Search Results (15)

Many kinds of silicones are a wide family of hybrid inorganic–organic polymers which have valuable physical and chemical properties and find plenty of practical applications, not only industrial, but also numerous medical and pharmaceutical ones, mainly due to their good thermal and chemical stability, hydrophobicity, low surface tension, biocompatibility, and bio-durability. The important biomedical applications of silicones include drains, shunts, and catheters, used for medical treatment and short-term implants; inserts and implants to replace various body parts; treatment, assembly, and coating of various medical devices; breast and aesthetic implants; specialty contact lenses; and components of cosmetics, drugs, and drug delivery systems. The most important achievements concerning the biomedical and pharmaceutical applications of silicones, their copolymers and blends, and also silanes and low-molecular-weight siloxanes have been summarized and updated. The main physiological properties of organosilicon compounds and silicones, and the methods of antimicrobial protection of silicone implants, have also been described and discussed. The toxicity of silicones, the negative effects of breast implants, and the environmental effects of silicone-containing personal care and cosmetic products have been reported and analyzed. Important examples of the 3D printing of silicone elastomers for biomedical applications have been presented as well. Full article

The aim to reduce health risks of workers related to inhalative exposure to potentially toxic dusts requires the selection of appropriate measures depending on the hazard classification of the dust-composing materials. Due to their biodurability, respirable carbon fibers and their fragments can impose such health risks but are currently lacking hazard classification. Here, a method is presented for fragmenting carbon fiber materials and enriching fibrous fragments to a level that is expected to allow differentiating between fiber and particle overload-related toxic effects. The method was applied to a commercial polyacrylonitrile-based carbon fiber. It was ground in an oscillating ball mill, homogenized in a liquid using ultrasonication and left undisturbed for gravitational settling. This way, a vertical gradient in particle size and shape formed, from which the supernatant was collected. Fragment morphologies were characterized with large ensemble statistics by semi-automated evaluation of scanning electron microscopy images employing an artificial neural network for binary semantic segmentation. The number of fibrous fragments of respirable and thus critical fiber morphology was increased from $0.36\times {10}^6$ to $6\times {10}^6$ WHO-analog fibers per mg. This corresponds to a factor of about 15 compared to the initial ground material. Since the mass percentage of non-fibrous objects was also significantly reduced, the requirements for a subsequently scheduled toxicological study with intraperitoneal application were fulfilled. Intraperitoneal testing is an accepted method for assessing the carcinogenic potential of biopersistent fibers. The developed method allows enriching fibrous fractions of concern at acceptable throughput and enables testing fiber toxicological effects of respirable fragments from disintegrated polyacrylonitrile-based carbon fibers. Full article

Although linseed oil (LO) has been used in wood protection for centuries, research continues to develop new and more effective formulations and treatment approaches. In the future, growing interest in LO use could be expected due to its cost and environmental friendliness. This review summarizes recent research (from 2000 onwards) on the use of LO in wood protection, published in peer-reviewed scientific journals and included in the online publication databases Scopus or Web of Science. The studies cover surface and impregnation treatments of various wood substrates using different LO formulations, including chemically modified LO and the use of LO as a base for the development of biofinish and as a medium for thermal modification of wood, as well as research into the mechanisms behind the changes in wood properties due to treatment methods and interaction with LO formulations. Although the improvement of wood hydrophobicity and biodurability dominates, other aspects such as weathering and color stability, adhesion, and environmental safety are included in these studies. In general, almost all of the studies show a greater or lesser potency of the proposed approaches to provide benefits in wood protection; however, the level of innovation and practical feasibility varies. Full article

This study focuses on the dissolution process and surface characterization of amosite fibres following interaction with a mimicked Gamble’s solution at a pH of 4.5 and T = 37 °C, up to 720 h. To achieve this, a multi-analytical approach was adopted, and the results were compared to those previously obtained on a sample of asbestos tremolite and UICC crocidolite, which were investigated under the same experimental conditions. Combining surface chemical data obtained by XPS with cation release quantified by ICP-OES, an incongruent behaviour of the fibre dissolution was highlighted for amosite fibres, similarly to asbestos tremolite and UICC crocidolite. In particular, a preferential release of Mg and Ca from the amphibole structure was observed, in agreement with their Madelung site energies. Notably, no Fe release from amosite fibres was detected in our experimental conditions (pH of 4.5 and atmospheric pO₂), despite the occurrence of Fe(II) at the M(4) site of the amphibole structure, where cations are expected to be rapidly leached out during mineral dissolution. Moreover, the oxidation of both the Fe centres initially present on the fibre surface and those promoted from the bulk, because of the erosion of the outmost layers, was observed. Since biodurability (i.e., the resistance to dissolution) is one of the most important toxicity parameters, the knowledge of the surface alteration of asbestos possibly occurring in vivo may help to understand the mechanisms at the basis of its long-term toxicity. Full article

