Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Dimethylpolysiloxanes”

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
PubMed1990

[Comparative study of 2 dosage forms of liquid dimethicone for ultrasound premedication].

A double-blind study was carried out to compare the effects of a premedication with 4 x 500 mg dimethylpolysiloxane (DPS)/24 hours and with 2 x 500 mg/12 hours before abdominal ultrasonography. The investigations covered 13 abdominal regions in specified planes. The incidence of the unobscured presentation of the selected organs and organ sections per patient served as a basis for a sonography index. This index was 67%, without significant difference between the two groups. We believe that the optimal conditions for sonography are given when the patient is fasting and two 500 mg doses of DPS are administered, one in the evening before and one in the morning at the day of investigation.

Abdomen, Acute↗
PubMed2002

Silicone granuloma of the facial tissues: a report of seven cases.

The liquid form of silicone, called dimethicone (dimethylpolysiloxane), has been used extensively in some countries during the past 4 decades for soft tissue augmentation. Although considered biologically inert, this material has been reported as potentially inducing, after tissue injection, a granulomatous inflammatory response of variable severity. Interestingly, a remarkable paucity of reports exists about the development of complications after injections of liquid silicone into the facial tissues, especially considering its high frequency of use. The purpose of this article is to describe the clinical and microscopic features of 7 cases of silicone-induced granulomas that developed after injection of the facial tissues for cosmetic purposes and to discuss the differential diagnosis and management of this condition.

Adult↗
PubMed2001

Estimation of molar heat capacities in solution from gas chromatographic data.

The temperature dependence of retention data (retention or capacity factors) is measured for 35 aliphatic ketones and aldehydes as model compounds on a dimethylpolysiloxane stationary phase. A novel model is derived to determine the heat of solution and the solution molar heat capacities from the fits of the log natural of the difference of the retention factor and the column temperature (T) versus 1/T and the temperature arrangement. The convex curvature present in the residual plots of a former defined equation of ours disappears when applying a newly defined model. A detailed statistical analysis clearly shows the superiority of the refined model to the earlier one in a broader temperature range. The validation of this model is made through a comparison of heat capacity values taken from literature determined by different methods. The molar heat capacity of a pure liquid oxo compound is similar to that of when the same compound is solvated in a stationary phase.

Journal Article↗
PubMedDate not supplied

Analysis of fenthion in postmortem samples by HPLC with diode-array detection and GC-MS using solid-phase extraction.

Fenthion (O,O-dimethyl-O-[3-methyl-4-(methylthio)-phenyl]-thiophos-phate ) is an organophosphate insecticide. A specific method to quantitate fenthion in postmortem matrices with solid-phase extraction combined with high-performance liquid chromatography-diode-array detection (HPLC-DAD) and gas chromatography-mass spectrometry (GC-MS) is presented. Fenitrothion (O,O-dimethyl-O-[3-methyl-4-nitrophenyl]-thiophosphate) is selected as the internal standard. For sample cleanup, a simple but selective solid-phase extraction is chosen after comparison with traditional liquid-liquid extraction procedures. Homogenized and appropriately diluted aqueous samples are applied, and the analytes are desorbed with 5 mL of dichloromethane. Aliquots of the extract are used for HPLC-DAD and GC-MS analysis, Liquid and GC conditions are as follows: gradient elution with a mixture of methanol and water (10:90 to 90:10, v/v) containing 0.0125M NaOH on an Aluspher RP-Select B column monitoring at 250 nm, and temperature programming from 60 to 300 degrees C on a dimethylpolysiloxane column in the SCAN mode, respectively. This method is applied to a suicidal case involving unsuspected acute intoxication with fenthion (concentration in blood, 3.8 micrograms/mL).

Aged↗
PubMed2002

A new method for determination of halogenated flame retardants in human milk using solid-phase extraction.

