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PubMed1996

Apatite-forming ability of silicate ion dissolved from silica gels.

It is known that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces, and a certain type of hydrated silica developed on their surfaces plays an important role in nucleating the apatite. In the present study, the apatite-forming ability of silicate ion dissolved from different silica materials into a simulated body fluid was examined as follows. Polyether sulfone substrates pretreated with O2 plasma were placed in parallel to plates of three kinds of silica gels prepared in different media and silica glass, with a distance of 0.5 mm between them in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for 4 days, and then soaked in a solution with ion concentrations 1.5 times those of the simulated body fluid for 6 days. After the first soaking, silicon combined with oxygen was detected on the surfaces of the substrates faced to all the silica gels, whereas it was not detected on that faced to the silica glass. After the second soaking, the former formed a bonelike apatite layer on their surfaces, but the latter did not. These results indicate that silicate ion which is dissolved from the silica gels and adsorbed on the substrates has an apatite-forming ability, irrespective of the microstructure of the original silica gels.

Apatites↗

PubMed1995

Bone-bonding behavior of three heat-treated silica gels implanted in mature rabbit bone.

Silica gel has been reported to induce apatite nucleation on its surface in vitro and it can act as a stimulant that induces formation of chemical apatite (Ca-P) layers on the surfaces of bioactive glass-ceramics. In this study, apatite formation in response to and the bone-bonding behavior of silica gels implanted in the tibiae of mature rabbits were studied. Implants were made from three silica gels treated at 400, 800, and 1000 degrees C, and the effects of such heat treatment on the above parameters were investigated. The silica gel was made by hydrolysis and polycondensation of tetraethoxysilane in aqueous solution containing polyethylene glycol. Rectangular implants (15 mm x 10 mm x 2 mm) of each heat-treated silica gel were implanted into both tibial bones of mature male rabbits, which were killed 4 or 8 weeks after implantation, and the tibiae containing the implants were dissected out. The bone-implant interfaces were investigated using Giemsa surface staining, contact microradiography, scanning electron microscopy-electron probe microanalysis, and X-ray diffraction. Histologically, no bonding of bone to any of the silica gels was observed at any time postimplantation. Soft tissue was observed at the bone-silica gel interface, but there were no giant foreign body or inflammatory cells. A Ca-P-rich layer was observed only on small areas of the surfaces of the silica gels treated at 400 and 800 degrees C 4 and 8 weeks after implantation. X-ray diffraction analysis confirmed the presence of hydroxyapatite in these Ca-P-rich layers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2000

Ion-chromatographic behavior of alkali metal cations and ammonium ion on zirconium-adsorbing silica gel.

The preparation and evaluation of zirconium-adsorbing silica gel (Zr-Silica) as an ion-exchange stationary phase in ion chromatography for inorganic anions and cations was carried out. The Zr-Silica was prepared by the reaction of silanol groups on the surface of the silica gel with zirconium butoxide (Zr(OCH2CH2CH2CH3)4) in ethanol. The ion-exchange characteristics of the Zr-Silica were evaluated using 10 mM tartaric acid at pH 2.5 as eluent. The Zr-Silica was found to act as a cation-exchanger under the eluent conditions. The retention behavior of alkali and alkaline earth metal cations was then investigated. The Zr-Silica column was proved to be suitable for the simultaneous separation of alkali metal cations and ammonium ion. Excellent separation of the cations on a 15 cm Zr-Silica column was achieved in 25 min using 10 mM tartaric acid as eluent.

Alkalies↗

PubMed2001

Lung cancer risk, silica exposure, and silicosis in Chinese mines and pottery factories: the modifying role of other workplace lung carcinogens.