Derelict asbestos mine sites in South Africa pose a considerable risk to human, environmental and socio-economic health. Comprehensive mineralogical and geochemical datasets for the existing hazardous geological materials still exposed in Southern African derelict asbestos mines remain largely non-existent, as very little published and up-to-date literature is available. In this study, three representative types of asbestos mineral fibres from derelict asbestos mines in Southern Africa, namely chrysotile from Havelock mine, amosite from Penge mine and crocidolite from Prieska mine, are characterized mineralogically and geochemically to critically evaluate actual hazards in rural and asbestos-fibre-contaminated regions. The samples were examined using polarising light microscopy, X-ray fluorescence (major and trace elemental analysis), X-ray diffraction (including Rietveld refinement), specific surface area analysis and bio-durability testing. Data are discussed in view of their potential toxicities on both human health and the environment in the context of developing countries. Finally, information on the mineralogical and geochemical status of asbestos mine waste and its importance as baseline data for rehabilitation considerations is also evaluated. Full article

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative. Full article

The potential for nanoparticles to cause harm to human health and the environment is correlated with their biodurability in the human body and persistence in the environment. Dissolution testing serves to predict biodurability and nanoparticle environmental persistence. In this study, dissolution testing using the continuous flow through system was used to investigate the biodurability and persistence of gold nanoparticles (AuNPs), silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO₂ NPs) in five different simulated biological fluids and two synthetic environmental media to predict their behaviour in real life situations. This study examined the physicochemical properties and agglomeration state of gold, silver and titanium dioxide nanoparticles before and after dissolution tests using three different techniques (UV-vis, XRD and TEM). The UV-vis spectra revealed that all three nanoparticles shifted to higher wavelengths after being exposed to simulated fluids. The titanium powder was found to be mixed with both rutile and anatase, according to XRD examination. The average diameter of gold nanoparticles was 14 nm, silver nanoparticles were 10 nm and titanium dioxide nanoparticles were 25 nm, according to TEM images. The gold and silver nanoparticles were observed to be spherical, but the titanium dioxide nanoparticles were irregular in shape, with some being spherical. The level of dissolved nanoparticles in simulated acidic media was higher in magnitude compared to that dissolved in simulated alkaline media. The results obtained via the continuous flow through dissolution system also displayed very significant dissolution rates. For TiO₂ NPs the calculated half-times were in the range of 13–14 days, followed by AuNPs ranging between 4–12 days, significantly longer if compared to the half-times of AgNPs ranging between 2–7 days. AuNPs and TiO₂ NPs were characterized by low dissolution rates therefore are expected to be (bio)durable in physiological surroundings and persistent in the environment thus, they might impose long-term effects on humans and the environment. In contrast, AgNPs have high dissolution rates and not (bio)durable and hence may cause short-term effects. The results suggest a hierarchy of biodurability and persistence of TiO₂ NPs > AuNPs > AgNPs. It is recommended that nanoparticle product developers should follow the test guidelines stipulated by the OECD to ensure product safety for use before it is taken to the market. Full article

High-N Ni-free stainless steels are used for their excellent mechanical properties combined with their high corrosion resistance, especially for biomedical applications. Even though it is well-known that secondary hardening during annealing after cold working has been observed in many materials, this phenomenon was not reported for these materials, one of the best known being Biodur108©, although numerous efforts have been made to increase its hardness. In this work, thermomechanical treatments at low temperature of cold-deformed Biodur108© were conducted to increase the hardness. Hardness as high as 830 Hv was obtained. For this material, the annealing of a deformed sample at intermediate temperature leads to a secondary hardening phenomenon. The mechanisms responsible for this secondary hardening were analyzed. It was found that for deformed samples, annealing at 575 °C leads to the formation of small Cr₂N precipitates along grain boundaries and sub-grain boundaries, and simultaneously with a new body-centered cubic (BCC) phase that possesses a super structure. The newly formed phases have sub-micrometric grain sizes. Full article

