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 163 records · Page 9Linked to original sources
PubMed2001

Quantum confinement in amorphous silicon quantum dots embedded in silicon nitride.

Amorphous silicon quantum dots (a-Si QDs) were grown in a silicon nitride film by plasma enhanced chemical vapor deposition. Transmission electron micrographs clearly demonstrated that a-Si QDs were formed in the silicon nitride. Photoluminescence and optical absorption energy measurement of a-Si QDs with various sizes revealed that tuning of the photoluminescence emission from 2.0 to 2.76 eV is possible by controlling the size of the a-Si QD. Analysis also showed that the photoluminescence peak energy E was related to the size of the a-Si QD, a (nm) by E(eV) = 1.56+2.40/a(2), which is a clear evidence for the quantum confinement effect in a-Si QDs.

Journal Article↗
PubMed2002

Metastability of amorphous silicon from silicon network rebonding.

We propose a network rebonding model for light-induced metastability in amorphous silicon, involving bonding rearrangements of silicon and hydrogen atoms. Nonradiative recombination breaks weak silicon bonds and generates dangling bond-floating bond pairs, with very low activation energies. The transient floating bonds annihilate, generating local hydrogen motion. Charged defects are also found. Support for these processes is found with tight-binding molecular dynamics simulations. The model accounts for major experimental features of the Staebler-Wronski effect including electron-spin resonance data, the t(1/3) kinetics of defect formation, two types of metastable dangling bonds, and hysteretic annealing.

Journal Article↗
PubMed2002

Limiting step involved in the thermal growth of silicon oxide films on silicon carbide.

Thermal growth of silicon oxide films on silicon carbide in O2 was investigated using oxygen isotopic substitution and narrow resonance nuclear reaction profiling. This investigation was carried out in parallel with the thermal growth of silicon oxide films on Si. Results demonstrate that the limiting steps of the thermal oxide growth are different in these two semiconductors, being diffusion limited in the case of Si and reaction limited in the case of SiC. This fact renders the growth kinetics of SiO2 on SiC very sensitive to the reactivity of the interface region, whose compositional and structural changes can affect the electrical properties of the structure.

Journal Article↗
PubMed1985

Occurrence of airborne silicon carbide fibers during industrial production of silicon carbide.

Airborne dust from the production of silicon carbide has been analyzed for particle morphology and composition. Fibers of alpha silicon carbide were identified by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) with selected area electron diffraction techniques (SAED). Micrographs taken at high magnification revealed several stacking periods along the fiber axis, and one or more of the polytypes 2H, 4H, or 6H could be distinguished. Preliminary investigations applying SEM showed that 80% of the fibers had diameters of less than 0.5 micron and a length greater than 5 micron. Fiber concentrations were examined by the counting of stationary and personal samples in an optical phase contrast microscope. The fiber levels in the three plants investigated were low and less than 1 fiber/cc of air (10(6) fibers/m3). Dust samples from the handling of raw material, including recycled material, contained up to 5 fibers/cc (5 X 10(6) fibers/m3).

Air Pollutants, Occupational↗
PubMed2002

A prospective study on silicone breast implants and the silicone-related symptom complex.

This cohort study prospectively evaluated the prevalence of the silicone-related symptom complex (SRSC) in relation to antinuclear antibodies (ANA) and magnetic resonance imaging (MRI) of silicone breast implants (SBI) 1 year after implantation. A total of 57 women undergoing mastectomy followed by immediate breast reconstruction (IBR) and SBI between March 1995 and March 1997 at the University Hospital Rotterdam/Daniel den Hoed Cancer Centre, were prospectively evaluated. Just before and 1 year after IBR the sera of these women were tested for the presence of ANA and they were screened for the prevalence of SRSC-related symptoms by questionnaire. All prostheses were evaluated by MRI 1 month and 1 year after IBR. Just before operation 11% of the women had a Sjögren score of more than 2, whereas 30% had such a score 1 year after IBR ( P = 0.01). One year postoperatively women had significantly more RA/Raynaud-related complaints: 21% preoperatively versus 40% 1 year after IBR ( P = 0.03). Within the undefined complaints-related group 19% had a score of 2 or more preoperatively and 33% 1 year after IBR ( P = 0.09). There were no new cases of ANA positivity 1 year after IBR. The linguine sign was seen by MRI in three implants: one 1 month after IBR and two 1 year after IBR. There was no relation to changes in SRSC expression and these MRI findings. In conclusion, 1 year after SBI implantation women had more SRSC-related complaints, especially Sjögren's and RA/Raynaud's. Moreover there was no correlation between elevated SRSC expression and changes in the presence of ANA or changes in MRI of the SBI 1 year after IBR.

