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PubMed2005

Self-assembled silicon nanotubes under supercritically hydrothermal conditions.

Self-assembled silicon nanotubes with one-dimensional structure have been synthesized from silicon monoxide powder under supercritically hydrothermal conditions with a temperature of 470 degrees C and a pressure of 6.8 MPa. The silicon nanotubes were identified by transmission electron microscopy and high-resolution transmission electron microscopy. The results show that the silicon nanotubes (SiNT) have closed caps. The structures of the silicon nanotubes are hollow inner pore, crystalline silicon wall layers with a 0.31 nm interplanar spacing and 2-3 nm amorphous silica outer layers. Pure crystalline silicon nanotubes survive after etching the silicon nanotubes with 5% HF acid for enough time to imply that the self-assembled silicon nanotubes are stable. A possible theoretical reason for the growth of SiNTs from SiO under supercritically hydrothermal conditions was also proposed.

Journal Article↗

PubMed2003

In vitro bioactivity of silicon-substituted hydroxyapatites.

Silicon-containing hydroxyapatites were synthesized by the controlled crystallization method. Chemical analysis, N(2) adsorption, Hg porosimetry, X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to characterize the hydroxyapatite and to monitor the development of a calcium phosphate layer onto the surface of the substrate immersed in a simulated body fluid, that is, in vitro bioactivity tests. The influence of the silicon content and the nature of the starting calcium and phosphorus sources on the in vitro bioactivity of the resulting materials were studied. A sample of silicocarnotite, whose structure is related to that of hydroxyapatite and contains isolated SiO(4) (4-) anions that isomorphically substitute some PO(4) (3-) anions, was prepared and used as reference material for XPS studies. An increase of the unit cell parameters with the Si content was observed, which indicated that SiO(4) (4-) units are present in lattice positions, replacing some PO(4) (3-) groups. By using XPS it was possible to assess the presence of monomeric SiO(4) (4-) units in the surface of apatite samples containing 0.8 wt % of silicon, regardless the nature of the starting raw materials, either Ca(NO(3))(2)/(NH(4))(2)HPO(4)/Si(OCOCH(3))(4) or Ca(OH)(2)/H(3)PO(4)/Si(OCOCH(3))(4). However, an increase of the silicon content up to 1.6 wt % leads to the polymerization of the silicate species at the surface. This technique shows silicon enrichment at the surface of the three samples. The in vitro bioactivity assays showed that the formation of an apatite-like layer onto the surface of silicon-containing substrates is strongly enhanced as compared with pure silicon-free hydroxyapatite. The samples containing monomeric silicate species showed higher in vitro bioactivity than that of silicon-rich sample containing polymeric silicate species. The use of calcium and phosphate salts as precursors lead to materials with higher bioactivity.

Calcium↗

PubMed2005

Reduced adherence of Candida to silane-treated silicone rubber.

Silicone rubber is widely used in the construction of medical devices that can provide an essential role in the treatment of human illness. However, subsequent microbial colonization of silicone rubber can result in clinical infection or device failure. The objective of this study was to determine the effectiveness of a novel silane-treated silicone rubber in inhibiting microbial adherence and material penetration. Test material was prepared by a combination of argon plasma discharge treatment and fluorinated silane coupling. Chemicophysical changes were then confirmed by X-ray photoelectron spectroscopy, contact-angle measurement, and atomic force microscopy. Two separate adherence assays and a material penetration assay assessed the performance of the new material against four strains of Candida species. Results showed a significant reduction (p < 0.01) of Candida albicans GDH 2346 adherence to silane-treated silicone compared with untreated controls. This reduction was still evident after the incorporation of saliva into the assay. Adherence inhibition also occurred with Candida tropicalis MMU and Candida krusei NCYC, although this was assay dependent. Reduced penetration of silane-treated silicone by Candida was evident when compared to untreated controls, plaster-processed silicone, and acrylic-processed silicone. To summarize, a novel silicone rubber material is described that inhibits both candidal adherence and material penetration. The clinical benefit and performance of this material remains to be determined.

Argon↗

PubMed1989

In vitro effects of fibrous and nonfibrous silicon nitride on bovine pulmonary macrophages.

