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PubMed1981

Ureteric displacement into a silicone cover as protection from an induced retroperitoneal fibrosis: a preliminary report of experiments in rats.

At present, the "therapy of choice" for patients presenting retroperitoneal fibrosis is uretrolysis with intraperitoneal transposition. This procedure, however, leaves the upper and lower part of the ureter vulnerable to recurrent fibrotic stricture since these portions still remain within the retroperitoneal space. In order to protect the ureter in its entire length from aggressive fibrosis an alloplastic cover might offer a better alternative. Following experimental induction of retroperitoneal fibrosis by phenol-mandelic acid in rats the entire ureter was displaced into a silicone envelope. Under the operating microscope the silicone sheath was closed around the renal pedicale by separate sutures of 8-0 prolene. The upper and lateral sealing of this pouch was done by continous sutres and the lower opening of this silicone envelope was fixed to the bladder wall. Progressive retroperitoneal fibrosis caused anterior displacement of the silicone pouch but neither a fibrotic infiltration into this coner nor ureteral stenosis was noted. Histological investigation of these animals in comparison with the control group showed effective protection by the silicone cover. Long-term results of experiments in larger animals well show whether thie procedure might be applied clinically.

Animals↗
PubMed1993

A new biologically, osmotically, and oncotically balanced gel that shows calcifications blocked by silicone.

The radiodensity of silicone gel-filled breast implants is well documented. It has been suggested that silicone gel may block the transmission of x-rays sufficiently to prevent visualization of microcalcifications that are frequently an indicator of malignancy. A new biologically, oncotically balanced gel has been developed that has increased radiotranslucency to approximately the density of normal breast tissue, increased lubrication qualities, and is quickly and safely eliminated by the body should the shell rupture. We present a case wherein a patient's mammogram was read as negative two years prior to breast reaugmentation due to Baker IV capsular contracture. During surgery, complete calcification of the capsule was discovered, as well as two ruptured prostheses; neither condition had been detected by the mammogram. These capsules, with their calcifications and scar intact, were removed in toto and radiographically compared through standard silicone gel-filled breast implants and through implants containing the new biologically, osmotically, oncotically balanced gel. The calcifications were completely obscured by the silicone gel-filled prosthesis and completely visible when viewed through the bio-oncotic gel-filled prosthesis. Postoperative mammograms confirmed the radiolucency of the new gel-filled prostheses. This new gel appears to be a reasonable alternative to silicone gel for filling breast implants.

Adult↗
PubMed1995

MRI of silicone vitreous ocular implants with phantom correlation.

We imaged two patients who had silicone oil injected their vitreous cavities. The images demonstrated an increased chemical shift artifact. We developed and tested an in vitro silicone oil model in an attempt to explain this. To our knowledge, this artifact has not been previously described. We constructed a phantom using medication cups containing water, lard and two types of silicone. Background control baths of water and lard were used to simulate different local environments. The phantoms were imaged with T1-and T2-weighted and T1-weighted fat suppression sequences. The artifacts were due to the pronounced chemical shift of silicone in relation to intraconal fat. Our model accurately reproduced our clinical images. Spectral analysis of the silicone model revealed different resonating frequencies for fat/silicone, thereby explaining the pronounced chemical shift artifact.

Artifacts↗
PubMed1997

Deposition of extracellular matrix on silicone intraocular lens implants in rabbits.

PURPOSE: To examine the deposition of extracellular matrix on silicone intraocular lenses (IOLs) implanted experimentally into rabbit eyes by electron microscopy and to determine the immunolocalization of extracellular matrix components, including collagen types and cellular fibronectin, on these IOLs. METHODS: We performed phacoemulsification and aspiration of the crystalline lens and implanted a foldable silicone IOL in the capsular bag of one eye of each of 26 adult albino rabbits under general anesthesia. After 8 weeks the animals were killed and the eyes were enucleated. The silicone IOLs were processed for electron microscopy and for immunohistochemical detection of collagen types I, III, and IV and cellular fibronectin. RESULTS: Electron microscopy revealed deposition of a presumed cell matrix complex on the optic portion of all silicone IOLs, as well as the adhesion of presumed macrophages and foreign-body giant cells. Cellular deposits showed immunoreactivity for cellular fibronectin. Fibrous or membranous deposits exhibited immunoreactivity for cellular fibronectin and collagen types I and III. A few type IV collagen-immunoreactive deposits were also seen. CONCLUSION: Deposits of extracellular matrix components were observed on silicone IOLs. These deposits may form the scaffolding for the adhesion and proliferation of cells. These matrix components appeared to be the products of cells adhering to the surfaces of IOLs, including lens epithelial cells, macrophages and foreign-body giant cells, indicating that the process of granulation was incomplete.

