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PubMed2001

Interfacial Behavior of Mixed Systems of Glycerylether-Modified Silicone and Polyoxyethylene-Modified Silicone.

Undecylglycerylether-modified silicone (GES; the glycerylether-type surfactant with a silicone segment and alkyl chains (carbon number, 11) as the hydrophobic portion) forms a molecular aggregate (M.A.) with a small amount of water. This M.A. is similar to the reversed hexagonal liquid crystal formed by alpha-mono long-chain alkylglycerylether (3-isooctadecyloxy-1,2-propanediol; GE). From the investigation of the phase behavior in the water/GES/polydimethylsiloxane (PDMS) ternary system, a wide three-phase region of water (W)+M.A.+oil (O) was observed. As this M.A. is insoluble in PDMS and easily orients in the interface between water and PDMS, the high water content silicone W/O emulsion using GES as a surfactant is well stabilized. However, as the PDMS content increased this W/O emulsion became less stable. In order to improve this stability, mixtures of GES and polyoxyethylene-modified silicone (PS) were applied to the silicone emulsion as co surfactant. By application of a PS with a methyl group at the end cap of the polyoxyethylene chain (PSM), the emulsion became most stable at a GES/PSM ratio of 1 : 2, and at the same time, the interfacial tension between the oil phase and the water phase became minimal. The reason for this was studied by the measurement of spin-lattice relaxation times (T(1)) of the alkyl chains of GES in the GES/PS/water system by (13)C NMR. We assumed that the W/O silicone emulsions were stabilized by the efficient orientation of the aggregates in the interface between the silicone phase and the water phase by using PSM as a cosurfactant. Copyright 2001 Academic Press.

Journal Article↗
PubMed2005

Atomic silicon in siloxanic networks: the nature of the oxo-oxygen-silicon bond.

The existence of atomic silicon cryptates in siloxanic networks has been studied theoretically via density functional calculations. By modeling with model molecules the candidate sites to host atomic silicon, we found that metastable adducts can be formed only in regions where the siloxanic network is not subjected to steric constraints; stationary states are instead unstable in highly reticulated siloxanic networks. The nature of the oxo-oxygen-silicon bond at the SiO2 surface is analyzed in detail. It is concluded that silicon is kept at the surface in atomic-like configuration by (i) sigma charge donation from oxo-oxygen atoms into the empty silicon psigma orbital; (ii) pi charge back-donation from singly occupied silicon 3ppi orbitals into empty sigma* model molecule orbitals. Surprisingly, these results attribute to atomic silicon the character of bifunctional Lewis acid.

Journal Article↗
PubMed1995

Failure of 29Si NMR to detect increased blood silicon levels in silicone gel breast implant recipients.

We have compared directly the results of atomic absorption (AA) spectroscopy and a 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) technique reported in the literature by Garrido et al. (Garrido, L.; et al. Magn. Reson. Med. 1994, 31, 328-330) for analyzing blood silicon levels in control patients versus patients with silicone gel breast implants. AA spectroscopy yielded blood silicon levels in the nanogram per milliliter range for control patients, while somewhat higher values were found in patients with implants. The 29Si MAS NMR technique applied to the identical blood samples was unable to detect silicon in any of the samples. Sensitivity calculations demonstrate that 29Si MAS NMR should not be expected to detect silicon at the levels determined by AA spectroscopy under the spectroscopic conditions employed and that the concentration of silicon-containing compounds would need to 10(4) times the level detected by AA in order to be detected by this NMR method.

Breast Implants↗
PubMed1988

Silicon in human breast tissue surrounding silicone gel prostheses. A scanning electron microscopy and energy dispersive X-ray investigation of normal, fibrocystic and peri-prosthetic breast tissue.

Implanted silicone breast prostheses leak silicone gel through the intact membrane. In order to determine the exact location and to achieve a semiquantitative estimation of the amount of silicone in the surrounding tissue, a method involving scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) was used. By this method we were able to demonstrate the presence of the element silicon (Si) (main component of silicone, a polymer with a general formula e.g. (CH3[Si(CH3)2O]n Si(CH3)3 along the inner border of vacuoles corresponding to the light microscopic localization of droplets and in macrophages. The tissue adjacent to the prostheses had a higher silicon content than the control tissue.

Breast↗
PubMed1992

Vitrectomy with silicone oil or sulfur hexafluoride gas in eyes with severe proliferative vitreoretinopathy: results of a randomized clinical trial. Silicone Study Report 1.

Between September 1985 and September 1987, 101 eyes with rhegmatogenous retinal detachment and severe (with a classification of at least C-3) proliferative vitreoretinopathy but without prior vitrectomy were treated with vitrectomy and randomized to either a mixture of 20% sulfur hexafluoride gas and air or to 1000 centistokes of silicone oil. Between 50% and 60% of eyes that received silicone oil had visual acuity better than or equal to 5/200 compared with 30% to 40% of the eyes that received sulfur hexafluoride gas (P less than .05). Macula attachment was more frequent in eyes that received silicone oil than in those that received sulfur hexafluoride gas (80% vs 60%, P less than .05). Hypotony was more prevalent in eyes with a detached macula (40% to 50% for sulfur hexafluoride gas vs 25% to 30% for silicone oil) when compared with those with attached maculas (less than 5% for either modality). Keratopathy was more prevalent in eyes with detached maculas (about 55% to 60% for either modality) compared with eyes with attached maculas (25% to 30% for sulfur hexafluoride gas vs 10% to 15% for silicone oil). In a companion article, we show that these differences between a gas tamponade and silicone oil are not found for perfluoropropane gas.

