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PubMed2006

Thermal conductivity and specific heat of thin-film amorphous silicon.

We report the thermal conductivity and specific heat of amorphous silicon thin films measured from 5-300 K using silicon-nitride membrane-based microcalorimeters. Above 50 K the thermal conductivity of thin-film amorphous silicon agrees with values previously reported by other authors. However, our data show no plateau, with a low T suppression of the thermal conductivity that suggests that the scattering of long wavelength, low Q vibrations goes as Q2. The specific heat shows Debye-like behavior below 15 K, with theta(D) = 487 +/- 5 K, and is consistent with a very small contribution of tunneling states in amorphous silicon. Above 15 K, the specific heat deviates less from Debye behavior than does its crystalline allotrope, indicating no significant excess modes (boson peak) in amorphous silicon.

Journal Article↗

PubMed2001

XANES analyses of silicon crystalline irradiated by nitrogen/oxygen ions.

X-ray absorption techniques have been applied to the characterization of 5 keV nitrogen / oxygen ions implanted silicon samples. The depth selective measurement of XANES by recording in PEY mode and the quantitative analysis by superposition of XANES spectra were carried out to elucidate the depth profile of implanted ions. It has been revealed that the silicon nitride phase were formed in silicon after prolonged N+ irradiation and it extended over the deep part of the damaged region from the surface. On the other hand, for the O+ irradiation, silicon dioxide phase were produced only in the shallow part of the damaged region, i.e., the silicon dioxide phase likely broke off during the irradiation.

Journal Article↗

PubMedDate not supplied

Liquid injectable silicone for soft tissue augmentation.

Liquid injectable silicone is a unique soft tissue augmenting agent that may be effectively utilized for the correction of specific cutaneous and subcutaneous atrophies. Although historical complications have occurred, resulting likely from the presence of adulterants and impurities, modern purified silicone products approved by the Food and Drug Administration for injection into the human body may be employed with minimal complications when strict protocol is followed. In this article the present authors review the history and controversy regarding silicone as well as describe the appropriate indications, patient selection, instrumentation, treatment protocol, and anticipated complications involved with the use of liquid injectable silicone for soft tissue augmentation. Although its use is controversial, the present authors maintain that liquid injectable silicone is an important and effective augmenting agent for the long-term correction of scars and facial contour defects such as HIV facial lipoatrophy. Furthermore, it is a treatment modality deserving of continued investigation.

Biocompatible Materials↗

PubMed2005

A stretchable form of single-crystal silicon for high-performance electronics on rubber substrates.

We have produced a stretchable form of silicon that consists of submicrometer single-crystal elements structured into shapes with microscale, periodic, wavelike geometries. When supported by an elastomeric substrate, this "wavy" silicon can be reversibly stretched and compressed to large levels of strain without damaging the silicon. The amplitudes and periods of the waves change to accommodate these deformations, thereby avoiding substantial strains in the silicon itself. Dielectrics, patterns of dopants, electrodes, and other elements directly integrated with the silicon yield fully formed, high-performance "wavy" metal oxide semiconductor field-effect transistors, p-n diodes, and other devices for electronic circuits that can be stretched or compressed to similarly large levels of strain.

Journal Article↗

PubMed2002

Activation of macrophages by silicones: phenotype and production of oxidant metabolites.

BACKGROUND: The effect of silicones on the immune function is not fully characterized. In clinical and experimental studies, immune alterations associated with silicone gel seem to be related to macrophage activation. In this work we examined in vivo, phenotypic and functional changes on peritoneal macrophages early (24 h or 48 h) and late (45 days) after the intraperitoneal (i.p.) injection of dimethylpolysiloxane (DMPS) (silicone). We studied the expression of adhesion and co-stimulatory molecules and both the spontaneous and the stimulated production of reactive oxygen intermediates and nitric oxide (NO). RESULTS: The results presented here demonstrate that the fluid compound DMPS induced a persistent cell recruitment at the site of the injection. Besides, cell activation was still evident 45 days after the silicone injection: activated macrophages exhibited an increased expression of adhesion (CD54 and CD44) and co-stimulatory molecules (CD86) and an enhanced production of oxidant metabolites and NO. CONCLUSIONS: Silicones induced a persistent recruitment of leukocytes at the site of the injection and macrophage activation was still evident 45 days after the injection.

Animals↗

PubMed2005

Simple compressive method for treatment of auricular haematoma using dental silicone material.

