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PubMed2006

Automated determination of silicon isotope natural abundance by the acid decomposition of cesium hexafluosilicate.

A procedure for the automated determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and from dissolved silicon in fresh or saltwaters is reported. Samples are purified using proven procedures through the reaction of Si with acidified ammonium molybdate, followed by precipitation with triethylamine and combustion of the precipitate to yield silicon dioxide. The silicon dioxide is converted to cesium hexafluosilicate by dissolution in hydrogen fluoride and the addition of cesium chloride. Isotopic analysis is accomplished by decomposing the cesium hexafluosilicate with concentrated sulfuric acid to generate silicon tetrafluoride gas. Silicon tetrafluoride is purified cryogenically and analyzed on a gas source isotope ratio mass spectrometer. Yields of silicon tetrafluoride are >99.5%. The procedure can be automated by modifying commercial inlet systems designed for carbonate analysis. The procedure is free of memory effects and isotopic biases. Reproducibility is +/-0.03-0.10 per thousand for a variety of natural and synthetic materials.

Acids↗
PubMed2003

Reductive dechlorination of carbon tetrachloride and tetrachloroethylene by zerovalent silicon-iron reductants.

Reductive dechlorination of carbon tetrachloride (CT) and tetrachloroethylene (PCE) by zerovalent silicon (ZVS, Si0) and the combination of Si0 with metal iron (Fe0) was investigated as potential reductants for chlorinated hydrocarbons. The X-ray photoelectron spectroscopy (XPS) was used to identify the surface characteristics of Si0. CT and PCE can be completely degraded via sequential reductive dechlorination to form lesser chlorinated homologues by Si0. Productions of chloroform (CF) and trichloroethylene (TCE) accounted for 80% of CT and 65% of PCE dechlorination, respectively. The degradation of CT and PCE by Si0 at pH 8.3 followed pseudo-first-order kinetics, and the normalized surface rate constants (k(sa)) were 0.288 and 0.003 L m(-2) h(-1), respectively, which react more efficiently than zerovalent iron in CT and PCE dechlorination. A linear relationship was also established between pH and the k(sa) value. The XPS results showed that the hydrogenated silicon surface and silicon oxides on the silicon surface were removed during the dechlorination processes, thus providing a relatively clean silicon surface for dechlorination reactions. The combination of zerovalent silicon with iron influences both the dechlorination rate and the distribution of products. Sequential reductive dechlorination was still the main reaction for CT dechlorination by Si0/Fe0, while reductive dechlorination and beta-elimination were the dominant reaction pathways for PCE dechlorination with ethane and ethene as the major end products. Also, the combination of silicon and iron constitutes a buffer system to maintain the pH at a stable value. A 0.3 unit of pH changed upon increasing the amount of Fe by a factor of 35 was observed, depicting that Si0 serves as a pH buffer in Si0/Fe0 system during dechlorination processes.

Carbon Tetrachloride↗
PubMed2001

Cataract surgery and transpupillary silicone oil removal through a single scleral tunnel incision under topical anesthesia; sutureless surgery.

The author evaluated the results of combined cataract extraction and transpupillary silicone oil removal through a single scleral tunnel incision, in eyes that had undergone pars plana vitrectomy with silicone oil tamponade. Twenty-four of the 46 eyes were operated on under topical anesthesia with Blumenthal mode mini-nucleus manual extracapsular cataract extraction technique (mini-nuc ECCE), and silicone oil was removed passively through planned posterior capsulorhexis via the scleral tunnel, followed by endocapsular intraocular lens (IOL) implantation. The operation was completed without any suturing. The remaining 22 eyes were similarly operated on with the same cataract extraction technique, but in these cases silicone oil was classically aspirated actively through pars plana sclerotomies. Results were evaluated by visual acuity measurement, duration of operation, and complications. The transpupillary silicone oil removal group had significantly less vitreous hemorrhage (0- 31.8%) and posterior capsule opacification (0-36.4%). Also, the mean duration of the operation was significantly shorter in this group. There was no significant difference between the two groups with regard to postoperative recurrence of retinal detachment (12.5-18.1%) and visual acuity outcome. The combination of mini-nuc ECCE with transpupillary silicone oil removal compares favorably with the combination of silicone oil aspiration through pars plana sclerotomies. This combined technique allows the surgeon to perform the operation under topical anesthesia and no sutures are required. The intervention period is shorter and no posterior capsule opacification or vitreous hemorrhage develops.

