Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SILICONES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed1997

Toxicity in vitro of some silicon carbides and silicon nitrides: whiskers and powders.

The objectives of this work were to investigate the toxicity of silicon carbide whiskers and powders and silicon nitride whiskers and powders and to compare their toxicity with the toxicity of crocidolite. The effects studied were inhibition of the cloning efficiency of V79 cells, formation of DNA strand breaks by means of a nick translation assay, formation of oxygen radicals in three different assays, and the ability to stimulate neutrophils to produce hydroxyl radicals. All materials showed concentration-dependent inhibition of the cloning efficiency of V79 cells. The inhibition by the most toxic whiskers was in the same order of magnitude as that of crocidolite. Milled whiskers and powders were less toxic than the whiskers. There was a high DNA breaking potential for crocidolite and four of the silicon carbide whiskers and a rather low one for the other materials. Formation of hydroxyl radicals was found for crocidolite and one of the silicon carbide whiskers. In the neutrophil activation test, there was a great variation in the different materials' abilities to activate neutrophils. There was also a good correlation between chemiluminescence and H2O2 formation. The highest activation was found in neutrophils exposed to two of the silicon carbide whiskers and one milled whisker. The conclusion of the investigation is that some of the ceramic materials studied had damaging biological effects comparable to or greater than those of crocidolite. The results from the investigation clearly imply that caution is needed in the introduction of new ceramic fiber materials, so that the correct precautions and protective devices are used in order to avoid harm to the personnel handling the material.

Air Pollutants, Occupational↗
PubMed1992

Silicon metabolism. The interrelations of inorganic silicon (Si) with systemic iron (Fe), Zinc (Zn), and copper (Cu) pools in the rat.

The influence of silicon treatment on the levels of trace elements zinc (Zn), copper (Cu), and iron (Fe) in serum and tissues was studied in rats. The concentrations of silicon, iron, and zinc were estimated in samples of sera and tissues of rats receiving per os a soluble, inorganic silicon compound--sodium metasilicate nonahydrate (Na2SiO3.9H2O), dissolved in the drinking water. An increase of copper concentrations in liver and aortic walls in the experimental group was observed, with simultaneous reduction of zinc amounts in serum and all the tissue samples in the course of the experiment. The iron concentrations in the analyzed samples did not show any significant changes between both groups. The silicon levels in serum and in all the examined tissues were significantly higher in the tested group. The results provide evidence for the silicon interaction with copper and zinc, which could result in a number of metabolic process modifications, antiatheromatous activity among them.

Animals↗
PubMed1996

Anterior proliferative vitreoretinopathy in the silicone study. Silicone Study Report Number 10.

BACKGROUND: As part of the design of the Silicone Study, a new classification of proliferative vitreoretinopathy (PVR) was developed that distinguishes the different types of contraction found in PVR. In contrast to the original Retina Society system that emphasized the post-equatorial retinal pathology (posterior PVR), the Silicone Study classification system included the characteristic types of contraction found in both the equatorial region and the pre-equatorial retina and vitreous base (anterior PVR). METHODS: The authors contrast (1) preoperative and intraoperative findings and (2) vision and anatomic outcomes in the cohort of anterior PVR eyes with the cohort of posterior-only PVR eyes. For the cohort of eyes randomized to perfluoropropane gas (C3F8) or silicone oil, the authors carry out univariate and multivariate analyses to assess the predictive value of baseline and intraoperative parameters on vision and anatomic outcome. RESULTS: Anterior PVR was present in 321 eyes (79%) and was more prevalent in eyes that had undergone an unsuccessful vitrectomy before study entry than in eyes that underwent a primary vitrectomy for PVR (88% versus 73%; P < 0.001). Compared with eyes that had posterior PVR at the preoperative examination, eyes that had anterior PVR tended to (1) be graded (Retina Society classification system) as D-1 or worse (86% versus 49%; P < 0.0001), (2) have worse (< 2/200) visual acuity (93% versus 86%; P = 0.003), (3) have more hypotony (24% versus 11%; P = 0.03), more edema (8% versus 2%; P = 0.04), more aqueous flare (P = 0.02), more macular pucker (69% versus 52%; P = 0.005), and more intravitreal contraction (21% versus 6%; P = 0.002). When compared with eyes that had anterior PVR, eyes with posterior PVR had a better outcome at the 6-month postoperative examination: complete attachment of the retina (76% versus 62%; P = 0.04), visual acuity of 5/200 or better (64% versus 45%; P = 0.006), and normal intraocular pressure (86% versus 71%; P = 0.04). For eyes with anterior PVR, significant predictors of poor (< 5/200) visual acuity were a preoperative PVR grade D-1 or worse and the use of C3F8 gas as the intraocular tamponade. CONCLUSION: The Silicone Study classification of anterior PVR permits greater specificity in characterizing PVR and is prognostic of anatomic and vision outcome. Eyes with anterior PVR and clinically significant posterior PVR changes had a better visual prognosis if silicone oil was used. With the current understanding of the pathoanatomy of anterior PVR and the recent development of new surgical techniques, the incidence of anterior PVR in eyes that previously underwent vitrectomy may decline, and the prognosis in eyes with anterior PVR may improve.