Adult↗
PubMed2004

Bond strength of silicone to polyurethane following immersion of silicone in cleaning solutions.

STATEMENT OF PROBLEM: The use of polyurethane liners beneath silicone facial prostheses is recommended to improve the effectiveness of water-based adhesives, reduce bacterial colonization, and allow very thin margins. Patients using silicone prostheses with a polyurethane lining often observe different degrees of debonding which may lead to failure of the prosthesis. Aggressive cleaning may be associated with debonding of the silicone to polyurethane. PURPOSE: The purpose of this investigation was to determine the effect on bond strength of soaking specimens of silicone to polyurethane in hot or room-temperature soapy water. MATERIAL AND METHODS: Specimens of silicone to primed polyurethane were divided into 3 groups of 16 specimens for testing: control (no soak), room-temperature soapy water soak, and hot soapy water soak. The soaked specimens were placed in soapy water at different temperatures for 1825 minutes to simulate 1 year of a 5 min/day cleaning cycle. One examiner performed the assessment of T-peel strength (N/mm) for all specimens. Each specimen was attached to an adhesive testing machine and separated in tension at the crosshead speed of 25.4 mm/min. Data were analyzed with a 1-way ANOVA followed by post hoc pairwise testing using the Tukey test (alpha=.05). RESULTS: A significant difference in bonding strength between the 3 groups was found (P<.001), with post hoc tests indicating that the control group bonding strength (6.06 +/- 1.84 N/mm) was significantly higher than both room-temperature water soapy soak (3.93 +/- 1.84 N/mm; P=.005) and the hot soapy water soak group values (2.49 +/- 1.75 N/mm; P<.001). However, there was no significant difference found between the hot and room-temperature soapy soak values. CONCLUSION: Within the limitations of this study, soaking in hot or room-temperature soapy water produced a significant reduction of bond strength of silicone to polyurethane.

Adhesiveness↗
PubMed1993

Postoperative intraocular pressure abnormalities in the Silicone Study. Silicone Study Report 4.

BACKGROUND: Chronically abnormal intraocular pressure (IOP) may follow surgery for proliferative vitreoretinopathy (PVR), using either long-acting gas or silicone oil tamponade. Its prevalence and clinical significance are unclear. METHODS: In the Silicone Study, 241 eyes with severe (> or = C-3) PVR were treated with vitrectomy, randomized to perfluoropropane gas (C3F8) or silicone oil, and followed for 6 months or longer. Chronic IOP abnormalities, based on findings at two consecutive or any three postoperative visits, were defined as (1) low IOP (hypotony), 5 mmHg or less, or (2) elevated IOP, more than 25 mmHg. RESULTS: Eleven (5%) eyes had chronically elevated IOP and 58 (24%) had chronic hypotony. Chronically elevated IOP was more prevalent in eyes randomized to silicone oil than in those randomized to C3F8 gas (8% versus 2%; P < 0.05). Chronic hypotony was (1) more prevalent in eyes randomized to C3F8 gas than in those randomized to silicone oil (31% versus 18%; P < 0.05); (2) more prevalent in eyes with anatomic failure (48% versus 16%; P < 0.01); and (3) correlated with poor postoperative vision (P < 0.0001), corneal opacity (P < 0.001), and retinal detachment (P < 0.001). Factors prognostic of chronic hyotony included preoperative hypotony (P < 0.01), diffuse contraction of the retina anterior to the equator (P < 0.01), rubeosis (P = 0.02), and large retinal breaks (P = 0.02). In a multivariate analysis, diffuse contraction of the retina anterior to the equator remained an independent factor prognostic of chronic hypotony (odds ratio = 4.2), regardless of whether the retina was attached postoperatively. CONCLUSION: Intraocular pressure abnormalities are a common postoperative complication in eyes with PVR, and may occur with either C3F8 gas or with silicone oil. The presence of diffuse contraction of the retina anterior to the equator should alert the vitrectomy surgeon that the eye is likely to be hypotonus postoperatively.

Chronic Disease↗
PubMed1991

Early failure of silicone radial head implants in the rheumatoid elbow. A complication of silicone radial head implant arthroplasty.

Three cases of early recurrent synovitis of the rheumatoid elbow following silicone radial head implant arthroplasty are presented. All three patients underwent synovectomy with silicone radial head implant for pain and loss of function due to rheumatoid synovitis. All three implants failed within 4-9 months after surgery. This failure was associated with radiographic medial joint space widening. At reexploration, recurrent synovitis with hemosiderin pigmentation was noted. Patterns of prosthetic failure included fracture, fraying, and compressive deformation or rotary wear ("motar and pestle") of the silicone radial head; a prosthetic stem fracture was also present. Histologic examination of the synovium revealed evidence of silicone-induced synovitis; particulate, refractile silicone debris was associated with inflammatory and foreign body giant cells. The presence of rheumatoid destruction of the joint surface may have accelerated this process and may be a relative contraindication to silicone radial head implant arthroplasty.

