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 1,063 records · Page 59Linked to original sources
PubMed2004

Double silicone intubation as treatment for persistent congenital nasolacrimal duct obstruction.

PURPOSE: The great majority of children with nasolacrimal duct (NLD) obstruction are successfully treated with probing or conventional silicone tube intubation. A small percentage of patients fail to have their NLD obstruction resolved with these procedures and require dacryocystorhinostomy (DCR). This study was conducted to assess the effectiveness of double bicanalicular silicone intubation with placement of two loops of silicone tubing through the NLD for treatment of persistent NLD obstruction in children as an alternative to DCR. METHODS: Ten eyes of 9 patients with nasolacrimal duct obstruction who had failed conventional therapies and were to otherwise undergo DCR were instead treated with double bicanalicular silicone tube intubation. Resolution of preoperative symptoms and signs of NLD obstruction were assessed. RESULTS: At an average follow-up of 40 +/- 5.6 months, all patients had improvement in symptoms and signs. The mean patient age was 31 +/- 3.2 months. The average duration of intubation was 15 +/- 0.73 months. Eight of 10 eyes had complete resolution of NLD obstruction symptoms. Two of 10 treated eyes had occasional symptoms of mattering with upper respiratory infection and exposure to wind or cold but required no further treatment. Nine of 10 eyes were treated for congenital NLD obstruction. The remaining patient had failed conventional bicanalicular intubation after repair of a traumatic common canalicular avulsion. CONCLUSIONS: Double bicanalicular silicone tube intubation is an effective alternative to DCR in selected children who have failed conventional therapies for NLD obstruction. This treatment obviated DCR in all patients in this study.

Biocompatible Materials↗
PubMed2006

Massive systemic silicone embolism: a case report and review of literature.

Subcutaneous injections of inert or quasi-inert plastic material designed to smooth out wrinkled skin or to create a more esthetically sought appearance have become very popular with the American public in general, and, in particular, with certain groups highly focused on their physical image. The case of the injection procedure has attracted into the field of plastic medicine a substantial number of illegal, incompetent, and unscrupulous operators. Their ignorance of involved medical risks and procedures not uncommonly results in severe complications, disfigurement, and death of patients. We report the typical pathological and chemical findings of a systemic fatal silicone embolism in a 53-year-old heterosexual woman following illegal chronic injections of silicone in her hips and buttocks. The injected subcutaneous silicone apparently migrated rapidly from the interstitial subcutaneous tissue into the general blood stream resulting in a fatal systemic silicone embolism. An analysis of the presented case in conjunction with a review of the pertinent medical literature, including a recent article, revealed a marked similarity in the clinicopathologic findings between silicone embolism and fat embolism.

Blood Chemical Analysis↗
PubMed1994

A micromachined silicon sieve electrode for nerve regeneration applications.

A micromachined silicon sieve electrode has been developed and fabricated to record from and stimulate axons/fibers of the peripheral nervous system by utilizing the nerve regeneration principle. The electrode consists of a 15-microns-thick silicon support rim, a 4-microns-thick diaphragm containing different size holes to allow nerve regeneration, thin-film iridium recording/stimulating sites, and an integrated silicon ribbon cable, all fabricated using boron etch-step and silicon micromachining techniques. The thin diaphragm is patterned using reactive ion etching to obtain different size holes with diameters as small as 1 micron and center-center spacings as small as 10 microns. The holes are surrounded by 100-200 microns 2 anodized iridium oxide sites, which can be used for both recording and stimulation. These sites have impedances of less than 100 k omega @ 1 kHz and charge delivery capacities in the 4-6 mC/cm2 range. The fabrication process is single-sided, has high yield, requires only five masks, and is compatible with integrated multilead silicon ribbon cables. The electrodes were implanted between the cut ends of peripheral taste fibers of rats (glossopharyngeal nerve), and axons functionally regenerated through holes, responding to chemical, mechanical, and thermal stimuli.

Animals↗
PubMed1990

Scaling limitations of silicon multichannel recording probes.