BACKGROUND: Aims of our study were to explore whether and to what extent exposure to other lung carcinogens, or staging and clinical features of silicosis modify or confound the association between silica and lung cancer. METHODS: We used data from a nested case-control study, conducted in the late 1980s in 29 Chinese mines and potteries (10 tungsten mines, 6 copper and iron mines, 4 tin mines, 8 pottery factories, and 1 clay mine), that included 316 lung cancer cases and 1,356 controls, matched by decade of birth and facility type. The previous analysis of these data presented results by type of mine or factory. RESULTS: In our study, pooling all 29 Chinese work sites, lung cancer risk showed a modest association with silica exposure. Risk did not vary after excluding subjects with silicosis or adjusting the risk estimates by radiological staging of silicosis. Strong correlation among exposures prevented a detailed evaluation of the role of individual exposures. However, lung cancer risk was for the most part absent when concomitant exposure to other workplace lung carcinogens, such as polycyclic aromatic hydrocarbons (PAHs), nickel or radon-daughters, was considered. The cross classification of lung cancer risk by categories of exposure to respirable silica and total respirable dust did not show an independent effect of total respirable dust. Silicosis showed a modest association with lung cancer, which did not vary by severity of radiological staging, or by radiological evidence of disease progression, or by level of silica exposure. However, among silicotic subjects, lung cancer risk was significantly elevated only when exposure to cadmium and PAH had occurred. CONCLUSIONS: Our results suggest that, among silica-exposed Chinese workers, numerous occupational and non-occupational risk factors interact in a complex fashion to modify lung cancer risk. Future epidemiological studies on silica and lung cancer should incorporate detailed information on exposure to other workplace lung carcinogens, total respirable dust, and on surface size and age of silica particles to understand whether and to what extent they affect the carcinogenic potential of silica.

Adult↗

PubMed1993

Fiberglass or silica exposure and increased nephritis or ESRD (end-stage renal disease).

The U.S. multiplant cohort mortality study of workers producing manufactured mineral fibers is finding increasing mortality from nephritis and/or nephrosis. We examine other data sets to see if similar effects can be identified. In a case-referent study among Michigan patients with end-stage renal disease (ESRD), men with exposures to silica have elevated odds ratio for ESRD. In a California occupational mortality study based on 1979-81 data, a number of the construction trades, farmers, and farm laborers show excess mortality for renal disease. The highest mortality ratio is found in the category including insulation workers. This ratio remains significantly elevated when adjusted for estimated exposures to smoking, alcohol, and for socio-economic status. California mortality data from 20 years earlier (1959-61) fail to show much excess renal disease in construction workers, but do for farmers. In Singapore, granite workers with a long-term exposure to silica have excess excretion of albumin and similar compounds compared to less exposed controls, leading to the presumption that silica exposure can lead to silica nephrotoxicity. Balkan nephropathy has been associated with consumption of well water high in silica. In the Negev of Israel, dust storms are a vehicle for increasing respiratory uptake of silica. The Beduin, thought to be a population with maximal exposures, have higher rates of ESRD than do Jews in the age groups over 60 years. Although high blood concentrations of silica are found in persons with renal failure, the close association with elevated creatinine has been interpreted as evidence that the buildup of silica is due to renal failure, rather than vice-versa.(ABSTRACT TRUNCATED AT 250 WORDS)

Cohort Studies↗

PubMed2004

Preparative protein purification on underivatized silica.

This article describes the use of underivatized silica gel as a preparative stationary phase for process purification of proteins. Although silica has been frequently used as a stationary phase backbone matrix, direct adsorption of proteins on underivatized silica has not been widely exploited for industrial applications. In this study an effort was made to fundamentally understand the interaction mechanisms between a protein and silica surface by using several proteins with a wide range of isoelectric points (pIs) and surface hydrophobicity. Interactions in silica were found to be largely dominated by a combination of ionic and hydrophobic forces. Accordingly, a predictive model was derived for describing linear retention of proteins on silica. Finally, a case study is described investigating the role of silica in an industrial purification process. It was found that the integration of the two modes of interaction confers silica with a unique selectivity that can be very effectively utilized in downstream bioprocessing.

Animals↗

PubMed2007

Silica-ceramic suppresses the expression of proinflammatory cytokines induced by lipopolysaccharide in macrophages.