Bovine pulmonary macrophages were exposed in vitro to 0.3, 0.1, 0.03, or 0.01 mg/ml of a fibrous silicon nitride, nonfibrous (milled) silicon nitride comminuted from the fibrous powder, alpha-quartz (an active control), or glass beads (an inert control). Functional evaluation of the exposed cells indicated that the fibrous silicon nitride was as cytotoxic as quartz, while the nonfibrous silicon nitride was relatively inert. To further evaluate the mechanisms of cytotoxicity, the cells were exposed to 1 mg/ml of the control and test materials and biochemical studies were performed. Quartz increased release of both the cytoplasmic enzyme, lactate dehydrogenase (LDH), and the lysosomal enzyme, acid phosphatase (AP), consistent with both cell membrane and lysosome lysis. In addition, total protein levels were significantly depressed, suggesting significant impairment of cellular synthetic processes. LDH, but not AP, values were increased with fibrous silicon nitride treatment, but not with the nonfibrous silicon nitride. In contrast to quartz, which increased LDH levels by 65%, the fibrous silicon nitride only increased LDH levels by 11%. Scanning electron micrographs further indicated that the fibrous silicon is cytotoxic and poorly tolerated by macrophages. These studies provide further evidence of morphology as a primary determinant of cytotoxicity since the milled powder test article was comminuted from the fibrous material.

Acid Phosphatase↗

PubMed1996

Molecular dynamics simulations of silicon-fluorine etching.

Molecular dynamics simulations of the reactions between gaseous fluorine atoms and (SiFx)n adsorbates on the Si(100) - (2 x 1) surface are performed using the SW potential and compared to simulations with the WWC reparameterization of the SW potential. Theoretical and experimental work has demonstrated that the reactive fluorosilyl layer during silicon-fluorine etching is composed of tower-like adspecies of SiF, SiF2 and SiF3 groups. The objective of the simulations is to determine how the chemical composition, mechanism of formation, and energy distribution of the etched gas-phase products depend on the identity of the reacting adsorbate, the incident kinetic energy, and the parameterization of the potential energy function. Three reactions are simulated: F(g) + SiF3(a), F(g) + SiF2-SiF3(a), and F(g) + SiF2-SiF2-SiF3(a). SiF4 is the major product and Si2F6 and Si3F8 are minor products. In Si2F6 and Si3F8, the silicon-fluorine bond that is formed is stronger than the silicon-silicon bond in the molecule and, therefore, the majority of these products have enough energy to dissociate and will fragment before reaching the detector. An SN2-like mechanism is the primary mechanism responsible for the formation of SiF4, Si2F6, and Si3F8. In addition, at higher energies, the simulations have discovered a previously unknown mechanism for the formation of SiF4, which involves an insertion between a silicon-silicon bond. The results of the simulations with the two potentials differ quite substantially in their prediction of the reactivity of the adsorbates. The SW potential predicts a 2- to 3-eV lower energy threshold for reaction and a much higher reaction cross-section, especially for the SiF4 product. These results are explained in terms of the differences in the potential energy functions used to describe the silicon-fluorine interactions. In addition, the results are compared to experimental data on silicon-fluorine etching.

Computer Graphics↗

PubMed1999

Methods for detecting silicones in biological matrixes.

Methods for analyzing for silicon and silicone in biological matrixes were developed. A silicone-specific technique involved microwave digestion of samples in acid solution to rapidly break down the biological matrix while hydrolyzing silicones to monomeric species. The resulting monomeric silanol species were then capped with trimethylsilyl groups, extracted into hexamethyldisiloxane, and analyzed by gas chromatography. In serum, positive identification of silicone species with detection limits below 0.5 microgram of Si/mL are possible with this technique. The technique is compared with a silicone-specific technique, 29Si NMR, and a non-silicone-specific technique, ICP-AES. 29Si NMR was far less sensitive, with a detection limit of only 64 micrograms of Si/mL in serum when analyzing for one compound with a single sharp resonance. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) has potentially lower detection limits, but the technique is not silicone-specific and suffers from species-dependent responses.

Animals↗

PubMed1995

Immunologic stimulation of T lymphocytes by silica after use of silicone mammary implants.