Adult↗
PubMed2002

New drug delivery system for water-soluble drugs using silicone and its usefulness for local treatment: application of GCV-silicone to GCV/HSV-tk gene therapy for brain tumor.

Controlled release of a water-soluble low-molecular-weight drug from silicone and its usefulness as a local therapeutic drug were studied. For application to ganciclovir/helpes simplex virus thymidine kinase (GCV/HSV-tk) suicide gene therapy for brain tumor, two kinds of GCV-containing silicone formulations were prepared for evaluation. In vitro, GCV release from matrix-type formulation consisting of a single matrix was characterized by Fickian diffusion, while covered-rod-type formulation, in which the side surface of the outer layer was covered with 100% silicone, exhibited a near-zero-order release pattern. In an in vivo study using a rat 9L glioblastoma model, administration of GCV-silicone formulation into brain tumor yielded sustained intracerebral GCV concentration for 4 days after administration, with excellent antitumor effect equal to or better than that of daily intraperitoneal administration of aqueous solution of GCV, at a dose less than 1/100 of the total dose of solution for intraperitoneal administration. Furthermore, GCV was undetectable in blood, suggesting that decrease in systemic adverse reactions can be expected with intracerebral administration of GCV-silicone formulation.

Algorithms↗
PubMed2001

Determination of low molecular weight silicones in plasma and blood of women after exposure to silicone breast implants by GC/MS.

A sensitive, one-step sample preparation method for detection of volatile, low molecular weight (LMW) cyclic silicones hexamethylcyclotrisiloxane (D3), octamethyl-cyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in plasma and blood using gas chromatography coupled with mass spectrometry (GC/MS, SIM mode) is presented. In spiked experiments, extraction efficiencies for these siloxanes (100-20 000 ng/mL) were approximately 90% for plasma and approximately 80% for blood; only in the case of D3 was the recovery very low. Plasma and blood of women who are or were exposed to silicone gel-filled implants and of control subjects were analyzed for low molecular weight silicones. D3-D6 were not detectable in control plasma or blood. Although the investigated numbers of patients samples are very limited, and thus, no statistical analysis is possible, our data clearly show a general increase in the amount of LMW cyclic siloxanes in the bodies of women with silicone implants. In particular, several years after ruptured silicone implants were removed, siloxanes could still be found in blood samples from several women. Siloxane compound D3 varied between 6 and 12 ng/mL (plasma) and between 20 and 28 ng/mL (blood), whereas the concentration range of D4 was 14-50 ng/mL (plasma) and 79-92 ng/mL (blood). D5 and D6, with one exception, could not be detected.

Adult↗
PubMed1955

Silicon metabolism in diatoms. III. Respiration and silicon uptake in Navicula pelliculosa.

1. Evidence is presented that silicon uptake in the diatom Navicula pelliculosa is linked with aerobic respiration. 2. Cyanide, fluoride, iodoacetate, arsenite, azide, and fluoroacetate, at concentrations inhibitory to respiration, were also inhibitory to silicon uptake. 3. 2,4-Dinitrophenol (1 to 2 x 10(-5)M) stimulated respiration by 100 per cent, but almost completely inhibited silicon uptake. 4. The respiratory quotient of non-Si-deficient cells decreased from 0.93 to 0.75 after 4 days of starvation in darkness. Glucose (1 per cent) raised the respiratory quotient of such starved cells to 1.05. 5. Silicate (20 mg. Si/liter) stimulated respiration of unstarved Si-deficient cells by about 40 per cent. The effect of silicate on the respiration of Si-deficient cells which had been starved in darkness for 4 days was less marked. 6. The respiratory quotient of Si-deficient cells decreased from 0.8-0.9 to 0.3 after 4 days of starvation in darkness. The addition of silicate to starved cells raised the quotient to 0.5. This represented a 25 per cent stimulation of oxygen uptake concomitant with a 90 per cent stimulation of carbon dioxide evolution. 7. Glucose (1 per cent) caused an increase of respiratory quotient in starved cells from 0.3 to 0.7-0.8. The addition of silicate had no effect on the R.Q. during the oxidation of exogenous glucose. 8. Substrates (glucose, fructose, galactose, lactate, succinate, citrate, glycerol), which caused a stimulation of respiration in starved cells, also stimulated silicon uptake by those cells. However, the stimulation of silicon uptake (50 to 100 per cent) was not proportional to the respiratory stimulation by these substrates (30 to 300 per cent).