A method has been developed for quantitation of a selection of halogenated flame retardants in human milk. The method has been validated for seven polybrominated diphenyl ethers (PBDEs), BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, and BDE-183, and the halogenated phenols 2,4,6-tribromophenol (TriBP), pentabromophenol (PeBP), tetrachlorobisphenol-A (TCBP-A), and tetrabromobisphenol-A (TBBP-A). The sample preparation includes solid-phase extraction using an N-vinylpyrrolidone-divinylbenzene copolymer with on-column lipid decomposition followed by additional cleanup on sulfuric acid-silica columns and methylation of the phenolic compounds. Separation and detection were performed by gas chromatography-electron capture mass spectrometry, using a 5% phenyl 95% dimethylpolysiloxane column. The method has been validated in the range of 1.8-180 pg/g milk for most of the halogenated flame retardants. The average absolute recoveries were from 49 to 83%, and the average recoveries with respect to internal standards were in the range of 53 to 121%. Estimated limits of detection were in the range of 0.3 to 1.0 pg/g milk using a sample size of 5 g for all compounds, except TCBP-A, for which the limit of detection was estimated to 6.7 pg/g milk.

Female↗
PubMed1995

Zinc is a possible toxic contaminant of silicone oil in microdrop cultures of preimplantation mouse embryos.

A batch of silicone oil (dimethylpolysiloxane) is described which had differential effects on the development of 1- and 2-cell preimplantation mouse embryos in vitro when used as a microdrop overlay over two culture media: CZB and KSOM. A high rate of development into blastocysts was observed when using CZB medium; in contrast, development was strongly inhibited when KSOM was used. Other batches of silicone oil or paraffin oil permitted development from the zygote to the blastocyst of an outbred strain of mouse without arrest at the 2-cell stage. Our results show that the higher concentrations of ethylenediaminetetraacetic acid (EDTA) and bovine serum albumin (BSA) in CZB medium, in comparison with KSOM, protect against the toxic component in the oil. Observations also gave circumstantial evidence that the toxic component in the oil is zinc. The beneficial effect of including EDTA in a medium is usually attributed to its chelating toxic metals introduced as impurities in other components of the medium. Our results now show that EDTA also protects against impurities in the oil overlay.

Animals↗
PubMed1997

Motor responses of cultured rat cerebral vascular smooth muscle cells to intra- and extracellular pH changes.

Alkalizing perivascular fluid constricts, whereas acidification dilates, cerebral arterioles. It is not known whether vascular smooth muscle cells (VSMCs), endothelium, or neuronal elements sense pH changes. We hypothesized that VSMCs themselves transduce extracellular pH (pHo) changes. We examined the motor responses of cultured adult rat middle cerebral arterial VSMCs during pHo and intracellular pH (pHi) changes. Motor responses were inferred from the deformation pattern of a silicone substratum, dimethylpolysiloxane, which wrinkles as cells contract. pHi was measured with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Cultured VSMCs retained motor responses to vasoconstrictors (5-hydroxytryptamine and K+), and to sodium nitroprusside, which were typical of intact arterioles. VSMCs contracted with increasing and relaxed with decreasing pHo. Hypocapnia contracted VSMCs when the pHo increased, and hypercapnia relaxed VSMCs when the pHo decreased. However, at a constant pHo, changes in PCO2 caused opposite responses despite equivalent changes in pHi. Thus VSMCs contract with increased pHo and relax with decreased pHo just as intact arterioles do. These responses do not reflect changes in pHi or PCO2. pHi changes paradoxically alter VSMC tone in the direction opposite that caused by pHo changes.

Animals↗
PubMed1988

Evidence for glomerular actions of epidermal growth factor in the rat.

