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PubMed2004

Oil coating on hydrophilic surfaces from emulsions and under shear flow.

We study the formation of silicone oil coating on negatively charged hydrophilic surfaces via emulsion deposition. Cationic surfactants usually adsorb and form bilayers onto negative surfaces. As a result, direct emulsions stabilized with cationic surfactants are paradoxically poorly efficient at coating negative substrates. We show in this work an alternative and new method, still based on electrostatic attractions, to coat negative substrates. Our method consists of using emulsions stabilized with nonionic surfactants and of adding to the oil cationic additives that are non-water-soluble and of high molecular weight to minimize their solubilization in the micelles formed by the neutral surfactant. The positively charged droplets stick efficiently onto the substrates. They form monolayer and uniform coatings. We study the kinetics and the density of the resulting coating using a flow cell experiment. This technique allows us to finely analyze the influence of several physicochemical parameters.

Emulsions↗
PubMed1993

Effects of initial temperature and tempering medium on thermal tempering of dental porcelains.

The objective of this study was to test the hypothesis that quenching of porcelain in silicone oil rather than in compressed air will significantly increase the flexure strength by reducing the potential for crack formation during transient cooling. A secondary hypothesis to be tested is that the initial tempering temperature can be reduced significantly below the porcelain maturing temperature of 982 degrees C but well above Tg without a decrease in strength. Opaque-body porcelain disks, 16 mm in diameter and 2 mm in thickness, with a thermal contraction mismatch (delta alpha) of -1.5, 0, and +3.2 ppm/degrees C were tempered from initial temperatures of 650, 750, 850, and 982 degrees C in silicone oil with kinematic viscosities of 50, 1000, and 5000 centistokes. Porcelain disks were also subjected to three cooling procedures in air: slow cooling in a furnace (SC), free convective cooling in a laboratory bench (FC), and tempering (T) by blasting the surface of body porcelain with air. The crack size induced by a Vickers microhardness indenter was measured within one minute after crack development. For determination of the influence of initial cooling temperature on biaxial flexure strength, six body porcelain disks (delta alpha = 0) were tempered in air from initial temperatures of 650, 750, 850, and 982 degrees C. The mean crack size of specimens tempered in oil was significantly smaller (p < or = 0.001) than that of specimens that were slowly-cooled or fast-cooled in air for all thermal contraction mismatch cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Silicates↗
PubMed2004

The influence of hydroxyapatite modification on the cross-linking of polydimethylsiloxane/HAp composites.

Hydroxyapatite (HAp) was modified by the action of various hydrophobic agents based on silicon-containing compounds. The influence of the type of applied agent on the thermodynamic and kinetic parameters of the cross-linking of poly(dimethyl siloxane)/HAp composites was investigated. All the modified HAp particles became hydrophobic and these samples were used to synthesize the polysiloxane/hydroxyapatite composites (PDMS/HAp). The possible modes of interaction between the hydroxyapatite and hydrophobing agents were discussed. The most probable interaction between hydroxyapatite and the applied hydrophobing agents is hydrogen bonding. PDMS/HAp composites were formed directly in the cell of the DSC and cross-linking was investigated in situ. It was determined that the introduction of hydroxyapatite into polysiloxane matrices changed the enthalpy of cross-linking, as well as the activation energy of cross-linking and reaction order, while the introduction of modified HAp led to thermodynamic and kinetic parameters more similar to those of the cross-linking of unfilled elastomer.

Biocompatible Materials↗
PubMedDate not supplied

Effects of different disinfectants on physical properties of four temporary soft denture-liner materials.