Diatoms↗
PubMed2005

First reaction of a bare silicon surface with acid chlorides and a one-step preparation of acid chloride terminated monolayers on scribed silicon.

Methyl-terminated and acyl chloride terminated monolayers are produced when silicon is scribed under mono- and diacid chlorides, respectively. To the best of our knowledge, this is the first report of the reaction between a bare silicon surface and acid chlorides. This reaction takes place by wetting the silicon surface in the air with the acid chloride and scribing. Scribing activates the silicon surface by removing its passivation layer. We propose that scribed silicon abstracts chlorine from an acid chloride to form an Si-Cl bond and that the resulting acyl radical diffuses back to the surface to condense with the surface and form an alkyl monolayer. X-ray photoelectron spectroscopy (XPS) confirms the presence of chlorine and shows a steady increase in the amount of carbon with increasing alkyl chain lengths of the acid chlorides. Time-of-flight secondary ion mass spectrometry shows SiCl(+) species and a steady increase in representative hydrocarbon fragments with increasing alkyl chain lengths of the acid chlorides. XPS indicates that diacid chlorides react primarily at one of their ends to create acyl chloride terminated surfaces in a single step. The resulting surfaces are shown to react with various amines (piperazine, morpholine, and octylamine) and a protein. Calculations at Hartree-Fock and density functional theory levels are consistent with the proposed mechanism.

Journal Article↗
PubMed2001

Monitoring metal ion contamination onset in hydrofluoric acid using silicon-diamond and dual silicon sensing electrode assembly.

Potentiometric detection of trace levels of metallic contamination onset in hydrofluoric acid using a silicon-based sensor in conjunction with two non-contaminating reference electrode systems is presented in this paper. In the first case, conductive diamond was used as a non-contaminating reference electrode. Cyclic voltammetry and open-circuit potential experiments demonstrated the feasibility of using a conductive diamond film electrode as a quasi-reference electrode in the HF solution. In the second case, a dual silicon electrode system was used with one of the silicon-based electrodes protected with an anion permeable membrane behaving as the quasi-reference electrode. The dual silicon sensing electrode system possessed an additional operational advantage of being unaffected by the solution acidity. Though both sensing configurations were able to detect the metal ion contamination onsets at the parts-per-trillion to parts-per-billion levels, the dual silicon electrode design showed a greater compatibility for the on-line detection of metallic impurities in HF etching baths commonly used in semiconductor processing.

Journal Article↗
PubMed1995

Experimental retinal tolerance to very low viscosity silicone oil (100 cs) as a vitreous substitute compared to higher viscosity silicone oil (5000 cs).

We evaluated the toxicity of very low viscosity (100 centistokes) and higher viscosity silicone oil (5000 centistokes) in rabbit eyes as a short-to-long-term postoperative vitreous substitute (6 weeks to 5 months). Emulsification of 100-cs and 5000-cs silicone oil did not occur in eyes which were followed for as long as 5 months. No toxic effects to retinal cells were detected by light or electron microscopy. Because no toxic effects were seen with 100-cs silicone oil, it can be used in an outpatient setting as a short-term postoperative tamponading agent. Electroretinographic responses of silicone-injected eyes were normal.

Animals↗
PubMed1998

The immunopathology of siliconosis. History, clinical presentation, and relation to silicosis and the chemistry of silicon and silicone.

Recent evidence confirms the fundamental involvement of the human immune system in the reaction to implantation of silicone-based medical devices. An as yet-to-be particularized epitope of many complex substances sharing siloxane structures is presented through the MHC-II apparatus with development and retention of T cell memory. This memory can be tested for in practical terms using one or more forms of silica, which links the immuno-histopathology and autoimmune attributes of "silicosis" with those of "siliconosis." The lesions of siliconosis are typical of those for persistent antigens and delayed, cell mediated hypersensitivity. The basic descriptive pathology of the reaction to silicone has been known since soon after introduction of silicones in medical procedures, with the exception of some details related to the more recent discoveries on the role of cytokines in the immunopathic process. The clinical consequences of siliconosis are common and can be severe in some individuals implanted with silicone devices.

