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 1,243 records · Page 69Linked to original sources
PubMed2000

[Surface Ramam spectropscopy for in situ investigating silicon etching process].

In situ surface Raman spectroscopy has been extended to study silicon electrode surfaces by optimizing the Raman system and the surface roughening method. The time-dependent etching processes were monitored in a dilute HF aqueous solution and the initial oxidation processes of the hydrogen-terminated surface in different pHs were studied at the open circuit potential. The results indicate that the silicon surface could be overwhelmingly terminated with hydrogen rather than fluorine in the HF-based solution. The smoothening effect of OH- on the silicon surface is through the attack of the = SiH2 site. It demonstrates that Raman spectroscopy is a powerful in situ technique for investigating the etching process of silicon surface.

Electrochemistry↗
PubMed2004

Coupled reduction of chlorinated hydrocarbons and heavy metals by zerovalent silicon.

The feasibility of using zerovalent silicon (Si0) as a novel reductant to remove chlorinated compounds and heavy metals in contaminated sites was investigated. The kinetics and degradation mechanism of carbon tetrachloride (CT) by Si0 were also examined. Results showed that zerovalent silicon could effectively dechlorinate the chlorinated compounds. A nearly complete dechlorination of CT by Si0 was obtained within 14 h. The produced concentrations of chloroform (CF) accounted for 71-88% loss of CT, showing that reductive dechlorination is the major degradation pathway for the degradation of chlorinated hydrocarbons by Si0. The degradation followed pseudo first-order kinetics and the normalized surface reaction rate constant (k(sa)) for CT dechlorination ranged between 0.0342 and 0.0454 L m(-2) h(-1) when CT concentrations were in the range of 3-20 microM. A linear relationship between the k(sa) and pH value was also established. In addition, zerovalent silicon has a high capability in the removal of heavy metals. 83% of Cr(VI) was removed by 0.5g Si0 within 5 h, which is higher than that by Fe0. The removal efficiency of divalent metal ions by Si0 followed the order of Cu(II) > Pb(II) > Ni(II). This indicates that zerovalent silicon is an alternative reductant and can undergo coupled reduction of heavy metals and chlorinated hydrocarbons in contaminated groundwater.

Carbon Tetrachloride↗
PubMedDate not supplied

A new, heavier-than-water silicone oil: a solution of perfluorohexyloctane in polydimethylsiloxane.

PURPOSE: To pre p a re and explore new solutions of semifluorinated alkane in silicone oil, which have a specific gravity slightly higher than silicone oil and vitreous fluid (referred to in the following as heavier-than-water silicone oils (HWSs), and to investigate, in vitro, whether HWSs can be used to plug retina holes, while allowing dehydration of the subretinal space. METHODS: HWS solutions were pre p a red with silicone oil 5000 and perfluorohexyloctane (F6H8). The stability was investigated under different conditions. The viscosity was determined by means of a capillary viscometer. The surface and interface tension were measured using the ring method. RESULTS: HWSs are insoluble in an aqueous medium. Densiron(R)68 (HWS 1.06) is a transparent homogeneous liquid which is slightly heavier (1.06 g/cm3) than water and has a refractive index close to that of vitreous liquid. Densiron68 (HWS 1.06) has a low viscosity (1480 mPas) and interface tension (40.82 mN/m), making it an effective tamponade in the surgical treatment of an inferior detached retina. In addition, the interfaces between Densiron68 and other perfluorocarbon liquids are clearly visible. However, the interface layer between Densiron68 and water is not clear. Finally, all HWSs are stable over the long term at ambient temperatures, as well as physically and thermally resistant. CONCLUSIONS. Due to its physiochemical properties, Densiron68 could meet the requirements for a heavier-than-water tamponade.

Adult↗
PubMed1989

Pathogenic and carcinogenic properties of silicon carbide.

The article presents the influence of silicon carbide upon an organism, on the basis of the publications which, according to Chemical Abstracts, appeared on this subject from 1944 until 1987. The insolubility of silicon carbide, in the liquids of an organism and its indigestibility are indicated. A connection is presented between the size and shape of micrograins and the probability of tumor formation in rats; and the difference between silicon carbide and other dusts in the absorption of x-rays, inhibition of the TTC-dehydrogenase activity, collagenisation of lesions, carcinogenicity are also presented. The problem of interpretation of radiological images of lungs in people exposed to the influence of carborundum dust is dealt with. The biological inertness of silicon carbide is questioned.

