Amorphous Silica Particles Research Articles

Relationship between size and surface modification of silica particles and enhancement and suppression of inflammatory cytokine production by lipopolysaccharide- or peptidoglycan-stimulated RAW264.7 macrophages

Although nanomaterials are used in an increasing number of commodities, the relationships between their immunotoxicity and physicochemical properties such as size or surface characteristics are not fully understood. Here we demonstrated that pretreatment with amorphous silica particles (SPs) of various sizes (diameters of 10–1000 nm), with or without amine surface modification, significantly decreased interleukin 6 production by RAW264.7 macrophages following lipopolysaccharide or peptidoglycan stimulation. Furthermore, nanosized, but not microsized, SPs significantly enhanced tumor necrosis factor-α production in macrophages stimulated with lipopolysaccharide. This altered cytokine response was distinct from the inflammatory responses induced by treatment with the SPs alone. Additionally, the uptake of SPs into macrophages by phagocytosis was found to be crucial for the suppression of macrophage immune response to occur, irrespective of particle size or surface modification. Together, these results suggest that SPs may not only increase susceptibility to microbial infection, but that they may also be potentially effective immunosuppressants.

Application of Hectorite-Coated Silica Gel Particles as a Packing Material for Chromatographic Resolution.

A new type of clay column particles was prepared, in which a hectorite layer (∼0.1 µm thickness) covered uniformly the surface of amorphous silica particles with an average radius of 5 µm (ref. Okada et al., The Journal of Physical Chemistry C, 116, 21864-21869 (2012)). The hectorite layer was fully ion-exchanged with Δ-[Ru(phen)3](2+) (phen = 1,10-phenanthroline) ions by being immersed in a methanol solution of Δ-[Ru(phen)3](ClO4)2 (1 mM). The modified silica gel particles thus prepared were packed into a stainless steel tube (4 mm (i.d.) × 25 cm) as a high-performance liquid chromatography column. Optical resolution was achieved when the racemic mixtures of several metal complexes or organic molecules were eluted with methanol. In the case of tris(acetylacetonato)ruthenium(III) ([Ru(acac)3]), for example, the Λ- and Δ-enantiomers gave an elution volume of 2.6 and 3.0 mL, respectively, with the separation factor of 1.2. The total elution volume (5 mL) was nearly one-tenth for the previously reported column of the same size (RU-1 (Shiseido Co., Ltd.)) packed with the spray-dried particles of synthetic hectorite (average radius 5 µm) ion-exchanged by the same Ru(II) complexes.

Mechanical Properties of Friction Stir Processed 1100 Aluminum Reinforced with Rice Husk Ash Silica at Different Rotational Speeds

This paper presents a study on friction stir processed 1100 aluminum withincorporation of rice huskash derived, amorphous silica particles and fabricated at different tool rotational speeds. During friction stirring amorphous silica powder was placed into a groove made in the joining line of Al 1100 plates. Friction stirringwas performed with clockwise tool rotational speeds of 600 rpm, 865 rpm, 1140 rpm or 1500 rpm with a constant 45 mm/min travelling speed and a 2° tilt angle. High rotational speed (1140 rpm) facilitated material flow in the stir zone, contributing to fine aluminum matrix grain size (30- 10μm) as a result of dynamic recrystallization. Stirring at this rotational speed also caused the fracturingrelated refinement of silica particles to 10μm particle sizethat isassociated with good distribution in the aluminum matrix. Reduction in wear rate of friction stir processed Al1100 with improved hardness was believed to be due to the presence of hard silicawith high interfacial strength and high hardness of recrystallized aluminum grains in the stir zone.

Analysis of Skin Permeability and Toxicological Properties of Amorphous Silica Particles.