Autoimmune Diseases↗
PubMed2000

Removing silicone oil droplets from the posterior surface of silicone intraocular lenses.

A 67-year-old woman had droplets of silicone oil adhering to her silicone intraocular lens (IOL) resulting from a previous silicone oil tamponade. A lens hook and intraocular irrigation were used in conjunction by inserting an infusion cannula to remove the droplets. This restored clarity of the visual axis, improved visual acuity, and eliminated the need for IOL replacement. The technique is simple and less invasive than IOL exchange and may become the preferred way to remove silicone droplets from an IOL.

Aged↗
PubMed2003

Pinpoint and bulk electrochemical reduction of insulating silicon dioxide to silicon.

Silicon dioxide (SiO(2)) is conventionally reduced to silicon by carbothermal reduction, in which the oxygen is removed by a heterogeneous-homogeneous reaction sequence at approximately 1,700 degrees C. Here we report pinpoint and bulk electrochemical methods for removing oxygen from solid SiO(2) in a molten CaCl(2) electrolyte at 850 degrees C. This approach involves a 'contacting electrode', in which a metal wire supplies electrons to a selected region of the insulating SiO(2). Bulk reduction of SiO(2) is possible by increasing the number of contacting points. The same method was also demonstrated with molten LiCl-KCl-CaCl(2) at 500 degrees C. The novelty and relative simplicity of this method might lead to new processes in silicon semiconductor technology, as well as in high-purity silicon production. The methodology may be applicable to electrochemical processing of a wide variety of insulating materials, provided that the electrolyte dissolves the appropriate constituent ion(s) of the material.

Calcium Chloride↗
PubMed1995

The incidence of corneal abnormalities in the Silicone Study. Silicone Study Report 7.

OBJECTIVE: To determine factors that were prognostic of corneal abnormalities in eyes following surgery for severe proliferative vitreoretinopathy. DESIGN: Subgroup analysis of the Silicone Study. SETTINGS: Community and university-based ophthalmology clinics. MATERIALS: Eyes with attached maculae at the 24-month follow-up examination that did not have a pre-existing corneal abnormality. INTERVENTIONS: Vitrectomy surgery with long-acting gas or silicone oil. OUTCOME MEASURES: Epithelial and/or stromal edema, corneal opacity and/or previous corneal transplant. RESULTS: The incidence of corneal abnormalities at 24 months was 27% and did not differ significantly between treatment groups. Prognostic factors were preoperative aphakia or pseudophakia (P = .003), preoperative iris neovascularization (P = .006), reoperation (P = .001), the absence of a fluid/gas exchange (P = .03), corneal touch by silicone oil (P = .02), and the presence of aqueous cells (P = .009) or aqueous flare (P = .08). In a multivariate analysis, independent prognostic factors were iris neovascularization (relative risk [RR] = 13.1), aphakia or pseudophakia (RR = 3.0), postoperative aqueous flare (RR = 5.4), and reoperations (RR = 3.4). Corneal abnormalities were correlated with poor visual acuity and hypotony (P < .001). CONCLUSIONS: To our knowledge, this is the first study to document that the incidence rates of corneal abnormalities are equivalent between oil and gas. The incidence of corneal abnormalities in gas-filled eyes was higher than expected, and remained high in oil-filled eyes, despite the use of an inferior iridectomy. Successful surgical repair of the retinal detachment with a single operation, and prevention and early management of corneal touch by silicone oil should help to prevent corneal abnormalities. If rubeosis iridis or severe aqueous flare is present, preoperative treatment with intense topical and possibly periocular steroids might reduce inflammation, which might mediate corneal damage.

Adult↗
PubMed1995

Simple technique for the preparation of silicone gel particles: the effect of silicone gel particles on oxidative responses of macrophages.