Animals↗
PubMed1997

An in vitro study of silicone migration from intravenous fluid tubing.

Migration of particulate matter from plastic tubing and solid plastic implants has been documented in a number of studies, including some with the use of cardiac bypass, haemodialysis, and pump-assisted intravenous infusions. In order to ascertain whether silicone embolisation occurs when children have an Ivac 560 pump-assisted IV infusion, we passed 180 ml of pumped fluid through a microfilter and compared the scanning electron micrographs of those filters with unused filters and with others through which a similar volume had been passed without using the pump. The particles on the filters were analysed for their elemental content using energy-dispersive X-ray analysis. In addition, the appearance of the silicone tubing used in the pump over 3 and 72 h was assessed and compared to that of flow-only and unused tubing. More particles were found on the microfilter when fluid had been delivered via the pump than on those through which non-pumped fluid had passed or that were unused. Elemental silicon-containing particles were only found on the filter when a pump had been attached to the IV line. The flow-only and unused tubing were found to have adherent particles on the inner surface that were not seen once the tubing had been used for 3 h in the Ivac 560 pump. Also, after 72 h use, the silicone tubing had a deformed inner layer. The clinical significance of these findings is yet to be determined, but it does appear that silicone embolisation occurs during pump-assisted infusions in children.

Biocompatible Materials↗
PubMed1986

Histopathological findings in eyes after silicone oil injection.

Eight eyes were examined histologically after silicone oil injection. Intraretinal deposits suggestive of silicone were not present in attached retinas, but were frequently observed in detached retinas when subretinal silicone occurred. This may possibly be due to defects in the horizontal conducting structures of the retina such as those occurring in persistent detachment with disorganization of the retina. Morphologically, the retina was essentially normal 3.5 years after the silicone injection. This observation contradicts the idea that silicone oil has a toxic effect.

Eye↗
PubMed2003

Systematic characterisation of silicon-embedded accelerometers for mechanomyography.

Silicon soft suction sockets (roll-on sleeves) currently used in passive prostheses for below-elbow amputees could also be used in externally powered prostheses, enhancing their functionality and comfort. However, as it is extremely difficult to hold currently used electromyography (EMG) sensors in place reliably within a silicon socket, an alternative measurement of muscular activity as the control input is necessary. Mechanomyography (MMG) is the epidermal measurement of the low-frequency vibrations produced by a contracting muscle. MMG sensors do not have to be in direct contact with the skin. Moreover, the embedding of sensors in the roll-on sleeve may also solve attachment issues, making sensor placement flexible. Therefore the objective was to determine the feasibility of recording MMG signals using silicon-embedded, micro-machined accelerometers. Fifteen embedded accelerometers were excited with predefined vibration patterns. The signal-to-noise ratio (SNR) and frequency response of each sample were measured and compared with those of non-embedded accelerometers. The SNR of embedded samples (approximately equal to 19 dB) was significantly higher than that of non-embedded samples (approximately equal to 12 dB), owing to the considerable mechanical damping effect of the silicon in the 300-900 Hz bandwidth (p=0.0028). This has implications for the application of silicon-embedded accelerometers for externally powered prosthesis control.

Amputation, Surgical↗
PubMed2001

Direct determination of silicon in powdered aluminium oxide by use of slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry.

A direct method for determination of silicon in powdered high-purity aluminium oxide samples, by slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry (GF-AAS), has been established. A slurry sample was prepared by 10-min ultrasonication of a powdered sample in an aqueous solution containing both sodium carbonate and boric acid as a mixed flux. An appropriate portion of the slurry was introduced into a pyrolytic graphite furnace equipped with a platform. Silicon compounds to be determined and aluminium oxide were fused by the in situ fusion process with the flux in the furnace under optimized heating conditions, and the silicon absorbance was then measured directly. The calibration curve was prepared by use of a silicon standard solution containing the same concentration of the flux as the slurry sample. The accuracy of the proposed method was confirmed by analysis of certified reference materials. The proposed method gave statistically accurate values at the 95% confidence level. The detection limit was 3.3 microg g(-1) in solid samples, when 300 mg/20 mL slurry was prepared and a 10 microL portion of the slurry was measured. The precision of the determination (RSD for more than four separate determinations) was 14% and 2%, respectively, for levels of 10 and 100 microg g(-1) silicon in aluminium oxide.