Nanomaterials (NMs) are defined as those which have nanostructured components less than 100 nm in diameter. They are widely used in various fields such as medicine, cosmetics, and the food industry. However, the toxicological effects of NMs are less well understood than their applications. In particular, the skin is exposed to the environment at all times, so is easily influenced by NMs. In this study, we investigated the skin permeability and toxicological properties of well-dispersed amorphous silica particles with diameters ranging from 70 to 1000 nm, to aid in the safe application of NMs. Amorphous silica particles of 70 nm in size (nSP70) penetrated the living epidermis, following pretreatment with acetone/diethyl ether to improve skin permeation. The application of unmodified nSP70, carboxyl group-modified nSP70, or amino group-modified nSP70 for long durations caused little skin irritation at the application site. Under the present experimental conditions, few adverse systemic effects were evident from blood tests and histopathologic examination. These results suggest that decreasing particle size increases the NMs skin permeability, but remarkably little corresponding skin irritation is observed.

焼成籾殻中の脆性炭化物を利用した非晶質シリカ微粒子の生成プロセス

焼成籾殻中の脆性炭化物を利用した非晶質シリカ微粒子の生成プロセス

Influence of pH, Temperature and Sample Size on Natural and Enforced Syneresis of Precipitated Silica

The production of silica is performed by mixing an inorganic, silicate-based precursor and an acid. Monomeric silicic acid forms and polymerizes to amorphous silica particles. Both further polymerization and agglomeration of the particles lead to a gel network. Since polymerization continues after gelation, the gel network consolidates. This rather slow process is known as “natural syneresis” and strongly influences the product properties (e.g., agglomerate size, porosity or internal surface). “Enforced syneresis” is the superposition of natural syneresis with a mechanical, external force. Enforced syneresis may be used either for analytical or preparative purposes. Hereby, two open key aspects are of particular interest. On the one hand, the question arises whether natural and enforced syneresis are analogous processes with respect to their dependence on the process parameters: pH, temperature and sample size. On the other hand, a method is desirable that allows for correlating natural and enforced syneresis behavior. We can show that the pH-, temperature- and sample size-dependency of natural and enforced syneresis are indeed analogous. It is possible to predict natural syneresis using a correlative model. We found that our model predicts maximum volume shrinkages between 19% and 30% in comparison to measured values of 20% for natural syneresis.

In vitro comet and micronucleus assays do not predict morphological transforming effects of silica particles in Syrian Hamster Embryo cells

Crystalline silica particles and asbestos have both been classified as carcinogenic by the International Agency for Research on Cancer (IARC). However, because of the limited data available, amorphous silica was not classifiable.In vitro, the carcinogenic potential of natural crystalline and amorphous silica particles has been revealed by the Syrian Hamster Embryo (SHE) cell transformation assay. On the other hand, the genotoxic potential of those substances has not been investigated in SHE cells. And yet, genotoxicity assays are commonly used for hazard evaluation and they are often used as in vitro assays of reference to predict a possible carcinogenic potential. The main objective of this study was to compare the genotoxic potential and the carcinogenic potential of different crystalline and amorphous silica particles in SHE cells. Three silica samples of different crystallinity were used: natural amorphous silica, partially crystallized silica and quartz silica particles. Their genotoxicity were tested through the in vitro micronucleus assay and the comet assay in SHE, and their carcinogenic potential through the SHE transformation assay. In addition, silica samples were also tested with the same genotoxicity assays in V79 hamster-lung cells, a common in vitro model for particle exposure.Results obtained in the micronucleus and the comet assays show that none of the silica was capable of inducing genotoxic effects in SHE cells and only the amorphous silica induced genotoxic effects in V79 cells. However in the SHE cell transformation assays, the partially crystallized and quartz silica were able to induce morphological cell transformation. Together, these data suggest that, in vitro, the short-term genotoxic assays alone are not sufficient to predict the hazard and the carcinogenic potential of this type of particles; SHE transformation assay appears a more reliable tool for this purpose and should be included in the “in vitro battery assays” for hazard assessment.

Infrared spectroscopy of spherical micromesoporous silica particles at formation and functionalization stages

Spherical micromesoporous particles of amorphous silica with a specific pore surface area to 1600 m2/g were synthesized. The particle inner surface was functionalized by amino groups and luminescent dye molecules chemically bound with them. Particle structure and chemical composition variations at formation and functionalization stages were studied by the IR spectroscopy method.