Adolescent↗
PubMed1998

In vitro effectiveness of silicone oil removal.

PURPOSE: To evaluate the effectiveness of silicone oil removal from the human eye under in vitro conditions. METHODS: Six keratoplasty donor eyes were vitrectomized and filled with silicone oil (5000 centistokes). After oil removal, the amount of residual oil was determined by quantifying the silicon content of the eyes. Six control eyes were prepared without oil filling. RESULTS: The six control specimens showed a silicon content of 2.83-10.2 microg (mean 5.06 microg, SD 3.19), the six test specimens a silicon content of 70.54-297.10 microg (mean 163.91 microg, SD 86.89). The difference is significant (p<0.05). The amount of residual oil in the test eyes was 192.0-856.2 microg (0.0037-0.0179% of the applicated oil quantity). CONCLUSION: The low magnitude of residual intraocular oil after oil removal shows that silicone oil could be removed to almost 100% when emulsification and biological mechanisms of oil retention are excluded. This could favour early silicone oil removal.

Cadaver↗
PubMed2005

Another continental pool in the terrestrial silicon cycle.

Silicon is the second most abundant element on Earth. It is an important nutrient for phytoplankton and is readily absorbed by terrestrial vegetation; it also assists the removal of carbon dioxide from the atmosphere through the weathering of silicates. But the continental cycle of silicon is not well known, and only a few studies have attempted to use silicon stable isotopes (28Si, 29Si and 30Si) to quantify the continental silicon reservoirs. Dissolved silicon in sea and river waters forms a reservoir of mean isotopic value +1.1 per thousand (refs 7, 10). It is enriched in 30Si with respect to the igneous rocks reservoir, which has a mean isotopic value of -0.3 per thousand (refs 4, 9). This enrichment can only be produced by a major fractionation during weathering, and should result in the formation of a continental 30Si-depleted reservoir. Such a reservoir, however, has not been identified to date. Here we analyse silicon isotopes of in situ quartz from a sandstone series in France, using a new-generation secondary ion mass spectrometry apparatus. We show that quartz that precipitates as siliceous cements forms a strongly 30Si-depleted reservoir with isotopic values down to -5.7 per thousand, a more negative value than any previously published for terrestrial samples. Our findings suggest that quartz re-precipitation plays an important role in the biogeochemical cycle of silicon.

Chemical Precipitation↗
PubMed2005

Optical gain and stimulated emission in periodic nanopatterned crystalline silicon.

Persistent efforts have been made to achieve efficient light emission from silicon in the hope of extending the reach of silicon technology into fully integrated optoelectronic circuits, meeting the needs for high-bandwidth intrachip and interchip connects. Enhanced light emission from silicon is known to be theoretically possible, enabled mostly through quantum-confinement effects. Furthermore, Raman-laser conversion was demonstrated in silicon waveguides. Here we report on optical gain and stimulated emission in uniaxially nanopatterned silicon-on-insulator using a nanopore array as an etching mask. In edge-emission measurements, we observed threshold behaviour, optical gain, longitudinal cavity modes and linewidth narrowing, along with a collimated far-field pattern, all indicative of amplification and stimulated emission. The sub-bandgap 1,278 nm emission peak is attributed to A-centre mediated phononless direct recombination between trapped electrons and free holes. The controlled nanoscale silicon engineering, combined with the low material loss in this sub-bandgap spectral range and the long electron lifetime in such A-type trapping centres, gives rise to the measured optical gain and stimulated emission and provides a new pathway to enhance light emission from silicon.

Crystallization↗
PubMed2002

Biometry of the silicone oil-filled eye: II.