OBJECTIVE: The purpose of this study was to evaluate the effects of some commonly used disinfectants on physical properties of four temporary soft denture-liner materials. METHOD AND MATERIALS: Soft-liner materials, including three plasticized acrylic resin-liners (Tempo, Immediate, Flexacryl Soft) and one silicone-based material (Ufi Gel P) were studied. Specimens prepared with the soft-liner materials were tested after the application of disinfectants (5% Deconex and 3.5% Savlex for 10 minutes; 2% sodium hypochlorite and 5.25% sodium hypochlorite for 5 minutes) and were compared with the control group (not disinfected; immersed in distilled water). Five specimens of each material were tested and data collected on days 4, 7, 11, and 15. The hardness values were determined using the Shore A hardness test. RESULTS: Water sorption test results showed that the disinfectants had statistically significant effects on water sorption values (except days 7 and 15 for Flexacryl Soft and days 4, 7, and 11 for Ufi Gel P). Water solubility and hardness test results also showed statistically significant effects on the materials by the disinfectants. CONCLUSION: Disinfectants significantly affected the physical properties of water sorption, water solubility, and hardness of the soft-liner materials.

Absorption↗
PubMed1996

Anatomical basis for a fasciocutaneous flap from the hypothenar eminence of the hand.

Thirty-two fresh cadaver hands were perfused with a silicone rubber compound (Microfil) and dissected to explore the vascular and neural anatomy of the hypothenar eminence, in order to assess the possibility for free or pedicled island flaps from this area. In five specimens Microfil was selectively injected into the ulnar palmar digital artery of the little finger to determine the skin territory nourished by this artery. The hypothenar eminence was divided into three territories according to the type of nutrient artery supplying each territory. Among the three territories, the distal half of the ulnar aspect of the hypothenar eminence (approximately 3 x 2 cm), located over the abductor and flexor digiti minimi muscles, had a constant vascular and neural supply from the ulnar palmar digital artery of the little finger and the dorsal or palmar cutaneous branch of the ulnar nerve. This fasciocutaneous area provides a new and feasible donor site for free or pedicled island skin flaps to repair palmar skin defects of the fingers.

Aged↗
PubMed1975

Microcirculation of the normal and inflamed canine pancreas.

Pancreas of normal dogs and the inflamed gland of experimental pancreatitis were studied by intra-arterial injection of Microfil, a silicone-rubber compound especially suited for study of the microcirculation. Duodenal vasculature and lobular vessels of the pancreas were studied as were those supplying the duct. Inter-lobular vessels were well visualized in the normal pancreas and intralobular vessels formed a fine reticular pattern throughout the cleared lobules. A complex network of vessels in the pancreatic duct was observed using this technique, apparently derived from the interlobular vessels. The blood supply of each layer of the duodenum was evaluated. Intraductal trypsin injection produced focal areas of pancreatitis associated with edema, poor vascular filling and spastic changes of the lobular vessels. Extravasation of Microfil, although not apparent on normal specimens, was prominent in inflamed specimens and suggested vascular weakness and disruption. Pancreatic lobules adjacent to inflammatory areas showed definite evidence of dilatation. The inflamed pancreatic ducts were markedly edematous, thickned, and showed incomplete vascular filling. When the duodenum adjacent to pancreatitis was injected with Microfil, edema and vasoconstriction were especially prominent in the duodenal muscular layer.

Animals↗
PubMedDate not supplied

Colorimetric determination of selenium in mineral premixes .

A method is described for determination of sodium selenite or sodium selenate in mineral-based premixes. It is based on the formation of intense-yellow piazselenol by Se(IV) and 3,3'-diaminobenzidine. Mineral premixes typically contain calcium carbonate as a base material and magnesium carbonate, silicon dioxide, and iron(III) oxide as minor components or additives. In this method, the premix is digested briefly in nitric acid, diluted with water, and filtered to remove any Iron(III) oxide. Ethylenediaminetetraacetic acid and HCl are added to the filtrate, which is heated to near boiling for 1 h to convert any selenate to selenite. After heating, the solution is buffered between pH 2 and 3 with NaOH and formic acid and treated with NH2OH and EDTA; any Se present forms a complex with 3,3'-diaminobenzidine at 60 degrees C. The solution is made basic with NH4OH, and the piazselenol is extracted into toluene. The absorbance of the complex in dried toluene is measured at 420 nm. The method was validated independently by 2 laboratories. Samples analyzed included calcium carbonate fortified with 100, 200, and 300 micrograms Se in the form of sodium selenite or sodium selenate, a calcium carbonate premix containing sodium selenite, a calcium carbonate premix containing sodium selenate, and a commercial premix; 5 replicates of each sample type were analyzed by each laboratory. Average recoveries ranged from 89 to 109% with coefficients of variation from 1.2 to 13.6%.