Difficulties in showing the biologic activity of silicones in vitro have contributed to the controversy over effects of silicone mammary implants in vivo. We adapted a standard lymphocyte stimulation test to detect evidence of cellular immunity in patients with silicone gel implants. Initially, lymphocytes were harvested from 70 implant patients, 76 normal controls without implants or symptoms, and 18 patients with classic rheumatic disorders and without a history of silicone implants. The harvested lymphocytes were stimulated with PWM, PHA, Con A, and pharmaceutical grade colloidal silicon dioxide (silica). Implant patients showed increased SI compared to controls and those with rheumatic disorders. The mean SI of implant patients was 195.0 +/- 19.3, 18-fold that of normal controls (< 0.0001). Patients with rheumatic disease showed the same SI as controls (P = 0.3577). A follow-up study included 220 normal controls without implants, 942 silicone gel implant patients with demonstrable rheumatic symptoms, and 34 implant patients without symptoms at the time of the study. The average SI for the 220 normal controls was 10.0 +/- 0.41. Among the symptomatic implant women, 860 (91.3%) had SI significantly above those of the normal controls. Of these, 171 (18.2%) had SI between 25 and 50, 316 (33.5%) had SI between 50 and 100, and 373 (39.6%) had SI over 100. The data presented confirms that silicone implant patients respond immunologically to the silicon dioxide contained in mammary prostheses.

Adult↗

PubMed1997

The artificial iris diaphragm for vitreoretinal silicone oil surgery.

BACKGROUND: Silicone keratopathy frequently develops as a complication of silicone oil tamponade in the management of severe trauma in eyes with partial or complete aniridia. We therefore designed an "open" artificial iris diaphragm to prevent silicone oil-endothelial contact. In hypotony, where insufficient circulation of aqueous allows silicone in the anterior chamber despite an open diaphragm, a new solution became necessary. The "closed" artificial diaphragm was developed. METHODS: In this retrospective study, two consecutive series of artificial iris diaphragms were compared. Forty-four patients received either an open type (20 eyes) or a closed type (24 eyes) and were observed for 409 +/- 421 days (range, 32-1912). All eyes were aphakic, normotonous, and had a traumatic, compromised iris diaphragm or were aphakic and hypotonic as a result of injury, proliferative vitreoretinopathy, proliferative diabetic retinopathy, or uveitis, with an intact natural iris diaphragm. RESULTS: Silicone oil was retained behind the open diaphragm throughout the observation period in 40% of the eyes. Major long-term complications were hypotony and fibrous overgrowth. Silicone was retained behind the closed diaphragm in 50% of the eyes. CONCLUSION: Because proliferative vitreoretinopathy is active for months and multiple surgical interventions become necessary to avoid phthisis in eyes with highly pathologic changes, longstanding or permanent silicone tamponade is used. The artificial diaphragm prevents silicone-corneal contact in approximately 50% of aphakic eyes for at least 1 year.

Adolescent↗

PubMed1999

Evaluation of polymers based on a silicone backbone as pseudostationary phases for electrokinetic chromatography.

The feasibility of polymeric phases based on a silicone polymer backbone as pseudostationary phases for electrokinetic chromatography has been investigated. Silicone phases were studied because of the range of chemistries that could be developed based on these backbones, and because successful development of silicone phases would make it possible to employ much of the stationary phase chemistry developed in the past thirty years. Three silicone polymer structures have been investigated, but only one had sufficient aqueous solubility to permit application in electrokinetic chromatography. This phase was characterized by a variety of methods and was shown to be a mixture of partially hydrolyzed poly(bis-(3-cyanopropyl) siloxanes. When employed as a pseudostationary phase, this material provided selective and efficient separations. The electrophoretic mobility of the silicone polymer is greater than that of sodium dodecyl sulfate (SDS) micelles and poly(sodium 10-undecenylsulfate), providing an extended migration time range. A striking characteristic of the polymer is that the electrophoretic mobility is greater than typical electroosmotic mobilities. The chemical selectivity of the phase is significantly different from that of SDS micelles or poly(sodium 10-undecenylsulfate). The silicone phase is a more cohesive, basic and polar phase than SDS micelles. In buffers modified with a high concentration of organic solvents, the chromatographic properties of the silicone polymer are inferior to those of the poly(sodium 10-undecenylsulfate). The greatest limitation of silicone polymers for this application appears to be limited aqueous solubility, which will make it difficult to realize a family of such polymers with different chemical selectivities.

Acetates↗

PubMed1987

Experimental demonstration of the immunogenicity of silicone-protein complexes.

Although silicones, as a class, are nontoxic in animal and tissue studies, implanted silicone prostheses and medical devices are associated with various local and systemic host inflammatory reactions. They also have been associated with a form of autoimmune disease. To test the hypothesis that silicones may evoke an immunologically mediated inflammatory reaction, 10 guinea pigs were stimulated for 1 month with intraperitoneal injections of sterile medical-grade silicone oil admixed with homologous serum and complete Freund's adjuvant. Ten controls were stimulated with saline. Four additional animals were passively sensitized with splenic homogenates from four sensitized animals. Intradermal antigenic challenges consisted of silicone-homologous serum, pure silicone, saline-homologous serum, and purified protein derivative. Cutaneous reaction patterns were graded grossly and microscopically. Silicone-serum and purified protein derivative antigens evoked three to four times greater palpable lesions in all 10 actively and all 4 passively sensitized animals at approximately 24 h compared to controls. Biopsies showed a moderate to marked lymphocytic infiltrate. Control sites and naive animals showed only edema at the challenge sites. The data suggest that silicone-protein complexes are potentially immunogenic.