Towards tunable size of silica particles from rice husk

Amorphous spherical silica particles were produced in a variety of sizes ranging from nanometer to micrometer from rice husk by varying the concentration of white rice husk from 0.7wt.% to 5.6wt.% in sodium hydroxide to form sodium silicate solutions. The effect of increased reaction temperature (65°C) and the addition of water on the size of silica particles was also studied. At low concentrations of white rice husk (0.7wt.% and 1.4wt.%), uni-modal silica particles in nanometer size range were produced while at higher concentrations (2.8wt.% and 5.6wt.%), bi- and tri-modal particles were produced, which were converted to uni- and bi-modal by changing the reaction conditions, i.e. water and temperature, respectively. X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectroscopy and atomic absorption spectroscopy were employed for the compositional analysis of white rice husk and sodium silicate solution. Scanning electron microscopy was used to study the morphology and particle size of silica while X-ray diffraction confirmed the amorphous state of silica particles. Surface area of silica particles was analyzed by using Brunauer–Emmett–Teller analysis.

The effects of size and surface modification of amorphous silica particles on biodistribution and liver metabolism in mice

Engineered nanoparticles, with unconventional properties, are promising platforms for biomedical applications. Since they may interact with a wide variety of biomolecules, it is critical to understand the impact of the physicochemical properties of engineered nanoparticles on biological systems. In this study, the effects of particle size and surface modification alone or in combination of amorphous silica particles (SPs) on biological responses were determined using a suite of general toxicological assessments and metabonomics analysis in mice model. Our results suggested that amino or carboxyl surface modification mitigated the liver toxicity of plain-surface SPs. 30 nm SPs with amino surface modification were found to be the most toxic SPs among all the surface-modified SP treatments at the same dosage. When treatment dose was increased, submicro-sized SPs with amino or carboxyl surface modification also induced liver toxicity. Biodistribution studies suggested that 70 nm SPs were mainly accumulated in liver and spleen regardless of surface modifications. Interestingly, these two organs exhibited different uptake trends. Furthermore, metabonomics studies indicated that surface modification plays a more dominant role to affect the liver metabolism than particle size.

Size and surface modification of amorphous silica particles determine their effects on the activity of human CYP3A4 in vitro

Because of their useful chemical and physical properties, nanomaterials are widely used around the world - for example, as additives in food and medicines - and such uses are expected to become more prevalent in the future. Therefore, collecting information about the effects of nanomaterials on metabolic enzymes is important. Here, we examined the effects of amorphous silica particles with various sizes and surface modifications on cytochrome P450 3A4 (CYP3A4) activity by means of two different in vitro assays. Silica nanoparticles with diameters of 30 and 70 nm (nSP30 and nSP70, respectively) tended to inhibit CYP3A4 activity in human liver microsomes (HLMs), but the inhibitory activity of both types of nanoparticles was decreased by carboxyl modification. In contrast, amine-modified nSP70 activated CYP3A4 activity. In HepG2 cells, nSP30 inhibited CYP3A4 activity more strongly than the larger silica particles did. Taken together, these results suggest that the size and surface characteristics of the silica particles determined their effects on CYP3A4 activity and that it may be possible to develop silica particles that do not have undesirable effects on metabolic enzymes by altering their size and surface characteristics.

Intestinal absorption and biological effects of orally administered amorphous silica particles

Although amorphous silica nanoparticles are widely used in the production of food products (e.g., as anticaking agents), there is little information available about their absorption and biological effects after oral exposure. Here, we examined the in vitro intestinal absorption and in vivo biological effects in mice of orally administered amorphous silica particles with diameters of 70, 300, and 1,000 nm (nSP70, mSP300, and mSP1000, respectively) and of nSP70 that had been surface-modified with carboxyl or amine groups (nSP70-C and nSP70-N, respectively). Analysis of intestinal absorption by means of the everted gut sac method combined with an inductively coupled plasma optical emission spectrometer showed that the intestinal absorption of nSP70-C was significantly greater than that of nSP70. The absorption of nSP70-N tended to be greater than that of nSP70; however, the results were not statistically significant. Our results indicate that silica nanoparticles can be absorbed through the intestine and that particle diameter and surface properties are major determinants of the degree of absorption. We also examined the biological effects of the silica particles after 28-day oral exposure in mice. Hematological, histopathological, and biochemical analyses showed no significant differences between control mice and mice treated with the silica particles, suggesting that the silica nanoparticles evaluated in this study are safe for use in food production.