This paper describes the scaling limitations of multichannel recording probes fabricated for use in neurophysiology using silicon integrated circuit technologies. Scaled silicon probe substrates 8 microns thick and 16 microns wide can be fabricated using boron etch-stop techniques. Theoretical expressions for calculating the thickness and width of silicon substrates have been derived and agree closely with experimental results. The effects of scaling probe dimensions on its strength and stiffness are described. The probe shank dimensions can be designed to vary the strength and stiffness for different applications. The scaled silicon substrates have a fracture stress of about 2 x 10(10) dyn/cm2, which is about six times that of bulk silicon, and are strong and very flexible. Scaling the feature sizes of recording electrode arrays down to 1 micron is possible with less than 1 percent electrical crosstalk between channels.

Electronics, Medical↗
PubMed1990

Strength characterization of silicon microprobes in neurophysiological tissues.

Strength characteristics of thin-silicon probes in neural tissues have been determined experimentally. It is shown that by proper selection of the substrate length, width, and thickness, silicon substrates can be designed and used to penetrate a variety of biological tissues without breakage or excessive dimpling. Thin-silicon structures have a maximum fracture stress which is a factor of six larger than bulk silicon, and are very flexible and capable of bending to angles larger than 90 degrees. Silicon substrates 15 microns thick x 30 microns wide can easily penetrate guinea pig and rat pia arachnoid layers with minimum dimpling and no breakage, while substrates 30 microns thick x 80 microns wide can penetrate guinea pig and rat dura mater repeatedly without breakage. Quantitative comparison on the relative toughness of neurophysiological tissues in rat and guinea pig have also been experimentally obtained.

Animals↗
PubMed1991

A silicon-based, three-dimensional neural interface: manufacturing processes for an intracortical electrode array.

A method has been developed for the manufacture of a "three-dimensional" electrode array geometry for chronic intracortical stimulation. This silicon based array consists of a 4.2 x 4.2 x 0.12 mm thick monocrystalline substrate, from which project 100 conductive, silicon needles sharpened to facilitate cortical penetration. Each needle is electrically isolated from the other needles, and is about 0.09 mm thick at its base and 1.5 mm long. The sharpened end of each needle is coated with platinum to facilitate charge transfer into neural tissue. The following manufacturing processes were used to create this array. 1) Thermomigration of 100 aluminum pads through an n-type silicon block. This creates trails of highly conductive p+ silicon isolated from each other by opposing pn junctions. 2) A combination of mechanical and chemical micromachining which creates individual penetrating needles of the p+ silicon trails. 3) Metal deposition to create active electrode areas and electrical contact pads. 4) Array encapsulation with polyimide. The geometrical, mechanical, and electrical properties of these arrays should make them well suited as interfaces to cortical tissue.

Animals↗
PubMed2002

Tissue reactions evoked by porous and plane surfaces made out of silicon and titanium.

Square-shaped silicon or titanium implants with plane or porous surfaces surrounded by a rim of silicone were implanted in the rat abdominal wall for evaluation of the tissue response after one, six, or 12 weeks. Cell damage was identified as increased membrane permeability using fluorescence microscopy by injection of propidium iodide prior to the killing of the rats. Capsule thickness and immunohistochemical quantification of macrophages were used as a further measure of the foreign-body reaction. There were no significant differences in capsular cell densities for macrophages, total cells (macrophages, fibroblasts, and other cells), or necrotic cells at the different time points for the four surfaces studied. However, significant differences in the kinetics of the response were found between plane surfaces compared with porous ones. Both types of plane surfaces developed a significant increase in capsule thickness over time in contrast to the porous implants. Porous silicon displayed a significant decrease in total cells in the reactive capsule over time. Furthermore, porous silicon and titanium surfaces displayed a significant decrease in total cell numbers at the implant interface between six and 12 weeks. The present study demonstrated that implanted silicon elicited soft-tissue reactions comparable to that of titanium.

Abdominal Muscles↗
PubMed2006

Interference in adhesion of bacteria and yeasts isolated from explanted voice prostheses to silicone rubber by rhamnolipid biosurfactants.

