Silica Particles Of Different Sizes Research Articles

Dissolution kinetics of mesoporous silica nanoparticles in different simulated body fluids

The application of mesoporous silica nanoparticles as a platform for drug delivery and bioimaging requires a good understanding of the degradability of these particles under physiological conditions. Optimally, the degradability should be studied in vivo using relevant administration routes and dosings, but such studies are complicated and expensive. Thus, the biodegradability is often studied in vitro using simulated body fluids. However, such studies are scarce to date, and the results are partially conflicting. The aims of this study were therefore (a) to determine the influence of the composition of different simulated body fluids on the observed silica dissolution rates and (b) to establish morphological key parameters that determine the dissolution kinetics of silica nanoparticles. As dissolution media, simulated body fluid (SBF), simulated lung fluid (SLF), simulated gastric juice (SGF) and PBS buffer were used, and the silica concentration was kept below the silica saturation limit. Three mesoporous silica particles of different sizes were studied together with one non-porous Stober-type silica particle. The observed silica dissolution rates followed the order SLF > SBF ≈ PBS ≫ SGF. Apart from general pH effects, the presence of organic acids in SLF is suggested to enhance the silica dissolution rate. The specific surface area was identified as the main parameter controlling the rate of dissolution of the different silica particles studied, while particle size influences were minor. The dissolution of mesoporous silicas with different particle sizes has been studied in four different physiological buffers.

Cytotoxicity and autophagy dysfunction induced by different sizes of silica particles in human bronchial epithelial BEAS-2B cells.

The adverse effects of silica nanoparticles are gaining attention due to their wide application in biomedicine. However, information about size-dependent toxicity induced by silica nanoparticles is insufficient. In this study, two size of nano-scale (40 nm, 60 nm) and one size of micro-scale (200 nm) silica particles were studied to investigate the possible mechanism of cytotoxicity and autophagy dysfunction in human bronchial epithelial BEAS-2B cells. The cell viability was decreased in a size- and dose-dependent manner, while the LDH activity, oxidative stress and mitochondrial damage significantly increased, induced by both nano- and micro-scale silica particles. Ultrastructural analysis showed that nano-scale silica particles could induce mitochondrial damage and autophagy, but not micro-scale particles. Verified by the autophagy inhibitor 3-MA, the expression of LC3 and SQSTM1/p62 was upregulated in nano-scale silica particles in a size- and dose-dependent manner, while the micro-scale particles had an inhibitory effect. In addition, autophagy activation and autophagy blockage were triggered by nano-scale silica particles via the PI3K/Akt/mTOR pathway. Our findings first demonstrated that exposure to nano-scale silica particles rather than micro-scale particles could lead to autophagy dysfunction and impair cellular homeostasis.

The Ballistic Performance of Multi-Layer Kevlar Fabrics Impregnated with Shear Thickening Fluids

This study investigates the ballistic penetration performance of aramid fabric impregnated with shear thickening fluid. The ballistic test was conducted at impact velocity of 445 m/s, and three types of shear thickening fluids prepared with silica particles of different sizes (200nm, 340nm and 480nm) are involved. The results demonstrate an enhancement in ballistic properties of fabric due to the impregnation of shear thickening fluids. The fabrics with smaller particle size show better ballistic performance. Microscopic observation of aramid fabric reveals that shear thickening fluids with smaller silica particles have a better adhesion on and between yarns, enhancinging the coupling effect between yarns. The corresponding mechanism was discussed in the paper.

Microfluidic Design of Magnetoresponsive Photonic Microcylinders with Multicompartments.

Colloidal photonic structures have been designed to have granular format to use them for paint pigments, encoded carriers, and display pixels. However, conventional approaches only provide spherical or discoid shapes, restricting their applications. Cylindrical granules with fan-shaped compartments in the cross section are appealing for microcarriers with abundant optical codes and active display pigments for color switching. In this work, a stratified laminar flow of concentrated silica particles is employed, formed in a cylindrical microchannel, to produce cylindrical photonic microparticles with multiple compartments. To accomplish this, a microfluidic device is designed to have one cylindrical main channel connected with four branch channels. Four different photocurable suspensions are independently injected through the branches to form quarter-cylindrically compartmentalized streams in the main channel. Local ultraviolet irradiation on the main channel polymerizes the suspension, thereby forming cylindrical microparticles with four compartments. In each compartment, silica particles form ordered array which develops particle size-dependent structural color. Therefore, different colors can be incorporated into single microcylinder by employing different sizes of silica particles. Moreover, one of the compartments can be rendered to be magnetoresponsive by embedding aligned magnetic particles, which enables the remote control of microcylinder orientation and therefore the switching of structural colors.