Bioactive materials have previously been used to coat implants. In a new development for bioactive materials, a silica-ceramic mixture was found to alleviate pain (Lee, Poster presented at the Ninth World Congress of Gynecological Endocrinology, Hongkong, 2001. Poster session (p47)). Here, we hypothesized that silica-ceramic can reduce the expression and activity of cyclooxygenase 2 (COX2) or cytokines associated with inflammation. The production of COX2 and proinflammatory cytokines was investigated by reverse transcriptase (RT)-PCR and ELISA assay in macrophages stimulated by lipopolysaccharide (LPS). Silica-ceramic had no effect of COX2 expression and prostaglandin production in macrophages. However, silica-ceramic suppressed the synthesis of cytokines involved in inflammation, in particular, the expression of IL-1beta and IL-6 was reduced at the transcriptional and translational levels. The involvement of NF-kappaB in the suppression of cytokines by silica-ceramic was examined by luciferase reporter assay. The NF-kappaB activity stimulated by LPS was inhibited by 20-60% with silica-ceramic compared with treatment with LPS alone. We suggest that inhibition of NF-kappaB activity by silica-ceramic might cause the attenuation of proinflammatory cytokine expression in macrophages. In conclusion, silica-ceramic could be an alternative approach to regulate the inflammation process.

Animals↗

PubMed2003

Some aspects of silica deposition in lithistid demosponge desmas.

Transmitted light microscope and SEM observations of various growth stages, including very young forms, of lithistid demosponge spicules called desmas provided a wealth of new observations on silica deposition in desmas of most lithistid demosponge groups. In typical (pachastrellid) demosponges a basic feature of silica deposition in young spicules is the formation of silica granules (100-160 nm in diameter) deposited in more or less regular concentric layers. Further growth stages in typical demosponges are similar, only silica granules are smaller and more densely packed. The shape of the spicule is controlled by an organic axial filament, while features of the outer spicule surface are also determined by silicalemma. In lithistid desmas the early stage of silica deposition is controlled by an organic axial filament or, in some cases, dispersed organic molecules only. The next step, after early arrest of axial filament growth and its total encasing by silica, is the deposition of various silica granules (40-300 nm in diameter), spheres, and/or cylinders (1,300-3,330 nm), which are either the result of precipitation or the effect of templating by organic molecules (proteins and polysaccharides), without direct control by the silicalemma. The later stages of desma growth are under direct control of the silicalemma, which molds secondary branches and/or elements of sculpture of the desmas. The tips of desmas, which articulate with older desmas, are also controlled by local spatial relationships. Differentiation of morphological forms of silica in desmas, which is at least genus-specific, clearly supports the polyphyletic nature of lithistid sponges.

Animals↗

PubMed2000

Synthesis of Microporous Silica Spheres.

Spherical microporous silica powders with a narrow size distribution have been prepared by a precipitation technique involving the hydrolysis reaction of a silicon alkoxide in ethanol. The formation of the important microporosity has been investigated following two templating methods: the co-hydrolysis and condensation of two alkoxides, one of which presents porogen function, and the adsorption of an organic compound (glycerol) as the porogen. In both processes, the organic porogen is removed by a simple calcination. In the first method, the addition of more than 20 mol% of the porogen alkoxide, necessary for generating enough microporosity, disturbs completely the condensation process resulting in microporous, nonuniform silica particles of large size distribution. The best result has been obtained with the glycerol method where submicrometer-sized silica spheres with a very narrow size distribution and about 40 vol% porosity have been synthesized. The presence of glycerol during the synthesis considerably affects the precipitation mechanism, resulting in a larger mean particle size. The use of an aggregative growth model has successfully been employed to explain the effect of the porogen during particle formation. The precipitation mechanism of silica involves the aggregation between particles of similar size until a critical size is reached, resulting in a uniform particle size distribution. In the presence of glycerol, it has been shown that a second aggregative growth between still-nucleating primary particles and large particles occurred with increasing reaction time. This second aggregative growth appears at an intermediate stage of the precipitation process and is due to both the precipitation of smaller primary particles and the destabilization of the colloidal stability of the system. This explains why the final particle size reached in this system is larger compared to silica particles synthesized without glycerol and shows how glycerol is incorporated in the silica particles. The synthesis of silica microporous spheres of narrow size distribution, by varying particle size and porosity, should yield a wide range of aqueous silica slurries for particular chemical mechanical polishing applications. Copyright 2000 Academic Press.

