolized particulates emitted during the printing process, identifying elements that could be present and at what specific concentrations is critical. The objective of the current research is to determine the range of metals present in thermoplastic filaments along with their relative abundance and chemical speciation as a function of polymer type, manufacturer, and color. A variety of filaments from select manufacturers were digested using a range of techniques to determine the optimal conditions for metal extraction from ABS and PLA polymers. The extraction potential for each method was quantified using by ICP-MS analysis. When possible, further characterization of the chemical composition of the filaments was investigated using X-ray Absorption spectroscopy to determine chemical speciation of the metal. Optimal digestion conditions were established using a high temperature, high pressure microwave-assisted acid digestion method to produce the most complete and repeatable extraction results. The composition and abundance of metals in the filaments varied greatly as a function of polymer, manufacturer, and color. Potential elements of concern present in the filaments at elevated concentration included that could pose a respiratory risk included Si, Al, Ti, Cu, Zn, and Sn. XAS analysis revealed a mixture of metal oxides, mineral, and organometallic compounds were present in the filaments that were being used to increase opaqueness impart color (dyes), polymeric catalysts, and flame retardants. This work shows that a variety of metals are present in the starting materials used for 3D printing and depending on their partitioning into 3D printed products and byproducts as well as the exposure route, may pose a health risk which merits further investigation.

Nanotoxicology research commonly utilizes pristine nanomaterials for toxicity assessment, which may not be perfectly representative of what is released into environmental systems. The goal of the present study was to develop a method to simulate human weathering of silver-containing textiles. To achieve this goal the roles of physical and chemical stress on X-Static® containing athletic textiles were investigated and compared to data collected from human weathering experiments and literature. Chemical weathering methods (artificial sweat) were used independently and alongside physical weathering methods (3D printed stretching and abrasion instruments). Non-weathered control textiles were found to release 29 ± 11 mg Ag/kg of textile into wash water effluent (ICP-MS), with 16% being released as ionic silver (ICP-MS) and the rest as metallic nanomaterials, nanosheets, and particulates of varying size (SEM/XANES). Real and simulated human weathered textiles released similar amounts of total silver (67 ± 11 mg Ag/kg, 84 ± 13 mg Ag/kg respectively) with the silver released being composed of ionic (1.5%, 2%) and a mixture of metallic and chlorinated nanomaterials, nanosheets, and particulates. The method was shown to effectively detach environmentally representative silver materials from silver-containing textiles and can provide such materials for future studies on the assessment of their fate, transport, and toxicity.

Research presented here utilizes silver nanoparticles (AgNPs) as a case study for how the immediate local environment alters the physical and chemical properties of nanomaterials. Dermal exposure is a primary route for exposure to many of the consumer products containing AgNPs. Interactions between AgNPs and human sweat/perspiration are critical for understanding how changes in Ag speciation will impact exposure. Previous studies have examined silver release from AgNP-containing products after exposure to artificial sweat (AS), however there is no basic assessment of how mixtures of AgNPs and AS alter the physical and chemical properties of AgNPs. The current research evaluated changes in size, aggregation, chemical composition, and silver speciation of four different sizes of AgNPs exposed to four different formulations of AS. The AS formulations were from standardized methods with different chemical compositions, ionic strengths, and pH. Samples were collected at four-time intervals for analysis using dynamic light scattering , UV-Vis spectroscopy, and single-particle inductively coupled plasma-mass spectrometry . Each mixture was also prepared for speciation analysis using X-ray absorption spectroscopy and scanning electron microscopy coupled to energy-dispersive X-ray analysis. The equivalent diameter measurements from the three techniques followed the order of DLS > UV-Vis > spICP-MS. Speciation analyses indicate significant changes for the smaller NPs, while the largest (100 nm) NPs had less measurable differences. This study shows the need to fully understand what specific information an analytical technique might provide and to use those techniques properly in tandem to give the fullest answer to a given research question. Published by Elsevier Ltd.