Adult↗
PubMed1997

Silicone assisted, argon laser confinement of recurrent proliferative vitreoretinopathy related retinal detachment: a technique to allow silicone oil removal in problem eyes.

AIMS/BACKGROUND: Recurrent peripheral retinal detachments may occur in eyes treated with vitrectomy and silicone oil for retinal detachments complicated by proliferative vitreoretinopathy (PVR). The aim of this study was to assess whether laser photocoagulation could be used in the presence of silicone oil to confine and stabilise recurrent PVR related peripheral retinal detachments enabling the timely removal of the oil. METHODS: 10 patients with recurrent peripheral retinal detachments after vitrectomy and silicone oil insertion were treated with posturing and subsequent focal argon laser to circumscribe the area of recurrent detachment. RESULTS: This technique alone was sufficient to limit the area of retinal detachment in seven of the cases. The remaining three cases required relieving retinotomies because of increasing retinal detachment despite the laser. In all 10 cases the silicone oil was later removed without progression of the detached areas. CONCLUSION: Silicone assisted argon laser 'confinement' can be effective in stabilising eyes with peripheral retinal detachments allowing the subsequent removal of silicone oil.

Adult↗
PubMed2004

[The effect of phacoemulsification combined silicone oil remove and intraocular lens implantation on the eyes with silicone oil temponade].

PURPOSE: To study the effect of phacoemulsification combined silicone oil remove and intraocular lens implantation on the eyes with silicone oil temponade. METHODS: Forty cases (41 eyes) performed phacoemulsification combined silicon oil remove and intraocular lens implantation were retrospectively studied and followed back for 2-18 months, analysis the recover of eyesight and complication of postoperation and during the operation. RESULTS: Except three cases had retina detachment after silicone oil remove, all others patients improved the eyesight in some degree. The main complication during the operation was the posterior capsule tear. The complication of postoperation was retinal detachment. CONCLUSION: It is an effective and safe way that the phacoemulsification combined silicone oil remove for eyes with silicone oil temponade.

Aged↗
PubMed2006

Study of properties of modified silicones at solid-liquid interface: fabric-silicone interactions.

Silicones are special reagents that impart desired surface properties such as softness, bounciness and antiwrinkle properties to fabrics and related materials. Although these finishing processes have been practiced routinely, very little is known about the mechanisms involved in modification so that they could be improved. The current study was undertaken to develop basic understanding of the mechanisms responsible for surface modification of fibers using silicones. PDMS based amino silicone emulsions, quaternized to various degrees using dimethyl sulphate, were used in the present study. The electrokinetic properties of the modified silicones were studied as a function of pH. It was expected that the silicone emulsions would show a steady positive zeta potential throughout the pH range due to the quaternization by dimethyl sulphate. Surprisingly, a sudden drop in the zeta potential was observed around pH 8 with the samples turning hazy in the pH range of 8-10. Turbidimetric studies also showed a sudden increase in the turbidity in the pH range 8-10 where commercial processes also encounter problems. It was concluded that the emulsions were destabilized at pH 8-10 thus rendering them ineffective for surface treatment. In order to identify reason for the improvement in fabric properties, fiber structure was monitored using atomic force microscopy. It was observed that the treated fibers were far smoother, relaxed and uniform as compared to the untreated fibers. Thus the morphology of the fabric is modified in a specific way by treatment with specialty silicones.

Journal Article↗
PubMed2004

Silicon monoxide clusters: the favorable precursors for forming silicon nanostructures.

Using density-functional calculations, we show that the energetically favorable configurations of silicon monoxide clusters (SiO)n for n> or =5 facilitate the nucleation and growth of silicon nanostructures as the clusters contain sp3 silicon cores surrounded by silicon oxide sheaths. The frontier orbitals of (SiO)n clusters are localized to a significant degree on the silicon atoms on the surface, providing high reactivity for further stacking with other clusters. The oxygen atoms in the formed larger clusters prefer to migrate from the centers to the exterior surfaces, leading to the growth of sp3 silicon cores.

Journal Article↗
PubMed2004

Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.

Journal Article↗
PubMed1995

Do patients with silicone-gel breast implants have elevated levels of blood silicon compared with control patients?

Whole blood silicon levels in 30 patients with silicon-gel implants (inserted between 1973 and 1991) were compared with those of 24 healthy, age-matched, female patients without breast implants using atomic absorption spectrometry with a graphite furnace. The blood silicon levels in the implant patients were significantly higher than those of controls (medians 33.45 vs 17.05 ng/ml; p = 0.005). Of the 30 patients with implants, 15 had received their implants between 1973 and 1985, and 15 had received implants between 1986 and 1991. Implants made between 1973 and 1985 have been shown to be weaker and to have higher silicone "bleed" levels than those made from 1986 onward. However, there were no significant differences in the blood silicone levels between these two groups of patients.

Breast Implants↗