Aluminum Oxide↗
PubMed2004

Biosurfactant from Lactococcus lactis 53 inhibits microbial adhesion on silicone rubber.

The ability of biosurfactant obtained from the probiotic bacterium Lactococcus lactis 53 to inhibit adhesion of four bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber with and without an adsorbed biosurfactant layer was investigated in a parallel-plate flow chamber. The microbial cell surfaces and the silicone rubber with and without an adsorbed biosurfactant layer were characterized using contact-angle measurements. Water contact angles indicated that the silicone-rubber surface with adsorbed biosurfactant was more hydrophilic (48 degrees) than bare silicone rubber (109 degrees). The results showed that the biosurfactant was effective in decreasing the initial deposition rates of Staphylococcus epidermidis GB 9/6 from 2,100 to 220 microorganisms cm(-2) s(-1), Streptococcus salivarius GB 24/9 from 1560 to 137 microorganisms cm(-2) s(-1), and Staphylococcus aureus GB 2/1 from 1255 to 135 microorganisms cm(-2) s(-1), allowing for a 90% reduction of the deposition rates. The deposition rates of Rothia dentocariosa GBJ 52/2B, Candida albicans GBJ 13/4A, and Candida tropicalis GB 9/9 were far less reduced in the presence of the biosurfactant as compared with the other strains. This study constitutes a step ahead in developing strategies to prevent microbial colonization of silicone-rubber voice prostheses.

Bacterial Adhesion↗
PubMedDate not supplied

Textured surface silicone breast implants: histology in the human.

Previous studies on the interaction of textured silicone breast implants has analyzed tissue expanders or used animal models. To date, the data on long-term results of the textured silicone breast implants have not examined permanent implants or in vivo effects in the human. A prospective study was designed to examine the interaction of textured silicone breast implants in a human over several years. A single surgeon, standard surgical technique, and single-type implant design were included. The results revealed 78% had silicone particles in the tissue immediately adjacent to the implant interface. No distant migration, metaplasia, or adverse effects were noted. Our results indicate that silicone fragmentation is common but appears to be confined to the local environment.

Adult↗
PubMed1997

[Acute retinal necrosis. Silicon oil tamponade in retinal detachment].

BACKGROUND: Because retinal necrosis syndrome seldom occurs, we present our results of silicone oil tamponade for associated retinal detachment. PATIENTS AND METHODS: Thirteen eyes from 13 patients undergoing retinal reattachment surgery for retinal detachment associated with acute retinal necrosis in a consecutive series between January 1988 and June 1995 were followed up. Patients were 25 to 56 years of age. Four patients had acquired immune deficiency syndrome (AIDS). Five eyes that were operated on with cryopexy and scleral buckling received vitrectomy, membrane peeling, silicone oil tamponade and endolaser treatment in a second operation. Eight eyes were primarily operated on with cryopexy, encircling buckle, vitrectomy with membrane peeling, silicone oil tamponade and endolaser treatment. All patients were treated with acyclovir. RESULTS: Postoperative complete reattachment was observed in 12 eyes and persistence of a peripheral detachment in one eye. Vision improved in eight eyes, but only five eyes achieved 20/200 or better vision. Limited functional results in our series were caused by retinal ischemia, optic atrophy and macula scars. After a median of 9.3 months silicone oil was removed in nine eyes. No retinal redetachment or recurrent retinitis was observed during a follow-up time of at least 6 months. CONCLUSIONS: Vitrectomy and silicone oil tamponade allowed all cases of retinal detachment associated with acute retinal necrosis to be successfully repaired. Further studies must be conducted to find out how we can improve the visual outcome-perhaps by earlier therapy with acyclovir or earlier vitrectomy.

Acquired Immunodeficiency Syndrome↗
PubMed1998

[Frequency of Nd:YAG capsulotomy after implantation of PMMA and silicon intraocular lenses].