As the market for “nano-enabled” products (NEPs) continues to expand in commercial and industrial applications, there is a critical need to understand conditions that promote release of nanomaterials and their degradation products from NEPs. Moreover, these studies must aim to quantify both the abundance and form (aggregates, ions, hybrids, etc.) of material released from NEPs to produce reasonable estimates of human and environmental exposure. In this work ZnO nanoparticles (NPs), a common additive in NEP surface coatings, were dispersed in Milli-Q water and a commercially available wood stain before application to pristine and weathered (outdoor 1 year) micronized copper azole pressure treated lumber (MCA). Coated lumber surfaces were sampled consecutively eight times using a method developed by the Consumer Product Safety Commission (CPSC) to track potential human exposure to ZnO NPs and byproducts through simulated dermal contact. Surprisingly, the highest total release of Zn was observed from aged lumber coated with ZnO NPs dispersed in wood stain, releasing 233 ± 26 mg Zn/m2 over the course of all sampling events. Alternatively, separate leaching experiments using a synthetic precipitation solution to simulate environmental release found aged lumber released significantly less Zn than pristine lumber when using the same coating formulation. Zinc speciation analysis also demonstrates that transformation of crystalline ZnO to Zn-organic complexes shortly after application to aged lumber. Regardless of experimental treatment, the majority of applied zinc (>75%) remains on the MCA surface. Finally, this work highlights how the nature of the screening technique (dermal contact vs. leaching) may result in different interpretations of exposure and risk.

Abstract Objective: Fused filament fabrication “3-dimensional (3-D)” printing has expanded beyond the workplace to 3-D printers and pens for use by children as toys to create objects. Materials and methods: Emissions from two brands of toy 3-D pens and one brand of toy 3-D printer were characterized in a 0.6 m3 chamber (particle number, size, elemental composition; concentrations of individual and total volatile organic compounds (TVOC)). The effects of print parameters on these emission metrics were evaluated using mixed-effects models. Emissions data were used to model particle lung deposition and TVOC exposure potential. Results: Geometric mean particle yields (106–1010 particles/g printed) and sizes (30–300 nm) and TVOC yields (<detectable to 590 µg TVOC/g printed) for the toys were similar to those from 3-D printers used in workplaces. Metal emissions included manganese (1.6–92.3 ng/g printed) and lead (0.13–1.2 ng/g printed). Among toys, extruder nozzle conditions (diameter, temperature) and filament (type, color, and extrusion speed) significantly influenced particle and TVOC emissions. Dose modeling indicated that emitted particles would deposit in the lung alveoli of children. Exposure modeling indicated that TVOC concentration from use of a single toy would be 1–31 µg/m3 in a classroom and 3–154 µg/m3 in a residential living room. Discussion: Potential exists for inhalation of organic vapors and metal-containing particles during use of these toys. Conclusions: If deemed appropriate, e.g. where multiple toys are used in a poorly ventilated area or a toy is positioned near a child’s breathing zone, control technologies should be implemented to reduce emissions and exposure risk.