AIMS: The effects and extent of adhesion of four different bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber with and without an adsorbed rhamnolipid biosurfactant layer obtained from Pseudomonasaeruginosa DS10-129 was studied. METHODS AND RESULTS: The ability of rhamnolipid biosurfactant to inhibit adhesion of micro-organisms to silicone rubber was investigated in a parallel-plate flow chamber. The anti-adhesive activity of the biosurfactant at different concentrations was significant against all the strains and depended on the micro-organism tested. The results showed an effective reduction in the initial deposition rates, and the number of bacterial cells adhering after 4 h, for all micro-organisms tested at the 4 g l(-1) undiluted rhamnolipid solution. Maximum initial reduction of adhesion rate (an average of 66%) occurred for Streptococcus salivarius GB 24/9 and Candida tropicalis GB 9/9. The number of cells adhering after 4 h on silicone rubber conditioned with biosurfactant was reduced to 48% for Staphylococcus epidermidis GB 9/6, Strep. salivarius GB 24/9, Staphylococcus aureus GB 2/1 and C. tropicalis GB 9/9 in comparison to controls. Perfusing the flow chamber with biosurfactant containing solution followed by the passage of a liquid-air interface, to investigate detachment of micro-organisms adhering to silicone rubber, produced high detachment (96%) of adhered cells for all micro-organisms studied, except for Staph. aureus GB 2/1 (67%). SIGNIFICANCE AND IMPACT OF THE STUDY: It is concluded that biosurfactant represent suitable compounds that should be considered in developing future strategies to prevent the microbial colonization of silicone rubber voice prostheses.

Actinomycetaceae↗
PubMed1996

Scleroderma and silicone gel breast prostheses--the Sydney study revisited.

BACKGROUND: Silicone augmentation mammoplasty has been postulated as a cause of environmentally-induced scleroderma. While representing a small proportion of all alleged causes of scleroderma, the issue has huge social, ethical and medicolegal ramifications. The hypothesis, however, has been recently questioned in results of comparative studies. We have previously reported no association between augmentation mammoplasty and scleroderma. However, all information was self-reported including augmentation mammoplasty status, and the prosthesis type was not identified. In addition, data were not available from untraceable cases. The current study addresses these issues. AIMS: To validate self-reported augmentation mammoplasty status, re-analyse rates of exposure to silicone gel breast prostheses in 556 scleroderma patients and 289 general practice controls and evaluate whether silicone gel breast prostheses are causally linked to scleroderma. METHODS: Study design-population-based case-control study; Cases-scleroderma patients resident in Sydney for at least six consecutive months between 1974-1988; Controls-patients from 29 randomly selected Sydney general practices, age- and gender-group-matched with cases. Validation of augmentation mammoplasty exposure was ascertained from the general medical practitioner of each interviewed case and control, or from the medical records of each deceased or untraceable case. Validation of the date of surgery and prosthesis type was from the relevant plastic surgeon. For each augmentation mammoplasty-positive case, validation of both the date and nature of the scleroderma onset was from the patient's medical records. Controls were given a "control date' for disease onset to adjust for duration of potential exposure. RESULTS: Validation of augmentation mammoplasty status was possible in 252 (87.2%) living controls, and 532 (95.7%) cases, of whom 287 were living. Self-reported augmentation mammoplasty status was highly reliable in living non-senile cases (kappa = 1), and living validated controls (kappa = 0.86). No association was identified between silicone gel augmentation mammoplasty and scleroderma with unadjusted odds ratios of 1.33 (95% CI: 0.26-6.71), and 1.00 (95% CI: 0.16-6.16) following adjustment for potential confounders of age, socioeconomic status and ethnicity. CONCLUSIONS: This validates the self-reported augmentation mammoplasty status previously reported and does not support the hypothesis that silicone gel augmentation mammoplasty is an environmental inducer of scleroderma in females.

Adult↗
PubMed2004

Using silicone gel sheet for the treatment of facial telangiectasias with sclerotherapy.