UNLABELLED: The aim of this investigation was to ascertain the frequency of secondary cataract after implantation of PMMA or Silicone IOLs. PATIENTS AND METHODS: In our series of patients we implanted 900 PMMA IOLs in a period of 4 years. In the following 3 years we implanted 1600 silicone IOLs. After the operation, a Nd:YAG laser capsulotomy was indicated there was a reduction in visual acuity and the patient asked for improvement. With the help of computer documentation we had the possibility to follow up a period of 6 years after PMMA and 3 years after silicone IOL implantation. RESULTS: (1) PMMA IOL: After implantation of PMMA IOLs we found a frequency of 22% capsulotomies during the investigation period of 6 years; 4.9% of them occurred during the 1st year and 8% during the 2nd year. (2) Silicone IOL: During the control period of 3 years we found a capsulotomy rate of 9.9%. Most happened in the 1st year. CONCLUSIONS: Our 22.9% capsulotomy rate after PMMA IOL implantation is lower than the rate mentioned in the literature. We noticed a peak of capsulotomies in the 2nd year after the operation. During a control period of only 3 years after implantation of silicone IOLs we found a capsulotomy rate of 9.9%.

Aged↗
PubMed2004

Initial experience with antibiotic-impregnated silicone catheters for shunting of cerebrospinal fluid in children.

INTRODUCTION: Infection is a major complication of cerebrospinal fluid (CSF) shunting procedures. Recently, rifampin-impregnated and clindamycin-impregnated silicone catheters have been developed in an attempt to prevent and/or reduce the incidence of shunt infections. In vitro and in vivo animal studies have shown their efficacy in reducing bacterial colonization of catheters. However, these shunts are yet to be evaluated in clinical trials and their safety and efficacy in preventing shunt infections is unknown. METHODS: Between April 2002 and April 2003, 31 children (age range 6 months to 17 years, mean 4.5 years) underwent implantation of an antibiotic-impregnated silicone catheter for CSF diversion. All surgeries were performed by a single neurosurgeon (HSM) at a single medical center. The Codman Hakim Bactiseal silicone catheter was used in all children. Thirty-two catheters were implanted in 31 children. All children have been followed since surgery (for an average of 19 months). For comparison, the previous 46 standard implanted shunts over a similar period of time were reviewed (average follow-up 31 months). RESULTS: Of the 32 implanted catheters, 11 involved placement of a new complete shunt system, 8 were distal revisions, and 13 were proximal/ventricular revisions. There were fewer early and late complications than in the standard shunt group (12.5 and 18.8% vs. 23.9 and 34.8%). There was no local reaction from implantation of the catheters. One child contaminated his distal catheter by disrupting his abdominal incision. None of the other patients have developed any evidence of shunt infection to date. CONCLUSION: Rifampin-impregnated and clindamycin-impregnated silicone catheters appear to be safe and well tolerated in children. Preliminary results suggest a low incidence of shunt infection. Longer follow-up and a larger number of patients are needed to more accurately assess the efficacy of these catheters compared with traditional silicone catheters.

Adolescent↗
PubMed2005

Central scotoma associated with intraocular silicone oil tamponade develops before oil removal.

BACKGROUND: Unexplained sudden visual loss after removal of silicone oil from the eye has recently been described. We report the occurrence and features of unexplained central scotoma developing with silicone oil in situ in the vitreous cavity. METHODS: A retrospective case series of five patients (from two centres) who reported a central scotoma commencing during silicone oil tamponade was studied. All patients had vitrectomy for macula-on retinal detachment, with ultra-purified silicone oil tamponade (four out of five had giant retinal tear). Investigations included visual acuity, intraocular pressure, optical coherence tomography, fluorescein angiography, visual fields and electrophysiology. RESULTS: All patients reported a central scotoma that appeared during oil tamponade. Visual acuity fell by a mean of 0.93 LogMAR units after onset of the scotoma. After cataract extraction and oil removal, vision remained reduced by a mean of 0.8 units. The mean duration of oil in the eye was 2.7 months when the scotoma was noted by the patient. Investigations were performed after removal of oil. Fluorescein angiography (FFA) was performed in two cases and optical coherence tomography (OCT) in five patients. No abnormality was demonstrated. Electrophysiology was performed in five patients with pattern electroretinography suggestive of macular dysfunction in four patients. CONCLUSION: This is the first case series describing central scotoma associated with silicone oil in situ. Electrophysiology indicated macular dysfunction in most cases. We suggest that early removal of oil in cases with good visual potential should be considered to avoid this sight-threatening complication.

Adult↗
PubMed2005

Differential responses of human lens epithelial cells to intraocular lenses in vitro: hydrophobic acrylic versus PMMA or silicone discs.