PURPOSE: In phakic silicone oil-filled eyes, removal of the silicone oil can be combined with phacoemulsification and intraocular lens (IOL) implantation. True axial length (AL) of the silicone oil-filled (viscosity 1300 centistokes) eye can be estimated from the measured AL (MAL) obtained on A and/or B scan echography, by multiplying MAL by a conversion factor of 0.71. IOL power can then be calculated using current biometry formulae (SRK/T). This study aims to evaluate the conversion factor in clinical practice. METHODS: Eleven patients undergoing combined removal of silicone oil and phacoemulsification with IOL implant were studied. Patients were divided into two groups. In Group 1 (seven patients), the IOL was placed in the capsular bag and in Group 2 (four patients) the IOL was placed in the ciliary sulcus. Calculated AL (CAL) was obtained by multiplying the MAL of the silicone oil-filled eye (as measured on A or B scan ultrasonagraphy) by the conversion factor of 0.71. IOL power was then estimated using the CAL in the SRK/T formula. The spherical equivalent of the postoperative refractive error was compared to predicted refractive error. RESULTS: The mean difference in actual and predicted refractive error was 0.74 dioptres (D) (standard deviation 0.75 D) for Group 1 and 1.31 D (standard deviation 1.4 D) for Group 2. CONCLUSIONS: The conversion factor of 0.71 corrects for the apparent increase in AL induced by silicone oil of viscosity 1300 centistokes. This allows accurate prediction of the required IOL power in eyes undergoing combined cataract extraction, removal of silicone oil and lens implant. Sulcus placement of the IOL gives a less predictable result than placement in the capsular bag.

Biometry↗
PubMed2006

Direct attachment of well-aligned single-walled carbon nanotube architectures to silicon (100) surfaces: a simple approach for device assembly.

A new approach for the attachment of vertically-aligned shortened carbon nanotube architectures to a silicon (100) substrate by chemical anchoring directly to the surface has been demonstrated for the first time. The ordered assembly of single-walled carbon nanotubes (SWCNTs) was accomplished by hydroxylating the silicon surface followed by a condensation reaction with carboxylic acid functionalised SWCNTs. This new nanostructure has been characterised by X-ray photoelectron, Raman and Fourier transform infrared (FTIR) spectroscopy as well as scanning electron and atomic force microscopy. The assembly behaviour of SWCNTs onto the silicon surface shows a fast initial step producing isolated functionalised carbon nanotubes or nanotube bundles anchored to the silicon surface followed by a slower step where the adsorbed nanotubes grow into larger aggregates via van der Waals interactions between adsorbed and solvated nanotubes. The electrochemical and optical properties of the SWCNTs directly attached to silicon have also been investigated. These new nanostructures are excellent electrochemical electrodes. They also fluoresce in the wavelength range 650-800 nm. The successful attachment of the SWCNTs directly to silicon provides a simple, new avenue for fabrication and development of silicon-based nanoelectronic, nano-optoelectronic and sensing devices. Compared to existing techniques, this new approach has several advantages including low operating temperature, low cost and the possibility of further modification.

Adsorption↗
PubMed2003

Longevity of silicone and polyurethane catheters in long-term enteral feeding via percutaneous endoscopic gastrostomy.

BACKGROUND: As percutaneous endoscopic gastrostomy (PEG) is often used for many months or years, the longevity of the feeding tubes plays an important role in the global outcome and costs of PEG. AIM: A retrospective study to evaluate the longevity of silicone and polyurethane PEG catheters. METHODS: The records of 297 patients who were fed via PEG for over 90 days were evaluated. The material of the PEG catheter, duration of follow-up, local complications, need to remove PEG because of tube deterioration or local complications and time from PEG placement to PEG removal were recorded and compared. RESULTS: Two hundred and twenty-eight patients had polyurethane and 69 had silicone PEG catheters. The follow-up ranged from 116 to 3207 days for the polyurethane group and from 98 to 1861 days for the silicone group. No differences were observed in either local complications or PEG removal because of local complications. Tube deterioration causing PEG removal occurred in 36 of the 228 polyurethane PEG catheters and in 25 of the 69 silicone PEG catheters (P = 0.0005). Tube deterioration occurred significantly earlier in the 25 silicone catheters than in the 36 polyurethane catheters. The mean time from PEG placement to PEG removal was 287 days (95% confidence interval, 239-335) for silicone tubes and 573.9 days (95% confidence interval, 425-723) for polyurethane tubes (P = 0.0024). CONCLUSION: Polyurethane PEG catheters seem to be more resistant to deterioration than silicone PEG catheters, and at present they should be preferred for long-term enteral feeding via PEG.