Journal Article↗

PubMed2001

Rheological Properties of Silica Suspensions in Aqueous Solutions of Block Copolymers and Their Water-Soluble Components.

Dynamic moduli of fumed silica suspensions in aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers and PEO homopolymers were measured as a function of surface coverage. Since the block copolymers and PEO are adsorbed on the silica surface through hydrogen bonding between the ether oxygen and the silanol group on the silica surface, the interaction between the silanol groups, which is dominant for the aggregation of silica particles, should be prohibited. Dynamic moduli in the silica suspensions were strongly related to the stability of the silica suspensions and the block copolymer, and the longest PEO portion was useful for stabilizing the silica particles. However, the PEO homopolymer did not support stability of the silica particles, suggesting that chain conformation of the PEO portion in the block copolymer is different from that for the PEO homopolymer. Copyright 2001 Academic Press.

Journal Article↗

PubMed2002

Polymer depletion-induced instability of silica suspensions in the presence of flexible and semiflexible polymers.

Polymer depletion-induced instability of silica suspensions in dilute toluene solutions of flexible polystyrene (PS) or semiflexible poly(hexyl isocyanate) (PHIC) was investigated by direct observation and oscillatory moduli measurements as functions of silica volume fraction and polymer molecular weight. Addition of the respective polymers to the gelled silica suspensions induces a gel settling. Below the silica volume fraction phi=4 vol%, PS chains compress the volume of the sediment silica phase, whereas PHIC chains expand it and play a role in swelling agents. Thus, PHIC chains lead to the formation of aggregates in the silica suspensions that are larger and less compact than those formed by the PS chains. On the other hand, above phi=4 vol% where the silica suspension occurs gelation, the effect of nonadsorbing polymers on changes in the volume of the silica phase is opposite. Moreover, polymer depletion interaction results in a mechanically stronger gelled phase, leading to the storage modulus G' values larger than those without polymer, but the effects of polymer concentration and polymer molecular weight on the G' values are not clear.

Journal Article↗

PubMed2002

Cleavage of the fifth component of human complement and release of a split product with C5a-like activity by crystalline silica through free radical generation and kallikrein activation.

The effects of the same form of crystalline silica variously modified were compared to investigate the mechanisms by which silica activates C5 molecules. After incubation in human plasma, silica generated C5a-type fragments that stimulated polymorphonuclear leukocyte chemotaxis. This activity was totally abolished when plasma, adsorbed with antiserum against C5a or thermally inactivated, was used. Pretreatment of plasma with deferoxamine, 1,3 dimethyl-2-thiourea, or aprotinin markedly inhibited or totally abolished C5 activation. Finally, a significant increase in kallikrein activity was detected after incubation of silica particles in plasma. The results seem to indicate that the activation of C5 by crystalline silica occurs through a complex mechanism: the redox-active iron possibly present at the silica surface catalyzes, via Haber-Weiss cycles, the production of hydroxyl radicals, which in turn convert native C5 to an oxidized C5-like form. This product is then cleaved by kallikrein, activated by the same silica particles, yielding oxidized C5a with the same functional properties as C5a. The different types of the same form of silica exhibited different reactivity. Two separate properties of the dusts seem to contribute to C5 activation: the potential to release hydroxyl radicals and the extent of C5 adsorption at the surface. The degree of surface hydrophobicity/hydrophilicity appeared sufficient to explain the different responses.

Adult↗

PubMed1997

Silane-coated silica particle colloid processing of human sperm.