BACKGROUND: Telangiectasias are superficial cutaneous vessels that are visible to human eye and are present as a dilated venule, capillary, or arteriole. They are a common cause of concern, especially when located in face. Sclerotherapy is among the treatment alternatives, but facial telangiectasias are less responsive than those located on the leg. OBJECTIVE: To show the effectiveness of silicone gel sheet in improving the results obtained by sclerotherapy in facial telangiectasias. METHODS: Between 1998 and 2003, 32 patients were treated with sclerotherapy and silicone gel sheet (group 1). Twenty-six patients were treated with sclerotherapy and cotton ball (group 2), and 30 patients were treated only sclerotherapy (group 3). Patients were evaluated for 12 weeks for the degree of improvement and side effects. All complications, side effects, and number of sessions were also recorded at each follow-up visit. The number of sessions is limited to six. After the final follow-up visit, the photographs taken of each treatment site at baseline and at final visit were reviewed in a double-blinded manner based on a 0 to 4 scale by two physicians. RESULTS: Fifty one of the 88 patients showed improvement totally. In the silicone sheet-sclerotherapy group, 22 of the 36 patients showed improvement. In the sclerotherapy-cotton ball group, 14 of the 26 patients showed improvement, and in the sclerotherapy-only group, 15 of the 30 patients showed improvement completely within the 12 weeks. The patients treated with sclerotherapy-silicone gel sheet (group 1) had more improvement than the other groups. CONCLUSION: Combining silicone gel sheeting to sclerotherapy increases the success rate in treating facial telangiectasias, especially facial subunits, which have bone support.

Adolescent↗
PubMed1997

Effects of ultrathin silicone coating of porous membrane on gas transfer and hemolytic performance.

To assess the effect of an ultrathin (0.2 microm) silicone-coated microporous membrane oxygenator on gas transfer and hemolytic performance, a silicone-coated capillary membrane oxygenator (Mera HP Excelung-prime, HPO-20H-C, Senko Medical Instrument Mfg. Co., Ltd., Tokyo, Japan) was compared with a noncoated polypropylene microporous membrane oxygenator of the same model and manufacturer using an in vitro test circuit. The 2 oxygenators showed little difference in the oxygen (O2) transfer rate over a wide range of blood flow rates (1 L/min to 8 L/min). The carbon dioxide (CO2) transfer rate was almost the same in both devices at low blood flow rates, but the silicone-coated oxygenator showed a decrease of more than 20% in the CO2 transfer rate at higher blood flow rates. This loss in performance could be partly attenuated by increasing the gas/blood flow ratio from 0.5 or 1.0 to 2.0. In the hemolysis study, the silicone-coated membrane oxygenator showed a smaller increase in plasma free hemoglobin than the noncoated oxygenator. The pressure drop across both oxygenators was the same. These results suggest that the ultrathin silicone-coated porous membrane oxygenator may be a useful tool for long-term extracorporeal lung support while maintaining a sufficient gas transfer rate and causing less blood component damage.

Adult↗
PubMed2005

Pharmacokinetics of intravitreal 5-fluorouracil prodrugs in silicone oil: experimental studies in pigs.

PURPOSE: To examine the in vivo pharmacokinetics of intravitreal 5-Fluorouracil (5-FU) following tamponade with 5-FU prodrug silicone oil formulations. METHOD: Two different alkoxycarbonyl 5-FU prodrugs denoted C12 and C18 were synthesized and formulated as silicone oil suspensions. A total of 26 pigs underwent conventional three-port lens-sparing pars plana vitrectomy. Approximately 1.6 ml of the prodrug-silicone oil formulation was placed in the vitreous cavity. Operated eyes were enucleated between 20 min and 168 hours postoperatively, and analysed for their content of free 5-FU by high performance liquid chromatography. RESULTS: With the C12 prodrug silicone oil formulation, the concentration of free 5-FU in the vitreous water phase 1 hour after surgery was 3.30 +/- 1.62 microg/ml. After 4 hours this concentration had declined to 1 microg/ml. With the C18 prodrug, the concentration of free vitreal 5-FU never reached 1 microg/ml during the 7 days these experiments lasted. A mathematical model is presented that can explain the measured data if the clearance of 5-FU from the vitreous water phase follows first order kinetics with a half-life of 20 min. CONCLUSION: These experiments, and the model analysis, suggest that the elimination half-life of 5-FU in the vitreous cavity of a vitrectomized, silicone oil-filled eye is very fast. The model analysis indicates that an alkoxycarbonyl 5-FU prodrug with a specific release rate constant of 10.7 microg/square root h cm(2) can maintain an intravitreal 5-FU concentration above 1 microg/ml for 5 days in the porcine eye.