Epidermal growth factor (EGF), an endogenous mitogenic peptide, has recently been shown to be a potent vasoconstrictor of vascular smooth muscle. In view of its potential role in proliferative and inflammatory renal glomerular diseases, we examined the effects of EGF both on cultured rat mesangial cells and on in vivo glomerular hemodynamics. Mesangial cells possess specific, saturable EGF receptors of differing affinities, with Kd's of 0.1 and 1.7 nM, respectively. EGF produced a rapid increase in intracellular pH of 0.12 +/- 0.01 pH U, which was sodium dependent and amiloride inhibitable. The addition of EGF to mesangial cells cultured on either glass or dimethylpolysiloxane substratum induced reproducible cell contraction. Intrarenal EGF infusion did not affect systemic blood pressure or hematocrit but reversibly decreased GFR and renal blood flow from 4.19 +/- 0.33 to 3.33 +/- 0.26 and from 1.17 +/- 0.09 to 0.69 +/- 0.07 ml/min, respectively. Glomerular micropuncture confirmed decreases in single nephron plasma flow and in single nephron GFR (from 142 +/- 9 to 98 +/- 8 and from 51.6 +/- 11.7 to 28.5 +/- 3.5 nl/min, respectively) which were due to significant increases in both pre- and postglomerular arteriolar resistances (from 1.97 +/- 0.31 to 2.65 +/- 0.36 and from 1.19 +/- 0.11 to 2.00 +/- 0.15 10(10) dyn.s.cm-5 respectively) and to a significant decrease in the ultrafiltration coefficient, Kf, which fell from 0.100 +/- 0.019 to 0.031 +/- 0.007 nl/(s.mmHg). These studies demonstrate that mesangial cells possess specific receptors for EGF, and exposure of these cells to physiologic concentrations of EGF results in an in vitro functional response characterized by activation of Na+/H+ exchange and by resultant intracellular alkalinization, as well as by cell contraction. EGF administration in vivo significantly reduces the glomerular capillary ultrafiltration coefficient, Kf, which, in combination with EGF-induced constriction of both preglomerular and postglomerular arterioles, results in acute major reductions in the rates of glomerular filtration and perfusion.

Animals↗
PubMed1975

Indomethacin release from silicone rubber: a suggested method for continuous inhibition of prostaglandin synthesis.

Indomethacin was vulcanized in dimethylpolysiloxane, an inert silicone suitable for tissue implantation. The drug is released from this polymer matrix gradually in amounts that can inhibit endogenous prostaglandin synthesis. The method is simple, rapid and inexpensive and eliminates repetitive administration in studies where prolonged inhibition of prostaglandin synthesis is desired.

Delayed-Action Preparations↗
PubMed2006

Granulomatous facial reaction to injected cosmetic fillers--a presentation of five cases.

The use of substances to augment soft tissues as aesthetic purpose is associated with, among other undesirable effects, the appearance of foreign body granulomas. The improvements made to these substances have reduced the incidence of adverse reactions, but not eliminated them. We present five cases of foreign body reactions to three different products, dimethylpolysiloxane (silicone), bovine collagen, and polylactic acid, which were injected into the subcutaneous cellular tissue of the patients (all five were women), between two and sixteen years before the appearance of the foreign body reaction. All five presented painless, diffuse facial tumefaction, of firm, elastic consistency. The magnetic resonance image (MRI) studies showed signs of intense inflammatory reaction in the affected areas. The histology revealed the presence of foreign body granulomas with giant multi-nucleated cells. The patients were treated with systemically administered corticoids, except in one case which did not require pharmacological treatment.

Aged↗
PubMed1991

A comparative "in vitro" study of permeability with different synthetic and biological membranes.

Permeability coefficients of seven compounds belonging to a true homologous series (4-alkylanilines) through several different synthetic and biological membranes were assayed in a two-chamber diffusion cell. Permeability-lipophilicity relationships for the experimental data were established and compared in order to ascertain whether the behaviour of these membranes was similar to that of the human skin. In all cases, the best fit for the permeation-lipophilicity correlation was provided by the bilinear model. It was demonstrated that this type of correlation, when a dimethylpolysiloxane membrane is used, is due to the existence of a supplementary stagnant aqueous layer adjacent to the membrane in the receptor compartment. This is clear from the fact that when Polysorbate 80 is added to the receptor solution, the effect of this layer is abolished. In these conditions, hyperbolic equation gives, consequently, the best fit for penetration-lipophilicity correlation. On the basis of the data obtained with rat skin and Polysorbate 80 in the receptor solution, it can be concluded that for biological membranes the bilinear model obtained is due to their heterogeneous nature. The optimum lipophilicity value for penetration according to the bilinear model was not the same for all the membranes assayed. Human and rat skin were qualitatively similar in behaviour.