PURPOSE: The purpose of this study was to determine differences in the quality of human sperm processed through different lots of silane-coated silica particle colloid solutions. The objectives were to compare (a) sperm kinematic parameters, (b) the sperm acrosome status, (c) the membrane integrity of the head and tail regions, (d) the DNA normality, and (e) the heat-inducible hyperactivation motility after processing sperm through either a Silane-coated silica particle colloid solution, a Percoll solution, or a simple centrifuge sperm wash (control). METHODS: Sperm cells were derived from pooled cryopreserved-thawed specimens of several donors (n = 10). The pooled sperm were divided and processed through either the centrifuge wash, the 90:47% two-layer Percoll, or one of three lots of silane-coated silica particle colloidal solutions from three vendors. Aliquots of sperm cells were analyzed using the Hamilton-Thorn HTM-C motility analyzer for differences in kinematics and hyperactivation. Sperm were also analyzed for membrane integrity at both head and tail regions, normal morphology, acrosome status, and viability. Sperm undergoing apoptosis were determined using the acridine orange stain. Processed sperm were also incubated at 40 degrees C for 4 hr and the quality of the sperm was assessed using the heat-induced hyperactivation and motility parameter. RESULTS: The data showed that after sperm processing, the number of sperm recovered was higher for the three lots of colloids (silane-coated silica particle colloid solutions) compared with Percoll processing. Total sperm motility was higher in the colloidal washes compared with the control. There were no differences in motility between Percoll- and colloid-processed sperm. In contrast, the percentages of sperm exhibiting progressive motility or hyperactivation varied among the different lots of colloid solutions. The Percoll wash solution yielded the highest percentage of sperm with intact tail membranes, whereas some lots of colloid solutions disrupted sperm head membranes. The percentages of sperm undergoing apoptosis varied for the different lots of colloid solutions. There was a marked increase in hyperactivation associated with one colloid solution after heat induction. CONCLUSIONS: The results demonstrated variability in the different lots of silane-coated silica particle colloid solutions for processing sperm. Each lot of colloid solution excelled at improving different sperm parameters. The silane-coated silica particle colloid solutions were shown to be effective in recovering motile sperm compared with Percoll but the types of motility and sperm quality varied for the different lots of colloid solutions. Due to the variability in lots of silane-coated silica colloid solutions, reported studies based on only one lot or one source of colloid solution may be difficult to interpret. Furthermore, it may be advantageous to select the best lot of silane-coated silica particle colloid solution to produce the highest number of sperm exhibiting the ideal parameters for use in assisted reproduction technologies.

Acridine Orange↗

PubMed2005

Adsorption of mercury ions by mercapto-functionalized amorphous silica.

Amorphous silicas have been functionalized by two different methods. In the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the silica surface to give the chlorinated silica Cl-Sil. In a second reaction, multifunctionalized N,S donor compounds were incorporated to obtain the functionalized silicas, which are denoted as L-Sil-Het (where L=mercaptothiazoline, mercaptopyridine or mercaptobenzothiazole). In the homogeneous route, the functionalization was achieved through a one-step reaction between the silica and an organic ligand containing the chelating functions; this gave the modified silicas denoted as L-Sil-Hom. The functionalized silicas were characterized by elemental analysis, IR spectroscopy and thermogravimetry. These materials were employed as adsorbents for mercury cations from aqueous and acetone solutions at room temperature. The results indicate that, in all cases, mercury adsorption was higher in the modified silicas prepared by the homogeneous method. Figure.

Adsorption↗

PubMed1984

The binding of silica to proteins from plasma and lungs of rat: in vitro.

Silica dissolving out from the slate dust was found to bind with plasma protein and purified bovine serum albumin. At 24 h of incubation at 37 degrees C binding affinity of silica (microgram of silica bound/mg of protein) with plasma protein and bovine serum albumin was found to be 0.59 and 0.44, respectively. By molecular exclusion chromatography using Sephadex G-200, silica binding protein of plasma was determined to be of mol. wt. around 67000. Similar proteins having silica binding capacity (mol. wt. 70000 and 85000) were also found in rat lung but these proteins unlike their plasma counterpart were glycoprotein in nature. Polyacrylamide gel electrophoresis of plasma and protein rich lung fraction show that proteins upon binding with silica undergo mobility changes. Significance of the existence of silica binding protein in plasma and lung of rat in relation to silica toxicity is discussed.

Animals↗

PubMed1993

Oxidative DNA damage by crystalline silica.