Animals↗

PubMed2005

In vitro interaction between silicone gel and human monocyte-macrophages.

Controversy remains regarding the ability of silicone materials to induce a specific immune reaction versus a nonspecific inflammatory response. Histopathological analysis of the tissue around failed breast implants reveals chronic inflammation with silicone gel droplets either surrounded by giant cells or engulfed by macrophages, areas of fibrosis, and necrosis. Macrophages are the key cells engulfing or forming foreign body giant cells. To address the mechanisms of silicone-induced inflammation a model of human monocyte-derived macrophages (MDMs) was developed. After sonication of silicone gel, the silicone droplets were embedded in Type I collagen and used to coat glass coverslips; human MDMs were subsequently seeded on the coverslips and maintained in culture for up to 7 days. The advantage of the model was that human macrophages could be studied histologically, and cytochemically as they interacted with well-characterized silicone materials. Initial analysis of the human macrophages shows phagocytosis of the silicone gel within hours of exposure to the material. Analysis for pro-inflammatory cytokines reveals significant transient secretion of IL-1 (p < 0.01) over controls by human macrophages upon exposure to silicone gel at 24 h.

Cell Survival↗

PubMed1993

In vivo degradation of silicones.

29Si nuclear magnetic resonance (NMR) spectroscopy is applied to study the degradation of polysiloxanes (silicones) in vivo. Our results with animal models show that silicone migrates from the implant to the liver (29Si resonance at -20 ppm) and new silicon containing compounds form after the silicones are introduced into the rats. The new 29Si resonances in the chemical shift range of -40 to -85 ppm are related to hydrolyzed silicone, those at -90 to -115 ppm are indicative of the presence of silica (SiO2), and the peaks observed at -120 to -150 are related to high coordinated silicon complexes. These resonances are not present in the 29Si spectra of the silicones before implantation. Our findings demonstrate that silicones are not metabolically inert.

Animals↗

PubMed1996

Autoantibodies in patients with silicone implants.

We assessed the prevalence of autoantibodies in women with silicone implants and controls. Five hundred consecutive patients with silicone implants, 25 age-matched normal women, 25 women with silicone implants and no rheumatic symptoms, and 100 women with fibromyalgia were tested. Immunofluorescence antinuclear antibodies (ANA) were performed using HEp-2 cells. Subtype autoantibodies were performed by enzyme-linked immunoassay and Western blot. ANA tests were positive in 30% of patients with silicone implants and rheumatic symptoms, 8% of age-matched normal women, 28% of women with silicone implants without clinical symptoms, and 25% of women with fibromyalgia and no silicone implants. The predominant ANA pattern was speckled (55%). ANA subtype testing was positive in 4.8% of patients and none of the controls. We conclude that a larger proportion of women with silicone implants have autoantibodies compared to age-matched asymptomatic women suggesting immune activation in women with silicone implants.

Adult↗

PubMed2002

An association of silicone-gel breast implant rupture and fibromyalgia.

Silicone-gel breast implant rupture is common. Silicone-gel from ruptured implants may escape the scar capsule that forms around breast implants and become "extracapsular silicone." Our previously published study found that women with extracapsular silicone gel were at higher risk of reporting that they were diagnosed with fibromyalgia. There has been a limited number of studies addressing this association in the literature. Some studies addressing the issue of silicone breast implants and connective tissue disease specifically exclude patients with fibromyalgia from the sample or do not include the syndrome in the analysis. Case series describing fibromyalgia in patients with implants have been published, but many of these papers lack information on extracapsular silicone and are not representative because the patients are typically from referral populations. In addition, most studies do not have control groups of women without implants for comparison or do not distinguish between saline and silicone implants. Additional observational studies of women from nonreferral populations are necessary to validate an association. These studies should provide information on how the rupture is diagnosed, state whether the rupture extended beyond the capsule, and provide an appropriate control group for comparison. The findings from such studies may be important to physicians as they describe potential risks associated with implants to their patients. These findings should also be important for regulatory decision making on silicone-gel breast implants.