Most of the previous treatment methods for auricular haematoma are inconvenient for both patients and doctors because they are time-consuming and complex and must be performed under sterile conditions. The purpose of this study was to evaluate the effectiveness of a simple compressive method using a dental (silicone) impression material and comparing it with other methods for treatment of auricular haematomas. The authors aspirated a haematoma and then placed a mixed base and catalyst of silicone putty material on the anterior and posterior surfaces of the auricle in the shape of an inverted U for seven days. From the 24 cases managed with this method, 23 cases (95.8 per cent) were successfully healed. Eight patients were treated with a collodion-cotton wool cast and 16 of 19 patients were successfully treated with dental cotton-wool rolls. The average number of those visiting the hospital was 2.7 for the collodion-cotton wool cast, 6.9 for the dental cotton-wool roll, and 3.1 for dental silicone. The mean treatment durations were 8.1 days for the collodion-cotton wool cast, 13.8 days for the dental cotton-wool roll, and 8.6 days for dental silicone. The authors believe that this compressive method using dental silicone material is simple and appropriate for the treatment of auricular haematoma.

Adolescent↗

PubMed2006

Oxidation of evaporated porous silicon rugate filters.

Rugate filters are thin-film optical interference coatings with sinusoidal variation of the refractive index. Several of these filters were fabricated with glancing angle deposition, which exploits atomic competition during growth to create nanoporous materials with controllable effective refractive index. This method enables the fabrication of devices with almost arbitrary refractive index profiles varying between the ambient, 1.0, and the index of the film material, in this case silicon with an index of 4.0 (at 600 nm). As these filters are inherently porous, oxidation of the silicon can occur throughout the device layer, and here we study the intentional oxidation of silicon filters by high-temperature reaction with gaseous oxygen. We find that a significant portion of the silicon filter oxidizes in approximately 10 min when heated to 600 degrees C-650 degrees C in an oxygen environment; oxidation then continues slowly over several hours. The presence of water vapor has little apparent effect on the oxidation reaction, and attempts to oxidize with ozone at room temperature were unsuccessful. As silicon filters oxidize to become silica, spectral blueshifts and increased short-wavelength transmittance are observed. Measured and calculated transmittance spectra generally agree, although the lack of absorption and dispersion in the theoretical model limits detailed comparison.

Journal Article↗

PubMed2006

Silicon-based and suspended-membrane-type guided-mode resonance filters with a spectrum-modifying layer design.

The concept of a spectrum-modifying layer is proposed for the design of a silicon-based guided-mode resonance filter. To realize such a novel device, a grating and waveguide structures are fabricated simultaneously in a suspended silicon nitride membrane. The cladding layer of the silicon substrate is replaced by the silicon dioxide membrane to reduce the absorption loss of the bulky substrate. Moreover, the silicon dioxide membrane plays a role in modifying the spectral response. According to the experimental results of the proposed structures, symmetrical line shapes and improved sidebands of nonresonance are demonstrated.

Journal Article↗

PubMed1993

Retention and strength of silicone-rubber catheters. A report of five cases of retention and analysis of catheter strength.

Five patients had a silicone-rubber catheter that broke during attempted removal. Mechanical testing was performed to determine the tensile strength of silicone-rubber as well as of polyvinyl chloride catheters. Silicone-rubber catheters were found to have a low tensile strength. The pull-out force of ten indwelling silicone-rubber catheters was also measured. The pullout force measured from a patient who had a cast was close to 40 per cent of the strength of the silicone-rubber catheters.

Bone Diseases↗

PubMed2003

Quantitative analysis of trace bulk oxygen in silicon wafers using an inert gas fusion method.

This paper describes a method for removing oxide film from the surface of silicon wafers using an inert gas fusion impulse furnace and precise determination of bulk oxygen within the wafer. A silicon wafer was cut to about 0.35 g (6 x 13 x 2 mm) and dropped into a graphite crucible. The sample was then heated for 40 s at 1300 degrees C. The wafer's oxide film was reduced by carbon and removed as carbon monoxide. The treated silicon sample was taken out of the graphite crucible and maintained again with the holder of the oxygen analyzer. The graphite crucible was then heated to 2100 degrees C. The treated silicon sample was dropped into the heated graphite crucible and the trace bulk oxygen in the wafer was measured using the inert gas fusion infrared absorption method. The relative standard deviations of the oxygen in silicon wafer samples with the removed surface oxide film were determined to be 0.8% for 9.8 x 10(17) atoms/cm3, and 2.7% for 13.0 x 10(17) atoms/cm3.

Journal Article↗

PubMed1976

In vivo tissue reactivity of radiation-cured silicone rubber implants.