Abstract Little is known about emissions and exposure potential from vat polymerization additive manufacturing, a process that uses light-activated polymerization of a resin to build an object. Five vat polymerization printers (three stereolithography (SLA) and two digital light processing (DLP) were evaluated individually in a 12.85 m3 chamber. Aerosols (number, size) and total volatile organic compounds (TVOC) were measured using real-time monitors. Carbonyl vapors and particulate matter were collected for offline analysis using impingers and filters, respectively. During printing, particle emission yields (#/g printed) ranged from 1.3 ± 0.3 to 2.8 ± 2.6 x 108 (SLA printers) and from 3.3 ± 1.5 to 9.2 ± 3.0 x 108 (DLP printers). Yields for number of particles with sizes 5.6 to 560 nm (#/g printed) were 0.8 ± 0.1 to 2.1 ± 0.9 x 1010 and from 1.1 ± 0.3 to 4.0 ± 1.2 x 1010 for SLA and DLP printers, respectively. TVOC yield values (µg/g printed) ranged from 161 ± 47 to 322 ± 229 (SLA printers) and from 1281 ± 313 to 1931 ± 234 (DLP printers). Geometric mean mobility particle sizes were 41.1–45.1 nm for SLA printers and 15.3–28.8 nm for DLP printers. Mean particle and TVOC yields were statistically significantly higher and mean particle sizes were significantly smaller for DLP printers compared with SLA printers (p < 0.05). Energy dispersive X-ray analysis of individual particles qualitatively identified potential occupational carcinogens (chromium, nickel) as well as reactive metals implicated in generation of reactive oxygen species (iron, zinc). Lung deposition modeling indicates that about 15–37% of emitted particles would deposit in the pulmonary region (alveoli). Benzaldehyde (1.0–2.3 ppb) and acetone (0.7–18.0 ppb) were quantified in emissions from four of the printers and 4-oxopentanal (0.07 ppb) was detectable in the emissions from one printer. Vat polymerization printers emitted nanoscale particles that contained potential carcinogens, sensitizers, and reactive metals as well as carbonyl compound vapors. Differences in emissions between SLA and DLP printers indicate that the underlying technology is an important factor when considering exposure reduction strategies such as engineering controls.

At present, including failed attempts, it takes about 15 years and costs totaling up to $2.6 billion to take a promising new compound from laboratory to the market. Increasing drug resistance among microbial pathogens has led to a growing interest in exploring novel methods to enhance the efficacy of existing drugs. Combination therapies involving two or more known antimicrobial methods, particularly those involving nanoparticles for combating the clinical problems associated with antibiotic resistance, have been garnering interest. In the current study, we determined whether a combination therapy involving silver nanoparticles, which are known for their antimicrobial activity, and the widely used antibiotic ampicillin can be effective against methicillin-resistant Staphylococcus aureus (MRSA). In the presence of sub-lethal dose of silver nanoparticles, ampicillin was found to be effective against MRSA. Indeed, the results show that silver nanoparticles and ampicillin act synergistically, with the effect being more pronounced when a lower concentration of ampicillin is present. When present at a higher concentration, ampicillin coats the silver nanoparticle, preventing the direct interaction of nanoparticles and bacteria. This study discusses the possible applications of combination antimicrobial therapies involving silver nanoparticles for therapeutic treatments.

A silicon-bridged viologen has been synthesized by methylation of 4,4'-dipyridinodimethylsilole, and represents a new addition to the growing family of heteroatom bridged viologens. The dicationic species emits at 360 nm and exhibits two chemically reversible one electron reduction waves in acetonitrile at E-1/2(2+/1+) = -0.829 V and E-1/2(1+/0)= -1.307 V (versus Fc/Fc(+)). The UV-Vis spectrum for each of the three charge states is similar to the corresponding unbridged methyl viologen species. The silanoviologen is susceptible to ring-opening hydrolysis. (C) 2017 Elsevier Ltd. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The chemistry of hexacoordinate silicon complexes containing one or more pyridine-like ligands is reviewed. Pyridine-containing ligands are excellent ligands for stabilizing hexacoordinate silicon complexes, and over 100 hexacoordinate silicon complexes containing at least one pyridine-like ligand have been deposited with the Cambridge Structural Database. This review focuses on advances since 2000 and covers complexes with substituted pyridines, pyridine-2-thiolates, oxyquinolates, thioquinolates, iminoquinolates, bipyridines, phenanthrolines, and terpyridines. Emerging applications in fluorescence, high-energy materials, biology, and electrochromism are discussed. (C) 2016 Elsevier B.V. All rights reserved.

Tris(bipyridyl)silicon(iv) was electrochemically reduced in acetonitrile to obtain the UV-vis spectra of its reduced species. Three stable, reversible reduced states (3+, 2+, and 1+) were observed with distinct isosbestic points for each of the redox reactions. The fully oxidized state (4+) is colorless, while the reduced states were green. The absorbance spectra for the three reduced states are consistent with ligand localized reductions. Potential advantages of using these complexes in electrochromic applications are discussed.