Adolescent↗
PubMed2001

Prevention of hypertrophic scars and keloids by the prophylactic use of topical silicone gel sheets following a surgical procedure in an office setting.

BACKGROUND: Topical silicone gel sheeting has been used for more than 20 years to help reduce the size of hypertrophic scars and keloids. Its clinical efficacy and safety is well established. OBJECTIVE: To determine whether topical silicone gel sheeting can be used to prevent hypertrophic scars and keloids from forming following dermatologic skin surgery. METHODS: Patients undergoing skin surgery were stratified into two groups: those with no history of abnormal scarring (low-risk group) and those with a history of abnormal scarring (high-risk group). Following the procedure, patients within each group were randomized to receive either routine postoperative care or topical silicone gel sheeting (48 hours after surgery). Patients were followed for 6 months. RESULTS: In the low-risk group, there were no statistical differences between individuals using routine postoperative care or using topical silicone gel sheets. In the high-risk group, there was a statistical difference (39% versus 71%) between patients who did not develop abnormal scars and used topical silicone gel sheeting and patients who developed abnormal scars after routine postoperative treatment. Those individuals having a scar revision procedure also showed a statistical difference if topical silicone gel sheeting was used following surgery. CONCLUSION: Topical silicone gel sheeting, with a 20-year history of satisfaction in dermatology, now appears to be useful in the prevention of hypertrophic scars and keloids in patients undergoing scar revision.

Adult↗
PubMed2001

Hygiene problems of residual limb and silicone liners in transtibial amputees wearing the total surface bearing socket.

OBJECTIVE: To determine whether washing the residual limb and silicone liner reduces the associated skin problems in transtibial amputees who wear a total surface bearing (TSB) socket. DESIGN: Case series. SETTING: General community. PATIENTS: Eighty-three transtibial amputees (65 men, 18 women; mean age, 53.4 yr) in western Japan who used or had used a TSB socket with a silicone liner in the previous 5 years. INTERVENTION: Participants took a self-administered questionnaire that included items concerning their personal profile, daily life activities, period of TSB use (yr), hours of TSB use daily, washing frequency of the residual limb and silicone liner, the method of washing, and any associated hygiene problems. MAIN OUTCOME MEASURES: Logistic regression analysis was applied to examine factors related to hygiene problems. Predicted values include hygiene problems (perspiration, eruptions, itching, odor) and explanatory values include TSB use, daily life activity, and washing of limb and prosthetic. RESULTS: Fifty-five subjects washed the residual limb, and 44 subjects washed the silicone liner every day. Itching, perspiration, eruption, and odor were frequent hygiene problems. Perspiration was noted less by women, eruption more by older subjects, and itching and odor more by younger subjects. Washing the silicone liner every day was associated with fewer reports of skin eruption. CONCLUSION: Keeping the residual limb and silicone liner clean is important to reduce skin problems, but hygiene problems of the residual limb and silicone liner still remain to be resolved.

Activities of Daily Living↗
PubMed1999

[Cataract extraction combined with trans-pupillary silicone oil drainage by planned posterior capsulorhexis].

BACKGROUND: A cataract is frequently observed after pars plana vitrectomy with silicone oil endotamponade. PATIENTS AND METHODS: Forty-three consecutive patients underwent cataract surgery combined with transpupillary removal of silicone oil. After phacoemulsification of the lens material through a sclerocorneal tunnel incision, a planned posterior capsulorhexis with a diameter of 3-4 mm was performed. By injecting saline through the capsulorhexis into the vitreous cavity, the silicone oil was rinsed out. Widening of the sclerocorneal tunnel facilitated the drainage of the silicone oil through the pupil and tunnel. After ophthalmoscopic evaluation of the fundus, a plano-convex PMMA posterior chamber lens was implanted into the capsular bag or ciliary sulcus, and the corneoscleral tunnel was closed by a 10-0 nylon suture. RESULTS: Depending on the underlying retinal disease the visual acuity improved in some eyes. Silicone oil bubbles left behind in the vitreous cavity were smaller than 0.5 mm in diameter. Persisting corneal decompensation or a clinically detectable cystoid macular edema related to cataract surgery did not occur. Due to the posterior capsulorhexis, secondary cataract did not develop postoperatively. Small postoperative vitreous hemorrhages resolved during the first three post-operative days. Retinal detachment recurred in 11 eyes (11/42 or 26.2%). In one eye, dislocation of the pseudophacos occurred which had to be corrected surgically. Since the pars plana region remained untouched, direct retinal lesions in the periphery of the fundus or marked vitreous hemorrhages were not encountered. CONCLUSIONS: Silicone oil removal can be combined with cataract surgery with transpupillary drainage of the silicone oil.