Titanium uptake and incorporation into silica nanostructures by the diatom Pinnularia sp. (Bacillariophyceae)

Diatoms are an ecologically successful group within the phytoplankton, and their special feature is a biofabricated silica cell encasement called a frustule. These frustules attract interest in material technology, and one potential application is to use them in solar cell technology. The silica frustule with its nanoscaled pattern is interesting per se, but the utility is enhanced if we succeed in incorporating other elements. Titanium is an interesting element because its oxide is a semi-conductor with a high band gap. However, doping with relevant elements through bioincorporation is challenging, and it is necessary to understand the biology involved in element uptake and incorporation. Here we present data on bioincorporation of Ti into the silica frustules of the pennate diatom Pinnularia sp. (Ehrenberg) and show that the distribution of the incorporated Ti is inhomogeneous both between and within valves. More than a tenfold increase of Ti in newly synthesised valves was achieved, and increased Ti around the pores was confirmed by both EDS and EELS analyses. HAADF STEM spectroscopy revealed a grainy surface with amorphous silica particles of 4 to 5 nm in size. These observations are explained by what is known from the physico-chemical processes involved in biosilification and frustule formation, looking into it from a biological point of view.

Large Pore Mesoporous Silica Induced Weight Loss in Obese Mice

There is a need for medical treatments to curb the rising rate of obesity. Weight reduction is correlated with a decrease in associated risk factors and cholesterol levels in humans. Amorphous silica particles have been found to exert a hypocholesterolemic effect in humans, making them popular dietary additives. To investigate the effect of mesoporous silica, which possess sharp pore size distributions, on: weight loss, cholesterol, triglycerides and glucose blood levels in obese mice. Mesoporous silicas with differing pore size were mixed in the high-fat diet of obese mice. Animals receiving large pore mesoporous silica with a high-fat diet show a significant reduction in body weight and fat composition, with no observable negative effects. Pore size is an important parameter for reduction of body weight and body fat composition by mesoporous silica, demonstrating promising signs for the treatment of obesity.

Effect of Silica Particle Size on Macrophage Inflammatory Responses

Amorphous silica particles, such as nanoparticles (<100 nm diameter particles), are used in a wide variety of products, including pharmaceuticals, paints, cosmetics, and food. Nevertheless, the immunotoxicity of these particles and the relationship between silica particle size and pro-inflammatory activity are not fully understood. In this study, we addressed the relationship between the size of amorphous silica (particle dose, diameter, number, and surface area) and the inflammatory activity (macrophage phagocytosis, inflammasome activation, IL-1β secretion, cell death and lung inflammation). Irrespective of diameter size, silica particles were efficiently internalized by mouse bone marrow-derived macrophages via an actin cytoskeleton-dependent pathway, and induced caspase-1, but not caspase-11, activation. Of note, 30 nm-1000 nm diameter silica particles induced lysosomal destabilization, cell death, and IL-1β secretion at markedly higher levels than did 3000 nm-10000 nm silica particles. Consistent with in vitro results, intra-tracheal administration of 30 nm silica particles into mice caused more severe lung inflammation than that of 3000 nm silica particles, as assessed by measurement of pro-inflammatory cytokines and neutrophil infiltration in bronchoalveolar lavage fluid of mice, and by the micro-computed tomography analysis. Taken together, these results suggest that silica particle size impacts immune responses, with submicron amorphous silica particles inducing higher inflammatory responses than silica particles over 1000 nm in size, which is ascribed not only to their ability to induce caspase-1 activation but also to their cytotoxicity.