Adult↗
PubMed2000

First evaluation study of the Dutch Working Party on silicone breast implants (SBI) and the silicone-related symptom complex (SRSC).

This cohort study evaluates the postoperative prevalence of antinuclear antibodies (ANA) in relation to symptoms related to the so-called silicone-related symptom complex (SRSC). A total of 63 women who underwent mastectomy followed by immediate breast reconstruction with a silicone implant (SBI) between Septembber 1990 and May 1995 at the University Hospital Rotterdam/Daniel den Hoed Cancer Center, participated voluntarily in the study. Their sera were tested for the presence of antinuclear antibodies (ANA) and at the same time they were screened for the prevalence of SRSC-related symptoms by questionnaire. All patients were also examined physically. Sixteen per cent of the women were ANA positive. There was no difference in SRSC expression between ANA-positive and ANA-negative women. The lack of difference in symptom expression between the ANA-positive and ANA-negative women and the rather low complaint percentage proves that if ANA positivity is related to the SRSC, we found no evidence that patients with a SBI with a positive ANA differed from the ANA-negative patients.

Adult↗
PubMed2005

[Breast implants and silicone: silicone crisis' history].

In 1992 the FDA declared a moratorium on silicone implants, after a fight with the manufacturers. This moratorium extended world wide and lasted differently among the different countries. In Europe, France was the most troublesome about this problem. It took 8 years of actions against several civil servants and at least a trial at the "Council of State" could succeed in 2000 and brough back the silicone implants to the market in 2001.

Breast Implants↗
PubMed1989

Classification of proliferative vitreoretinopathy used in the silicone study. The Silicone Study Group.

The Silicone Study is a multicenter randomized clinical trial that compares a long-acting gas with silicone oil for the surgical treatment of proliferative vitreoretinopathy (PVR). As part of the study, a topographic classification of PVR has been developed that is based on the characteristic patterns of retinal distortion produced by the contraction of proliferative membranes on the retina or within the vitreous base. This classification is used to document the extent and anatomic distribution of PVR present preoperatively and to help standardize the surgical treatment. Experience has shown that this classification facilitates the identification of these membranes and their systematic dissection, and the authors therefore suggest that it be used to augment the Retina Society classification of PVR.

Humans↗
PubMed2004

Comparing study of the effect of nanosized silicon dioxide and microsized silicon dioxide on fibrogenesis in rats.

This study compares the effect of nanosized silicon dioxide (nanosized SiO2) and microsized silicon dioxide (microsized SiO2) particles on fibrogenesis in rats. Wistar rats were instilled intratracheally with saline, 20 mg of nanosized SiO2 or 20 mg of microsized SiO2, and were sacrificed at 1 and 2 months after instillation. The lungs of rats were analysed for the changes of lung/body coefficient and hydroxyproline content. Changes in pathology and fibrotic grade were observed by use of hematoxylin and eosin and Van Gieson dyeing. The expression of interleukin-4 (IL-4) and transforming growth factor-beta1 (TGF-beta1) was observed by use of immunohistochemical technique, and protein expression quantitatively analysed by image analysis. The lung/body coefficient and hydroxyproline content of nanosized SiO2 groups were significantly lower than those of microsized SiO2 groups at both 1 and 2 months after instillation (P<0.05 or P<0.01), but without significant differences from those of saline control groups. At 1 month after instillation, there were mainly cellular nodules (Stage I) in nanosized SiO2 group, while in microsized SiO2 group Stage II, II+ of silicotic nodules were observed. At 2 months after instillation, there were still Stage I of silicotic nodules in nanosized SiO2 group. In microsized SiO2 group mainly Stage II+, III of silicotic nodules were found. Quantity image analysis showed that the expressions of IL-4 and TGF-beta1 in nanosized SiO2 groups were significantly lower than those in microsized SiO2 groups (P<0.01), but without significant difference from those of saline control groups. Our experiment revealed that the effect of fibrogenesis of nanosized SiO2 might be milder than that of microsized SiO2 in rats, potentially resulting from nanoparticals tending to be diffused and easily translocated due to their ultrafine particle size compared to microsized particles.