Animals↗
PubMed1989

[Invasive and non-invasive studies of the protective action of a silicon-containing cream and its excipient in skin irritation induced by sodium laurylsulfate].

The purpose of our study was to evaluate the protective effect of a new silicone-containing barrier-cream (Anthydro) and its vehicle (Anthydro without silicone) in the prevention of cutaneous irritation by detergents. We therefore planned a study in several stages, using an anionic surfactant well known for its irritant properties: sodium laurylsulphate (SLS) in aqueous solution. In a first series of experiments, the protective effect of the Anthydro cream against SLS was studied by invasive methods on guinea-pigs in order to determine histologically the protective effect of the cream when a 10 p. 100 SLS solution was applied on the skin under occlusion during 24 hours (Square chambers, Van der Bend). Typical and reproducible lesions were apparent, and the protected sites were compared with the unprotected sites. In parallel, we used non-invasive methods (conductivity, transepidermal water loss and cutaneous blood flow) to determine in humans the protective effect of Anthydro cream in comparison with unprotected sites after application during 24 hours of patches soaked with a 5 p. 100 SLS solution on the forearms of 13 adult and healthy volunteers (Silver patch tests, Van der Bend). In both experiments the Anthydro cream was effective in reducing the SLS-induced cutaneous irritation. In a second series of experiments, the Anthydro barrier-cream was compared with its "base" (Anthydro without silicone) in terms of effectiveness, following the same experimental procedure (invasive on guinea-pigs, and non-invasive on humans). The base was shown to be effective in protecting against irritation. However, the histological lesions were less intense when the skin was protected by Anthydro than by its vehicle. Concerning the non-invasive methods in humans, no significant statistical differences appeared in the measurement of various parameters between the sites protected by Anthydro and the sites protected by the vehicle. These results lead us to suggest the existence of an essentially mechanical protective effect in which the silicone plays a very small part in terms of effectiveness. These experimental results necessitates further investigations to be extrapolated to occupational conditions without tests performed in industries and well-conducted epidemiological investigations.

Animals↗
PubMedDate not supplied

Enhanced albumin affinity of silicone rubber.

The authors have developed a method to increase the albumin affinity of silicone rubber-containing medical devices. A vinyl-methyl silicone co-monomer was hydroxylated via an oxymercuration-demercuration reaction and then film-coated on a silicone rubber sheet. C16 acylation of the -OH coated sheet was carried out by an esterification reaction catalyzed by 4-DMAP. FTIR spectroscopy confirmed the presence of -OH groups following the hydroxylation reaction, and (CH2)n groups following the acylation reaction. 125I-labeled albumin binding studies indicated graded enhancements, according to reagent concentration, with maximal 2.7X and 2.5X increases for 20% -OH coated and 20% -OH/C16 acylated surfaces, respectively. Incubation with a protein denaturant, sodium dodecyl sulfate (SDS), removed 73% of adsorbed albumin from unmodified controls, with only 25 and 34% removal from 20% -OH coated and 20% -OH/C16 acylated surfaces, respectively. These results suggest that -OH and C16 modified surfaces not only preferentially adsorb albumin, but also retain it in a more stable configuration; this is an unexpected finding for -OH modified surfaces. Based on similar albumin affinities for biocompatible C18 alkylated and C16 acylated polyether polyurethanes, the authors expect significant improvements in thromboresistance and complement-activating potential for this modified silicone rubber.

Acylation↗
PubMed1988

Pathology of silicon carbide pneumoconiosis.

Silicon carbide is a widely used synthetic abrasive manufactured by heating silica and coke in electric furnaces at 2400 degrees C. Until recently it had been considered a relatively inert dust in humans and animals. However, several roentgenologic surveys had revealed lesions similar to low-grade silicosis. A recent epidemiological study has revealed a 35% incidence of pulmonary problems. Tissues from three such workers were available for light microscopy. A mixed pneumoconiosis was found, and lesions can be summarized as follows: (a) abundance of intraalveolar macrophages associated with a mixture of inhaled particles including carbon, silicon, pleomorphic crystals, silicon carbide, and ferruginous bodies showing a thin black central core; (b) nodular fibrosis, generally profuse, containing silica and ferruginous bodies and associated with large amount of carbon pigment; (c) interstitial fibrosis, less prominent than the nodular form; (d) carcinoma in two cases. We believe this pneumoconiosis is sufficiently characteristic to be recognized as a distinct entity. The Stanton hypothesis on fiber properties and carcinogenesis could be applied to silicon carbide dust. At present, it appears that the occupational hazard is limited to the manufacturing process and powdered product used in some industries.