Adult↗
PubMed1995

[Surface quality of flexible silicone intraocular lenses. A scanning electron microscopy study].

BACKGROUND: Soft intraocular lenses (IOLs) have been developed to be folded during insertion to allow implantation through a small incision. The surface of the IOL is of great importance in postoperative inflammation and long-term acceptance of the implant. Rough and sharp edges can damage delicate intraocular tissues. The purpose of this study was to analyze new, foldable silicone IOLs for surface quality prior to and following folding. MATERIALS AND METHODS: Eleven silicone IOLs of different types were included in this study (four one-piece plate-haptic silicone IOLs and seven three-piece silicone IOLs with polypropylene, PMMA or polyimid haptics). We performed scanning electron microscopy on brand-new IOLs prior to and following folding either with forceps or inserter. Special attention was given to the silicone optic surface, optic edges, haptic-optic junctions and the haptic itself. Photographs were taken at 5-350 times magnification. RESULTS: All IOLS demonstrated a smooth and homogeneous optic surface at low magnification. At high-power magnification (X 350), distinctive surface patterns were evident in some IOLs, which turned out to be artefacts. The edge finish showed surplus silicone material and molding flash in six of 11 IOLs. Positioning holes of the 4 plate-haptic IOLs were, except in one IOL, rounded and not rough. Photographs of the haptic-optic junctions revealed surplus material or clefts between the haptic and optic in six of the 7 three-piece IOLs; the loop ends of two IOLs showed a roughened or irregular surface. We did not detect any IOL changes produced by folding. CONCLUSIONS: The silicone IOLs tested demonstrated generally acceptable surface properties, but most IOLs had regional surface irregularities of varying magnitude. The clinical impact of these remains to be established, but surplus material or surface defects might result in deposition of inflammatory cells, protein or microorganisms and synechia formation. Folding of the IOLs did not produce superficial defects.

Cataract Extraction↗
PubMed1993

[Biocompatibility of silicone intraocular lenses].

BACKGROUND: In order to the biocompatibility of silicone intraocular lenses, which is described contradictory in literature, we compared IOLs made of silicone caoutchouc and PMMA-IOLs with regards to the presence of macrophages (i.e. giant cells or spindle-shaped cells) in a prospective, randomized study. PATIENTS AND METHODS: Totally 125 patients were examined 2 months post-operatively with the slitlamp in the refractive zone. The single-piece PMMA-IOLs with an open haptic used in this study had a 6 mm optical zone and a total diameter of 11 mm; the silicone-IOLs were disc-shaped lenses with a total diameter of 9.75 mm and an optical zone of 6 or 5.5 mm, resp. RESULTS: Giant cells were observed with 16% of PMMA-lenses and 19% of the silicone-lenses. The maximal density of the giant cells on the PMMA-lenses at the median was 3/mm2 compared to 2/mm2 on the silicone IOLs. Small and spindle-shaped cells were found in 54% of the PMMA-IOLs and 46% of the silicone-lenses. The maximal cell density at the median was 10/mm2 with both lens types. CONCLUSIONS: The differences between the two lens materials are statistically non-significant. Thus, silicone caoutchouc and PMMA possess a comparable biocompatibility when used as material for intraocular lenses.

Aged↗
PubMedDate not supplied

Silicon in foods and diets.

Information on the silicon content of foods and diets is summarized from published literature, and the silicon content of US diets is calculated based on the Food and Drug Administration's Total Diet Study model and literature values for silicon in foods. Silicon levels tend to be higher in foods derived from plants than in foods from animal sources. Foods highest in silicon include grains, especially oats, barley and some rice fractions. Average daily intakes of silicon probably range from about 20 to 50 mg/day with the lower values for animal-based diets and the higher values for plant-based diets. The silicon content of adult US diets, based on the Total Diet Study model, is 19 mg/day for women and 40 mg/day for men.