Breast Implants↗

PubMed1995

Silicone breast implants: immunotoxic and epidemiologic issues.

Silicone gel implants for breast augmentation and reconstruction have been in use since 1962. Significant local complications include capsular contracture, rupture, gel "bleed", and spread of the implant material to regional lymph nodes (1-7) as well as histologic findings of foreign body granulomas in the capsular tissue and in lymph nodes (7-9). Through magnetic resonance spectroscopy and atomic emission spectroscopy, silicon compounds were found in the blood of some women with silicone breast implants; silicone and silica have also been found in liver (10). Well-publicized case reports have raised significant concerns regarding an association between implants and systemic disease. However, despite the availability of silicone implants for over 30 years, controlled epidemiological studies were not carried out until 1992. Currently available epidemiologic data are extremely limited. In part, because the majority of implants were used after 1981, the incidence of long-term problems is not yet known. In 1992, due to the unavailability of studies demonstrating the safety of implants, the U.S. Food and Drug Administration advised that silicone breast implants should be used only in reconstructive surgery and as part of clinical trials (11). This decision spurred a wave of research on the bioreactivity of silicone and clinical observations of patients with implants. Herein, we review the adverse immune effects following contact with silicone as well as the epidemiologic data available.

Animals↗

PubMed1993

Biodeterioration of medical-grade silicone rubber used for voice prostheses: a SEM study.

Silicone voice prostheses used for rehabilitation of speech after total laryngectomy are inserted in an non-sterile habitat. Deposits on explanted Groningen Button voice prostheses revealed a biofilm, due to heavy colonization of the silicone surface by bacteria and yeasts. Furthermore, it was demonstrated by scanning electron microscopy on sectioned explants that the silicone material was deteriorated by filamentous and vegetative yeast cells. The different explants showed a variety of sharp-edged, discrete yeast colonies. The yeasts grew just under the silicone surface and up to 700 microns into the silicone material. Finally, nine different types of defects in the silicone material created by the yeasts are described. This deterioration of the silicone by yeasts seems to be the main reason for the failure and the frequent replacement of the prostheses. The mechanisms of silicone deterioration are still hypothetical.

Bacterial Adhesion↗

PubMed1993

Silicon-responsive cDNA clones isolated from the marine diatom Cylindrotheca fusiformis.

In organisms ranging from single-celled algae to mammals, including humans, silicon is essential for, and actively participates in, a variety of life processes. It has become clear that silicon (i) acts as a metabolite affecting a variety of cellular processes, and (ii) regulates gene expression. However, the mechanisms by which silicon (i.e., Na2SiO3.9H2O, in the present study) acts are not clear, due to inherent methodological difficulties. As part of our program to understand how silicon acts in biological systems, we present the first isolation of cDNA clones derived from silicon-responsive mRNAs, from the marine diatom Cylindrotheca fusiformis. We distinguish between clones responding only to silicon starvation and replenishment, and those also responding to other cellular conditions. Some of the clones can be identified by similarity to other genes, and should be useful as probes to isolate genes from other organisms. Isolation of these clones provides the means to (i) identify metabolic pathways affected by silicon, and (ii) investigate the mechanism(s) of silicon-regulated gene expression.

Cloning, Molecular↗

PubMed2005

Porous silicon-based biosensor for pathogen detection.

A porous silicon-based biosensor for rapid detection of bacteria was fabricated. Silicon (0.01 ohmcm, p-type) was anodized electrochemically in an electrochemical Teflon cell containing ethanoic hydrofluoric acid solution to produce sponge-like porous layer of silicon. Anodizing conditions of 5 mA/cm2 for 85 min proved best for biosensor fabrication. A single-tube chemiluminescence-based assay, previously developed, was adapted to the biosensor for detection of Escherichia coli. Porous silicon chips were functionalized with a dioxetane-Polymyxin B (cell wall permeabilizer) mixture by diffusion and adsorption on to the porous surface. The reaction of beta-galactosidase enzyme from E. coli with the dioxetane substrate generated light at 530 nm. Light emission for the porous silicon biosensor chip with E. coli was significantly greater than that of the control and planar silicon chip with E. coli (P<0.01). Sensitivity of the porous silicon biosensor was determined to be 101-102 colony forming units (CFU) of E. coli. The porous silicon-based biosensor was fabricated and functionalized to successfully detect E. coli and has potential applications in food and environmental testing.

Biosensing Techniques↗