Aged↗
PubMed1984

Pneumoconiosis in workers exposed to silicon carbide.

Two men who had been exposed only to silicon carbide for many years in a factory manufacturing refractory bricks developed bilateral reticulonodular densities, as shown on chest radiograms, and complained of dyspnea. An open lung biopsy of one of them showed a large amount of black material in the fibrosed alveolar septums. Studies by X-ray diffraction revealed that the silicon carbide to which they were exposed did not contain quartz; X-ray powder diffraction analysis of the lung tissue revealed at least 6 different silicon carbides, traces of tungsten carbide, and an insignificant amount of quartz. Line-width analysis of the pattern suggested that the lung contained foreign material, with a significant number of particles smaller than 0.1 micron. The etiologic role of silicon carbide for tissue fibrosis is discussed.

Adult↗
PubMed1994

Bubbles in the bleb--troubles in the bleb? Molteno implant and intraocular tamponade with silicone oil in an aphakic patient.

A 14-year-old aphakic girl who had had previous bilateral glaucoma surgery with a Molteno implant underwent pars plana vitrectomy and silicone-oil tamponade for proliferative-vitreoretinopathy retinal detachment in both eyes. The filtering bleb of the left eye was functional for 5 months before becoming available for histologic examination. We found numerous foreign-body granulomas coating the inner surface of the bleb, as well as intracellular and extracellular deposits of emulsified silicone oil in the wall of the bleb. In the fellow eye, the filtering bleb remained functional despite repeated vitreous surgery with silicone oil. Filtration in aphakic eyes with previous Molteno surgery and silicone-oil tamponade after vitrectomy may continue normally for a prolonged period of time, although emulsified oil droplets likely will have accumulated in the bleb and become incorporated in its fibrous capsule.

Adolescent↗
PubMedDate not supplied

Tissue response to expanded polytetrafluoroethylene and silicone implants in a rabbit model.

BACKGROUND: Expanded polytetrafluoroethylene (ePTFE) and silicone are safe and relatively biocompatible materials. OBJECTIVE: To compare, using multiple histologic parameters, the tissue response to a standard silicone soft tissue implant with the response to a modified ePTFE implant. The modified form of ePTFE is reinforced with fluorinated ethylene propylene (FEPRePTFE), which provides increased pliability and material integrity. METHODS: The implants were placed into a subperiosteal pocket over the skull of adult New Zealand white rabbits. At 7, 30, and 90 days after implantation, en bloc tissue specimens, including skin, implants, surrounding soft tissue, and underlying bone were harvested for gross and histologic evaluation. OUTCOME MEASURES: The tissue response to the implants was assessed with respect to the number of foreign body giant cells present, the thickness of the fibrous capsule, and the general inflammatory response (n = 6 for each implant at each evaluation period). RESULTS: There were no cases of rejection, extrusion, or infection. The silicone implants elicited a significantly thicker capsule and less neovascularization (P<.05). CONCLUSION: The FEPRePTFE demonstrated a favorable tissue response when compared with silicone, particularly in regard to capsule thickness and vascular ingrowth.

Animals↗
PubMedDate not supplied

Combined silicone and cartilage implants: augmentation rhinoplasty in Asian patients.

Various alloplastic materials are used for nasal augmentation in Asian patients. Of these, silicone is the most prevalent because it is durable and facilitates sculpting. However, silicone grafts have been associated with complications, including tip extrusion, infection, and graft shifting. Often the nasal tip is involved, with skin discoloration and possible implant extrusion due to increased mechanical pressure. Autogenous material provides a safer alternative for nasal augmentation, but the supply of septal or auricular cartilage in Asian patients is limited. To augment optimally and reduce extrusion risk, we use auricular cartilage grafts at the nasal tip and silicone implants for the nasal dorsum in Asian patients. We report the results of this technique in 100 Asian patients with up to 5 years of follow-up. Patients were extremely satisfied, and no implant extrusions resulted. Other complications included further surgical revision due to misalignment of the silicone dorsal implant (5 patients), tip graft shifting (2 patients), and recurrent dorsal edema over the implant requiring removal (1 patient).