3,3'-Diaminobenzidine↗
PubMed2006

Adsorption of cationic lipid bilayer onto flat silicon wafers: effect of ion nature and concentration.

The effect of monovalent salt nature and concentration over a range of low ionic strengths (0-10 mM LiCl, NaCl, KCl, or CsCl) and at two different pH values (6.3 and 10.0) on adsorption of dioctadecyldimethylammonium bromide (DODAB) bilayer fragments (BF) onto flat SiO(2) surfaces was systematically evaluated by means of in situ ellipsometry. High-affinity adsorption isotherms fitted by the Langmuir model indicated that adsorption maxima were consistent with bilayer deposition only around 10 mM monovalent salt at both pH values. In pure water, the mean thickness of the DODAB adsorbed layer was close to zero with bilayer deposition taking place only around 10 mM ionic strength. In the presence of 10 mM CsCl or LiCl, the highest and the lowest affinity constants for DODAB adsorption onto SiO(2) were, respectively, obtained consistently with the expected facility of cation exchange at the surface required for DODAB adsorption. The cation more tightly bound to the solid surface should be Li(+), which would present the largest resistance to displacement by the DODAB cation, whereas the less tightly bound cation should be Cs(+) due to its largest ionic radius and lowest charge density. In other words, DODAB adsorption proceeds in accordance with charge density on the solid surface, which depends on the nature and concentration of bound counterions as well as DODAB cation ability to displace them. AFM images show a very smooth DODAB film adsorbed onto the surface in situ with a large frequency of BF auto-association from their edges. The present results for flat surfaces entirely agree with previous data from our group for DODAB adsorption onto silica particles.

Adsorption↗
PubMed1999

Quality assessment of atomic force microscopy probes by scanning electron microscopy: correlation of tip structure with rendered images.

While image quality from instruments such as electron microscopes, light microscopes, and confocal laser scanning microscopes is mostly influenced by the alignment of optical train components, the atomic force microscope differs in that image quality is highly dependent upon a consumable component, the scanning probe. Although many types of scanning probes are commercially available, specific configurations and styles are generally recommended for specific applications. For instance, in our area of interest, tapping mode imaging of biological constituents in fluid, double ended, oxide-sharpened pyramidal silicon nitride probes are most often employed. These cantilevers contain four differently sized probes; thick- and thin-legged 100 microm long and thick- and thin-legged 200 microm long, with only one probe used per cantilever. In a recent investigation [Taatjes et al. (1997) Cell Biol. Int. 21:715-726], we used the scanning electron microscope to modify the oxide-sharpened pyramidal probe by creating an electron beam deposited tip with a higher aspect ratio than unmodified tips. Placing the probes in the scanning electron microscope for modification prompted us to begin to examine the probes for defects both before and after use with the atomic force microscope. The most frequently encountered defect was a mis-centered probe, or a probe hanging off the end of the cantilever. If we had difficulty imaging with a probe, we would examine the probe in the scanning electron microscope to determine if any defects were present, or if the tip had become contaminated during scanning. Moreover, we observed that electron beam deposited tips were blunted by the act of scanning a hard specimen, such as colloidal gold with the atomic force microscope. We also present a mathematical geometric model for deducing the interaction between an electron beam deposited tip and either a spherical or elliptical specimen. Examination of probes in the scanning electron microscope may assist in interpreting images generated by the atomic force microscope.

DNA↗
PubMed1999

Imaging of collagen type III in fluid by atomic force microscopy.