Animals↗
PubMed1996

Evaluation of ion-implanted-silicon detectors for use in intraoperative positron-sensitive probes.

The continuing development of probes for use with beta (positron and electron) emitting radionuclides may result in more complete excision of tracer-avid tumors. Perhaps one of the most promising radiopharmaceuticals for this task is 18F-labeled-Fluoro-2-Deoxy-D-Glucose (FDG). This positron-emitting agent has been demonstrated to be avidly and rapidly absorbed by many human cancers. We have investigated the use of ion-implanted-silicon detectors in intraoperative positron-sensitive surgical probes for use with FDG. These detectors possess very high positron detection efficiency, while the efficiency for 511 keV photon detection is low. The spatial resolution, as well as positron and annihilation photon detection sensitivity, of an ion-implanted-silicon detector used with 18F was measured at several energy thresholds. In addition, the ability of the device to detect the presence of relatively small amounts of FDG during surgery was evaluated by simulating a surgical field in which some tumor was left intact following lesion excision. The performance of the ion-implanted-silicon detector was compared to the operating characteristics of a positron-sensitive surgical probe which utilizes plastic scintillator. In all areas of performance the ion-implanted-silicon detector proved superior to the plastic scintillator-based probe. At an energy threshold of 14 keV positron sensitivity measured for the ion-implanted-silicon detector was 101.3 cps/kBq, photon sensitivity was 7.4 cps/kBq. In addition, spatial resolution was found to be relatively unaffected by the presence of distant sources of annihilation photon flux. Finally, the detector was demonstrated to be able to localize small amounts of FDG in a simulated tumor bed; indicating that this device has promise as a probe to aid in FDG-guided surgery.

Beta Particles↗
PubMed1997

Streptococcus thermophilus and its biosurfactants inhibit adhesion by Candida spp. on silicone rubber.

The adhesion of yeasts, two Candida albicans and two Candida tropicalis strains isolated from naturally colonized voice prostheses, to silicone rubber with and without a salivary conditioning film in the absence and presence of adhering Streptococcus thermophilus B, a biosurfactant-releasing dairy isolate, was studied. Coverage of 1 to 4% of the surface of silicone rubber substrata with adhering S. thermophilus B gave significant reductions in the initial yeast adhesion regardless of the presence of a conditioning film. Mechanistically, this interference in yeast adhesion by S. thermophilus B was not due to direct physical effects but to biosurfactant release by the adhering bacteria, because experiments with S. thermophilus B cells that had released their biosurfactants prior to adhesion to silicone rubber and competition with yeasts did not show interference with initial yeast adhesion. The amounts of biosurfactants released were highest for mid-exponential- and early-stationary-phase bacteria (37 mg.g of cells-1 [dry weight]), but biosurfactants released by stationary-phase bacteria (14 mg.g of cells-1 [dry weight]) were the most surface active. The crude biosurfactants released were mixtures of various components, with a glycolipid-like component being the most surface active. A lipid-enriched biosurfactant fraction reduced the surface tension of an aqueous solution to about 35 mJ.m-2 at a concentration of only 0.5 mg.ml-1. The amount of biosurfactant released per S. thermophilus B cell was estimated to be sufficient to cover approximately 12 times the area of the cross section of the bacterium, making biosurfactant release a powerful defense weapon in the postadhesion competition of the bacterium with microorganisms such as yeasts. Preadsorption of biosurfactants to the silicone rubber prior to allowing yeasts to adhere was as effective against C. albicans GB 1/2 adhesion as covering 1 to 2% of the silicone rubber surface with adhering S. thermophilus B, but a preadsorbed biosurfactant layer was less effective against C. tropicalis GB 9/9.