Asian People↗
PubMed1999

Elevated intraocular pressure and hypotony following silicone oil retinal tamponade for complex retinal detachment: incidence and risk factors.

OBJECTIVE: To evaluate the incidence of and risk factors for persistently elevated intraocular pressure (IOP) and hypotony in patients who have undergone pars plana vitrectomy with silicone oil injection for the management of complex retinal detachment. SUBJECTS AND METHODS: The medical records of 532 patients who underwent silicone oil injection for the management of complex retinal detachments between January 1, 1991, and December 31, 1996, at the Bascom Palmer Eye Institute, Miami, Fla, were reviewed. Elevated IOP was defined as elevated IOP requiring an operation at any time postoperatively or a persistently elevated IOP of greater than 25 mm Hg at or after the 6-month visit. Hypotony was defined as a persistent IOP of 5 mm Hg or less at or after the 6-month visit. Patients with transient perioperative IOP fluctuations were not counted. RESULTS: Survival analysis for patients without cytomegalovirus retinitis (n = 383) revealed that 12.9% had an elevated IOP and 14.1% had hypotony by 6 months, 21% had an elevated IOP and 20.3% had hypotony by 1 year, and 29.5% had an elevated IOP and 27.3% had hypotony by 2 years. Among patients with cytomegalovirus retinitis (n = 149), none had a persistently elevated IOP, 10% had hypotony by 6 months, and 5.9% had persistently elevated IOP and 10% developed chronic hypotony by 1 year. A history of glaucoma before silicone oil retinal tamponade (P = .03), diabetes mellitus (P = .02), and a high IOP on the first postoperative day (P = .006) were risk factors for elevated postoperative IOP in patients without cytomegalovirus retinitis. Risk factors for postoperative hypotony in patients without cytomegalovirus retinitis included preoperative hypotony (P<.001) and aphakia (P = .03). CONCLUSIONS: An elevated or low IOP often develops postoperatively in patients without cytomegalovirus retinitis who undergo silicone oil injection for the management of complex retinal detachment. Risk factors for an elevated postoperative IOP include a history of glaucoma, diabetes mellitus, and a high IOP on the first postoperative day. Risk factors for hypotony include preoperative hypotony and aphakia.

Adolescent↗
PubMed1985

The effect of silicone oil on the cornea.

Intraocular silicone oil tamponade is being used with increasing frequency as an adjunct to conventional vitrectomy techniques in the treatment of proliferative vitreoretinopathy. When used in patients with aphakia, corneal decompensation is a common long-term complication. In this study, we evaluated the clinical and morphologic changes that occurred in the corneas of 14 rabbits and seven cats when the anterior chamber was filled with silicone oil. Within six days, wide-field specular microscopy showed a 40% reduction in endothelial density in the area of the silicone oil bubble in both groups. Progressive stromal thinning occurred in the rabbit cornea, with gradual development of a retrocorneal membrane at the junction of silicone-endothelial cell contact. In contrast, persistent stromal edema, peripheral vascularization, irregular plaques on the endothelium, and eventual epithelial ulceration and corneal thinning occurred in cat eyes.

Animals↗
PubMed1987

Comparison of complement activation by silicone intraocular lenses and polymethylmethacrylate intraocular lenses with polypropylene loops.

Silicone intraocular lenses are undergoing clinical investigation for use in the United States. We compared the ability of silicone intraocular lenses to activate the complement system in human sera with that of polymethylmethacrylate intraocular lenses with polypropylene loops using a radioimmunoassay that measures levels of activated complement fragments. Sera incubated with polymethylmethacrylate lenses with polypropylene loops had higher levels of C3a and C5a, but not C4a, than control sera incubated without intraocular lenses. On the other hand, there were no differences in levels of C3a, C4a, and C5a between sera incubated with silicone lenses and control sera. These results suggest that polymethylmethacrylate lenses with polypropylene loops activate the alternative pathway of complement, while silicone lenses do not.

Complement Activation↗
PubMed1989

Transient hypopyon with marked anterior chamber fibrin following pars plana vitrectomy and silicone oil injection.