Silicone rubber implants are clinically used in large numbers and elicit a milk tissue reaction. An occasional patient develops an accentuated reaction, an observation which has stimulated clinicians to try to understand this process more fully. The chemistry of medical silicone implants, including quantitative composition, is reviewed. This in vitro laboratory study show less tissue reaction-cured silicone with SiO2 filler. A proposed system for fabrication and curing of a silicone implant, with the qualities of strength and diminished tissue reactivity, is discussed.

Animals↗

PubMed1994

In vivo experimental analysis of silicone implants on bone and soft tissue.

We report experimentally produced silicone microparticles (synovitis) in 47 white rabbits and discuss the implications for clinical practice. Silastic HP100 (Dow Corning Wright, Arlington, TN) finger hinges (size 5) were inserted in 20 rabbit's knees. The upper tibia was replaced with Swanson design great toe implants in another 15 rabbits; articular cartilage was removed and endosteal drilling was performed in 6 animals as a "sham" arthroplasty. Small silicone blocks were inserted in the proximal tibial endosteal canal of 6 others. Animals were followed by monthly x-ray films and killed at 2, 4, 6, 12, and 16 months. Implant wear, bone surfaces, and soft tissue were examined under the operating microscope and by light microscopy; implant surfaces were examined with scanning electron microscopy. X-ray changes included reactive endosteal bone formation around implant stems as early as 1 month postoperatively; at 2-3 months the new bone line was clearest but it became progressively homogeneous and less evident. Extensive cortical erosion around the stems was observed in one third of the animals. Neither ossification nor lysis was observed around the silicone block. Proliferative synovitis was found at post-mortem examination beginning after 4 months; femoral condylar erosions were observed in most animals after 12 months. Wherever there was bone destruction, silicone particles were confirmed by x-ray spectrography.

Animals↗

PubMed2006

Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties.

The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging.

Air Pollutants, Occupational↗

PubMed1999

Development of a synthetic bolus using silicone elastomer for the study of masticatory efficiency.

STATEMENT OF PROBLEM: Masticatory efficiency has been proposed as an outcome measure for prosthetic rehabilitation. However, no standardized method is available for this type of assessment. PURPOSE: This study developed a normalized synthetic test food with reproducible physical and rheologic properties. MATERIAL AND METHODS: Two silicone putties of different hardness were studied. The texture of each putty varied by the addition of silicone oil. Rheologic characteristics of 7 samples were compared with the same properties of 5 natural food substances. RESULTS: Seven varieties of synthetic bolus were produced, each of which were of a different hardness, modulus of elasticity, and tensile strength. The natural food substances demonstrated great rheologic variability. The synthetic bolus samples exhibited a texture profile approaching that of natural foods. The principal difference between the 2 groups tested was that of the homogeneity of the silicone samples. CONCLUSION: None of the samples reproduced all the rheologic properties of the natural food substances; however, the results showed that their characteristics were sufficiently similar for the silicone samples to be suggested as a reproducible alternative for the testing of masticatory efficiency.

Bread↗

PubMed2005

Cohesive silicone gel breast implants in aesthetic and reconstructive breast surgery.

BACKGROUND: Cohesive silicone gel breast implants are composed of a textured silicone elastomer shell and are filled with cohesive silicone gel. Cohesive gel is formed by increasing the number of cross-links between gel molecules, which results in an implant that has better retention of shape and is less likely to fold or collapse, especially in the upper pole. METHODS: The initial 150 consecutive patients who received cohesive gel breast implants by the senior author (Brown) were included in the study. A retrospective chart review was carried out to analyze patient demographics, diagnosis, indication for cohesive gel selection, procedure performed, implant selected, and complications. All implants were manufactured by Inamed Aesthetics and were either style 410, CML, or CMH. RESULTS: One woman underwent unilateral augmentation for breast asymmetry and 117 women underwent bilateral breast augmentation. Of the 235 implants used, all were model 410 anatomical implants, with the majority being MM, MF, FM, or FF styles. Complications occurred in four of 118 patients (3.4 percent). There was one immediate postoperative hematoma, two cases of unilateral Baker II contracture, and one case of asymmetry related to excessive lowering of an inframammary fold. There were no cases of rotation, malposition, infection, rippling, or loss of implant integrity. Thirty-two women underwent breast reconstruction with cohesive gel implants. A total of 50 implants were used in the 32 patients (27 style 410, 19 style CML, and four style CMH). Complications occurred in six of 32 patients (18.8 percent), although five of the six were minor and only one of 32 patients (3.1 percent) required a secondary procedure. There were two seromas, three capsular contractures, and one implant exposure following a skin-sparing mastectomy. CONCLUSIONS: Cohesive gel implants have the potential for providing a natural breast shape, minimizing the risk of postoperative rippling, and providing a greater degree of safety should the implant lose its integrity. The wide variety of implant shapes and sizes allows for great flexibility in reconstructive surgery, in cases of breast asymmetry, and in primary breast augmentation. Results in our initial 150 patients have been excellent, with a high degree of patient satisfaction, excellent aesthetic outcomes, and very few implant-related complications. Cohesive gel implants are likely to play an important role in aesthetic and reconstructive breast surgery when silicone gel implants are reintroduced into the North American market.