Amines↗
PubMed1997

Silicone granulomatous lymphadenopathy and siliconomas of the breast.

In the present study, two histologically-distinct cases of granulomatous lymphadenitis induced by dimethylpolysiloxane (silicone polymer) implants were studied. Four and six years after implant, and following surgery for breast cancer, painful homolateral axillary adenopathies were observed and biopsied. In both cases, histological examination led to a diagnosis of "silicone-induced granulomatous adenitis" requiring removal of implants. Foreign-body granulomas (siliconomas) were observed in surrounding tissue with no apparent rupture of implant capsules; however, visible retraction, hardening and scattered calcifications were noted. The presence of silica was revealed by incineration of a number of biopsied lymph nodes, a technique not hitherto used in the study of this pathology. A review is offered of the literature available.

Breast↗
PubMedDate not supplied

Resorption beneath silastic mandibular implants. Effects of placement and pressure.

OBJECTIVE: To evaluate the extent to which silicone rubber mandibular implant (Silastic; Dow Corning, Midland, Mich) pressure and placement (supraperiosteal or subperiosteal) affect underlying mandibular resorption. DESIGN: A randomized, controlled animal trial. SUBJECTS: Ten mixed-breed adult hounds. INTERVENTIONS: Each animal's mandible was implanted with 6 Silastic blocks, 3 inserted supraperiosteally and 3 subperiosteally. Within each grouping of 3 implants, pressure was varied from "minimum" to "moderate" to "maximum" by compressing the implant with titanium miniplates. After 4 months, the animals were killed and their mandibles sectioned for microscopic examination. RESULTS: Mandibular resorption occurred in varying degrees beneath all implants by the end of the study period. The extent of resorption was consistent with retrospective studies in humans. No statistically significant difference was found between supraperiosteal or subperiosteal placement of the implants. However, higher-pressure implants tended to produce less resorption than lower-pressure implants. CONCLUSIONS: While some bone resorption seems inevitable with Silastic mandibular implants, these results would seem to suggest that the placement of implants above or below the periosteum need not be a concern for the surgeon attempting to minimize this consequence. On the other hand, increased pressure may actually decrease resorption, contrary to current assumptions.

Animals↗
PubMed2002

Microcontact printing on human tissue for retinal cell transplantation.

OBJECTIVES: To demonstrate that microcontact printing, a modern materials fabrication technique, can be used to engineer the surface of human tissue and to show that inhibitory molecules can be used to pattern the growth of retinal pigment epithelial cells or iris pigment epithelial cells on human lens capsule for transplantation. METHODS: Photolithographic techniques were used to fabricate photoresist-coated silicon substrates into molds. Poly(dimethylsiloxane)stamps for microcontact printing were made from these molds. The poly(dimethylsiloxane) stamps were then used to "wet-transfer" growth inhibitory molecules to the surface of prepared human lens capsules that were obtained during cataract surgery. Human retinal pigment epithelial and rabbit iris pigment epithelial cells were grown on a lens capsule substrate in the presence and absence of a patterned array of inhibitory factors. RESULTS: We found that human lens capsule could be microprinted with a precision similar to that obtained on glass or synthetic polymers. Retinal pigment epithelial cells and iris pigment epithelial cells cultured onto an untreated lens capsule showed spreading and formed into fusiform-appearing cells. In contrast, cells cultured on a lens capsule with a hexagonal micropattern of growth inhibitory molecules retained an epithelioid form within the inhibitory hexagons. CONCLUSION: Inhibitory growth molecules can be micropatterned onto human lens capsule, and these micropatterns can control the organization of retinal pigment epithelial cells or iris pigment epithelial cells cultured onto the lens capsule surface. CLINICAL RELEVANCE: Microprinting on autologous human tissue may facilitate efforts to effectively organize cell cultures and transplantations for the replacement of vital ocular tissues such as the retinal pigment epithelium in age-related macular degeneration.

Animals↗