In a retrospective review of 30 cases of complex retinal detachment, which had been managed by pars plana vitrectomy techniques together with silicone oil injection, we found that two patients developed marked postoperative anterior chamber fibrin and hypopyon. In all 30 cases, the same silicone oil was used: purified and heat-sterilized trimethylsiloxy-terminated, polydimethylsiloxane of 1000-centistoke viscosity. Although the silicone oil itself remained clear and without emulsification, the differential diagnosis of this postoperative inflammation included microbial endophthalmitis. These two cases were treated with frequent topical steroids and antibiotics while we closely monitored the retraction of the anterior chamber fibrin. In both cases, clinical improvement and long-term retinal reattachment with satisfactory visual function were achieved. The use of intense scatter laser endophotocoagulation and the presence of impurities in the silicone oil may have contributed to the excessive postoperative inflammation in these cases.

Anterior Chamber↗
PubMed1995

Silicone oil in repair of retinal detachments caused by necrotizing retinitis in HIV infection.

OBJECTIVE: To evaluate the safety and efficacy of 1000- and 5000-centistoke silicone oil as retinal tamponades for the treatment of retinal detachments secondary to necrotizing retinitis in patients with human immunodeficiency virus (HIV) infection. DESIGN: A prospective observational study. SETTING: Community and university-based ophthalmology clinics. PATIENTS: Three hundred fifty patients with HIV infection, who had 407 eyes with retinal detachments secondary to necrotizing retinitis. INTERVENTION: Vitrectomy surgery for retinal detachment with 1000- or 5000-centistoke silicone oil as the retinal tamponade. OUTCOME MEASURES: Efficacy was measured both by anatomic success (defined as complete retinal attachment or macular attachment) and by visual acuity success (defined as preservation of visual acuity or ambulatory vision). Safety was determined by the rate of complications, including abnormal intraocular pressure and corneal and lens opacification. RESULTS: At the last follow-up examination, the retina was completely attached in 287 (73%) of 393 eyes, the macula was attached in 370 eyes (94%), 268 eyes (68%) had ambulatory vision, and visual acuity was preserved in 219 (56%) of 388 eyes. Corneal opacification, hypotony, and silicone oil emulsification were present in 4%, 2%, and 1% of eyes, respectively. One eye had elevated intraocular pressure. Of the 57 patients who had both eyes treated, 35 died, of whom four (11%) had nonambulatory vision in both eyes. Of the 293 patients who had one eye treated, 122 died, of whom 44 (36%) died with nonambulatory vision in the treated eye. The median time to cataract was 192 days; to nonambulatory vision, 474 days; and to death, 204 days. CONCLUSIONS: Silicone oil repair of retinal detachments in necrotizing retinitis is an efficacious and safe procedure that delays or prevents loss of vision in advanced HIV disease.

Adult↗
PubMed1986

Injectable silicone for facial soft-tissue augmentation.

Medical-grade injectable silicone has been safely and efficiently used for facial soft-tissue augmentation in 235 patients. Our 20-year experience with the microdroplet technique included 2,811 treatments performed for camouflaging furrows and grooves, augmentation of facial eminences, and elevation of certain depressed scars. The indications and techniques of injection are discussed. The augmenting effect is greater than that produced by the small volumes of silicone injected. Our study supports other work indicating induction of collagen deposition in the patients around the microdroplets of silicone, thus providing augmentation from volumes of collagen and silicone as well.

Adult↗
PubMed1975

Total intravenous nutrition with peripherally inserted silicone elastomer central venous catheters.

Long-term indwelling central venous catheters inserted peripherally for total intravenous nutrition have been complicated by thrombophlebitis in most instances. However, experiences with silicone elastomer catheters used in this manner have not been previously reported. In this investigation a crank introducer unit has been developed that has allowed 61-cm silicone elastomer catheters to be placed in the superior vena cava with insertion in the basillic or cephalic vein. Thirty-five patients (36 catheter placements) received total intravenous nutrition exclusively via these silicone elastomer catheters. The mean time indwelling was 20.4 days (range, four to 56 days). Thirty of the 36 catheters were removed when total intravenous nutrition was discontinued. Only six catheters were removed for nonvenous and venous reactions. These results have shown the safety and efficacy of peripherally inserted silicone elastomer central venous catheters.

Catheterization↗