The potential for multiple signatures of invasive species in the geologic record

Abstract During the Anthropocene, the rapid spread of invasive species into new habitats has repeatedly led to major ecosystem change. Invasive species succeed by outcompeting native species or significantly altering the physical or chemical properties of a habitat. Here we propose that invasive species, which by definition have a large impact on an ecosystem, will leave multiple signatures in sediments. As a case study, a reach of the Platte River (Nebraska, USA) where a Eurasian lineage of the grass Phragmites australis invaded the river channel in 2003, was investigated. This study focuses on the effects of this invasion on silica, a micronutrient that can limit productivity of phytoplankton like diatoms. Dissolved silica (DSi) and particles of amorphous silica (ASi), which are produced by phytoplankton and terrestrial plants, comprise the pool of bioavailable silica in aquatic ecosystems. ASi concentrations were measured in sediments accumulated under Phragmites stands. These values were compared to ASi concentrations in unvegetated sediments and sediments accumulating under native Salix spp. (willows). Non-native Phragmites sediments had more than twice as much ASi as Salix sediments, and a first-order estimate revealed that in 8 years Phragmites sequestered approximately half a year's worth of the DSi load carried by the Platte. Given the importance of ASi in driving aquatic food webs, increased storage due to Phragmites is likely having a substantial effect on downstream ecosystems. Furthermore, because Phragmites accumulated thicker layers of fine-grained sediments, we demonstrated that this invasive species is leaving a record of both physical and biochemical ecosystem change.

Influence of amorphous silica on the hydration in ultra-high performance concrete

Amorphous silica particles (silica) are used in ultra-high performance concretes to densify the microstructure and accelerate the clinker hydration. It is still unclear whether silica predominantly increases the surface for the nucleation of C–S–H phases or dissolves and reacts pozzolanically. Furthermore, varying types of silica may have different and time dependent effects on the clinker hydration. The effects of different silica types were compared in this study by calorimetric analysis, scanning and transmission electron microscopy, in situ X-ray diffraction and compressive strength measurements. The silica component was silica fume, pyrogenic silica or silica synthesized by a wet-chemical route (Stoeber particles). Water-to-cement ratios were 0.23. Differences are observed between the silica for short reaction times (up to 3days). Results indicate that silica fume and pyrogenic silica accelerate alite hydration by increasing the surface for nucleation of C–S–H phases whereas Stoeber particles show no accelerating effect.

Leaching behaviour of cement pastes containing nanosilica

The influence of nanosilica (nanoscale-size particles of amorphous silica) on the leaching behaviour of Portland cement pastes made with a relatively low water/binder ratio (w/b = 0·36) and different nanosilica contents (0–3·8 wt% of binder) was investigated through the use of an ultra-accelerated leaching test (using concentrated ammonium nitrate solution as a leachant) coupled with scanning electron microscopy-energy dispersive spectroscopy and differential scanning calorimetry-thermogravimetric analyses. The effect of leaching on the physical and mechanical properties of such pastes was assessed and their chemical resistance to leaching was evaluated through a parametric model. It was found that the addition of nanosilica improves the chemical resistance of cement pastes by producing a significant leaching deceleration (up to 69%). As a result, the decay of compressive strength of leached specimens (about 60% reduction) is significantly retarded. Higher residual compressive strengths were also obtained for totally leached specimens containing nanosilica, as a result of the ability of this admixture to consume portlandite during cement hydration and then reduce the porosity associated with portlandite dissolution during leaching.

Antireflective coatings based on amorphous submicron silica particles for silicate glass: Preparation, morphology of surface, optical properties

The structure and properties of dense and porous single-layer antireflective coatings based on fractal and spherical silica particles, respectively, used for silicate glass have been studied. The conditions needed for the synthesis of SiO2 particles of a preset structure and size, as well as physicochemical processes taking place upon the deposition of coatings using the technique of adsorption from solution, are considered. The morphology and optical properties of the coatings are studied. The results of abrasion hardness tests of coatings are presented.

Study of fluoride processing of kyanite concentrates

Specific features of the physicochemical processes occurring in the interaction of kyanite concentrates with ammonium hydrodifluoride, sublimation of ammonium hexafluorosilicate, recovery of alumina and aluminum fluoride, synthesis of amorphous silica particles, and reduction of additional reagents were studied. The thermodynamic parameters, rate constants, and activation energies of the occurring chemical reactions were determined. The optimal conditions of the fluoride processing of kyanite concentrates with integrated recovery of various useful components were found.