Alveolar macrophages are the first line of defence against detrimental inhaled stimuli. To date, no comparative data have been obtained on the inflammatory response induced by different carcinogenic mineral fibres in the three main macrophage phenotypes: M0 (non-activated), M1 (pro-inflammatory) and M2 (alternatively activated). To gain new insights into the different toxicity mechanisms of carcinogenic mineral fibres, the acute effects of fibrous erionite, crocidolite and chrysotile in the three phenotypes obtained by THP-1 monocyte differentiation were investigated. The three mineral fibres apparently act by different toxicity mechanisms. Crocidolite seems to exert its toxic effects mostly as a result of its biodurability, ROS and cytokine production and DNA damage. Chrysotile, due to its low biodurability, displays toxic effects related to the release of toxic metals and the production of ROS and cytokines. Other mechanisms are involved in explaining the toxicity of biodurable fibrous erionite, which induces lower ROS and toxic metal release but exhibits a cation-exchange capacity able to alter the intracellular homeostasis of important cations. Concerning the differences among the three macrophage phenotypes, similar behaviour in the production of pro-inflammatory mediators was observed. The M2 phenotype, although known as a cell type recruited to mitigate the inflammatory state, in the case of asbestos fibres and erionite, serves to support the process by supplying pro-inflammatory mediators. Full article

Water-based antimicrobial agents, used in environmentally friendly applications, are widely used in wood protection industries. Furthermore, nanomaterials as antimicrobial agents, because of their biocidal component, huge specific surface area, and unique nanoscale effect, have attracted attention in the field of biodurability. We employed aqueous dispersed nano-silver with a diameter of 10 nm~20 nm to treat poplar wood and evaluated its leaching resistance and anti-mold effect on the wood surface. The results revealed that the higher the retention of the nano-silver, the stronger the protection efficiency of the wood surface against three molds (Aspergillus niger V. Tiegh, Penicillium citrinum Thom, and Trichoderma viride Pers. ex Fr); and the leachability of the nano-silver presented a slowly growing trend with the increase in the retention. When the wood surface attained a silver retention of 0.324 g·m⁻², its anti-mold efficiency against Aspergillus niger V. Tiegh, Penicillium citrinum Thom, and Trichoderma viride Pers. ex Fr reached 80, 75, and 80%, respectively, which achieved or even exceeded the required standard value of effective mold inhibition (75%). Notably, the nano-silver leaching rate at this retention attained merely 4.75 %. The nanoparticle, well distributed on a wood surface, may promote sufficient contact with fungi as well as strong interaction with wood cell wall components, which probably contributed to the effective anti-mold efficiency and the leaching resistance. This study provided positive evidence for the anti-mold effect of nano-silver on wood surface. Full article

Today, despite considerable efforts undertaken by the scientific community, the mechanisms of carcinogenesis of mineral fibres remain poorly understood. A crucial role in disclosing the mechanisms of action of mineral fibres is played by in vitro and in vivo models. Such models require experimental design based on negative and positive controls. Commonly used positive controls are amosite and crocidolite UICC standards, while negative controls have not been identified so far. The extensive characterisation and assessment of toxicity/pathogenicity potential carried out in this work indicate that the commercial fibrous wollastonite NYAD G may be considered as a negative standard control for biological and biomedical tests involving mineral fibres. Preliminary in vitro tests suggest that wollastonite NYAD G is not genotoxic. This material is nearly pure and is characterized by very long (46.6 µm), thick (3.74 µm) and non-biodurable fibres with a low content of metals. According to the fibre potential toxicity index (FPTI) model, wollastonite NYAD G is an inert mineral fibre that is expected to exert a low biological response during in vitro/in vivo testing. Full article

The risk assessment of ingested nanomaterials (NMs) is an important issue. Here we present nine integrated approaches to testing and assessment (IATAs) to group ingested NMs following predefined hypotheses. The IATAs are structured as decision trees and tiered testing strategies for each decision node to support a grouping decision. Implications (e.g., regulatory or precautionary) per group are indicated. IATAs integrate information on durability and biopersistence (dissolution kinetics) to specific hazard endpoints, e.g., inflammation and genotoxicity, which are possibly indicative of toxicity. Based on IATAs, groups of similar nanoforms (NFs) of a NM can be formed, such as very slow dissolving, highly biopersistent and systemically toxic NFs. Reference NMs (ZnO, SiO₂ and TiO₂) along with related NFs are applied as case studies to testing the oral IATAs. Results based on the Tier 1 level suggest a hierarchy of biodurability and biopersistence of TiO₂ > SiO₂ > ZnO, and are confirmed by in vivo data (Tier 3 level). Interestingly, our analysis suggests that TiO₂ and SiO₂ NFs are able to induce both local and systemic toxicity along with microbiota dysbiosis and can be grouped according to the tested fate and hazard descriptors. This supports that the decision nodes of the oral IATAs are suitable for classification and assessment of the toxicity of NFs. Full article