Animals↗
PubMed1995

Retinoic acid in silicone and silicone-fluorosilicone copolymer oils in a rabbit model of proliferative vitreoretinopathy.

PURPOSE: The authors evaluated the effect of retinoic acid (RA) in silicone oil (SiO) and in silicone-fluorosilicone (SiFO) copolymer oil in a new rabbit model of proliferative vitreoretinopathy (PVR). METHODS: To create the PVR model, three groups of rabbits were administered vitreous injections of approximately 100,000 homologous fibroblasts, 75,000 platelet-rich plasma (PRP), and fibroblasts + PRP, respectively. These rabbits were followed up ophthalmoscopically and histopathologically for as long as 2 months. Five additional groups of rabbits underwent gas-compression vitrectomy in one eye. Four days later, group 1 was administered intravitreous RA in SiFO (9 micrograms/ml) with approximately 150,000 fibroblasts and 70,000 PRP. Group 3 was administered the same amount of fibroblasts and PRP as group 1 with RA in SiO (9 micrograms/ml). Groups 2, 4, and 5 were administered the same amount of fibroblasts and PRP as groups 1 and 3 with 1 ml of SiFO, SiO, or balanced salt solution only, respectively. To evaluate RA toxicity, RA was injected in SiO (15 and 20 micrograms/ml) and RA in SiFO (10 micrograms/ml). RESULTS: All eyes that were administered fibroblasts or PRP developed vitreous membranes, but those with PRP alone did not develop proliferative changes or retinal detachment; fibroblasts alone produced proliferative changes and retinal detachment after 2 to 3 weeks; fibroblasts + PRP produced similar changes within 3 days of injection. Retinoic acid (15 micrograms/ml) in SiO and RA (10 micrograms/ml) in SiFO was well tolerated. Retinal atrophic changes were found in eyes with 20 micrograms/ml RA in SiO. The retinal detachment rate was lower (P < 0.05) in the eyes that were administered fibroblasts + PRP and RA than in the controls. Significant differences were found in the degrees of PVR among the groups. CONCLUSIONS: RA could be useful in PVR treated with SiO or for eyes treated intraoperatively with heavier-than-water SiFO when it is used as a short-term retinal tamponade.

Animals↗
PubMedDate not supplied

Silicon, silicone, and silica: the importance of the right ending.

Although organic polymers based on carbon have revolutionized the use of commodity materials during the latter half of the twentieth century, polymers based on silicon have also had a remarkable impact in certain speciality areas, especially in medical technology. This article clarifies some of the chemical uncertainties associated with these materials.

Equipment and Supplies↗
PubMed2004

A stable compound containing a silicon-silicon triple bond.

The reaction of 2,2,3,3-tetrabromo-1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasilane with four equivalents of potassium graphite (KC8) in tetrahydrofuran produces 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyl-2-tetrasilyne, a stable compound with a silicon-silicon triple bond, which can be isolated as emerald green crystals stable up to 100 degrees C in the absence of air. The SiSi triple-bond length (and its estimated standard deviation) is 2.0622(9) angstroms, which shows half the magnitude of the bond shortening of alkynes compared with that of alkenes. Unlike alkynes, the substituents at the SiSi group are not arranged in a linear fashion, but are trans-bent with a bond angle of 137.44(4) degrees.

Journal Article↗
PubMed1998

Coaxial nanocable: silicon carbide and silicon oxide sheathed with boron nitride and carbon

Multielement nanotubes comprising multiple phases, with diameters of a few tens of nanometers and lengths up to 50 micrometers, were successfully synthesized by means of reactive laser ablation. The experimentally determined structure consists of a beta-phase silicon carbide core, an amorphous silicon oxide intermediate layer, and graphitic outer shells made of boron nitride and carbon layers separated in the radial direction. The structure resembles a coaxial nanocable with a semiconductor-insulator-metal (or semiconductor-insulator-semiconductor) geometry and suggests applications in nanoscale electronic devices that take advantage of this self-organization mechanism for multielement nanotube formation.

Journal Article↗
PubMed2005

Assessment of exposure to quartz, cristobalite and silicon carbide fibres (whiskers) in a silicon carbide plant.