A simple technique was developed to prepare phagocytosable-size particles from the silicone gel used in breast implants. Sonication of silicone gel (1 g) in 5 ml of 20 mM sodium phosphate buffer (pH 7.2) containing 1% (wt/vol) polyoxypropylene-polyethylene block surfactant (F-68 or F-108) produced silicone gel particles ranging from 1-50 microns in diameter. Passage of the suspension through a series of filters yielded phagocytosable particles (1-5 microns in diameter) at a concentration of ca. 2 x 10(9) particles/ml. The particles remained as individual particles, did not coalesce to form large clumps, and were not pelleted by centrifugation (2000 x g, 20 min). They were not toxic for rabbit alveolar macrophages (AM) during 24 h of incubation at 37 degrees C, did not elicit an oxidative burst from AM in vitro in a luminol-enhanced chemiluminescent assay, and did not significantly increase the phorbol myristate acetate (PMA)-elicited oxidative burst by AM. AM isolated from rabbits 2 days after the intravenous injection of silicone particles were not primed or activated (i.e., the AM did not show an enhanced oxidative burst when elicited with PMA in vitro). However, AM isolated from rabbits 2 days after intratracheal injection of the particles were primed but only exhibited a 4-6-fold increase in the oxidative burst elicited with PMA.

Animals↗
PubMed1988

Effect of contaminants on the adhesion of light-bodied silicones to putty silicones in putty-wash impression technique.

This study was concerned with the adhesion of a light-bodied silicone to a putty silicone in a putty-wash impression technique when the preliminary putty impression was contaminated with human saliva or residues from acrylic resins used in the fabrication of provisional restorations by direct technique. Data indicated that condensation and addition silicones differed in their susceptibility toward the tested contaminants. Salivary contamination and chemical residues from the autopolymerizing acrylic resins weakened the bond strength and caused adhesive failure dependent upon the type of silicone impression material used.

Acrylic Resins↗
PubMed2006

Locoregional silicone spread after high cohesive gel silicone implant rupture.

A 45-year-old patient had routine cosmetic bilateral breast augmentation 6 years previously using cohesive gel implants. She presented 4 years later with a breast lump and multiple axillary lymph nodes. Exploration revealed that the breast implant had a large tear at the posterior wall of the shell with intra-capsular leakage of silicone. The axilla had eight enlarged lymph node--all were removed. Histology showed silicone granuloma in the capsule and silicone lymphadenitis. High cohesive gel implants may not be as safe as is commonly believed and all implant ruptures, irrespective of the cohesiveness of the silicone gel, should be investigated thoroughly.

Axilla↗
PubMed2000

Migration of silicone oil into the brain: a complication of intraocular silicone oil for retinal tamponade.

PURPOSE: To report a case in which intravitreal silicone oil migrated along the intracranial portion of the optic nerve and into the lateral ventricles of the brain after the repair of a retinal detachment secondary to cytomegalovirus retinitis. METHODS: A 42-year-old man with acquired immunodeficiency syndrome (AIDS) developed a rhegmatogenous retinal detachment in his left eye secondary to a cytomegalovirus infection of the retina. The detachment was repaired using 5000 cs intraocular silicone oil for a long-term tamponade. Subsequently, the affected eye developed glaucoma, which was poorly controlled. Fifteen months after the retinal surgery, he developed a peripheral neuropathy that was thought to be AIDS related. Computed tomography and magnetic resonance imaging of the head were performed to investigate the neuropathy. RESULTS: The patient was found to have a foreign substance within his lateral ventricles that shifted with position and was identical with respect to its imaging properties to the remaining intraocular silicone oil. Additional material was found along the intracranial portion of his optic nerve. CONCLUSION: Under certain circumstances, intraocular silicone oil may migrate out of the eye, along the intracranial portion of the optic nerve, and into the lateral ventricles of the brain.

AIDS-Related Opportunistic Infections↗
PubMed1993

Postoperative complications and uncorrected acuities after implantation of plate haptic silicone and three-piece silicone intraocular lenses.

Complications after implantation of 503 plate haptic silicone intraocular lenses were compared with those after implantation of 253 silicone three-piece polypropylene loop lenses. The uncorrected visual acuities were also compared. Capsulorhexis and endocapsular phacoemulsification were used in all cases. The incidence of cystoid macular edema and posterior capsule opacification requiring a YAG capsulotomy were significantly higher in the cases with polypropylene three-piece loop lenses. Pigment dispersion and decentration also occurred more frequently in this group. This is probably because the 10.5 mm plate haptic lens is more rigid than the polypropylene loop lens. It also fixates more posteriorly within the capsular bag than the anteriorly located polypropylene lens. Patients implanted with a plate haptic silicone intraocular lens through a 3.5 mm scleral incision had significantly better uncorrected visual acuity at five to six weeks postoperatively than those with a three-piece silicone lens that required a 4.5 mm incision for insertion.

Aged↗