Toxicity of colloidal silica nanoparticles administered orally for 90 days in rats.

This study was undertaken to investigate the potential toxicity and establish the no observed adverse effect level (NOAEL) and target organ(s) of negatively charged colloidal silica particles of different sizes, ie, SiO2EN20(−) (20 nm) or SiO2EN100(−) 2(100 nm), administered by gavage in Sprague-Dawley rats. After verification of the physicochemical properties of the SiO2 particles to be tested, a preliminary dose range-finding study and 90-day repeated dose study were conducted according to the Organisation for Economic Cooperation and Development test guideline. Based on the results of the 14-day dose range-finding study, a high dose was determined to be 2,000 mg/kg, and middle and low doses were set at 1,000 and 500 mg/kg, respectively. In the 90-day toxicity study, there were no animal deaths in relation to administration of SiO2 particles of either size. In addition, no treatment-related clinical changes or histopathological findings were observed in any of the experimental groups. Moreover, no difference in toxic effects from chronic exposure to SiO2EN20(−)(20 nm) or SiO2EN100(−) (100 nm) was observed. The results of this study indicate that the NOAEL for SiO2EN20(−) and SiO2 EN100(−) would most likely be 2,000 mg/kg, and no target organ was identified in rats of either sex.

Colloidal Silica/Poly(Methacrylsiloxane) Nanocomposite Particles: Synthesis, Characterization, and Application in Toners.

ABSTRACTWe report on a new class of materials for laser printer toner applications. These materials were prepared from methacrysilane-in-water emulsions stabilized with colloidal silica particles. In this elegant system, the colloidal silica particles reside at the water/oil interface helping to emulsify the oil droplet, self-organizing into a raspberry-like morphology. The emulsion formation is followed by free-radical polymerization, hydrophobic treatment, and drying steps. This one pot synthesis in water affords a hydrophobic material with a particle size in the range of 80 to 300 nm. The particle size could be fine-tuned by changing the oil-to-silica mass ratio or by using colloidal silica particles of different sizes. Results of material characterization by solid-state NMR, electron microscopy, and particle size measurements methods will be presented. Examples of possible extensions of the synthesis towards materials with methacrylsilane partially substituted with other methacrylates will be provided. Application of the new material in toners will be described as will the comparison of its performance with the incumbent material - hydrophobic colloidal silica.

Influence of Micro and Nano Silica on Mechanical Properties of Plasticized Sulfur Composites

In this paper the influence of two different sizes of silica particles (micro-silica and nano-silica) was studied on mechanical properties of sulfur and sulfur composite. To improve the structural properties, sulfur was plasticized using dicyclopentadiene (DCPD) and methyl styrene (MSt). Plasticized sulfur composite was prepared by melt blending of plasticized sulfur and silica particles. The increment in compressive and flexural strengths revealed that the micro-particles enhance mechanical properties of sulfur while nano-particles improved mechanical properties of plasticized sulfur. Viscosity measurements indicated that mechanical properties of nano composites containing matrix with low viscosity (sulfur plasticized with methyl styrene) are improved with increasing mixer speed but increasing the mixer speed had negative effect on composites containing matrix with higher viscosity (sulfur plasticized with dicyclopentadiene).

Effect of Colloidal Substrate Curvature on pH-Responsive Polyelectrolyte Brush Growth

Coatings consisting of polymer brushes are an effective way to modify solid interfaces. Polymer brush-modified hybrid particles have been prepared by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP) of 2-(diethylamino)ethyl methacrylate (DEA) on silica particles. We have optimized the synthesis with respect to changing the reducing agent, temperature, and reaction solvent from an aqueous ethanol mixture to an aqueous methanol mixture. Our flexible electrostatically adsorbed macroinitiator approach allows for the modification of a variety of surfaces. Polybasic brushes have been grown on silica particles of different sizes, from 120 to 840 nm in diameter, as well as on wafers, and a comparison of the products has allowed the effect of surface curvature to be elucidated. An examination of the thickness of the dry brush and the aqueous hydrodynamic brush at both pH 7 and at 4 demonstrated that growth increased substantially with substrate curvature for particles with a diameter below 450 nm. This is attributed to the increasing separation between active chain ends, reducing the rate of termination. This is believed to be the first time that this effect has been demonstrated experimentally. Furthermore, we have seen that polymer brush growth on planar wafers was significantly reduced when the reaction mixture was stirred.