The main objective of the present paper is to report on the concentration of silicon carbide (SiC) fibres, crystalline silica and respirable dust in a Canadian SiC production plant and to compare the results with earlier investigations. The second objective is to tentatively explain the differences in concentration of the fibrogenic substances between different countries. The assessment of SiC fibres, dusts, respirable quartz and cristobalite was performed according to standard procedures. The highest 8 h time-weighted average concentrations of fibres were found among the crusher and backhoe attendants and the carboselectors with an arithmetic mean of 0.63 fibres ml(-1) for the former group and 0.51 fibres ml(-1) for the latter group. The results of respirable SiC fibres in the Canadian plant were lower than in the Norwegian and Italian industries. Most of the 8 h time-weighted average concentrations for quartz were less than or around the limit of detection of 0.01 mg m(-3). The maximum 8 h time-weighted average concentration for quartz was found among the carboselectors (0.157 mg m(-3)), followed by the labourers (0.032 mg m(-3)). Similarly, most of the 8 h time-weighted average cristobalite measurements were less than the limit of detection of 0.01 mg m(-3) except for the carboselectors where it was found to be 0.044 mg m(-3). The assessment of the Italian occupational settings exposure demonstrated elevated quartz concentrations, while cristobalite was absent. The authors have concluded that the investigations that were performed in the last two decades in this field by researchers from different countries seem to support that SiC fibres (whiskers) constitute a major airborne health hazard.

Air Pollutants, Occupational↗
PubMed1998

Development of a new silicon-based transdermal system. I. Study of silicone elastomers and effect of liquid ingredients.

The polarities of four elastomers made of silicon oligomers of different viscosities were investigated by measuring the uptake of swelled solvent in different polarity solvents after 24, 48, and 72 hr of treatment. The solvent uptake provides a good characterization for the polarity of the inside of the matrix. On the basis of the results the oligomers were divided into two groups. The same method has been used for the investigation of the change of the inner polarity of samples containing various amounts of polar and apolar liquid ingredients. It was shown that the polarity of the inside of the matrix is related to the swelling properties. The ingredients used changed the matrix framework, which was also influenced by the type of oligomers. The solvent uptake shows large dependence on the timing of the measurement. Measurements carried out after 48 hr of polymer production showed constant solvent uptakes, indicating that the final structure of the polymer was formed.

Administration, Cutaneous↗
PubMed1996

Novel anti-silicone surface-associated antigen antibodies (anti-SSAA(x)) may help differentiate symptomatic patients with silicone breast implants from patients with classical rheumatological disease.

The frequency of novel autoreactive antibodies to silicone surface associated antigens (anti-SSAA(x)) was measured in healthy control patients, symptomatic patients with breast implants, asymptomatic patients with breast implants, and control patients with classical rheumatological diseases. The frequencies of elevated anti-SSAA(x) antibodies in 310 symptomatic breast implant patients were 17.4% anti-SSAA(fn), 12.9% anti-SSAA(col1), and 7.4% anti-SSAA(col3) and 7.1% anti-SSAA(fbgn) [Normal (n = 173) = 0.6% for all four tests] (p < .005). In 11 asymptomatic breast implant patients, the frequencies of elevated values for the same anti-SSAA's were 0%, 9%, 0%, and 0% respectively, while in 50 patients with rheumatoid arthritis, the frequencies were 4%, 0%, 6% and 2% respectively. The anti-SSAA(x) profile for symptomatic patients with breast implants was different than the profile for control healthy patients (p < .005 on all eight tests) but differed significantly by two measures, anti-SSAA(fbgn) and anti-SSAA(col3), from the profile for the 19 patients with systemic lupus erythematosus. We conclude that anti-SSAA(x) antibodies levels in symptomatic patients with breast implants are elevated, that the antibodies are associated with symptoms, and that they differ both qualitatively and quantitatively from healthy controls, asymptomatic patients with breast implants, and symptomatic patients with classical rheumatological diseases.

Adult↗
PubMed1993

Silicone rubber-hydrogel composites as polymeric biomaterials. IV. Silicone matrix-hydrogel filler interaction and mechanical properties.

Composite materials consisting of a silicone rubber matrix and particulate synthetic hydrogels were prepared and their mechanical properties were studied. The influence of the size, shape, aggregation of hydrogel particles, chemical reactions of polymer phases on tensile properties and tear strength of the composite materials were investigated. The relations between the properties, structure and chemical composition of polymer phases of the composite materials and their mechanical properties are discussed.

Biocompatible Materials↗