BACKGROUND: The purpose of this study was to determine the influence of different materials of intraocular lenses (IOLs) on human lens epithelial cell behavior, including adhesion, migration, proliferation, apoptosis, and epithelial-mesenchymal transdifferentiation (EMT) in vitro. METHODS: Human lens epithelial cells (SRA 01/04) were grown on hydrophobic acrylic (Acrysof), polymethylmethacrylate (PMMA), and silicone IOLs. Cellular adhesion, migration, proliferation, and apoptotic assays were performed to assess cell behavior. The expression of EMT markers (fibronectin and type I collagen) produced by cells on IOLs was determined by immunoblotting and immunocytochemistry. RESULTS: Human lens epithelial cells exhibited preferred adhesion and reduced apoptosis when cultured on acrylic IOLs, in comparison to PMMA and silicone IOLs. Cells grown on acrylic lenses formed a confluent epithelial monolayer. Migration of lens epithelial cells under the acrylic lens was substantially blocked in an in vitro assay. In contrast, cells grown on PMMA and silicone lenses displayed a spindle-shaped, myofibroblast-like morphology, increased apoptosis, reduced adhesion, and enhanced production of EMT proteins such as fibronectin and type I collagen. The migration of lens epithelial cells under PMMA and silicone IOLs was substantial in the in vitro assay. CONCLUSION: This report demonstrates that hydrophobic acrylic lenses are more capsular biocompatible than PMMA and silicone lenses. The in vitro assays are reliable measurements for evaluating the responses of human lens epithelial cells to different IOL materials, and could advance our understanding of the preferential capsular opacification conferred by different IOL materials.

Apoptosis↗
PubMed2005

Crystal imperfection studies of pure and silicon substituted hydroxyapatite using Raman and XRD.

Hydroxyapatite (HA) is important in biomedical applications because of its chemical similarity to the mineral content of bone and its consequent bioactivity. Silicon substitution into the hydroxyapatite crystal lattice was found to enhance its bioactivity both in vitro and in vivo [1, 2]. However, the mechanism for the enhancement is still not well understood. In this paper, the crystal imperfections introduced by silicon substitution were studied using XRD and Raman spectroscopy. It was found that silicon substitution did not introduce microstrain, but deceased the crystal size in the hk0 direction. Three new vibration modes and peak broadening were observed in Raman spectra following silicon incorporation. The imperfections introduced by silicon substitution may play a role in enhancing bioactivity. A phenomenological relationship between the width of the PO4 v1 peak and crystal size was established.

Crystallization↗
PubMed2007

Density functional calculations of the properties of silicon-substituted hydroxyapatite.

Ab initio density functional plane-wave calculations are performed on silicon-substituted hydroxyapatite (SiHA). Formation energies are obtained for the substitution of a phosphorus atom by a silicon atom in each of the six phosphate groups of the unit cell in turn. It is found that the co-removal of a hydroxyl group to maintain charge neutrality is energetically favourable and the calculated unit cell volumes for the single silicon substitutions agree extremely well with experimental observation. The substitution of a second silicon atom in the unit cell is found to be almost as energetically favourable as the first (and on one site more favourable) and there can be an attractive interaction between the two Si substituents when they are closely separated. However, experimental observation suggests that for this concentration of silicon a phase transformation to a different structure occurs which, because of the imposed boundary conditions, could not be accessed in the calculations. The density of states of the SiHA indicates that new states are introduced deep into the valence band and the band gap decreases by 1.6 eV compared to phase-pure HA. No new states are introduced into the band gap indicating that the Si incorporation does not make the material inherently electrically active. Furthermore a population analysis shows that the Si impurity has only a small effect on the neighbouring ionic charge.

Biocompatible Materials↗
PubMed1977

Uses of RTV silicone in orbital reconstruction.

In a five-year follow-up of 42 patients with unsatisfactory cosmetic results after enulceation, room-temperature vulcanizing (RTV) silicone was used in the surgical correction of enophthalmos and superior sulcus depression. RTV silicone with a catalyst was placed in a dissected pocket subperiosteally along the floor and lateral wall of the orbit to correct the volume deficit. When vulcanizing in situ into soft silicone rubber, the implant conformed to the orbital wall and did not migrate. We determined tissue tolerance to in situ vulcanizing silicone histologically in 30 rats by inserting prevulcanized and in situ vulcanized material in paired subcutaneous pockets. No statistical difference was noted between the two methods. In 11 cases, the same material was used as a convenient stent to maintain the pressure over a graft and to maintain socket size after the reconstruction of a contrated socket, by filling the socket with RTV silicone which surrounded a Kirschner wire drilled through the lateral orbital rim.

Animals↗