Adult↗

PubMed1996

Cytokine mRNA changes during the treatment of hypertrophic scars with silicone and nonsilicone gel dressings.

BACKGROUND: Treatment of hypertrophic scars can be difficult for both patients and physicians. Silicone-containing gel dressings have been reported to be an effective alternative treatment for hypertrophic scars, yet the mechanism of action of these dressings is unknown. OBJECTIVE: To determine whether silicone is an essential factor in the treatment of hypertrophic scars and investigate the effects of occlusive dressing therapy on the expression of key wound healing mediators. METHODS: A pilot paired comparison, nonrandomized study was conducted comparing a silicone gel sheeting (Silastic [SGS]) with a hydrogel dressing (ClearSite). The effects of the dressings were compared side by side in the treatment of 15 hypertrophic scars at both the clinical and molecular levels through the use of reverse transcriptase/polymerase chain reaction to evaluate effects on the expression of interleukin 8 (IL-8), basic fibroblast growth factor (bFGF), granulocyte-macrophage colony-stimulating factor (GMCSF), epidermal growth factor (EGF), transforming growth factor beta (TGF-beta), and fibronectin. RESULTS: Comparable clinical improvement of the hypertrophic scars was obtained with both dressings. Treatment of hypertrophic scars resulted in increased mean levels of IL-8, bFGF, and GMCSF mRNA; while mean TGF beta and fibronectin mRNAs decreased after treatment with both dressings. Comparison between the two dressings revealed significant changes in IL-8 and fibronectin mRNA levels after treatment with ClearSite, while only fibronectin changes were significant after treatment with SGS with respect to normal skin. Only ClearSite induced significant changes in IL-8 and bFGF levels when untreated scars were compared with posttreatment lesions, suggesting that the hydrogel augments collagenolysis via promotion of inflammation. CONCLUSIONS: This study demonstrates that silicone is not a necessary component of occlusive dressings in the treatment of hypertrophic scars. The pathogenesis of hypertrophic scars is further elucidated by demonstrating that there is molecular evidence for extensive connective tissue remodeling occurring during occlusive dressing therapy.

Adult↗

PubMed2004

Highly purified 1000-cSt silicone oil for treatment of human immunodeficiency virus-associated facial lipoatrophy: an open pilot trial.

BACKGROUND: Among human immunodeficiency virus-infected individuals, facial lipoatrophy has become epidemic. Those affected are stigmatized, leading to psychological distress, social and career impediments, and impaired compliance to human immunodeficiency virus medications. Temporary treatment options are limited by excessive cost, necessity of frequent treatments, and lack of a natural look or feel beneath the skin. Affected patients require more persistent, affordable, safe, and effective treatment options. OBJECTIVE: The objective was to evaluate the safety and efficacy of highly purified 1000-cSt silicone oil injected by microdroplet serial puncture technique for the treatment of human immunodeficiency virus-associated lipoatrophy. METHODS: Data on 77 patients with a complete correction were analyzed to determine the number of treatments, amount of silicone, and time required to reach complete correction, relative to initial severity. RESULTS: The volume of silicone, number of treatments, and time required to reach a complete correction were directly related to initial severity of lipoatrophy (p < 0.0001). Supple, even facial contours were routinely restored, with all patients tolerating treatments well. No adverse events were noted. CONCLUSION: In this pilot trial, we have demonstrated that highly purified 1000-cSt silicone oil is a safe and effective treatment option for human immunodeficiency virus facial lipoatrophy. Longer-term safety and efficacy in human immunodeficiency virus patients remain to be proven.

Adult↗

PubMed1994

Immunology of silicone breast implants.

Understanding the immunology of silicone breast implants, at present, consists of reconciling an increasingly large body of data with an older, established, but otherwise unsubstantiated theory. Despite the variety of silicone breast implants, there are nevertheless certain phenomena that occur with all silicone gel-filled devices. Recent clinical findings suggest that in some patients, silicone will act as an adjuvant on native macromolecules and render them immunogenic. The purpose of this review is to highlight biophysical and clinical phenomena that warrant further investigation.

Adjuvants, Immunologic↗