Genotoxicity of amorphous silica particles with different structure and dimension in human and murine cell lines

Although amorphous silica is used in food products, cosmetics and paints and as vector for drug delivery, data on its potential health hazard are limited. The aim of this study was to investigate the cytotoxic and genotoxic potential of silica particles of different sizes (250 and 500nm) and structures (dense and mesoporous). Dense silica (DS) spheres were prepared by sol-gel synthesis, mesoporous silica particles (MCM-41) were prepared using hexadecyltrimethyl ammonium bromide as a structure-directing agent and tetraethylorthosilicate as silica source. Particles were accurately characterised by dynamic light scattering, nitrogen adsorption, X-ray diffraction and field emission scanning electron microscopy. Murine macrophages (RAW264.7) and human epithelial lung (A549) cell lines were selected for investigation. Genotoxicity was evaluated by Comet assay and micronucleus test. Cytotoxicity was tested by the trypan blue method. Cells were treated with 0, 5, 10, 20, 40 and 80 µg/cm(2) of different silica powders for 4 and 24 h. The intracellular localisation of silica was investigated by transmission electron microscopy. Amorphous particles penetrated into the cells, being compartmentalised within endocytic vacuoles. DS and MCM-41 particles induced cytotoxic and genotoxic effects in A549 and RAW264.7 although to different extent in the two cell lines. A549 were resistant in terms of cell viability, but showed a generalised induction of DNA strand breaks. RAW264.7 were susceptible to amorphous silica exposure, exhibiting both cytotoxic and genotoxic responses as DNA strand breaks and chromosomal alterations. The cytotoxic response of RAW264.7 was particularly relevant after MCM-41 exposure. The genotoxicity of amorphous silica highlights the need for a proper assessment of its potential hazard for human health.

Nanoscale Particle Removal Using Wet Laser Shockwave Cleaning

A physical scalable Wet Laser Shockwave Cleaning (WLSC) process is presented for the removal of nanoscale particles, particularly organic nanoparticles, from Si wafers. The WLSC takes advantage of a very thin water film on the surface to increase the drag force by three orders of magnitude, reduce the adhesion force, utilize the double layer repulsive force and eliminate the capillary force. The removal of polystyrene latex (PSL) and silica particles of different sizes was investigated and compared with the original dry Laser Shock Cleaning (LSC). PSL particles as small as 28 nm were successfully removed using the proposed WLSC. The removal mechanism for the wet laser shockwave cleaning was investigated. Numerical computation of the laser-induced hydrodynamics and shadowgraphic imaging of the water film motion were used. The analysis suggests that the water film moves at a speed as high as 35 m/s as the impinging shockwave exerts a hydrodynamic drag force on the water film and consequently a sufficient removal force on the particle.

Size-dependent cytotoxicity of amorphous silica nanoparticles in human hepatoma HepG2 cells

The purpose of this study is to compare the potential cytotoxicity induced by amorphous silica particles with different sizes. The effects of one fine particle (498nm) and three nanoparticles (68, 43, and 19nm) on cultured human hepatoma (HepG2) cells were investigated by detecting morphological changes, cell viability, cytomembrane integrity, DNA damage, cell cycle distribution, and apoptosis after the cells were treated with 100μg/mL of four silica particles for 24h. The results indicated that in HepG2 cells, the cytotoxicity generated by silica particles strongly depended on the particle size, and smaller silica particle possessed higher toxic effect. In order to further elucidate the possible mechanisms of cell injuries, intracellular reactive oxygen species (ROS) was measured. Increased ROS level was also observed in a size dependent way. However, the result showed the fine particle did not promote intracellular ROS level significantly, while cell injuries were detected in this treated group. Thus, our data demonstrated that exposure to different sizes of silica particles resulted in a size dependent cytotoxicity in cultured HepG2 cells, and ROS generation should be one possible damage pathway but might not be completely responsible for the toxic effect produced by silica particles.