Using a simple DNA strand breakage assay, we detected the production of oxidant species, probably hydroxyl free radicals, in buffered suspensions of crystalline silica at pH 7.4. DNA damage was affected by the presence of oxygen and was accelerated by superoxide dismutase and by hydrogen peroxide. Deferoxamine blocked damage by hydrogen peroxide and silica but accelerated DNA damage by silica alone and by superoxide dismutase and silica. DNA damage was blocked by catalase and by the scavenging agents dimethyl sulfoxide and sodium benzoate. Chemical etching of crystalline silica to remove impurities by treatment of the surface with hydrofluoric acid resulted in markedly diminished DNA damaging ability. Even preparations of crystalline silica previously characterized as highly pure contained trace iron impurities in amounts significant enough to produce oxygen free radicals in aqueous suspension. Both superoxide and Fenton reaction oxidants were produced. We conclude that silica is able to mediate DNA strand breakage in vitro and that this DNA damage may be an important factor in silica toxicity.

Catalase↗

PubMed2005

Comparison of titania, zirconia, and silica stationary phases for separating diesel fuels according to hydrocarbon group-type by supercritical fluid chromatography.

Silica, zirconia, and titania columns were compared for their ability to separate diesel samples into saturates, mono-, di-, tri-, and polyaromatics by supercritical fluid chromatography (SFC) using pure CO(2) according to ASTM method D 5186-03. A titania column coupled in series to a silica column was found to provide the highest overall group-type resolutions based on 20 model compounds, with resolutions as high as 14.7 for saturates versus monoaromatics and 11.9 for monoaromatics versus diaromatics. An oilsands-derived Synfuel light diesel, a commercial Ontario diesel, and a heavy Shell Canada Ltd. diesel blending feedstock were studied on a titania-silica coupled column as well as on a conventional silica column. The Synfuel results were similar (within 0.5 mass%) on both the conventional bare silica column and the titania-silica coupled column. The heavier commercial diesel and diesel blending feedstock samples yielded different results on the titania-silica coupled column compared to the silica column alone, demonstrating the importance of achieving the highest possible resolutions when baseline separation of group-types is not obtained.

Chromatography, Supercritical Fluid↗

PubMed2006

Silica particles encapsulated poly(styrene-divinylbenzene) monolithic stationary phases for micro-high performance liquid chromatography.

In the paper we demonstrate a new approach for the preparation and application of continuous silica bed columns that involve encapsulation (entrapment) of functionalized silica microparticles, which can be used as packing material in micro high performance liquid chromatography (micro-HPLC) and capillary electrochromatography (CEC). Like traditional packed columns, these capillaries possess characterized silica particles that offer high phase ratio and narrow pore size distribution leading to high retention and separation efficiency, respectively. More importantly, immobilization of the microparticles stabilizes the separation bed and eliminates the need for retaining frits. The developed capillary columns were fabricated in exactly the same way as a packed capillary column (slurry packing) but with an additional entrapment step. This immobilization of the packed bed was achieved by in situ polymerization of styrene and divinylbenzene in presence of decanol as a porogen and azobisisobutyronitrile as thermal initiator. Silica particles with different particle sizes and pore sizes ranging from 60 to 4000 A were studied. In addition different modified silica was used, including C-18 reversed phase, anion exchange and chiral stationary phases. Efficient separation of polyphenolic compounds, peptides, proteins and even DNA mutation were achieved using the developed technique depending on the properties of the silica particles used (particles pore size). For example, using 3 microm ProntoSIL C-18 particles with 300 A pore size, separation efficiencies in the range of 120,000-200,000 plates/m were obtained for protein separation, in a 6 cm x 200 microm i.d. capillary column. Using encapsulated silica C-18 with 1000 A pore size, separation of DNA homo and hetero duplexes were achieved under denaturing HPLC conditions for mutation detection. In addition, nucleotides were separated using anion exchange material encapsulated with poly(styrene-divinylbenzene) (PS/DVB), which indicated that the chromatographic properties of the silica packing material were still active after polymerization. The prepared capillary columns were found to be stable and could easily be operated continuously up to a pressure of 350 bar without column damage and capillary can be cut to any desired length.

Chromatography, High Pressure Liquid↗