Adsorption↗
PubMed1987

Basal iridectomy at 6 o'clock in the aphakic eye treated with silicone oil: prevention of keratopathy and secondary glaucoma.

In the aphakic eye, with intact iris diaphragm, silicone oil has frequently caused a pupillary block. In this situation aqueous humour accumulates behind the iris and forces silicone oil through the pupil into the anterior chamber. An iridectomy at the 6 o'clock position can effectively prevent this pupillary block. The iridectomy allows free passage of aqueous to the anterior chamber which remains free of silicone oil. No permanent contact with silicone oil and the cornea is established, and development of keratopathy is prevented. The effect of this iridectomy in 62 eyes with intact iris diaphragm in patients in Rotterdam (35 cases) and Nagoya (27 cases) is demonstrated. Only in 6.5% of the cases was silicone oil present in the anterior chamber at the end of the follow-up period of 7 months.

Aphakia, Postcataract↗
PubMed1971

Evaluation of silicone as an artificial lubricant in osteoarthrotic joints.

Silicone 300 has been evaluated as an artificial lubricant in osteoarthrotic joints by means of a pilot study in five inpatients and a control trial of 25 outpatients with 40 osteoarthrotic knees. Sequential analysis showed a significant benefit from saline compared with silicone at one week follow-up and no significant difference at one month.Measurement of stiffness with a knee arthrograph showed no difference in reduction of stiffness between the two substances. In a study of 18 rabbits there was no evidence that silicone was retained in the joint cavity for longer than 48 hours. There was a failure of clearance of iodinated serum albumin for as long as three to four days after the injection of silicone, suggesting some obstruction to lymphatic outflow. Experimentally produced cartilaginous defects did not heal quicker with the injection of silicone into the joint.

Animals↗
PubMed1992

Silicone breast implants in vivo: MR imaging.

This study was designed to evaluate pulse sequences and patient positioning for MR imaging of silicone breast implants in patients. One hundred forty-three patients (281 silicone implants) underwent imaging over a 21-month period. The combination of a T2-weighted fast spin echo technique (SE), T2-weighted fast SE with water suppression, and T1-weighted SE with fat suppression is recommended to reliably differentiate silicone from other breast tissues and to identify intracapsular and extracapsular ruptures or leaks. Seventy of the 143 patients underwent removal of their silicone implants. The sensitivity for detection of silicone implant rupture was 76%, with a specificity of 97%. Positioning the patient prone improved image quality.

Adult↗
PubMed1997

Transjugular intrahepatic portosystemic shunt with silicone-covered Wallstents: results in a swine model.

PURPOSE: To evaluate the use of impermeable silicone-covered Wallstents for transjugular intrahepatic portosystemic shunt creation. MATERIALS AND METHODS: A transjugular intrahepatic portosystemic shunt was created in 14 young swine (weight, 20-32 kg) by using impermeable silicone-covered Wallstents. In eight animals, the silicone covering extended from the portal vein to the inferior vena cava. In two swine, the silicone covering ended short of the inferior vena cava, in two it ended short of the portal vein wall, and in two it ended short at each end. Follow-up transhepatic portal venography was performed weekly for 6 weeks or until the shunt was occluded. Animals were then sacrificed for gross and histologic evaluation. RESULTS: Only two of 14 shunts were patent after 3 weeks; both were stenosed with luminal narrowing of more than 50% in the middle of the shunt. By 6 weeks, all shunts were occluded. At histologic evaluation, a marked foreign-body reaction with superimposed thrombosis was demonstrated. CONCLUSION: In comparison with uncovered Wallstents, impermeable silicone-covered Wallstents are associated with decreased patency at transjugular intrahepatic portosystemic shunt creation. This is likely due to increased thrombogenicity and a foreign-body reaction.

Animals↗