Integrated metabonomics analysis of the size-response relationship of silicananoparticles-induced toxicity in mice

Understanding the underlying properties-dependent interactions of nanostructures withbiological systems is essential to nanotoxicological research. This study investigates therelationship between particle size and toxicity, and further reveals the mechanism of injury,using silica particles (SP) with diameters of 30, 70, and 300 nm (SP30, SP70, and SP300) asmodel materials. The biochemical compositions of liver tissues and serum of mice treatedwith SP30, SP70, and SP300 were analyzed by integrated metabonomics analysis based ongas chromatography–mass spectrometry (GC–MS) and in combination with patternrecognition approaches. Histopathological examinations and serum biochemical analysiswere simultaneously performed. The toxicity induced by three different sizes of SP mainlyinvolved hepatocytic necrosis, increased serum aminotransferase, and inflammatorycytokines. Moreover, the toxic effects of SP were dose-dependent for each particle size. Thedoses of SP30, SP70, and SP300 that were toxic to the liver were 10, 40, and 200 mg kg − 1, respectively. In this study, surface area has a greater effect than particle number on thetoxicity of SP30, SP70, and SP300 in the liver. The disturbances in energy metabolism,amino acid metabolism, lipid metabolism, and nucleotide metabolism may beattributable to the hepatotoxicity induced by SP. In addition, no major differences werefound in the response of biological systems caused by the different SP sizes amongthe metabolite profiles. The results suggest that not only nano-sized but alsosubmicro-sized SP can cause similar extents of liver injury, which is dependenton the exposure dose, and the mechanism of toxicity may be almost the same.

Determination of the photoluminescence quantum yield of diluted dye solutions in highly scattering media by pulsed photoacoustic spectroscopy

A pulsed photoacoustic system is used to determine the fluorescence quantum yield of diluted dye solutions in highly scattering media. In order to show its accuracy, the quantum yield of Rhodamine 6G in water and ethanol was calculated. The chemical Fuchsin was utilized as a dye reference because the entire excitation energy is converted into nonradiative relaxation processes. The scattering coefficient of the samples was incremented by using spherical silica particles of different sizes and concentrations. The determined mean values in the studied scattering optical density range (0-3 cm(-1)) were 0.95 for ethanol and 0.96 for water. These measurements are in excellent agreement with the best literature values.

Luminescent enhancement with tunable emission in Sr2SiO4: Eu2+ phosphors for white LEDs

Europium ion doped strontium silicate (Sr2SiO4: Eu2+) phosphors were synthesized via the solid-state method using different sizes of silica precursor. Remarkable enhancement in luminescence characteristics was shown when nano-sized silica (10 nm) was used. This phenomenon is ascribed to improved reactivity through the reaction, leading to the increase in crystallinity and the formation of enlarged particles. In addition, as 10-nm silica was used, the emission wavelength of Sr2SiO4: Eu2+ phosphors blue-shifted (from the orange to yellow region) with prolonged heating durations. This feature is attributed to the microstructural changes, eventually leading to a decrease in the non-radiative energy transfer between Eu2+ ions. In this study, color-tunable Sr2SiO4: Eu2+ phosphors with improved emission intensity were successfully prepared via using different sizes of silica particles.

Efficient internalization of mesoporous silica particles of different sizes by primary human macrophages without impairment of macrophage clearance of apoptotic or antibody-opsonized target cells

Macrophage recognition and ingestion of apoptotic cell corpses, a process referred to as programmed cell clearance, is of considerable importance for the maintenance of tissue homeostasis and in the resolution of inflammation. Moreover, macrophages are the first line of defense against microorganisms and other foreign materials including particles. However, there is sparse information on the mode of uptake of engineered nanomaterials by primary macrophages. In this study, mesoporous silica particles with cubic pore geometries and covalently fluorescein-grafted particles were synthesized through a novel route, and their interactions with primary human monocyte-derived macrophages were assessed. Efficient and active internalization of mesoporous silica particles of different sizes was observed by transmission electron microscopic and flow cytometric analysis and studies using pharmacological inhibitors suggested that uptake occurred through a process of endocytosis. Moreover, uptake of silica particles was independent of serum factors. The silica particles with very high surface areas due to their porous structure did not impair cell viability or function of macrophages, including the ingestion of different classes of apoptotic or opsonized target cells. The current findings are relevant to the development of mesoporous materials for drug delivery and other biomedical applications.