Animals↗
PubMed2000

General characteristics of the use of silicon diode detectors for clinical dosimetry in proton beams.

The properties of silicon diode detectors, used for dosimetry in clinical proton beams, were investigated with special regard to the measurement of relative dose distributions in water. Different types of silicon diode detector were studied, and the resulting distributions of detector signal versus depth in the water phantom were compared with the corresponding distributions obtained with a plane-parallel NACP ionization chamber. The measurements were performed in a proton beam with an initial energy of 173 MeV. It is shown that the Hi-p silicon detector gives a signal which is proportional to the ionization density in the silicon crystal in all parts of the Bragg curve, and for all levels of accumulated dose to the detector. This is in contrast to detectors based on n-type silicon, or on low resistivity p-type silicon. After pre-irradiation, these latter detectors show a stopping-power dependent recombination, yielding an increase in the detector signal per unit dose with increasing LET. This effect leads to an over-response in the Bragg peak, which increases gradually with the accumulated detector dose. Using the Hi-p silicon diode detector, the depth ionization distribution was found to be equal to the distribution obtained with the plane-parallel NACP ionization chamber at all pre-irradiation levels, within the experimental accuracy. This implies that the quotient between the ionization in the detector and the absorbed dose to the surrounding water is equal for these detectors.

Calibration↗
PubMed1995

Debilitating silicone granuloma of the penis and scrotum.

The restoration and improvement of body contour have intrigued surgeons for over 100 years, generating much interest in the subcutaneous/intradermal injection of highly viscous fluids. The local complications of liquid silicone injection have been well documented over the past 30 years. Although Dow-Corning has not made medical-grade liquid silicone available for use in humans without an approved research application since 1966, practitioners, both licensed and unlicensed, have administered these injections worldwide for a variety of indications throughout the body. There is little or no information concerning the adulteration of these injectates. To date, there have been four case reports of penile injections--the indications being evenly split between the treatment of impotence/sexual inadequacy and augmentation. The most recent description was published in 1982. We present a case of debilitating silicone granuloma of the penis and scrotum secondary to large-volume injections into the corpora cavernosae and penile soft tissues administered in Belgium 14 years prior to presentation. The development of a silicone foreign body reaction, massive edema, and subsequent impotence lends itself to a clinical diagnosis and aggressive treatment with wide local excision and appropriate soft-tissue coverage. The metabolic fate of silicone in vivo remains inadequately characterized and a fertile area for research as new methods involving nuclear magnetic resonance spectroscopy have been devised to identify silicone and highly coordinated silicone complexes.

Adult↗
PubMed1999

The deposition of talc in patients with silicone gel-filled breast implants.

This study was initiated to understand why talc was found in the entrance wounds and pericapsular scars of patients with silicone breast implants. Twenty-five surgical gloves made between 1977 and 1992 by a major glove manufacturer were evaluated with infrared spectroscopy. Seven gloves manufactured before early 1983 contained talc. Later manufactured gloves contained calcium carbonate instead of talc. Talc-containing gloves were submitted to independent laboratories for scanning electron microscopic examination and x-ray microanalysis to obtain finer detail. Remnants of the mold-release agent talc were found in the matrix of the patient-contact side of the glove. Wetting studies showed that silicone oil (gel bleed) immediately wet the surface of rubber glove. After donning, silicone oil was massaged between the thumb and index finger of each washed, talc-containing glove for 1 minute and then daubed from the glove to a microscopic slide. The slide was viewed with polarized light microscopy for the presence of talc crystals. Transfer of talc occurred using silicone oil, but not saline, in each talc-containing glove. Three factors were likely involved in the greater talc deposition that occurred with patients undergoing silicone gel-filled breast implantation than in patients undergoing other surgical procedures. (1) The wetting of the gloves with silicone gel bleed from implants loosened the talc in the glove matrix. (2) Hand-intensive surgical use freed the talc from the gloves. (3) Loose talc adhered to the silicone elastomer of the breast implants and was deposited with implant placement.

Breast Implantation↗