This study aimed at investigating both the surface and bulk modifications occurring on fibrous erionite during leaching in a mimicked Gamble’s solution (MGS) at pH of 4.5 and T = 37 °C, up to one month of incubation. Samples were characterized by a multi-analytical approach: field-emission scanning electron microscopy (FE-SEM) was employed to investigate the morphological changes of both pristine and reacted fibres, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to measure the concentration of the released cations; X-ray photoelectron spectroscopy (XPS) was exploited for highlighting possible modifications of surface chemistry; X-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HR-TEM) were applied aiming to get information on the structural state of the fibres following the incubation. ICP results integrated with those obtained by both bulk- and surface-chemical characterization highlighted that erionite binds Na especially in the first 24 h of sample incubation in the MGS, following ion exchange with the extra framework cations, in particular Ca. Moreover, our new results show that the Na binding process caused structural modifications with the migration of Na toward the Ca2 site and redistribution of the cations within the erionite cage. TEM investigation pointed out that the interaction between erionite and MGS results in the formation of a new surface amorphous layer with an irregular lobate pattern on an earlier surface weathered layer. However, the silicate framework is not weakened by incubation in the MGS at acidic pH. In addition, on the basis of the Si release normalized to the mineral surface area, fibrous erionite resulted significantly more biodurable than amphibole asbestos. Notably, considering the primary role played by biodurability in inducing pathogenicity, this result certainly supports in vivo observations showing that erionite is much more tumorigenic than asbestos. Moreover, the ions released by erionite when immersed in MGS may trigger biological effects, such as those on lipid packing and membrane permeability. On this basis, we expect a regulatory definition that would provide protection from this carcinogenic fibre. Full article

Despite compelling reports on asbestos-like pathogenicity, regulatory bodies have been hesitant to implement fiber number-based exposure limits for biodurable nanoscale fibers. One reason has been the lack of a practicable strategy for assessing airborne fiber number concentrations. Here, a method is proposed, detailed and tested for compliance checking concentrations of airborne nano- and microscale fibers. It relies on Poisson statistical significance testing of the observed versus a predicted number of fibers on filters that have sampled a known volume of aerosol. The prediction is based on the exposure concentration to test. Analogous to the established counting rules for WHO-fibers, which use a phase contrast microscopy-related visibility criterion of 200 nm, the new method also introduces a cut-off diameter, now at 20 nm, which is motivated by toxicological findings on multi-walled carbon nanotubes. This cut-off already reduces the workload by a factor of 400 compared to that necessary for imaging, detecting and counting nanofibers down to 1 nm in diameter. Together with waiving any attempt to absolutely quantify fiber concentrations, a compliance check at the limit-of-detection results in an analytical workload that renders our new approach practicable. The proposed method was applied to compliance checking in 14 very different workplaces that handled or machined nanofiber-containing materials. It achieved detecting violations of the German benchmark exposure level of 10,000 nanofibers per cubic meter. Full article

In nature, a huge number of unregulated minerals fibers share the same characteristics as asbestos and therefore have potential adverse health effects. However, in addition to asbestos minerals, only fluoro-edenite and erionite are currently classified as toxic/pathogenic agents by the International Agency for Research on Cancer (IARC). Mordenite is one of the most abundant zeolites in nature and commonly occurs with a fibrous crystalline habit. The goal of this paper is to highlight how fibrous mordenite shares several common features with the well-known carcinogenic fibrous erionite. In particular, this study has shown that the morphology, biodurability, and surface characteristics of mordenite fibers are similar to those of erionite and asbestos. These properties make fibrous mordenite potentially toxic and exposure to its fibers can be associated with deadly diseases such as those associated with regulated mineral fibers. Since the presence of fibrous mordenite concerns widespread geological formations, this mineral fiber should be considered dangerous for health and the precautionary approach should be applied when this material is handled. Future in vitro and in vivo tests are necessary to provide further experimental confirmation of the outcome of this work. Full article