Dynamics and Microstructure Analysis of N-Isopropylacrylamide/Silica Hybrid Gels

The mechanical properties, gelation process, and microstructure of N-isopropylacrylamide (NIPAm)/silica hybrid gels were investigated by using mechanical measurements, dynamic light scattering (DLS), and contrast-variation small-angle neutron scattering (CV-SANS). The three different hybrid gels, containing an equal total volume fraction of silica particles of different sizes (NS_S: small = 20-30 angstroms radius; NS_M: medium = 40-55 angstroms; and NS_L: large = 100-150 angstroms), were employed for comparison. An obvious effect on the compressive properties due to the size of the silica particles was observed, with harder materials produced from particles of smaller size. The gelation process was strongly dependent on the competition between silica aggregation and NIPAm polymerization, as measured by using the DLS methods. In the case of NS_S, the rate of aggregation was larger than NIPAm polymerization, resulting in the formation of an aggregate-dominant microstructure. The aggregation rate for NS_M and NS_L, however, was comparable to the NIPAm polymerization rate, leading to simultaneous aggregation and polymerization. CV-SANS determined that the NIPAm adsorption layer on the silica surface was clearly affected on a microscopic scale by the silica particle sizes.

Absorption of carbon dioxide into aqueous colloidal silica solution with different sizes of silica particles containing monoethanolamine

Carbon dioxide was absorbed into an aqueous nanometer-sized colloidal silica solution in a flat-stirred vessel at 25 °C and 101.3 kPa to measure the absorption rate of CO2. The concentrations of silica were in the range of 0–31 wt% and the sizes were 7, 60, and 111 nm. The solution contained monoethanolamine (MEA) of 0–2.0 kmol/m3. The volumetric liquid-side mass transfer coefficient (k L a) of CO2 was correlated with the empirical formula representing the rheological property of silica solution. The use of the aqueous colloidal silica solution resulted in a reduction of the absorption rate of CO2 compared with Newtonian liquid based on the same viscosity of the solution. The chemical absorption rate of CO2 was estimated by film theory using k L a and physicochemical properties of CO2 and MEA.

Brownian diffusion of ultrafine particles to an air–water interface

Fluorescent core-plain shell silica particles of different sizes were synthesized in order to investigate the interaction of ultrafine particles with bubbles. The morphology, surface chemistry and rate of diffusion of these synthesized particles were characterized by various techniques. The collection efficiency of particles by bubbles was measured in single bubble flotation experiments. Results show that particle-bubble collection efficiency increased with decreasing particle size and increasing particle surface hydrophobicity. These results are interpreted by taking into account the influence of particle size and surface hydrophobicity on particle-bubble collision and attachment efficiencies.

Size‐Dependent Cytotoxicity of Monodisperse Silica Nanoparticles in Human Endothelial Cells

The effect that monodisperse amorphous spherical silica particles of different sizes have on the viability of endothelial cells (EAHY926 cell line) is investigated. The results indicate that exposure to silica nanoparticles causes cytotoxic damage (as indicated by lactate dehydrogenase (LDH) release) and a decrease in cell survival (as determined by the tetrazolium reduction, MTT, assay) in the EAHY926 cell line in a dose-related manner. Concentrations leading to a 50% reduction in cell viability (TC(50)) for the smallest particles tested (14-, 15-, and 16-nm diameter) ranging from 33 to 47 microg cm(-2) of cell culture differ significantly from values assessed for the bigger nanoparticles: 89 and 254 microg cm(-2) (diameter of 19 and 60 nm, respectively). Two fine silica particles with diameters of 104 and 335 nm show very low cytotoxic response compared to nanometer-sized particles with TC(50) values of 1095 and 1087 microg cm(-2), respectively. The smaller particles also appear to affect the exposed cells faster with cell death (by necrosis) being observed within just a few hours. The surface area of the tested particles is an important parameter in determining the toxicity of monodisperse amorphous silica nanoparticles.

Texture Etching of Si with Atomic Hydrogen Generated by Hot Wire Method through SiO2 Masks for Solar Cell Applications

Texture etching of (100) and (111) single-crystal silicon using atomic hydrogen generated by the hot wire method was examined both by direct etching and etching through masks formed from SiO2 particles. Etching with SiO2 masks formed from colloidal silica solution produced a crater like texture on both oriented substrates. It was also found that the thickness of the mask region can be adjusted by changing the concentration of colloidal silica and by mixing different sizes of silica particles. The reflectivities of the substrates with textures generated by optimized mask formation were found to reach minima of about 13% for Si(100) and 19% for Si(111), which were lower than those of multicryastalline substrates with textures generated by alkali etching.