Type III collagen is a component of the basement membrane of endothelial cells, and may play a role in the interaction between hemostatic system proteins and the basement membrane of blood vessels. To begin to investigate these structural interactions, we have imaged type III collagen in solution by atomic force microscopy. A 20 microg/ml solution of type III collagen in bicarbonate buffer (pH 9.5) from calf skin was deposited onto a freshly cleaved mica substrate. Atomic force microscopy images were acquired using a fluid cell and tapping mode with oxide-sharpened silicon nitride probes 2, 3, and 4 hours after deposition of the collagen onto the mica. Two-hour preparations displayed fibrillar networks with well-defined sites of nucleation and lateral growth. At 3 and 4 hour polymerizations, more mature fibrils of increasing lengths, diameters, and complexity were observed. Fibrils appeared to be aligning and twisting (helical formation) to form a mature fibril with a higher mass per unit area. Interestingly, the mature fibrils appeared larger centrally with tapered ends displaying declining slopes. These observations compare favorably with those previously published on collagen type I assembly [Gale et al. (1995) Biophys. J. 68:2124-2128]. High resolution atomic force microscopy images of type III collagen in solution should provide a template for observation of the interactions between basement membrane components and hemostatic system proteins present in cardiovascular disease.

Animals↗
PubMed1996

Complement activation by IgG immobilized on methylated silicon.

Activation of the complement system by immobilized IgG on methylated silicon was studied by ellipsometry/antibody-, ELISA-, and RIA techniques after exposure to human serum at 37 degrees C for up to 1 h. The IgG-covered surfaces rapidly activated the complement system and the combined results suggest an initial classical pathway activation. Complement factor 1q (C1q) and IgG were antibody-detectable on the surfaces for serum incubations up to 5 min but not thereafter. Anti-C3c and anti-properdin bound to the surfaces at all serum incubation times. Experiments with 125I-IgG preadsorbed to surfaces, or added to normal-, EGTA-, and EDTA-sera, showed that IgG was not displaced from the protein film by serum.

CD4 Antigens↗
PubMed1999

Calcium phosphate formation on porous sol-gel-derived SiO2 and CaO-P2O5-SiO2 substrates in vitro.

Sol-gel-derived SiO2 and CaO-P2O5-SiO2 have been shown to be bioactive and bone bonding. In this study bioactive sol-gel-derived SiO2 and CaO-P2O5-SiO2 systems were tested for in in vitro bioactivity. The calcined ceramic monoliths were immersed in a simulated body fluid and analyzed to follow the hydroxyapatite formation on the ceramic surface. Apatite-forming ability was investigated in terms of structural changes by changing the composition and the preparation method. The role of Ca and P dopants in the substrate structure is complicated, and careful characterization is needed. The composition and structure together determine the in vitro bioactivity. The pore structure was analyzed using N2-adsorption/desorption isotherms. The results indicate that a great mesopore volume and a wide mesopore size distribution favor hydroxycarbonate apatite nucleation and a great surface area is not needed. The performed preparation process for silica in a basic environment provides a convenient way to prepare a mesoporous material.

Adsorption↗
PubMed1999

Silicon nitride coating on titanium to enable titanium-ceramic bonding.

Failures that occur in titanium-ceramic restorations are of concern to clinicians. The formation of poorly adhering oxide on titanium at dental porcelain sintering temperatures causes adherence problems between titanium and porcelain, which is the main limiting factor in the fabrication of titanium-ceramic restorations. To overcome this problem a 1-microm thick Si3N4 coating was applied to a titanium surface using a plasma-immersion implantation and deposition method. Such a coating serves as an oxygen diffusion barrier on titanium during the porcelain firings. The protective coating was characterized in the as-deposited condition and after thermal cycling. Cross sections of Ti/Si3N4-porcelain interface regions were examined by various electron microscopy methods and by energy dispersive analysis of X-rays to study the Si3N4 film's effectiveness in preventing titanium oxidation and in forming a bond with porcelain. The experiments have shown that this Si3N4 coating enables significant improvement in Ti-ceramic bonding.

Dental Porcelain↗
PubMed2000

Proinflammatory cytokine expression of IL-1beta and TNF-alpha by human osteoblast-like MG-63 cells upon exposure to silicon nitride in vitro.

This study was designed to determine the effect of Si(3)N(4) disks and particulates on human osteoblast-like MG-63 cells in vitro. The MG-63 (10(5)/mL) cells were plated onto 24-well polystyrene plates fitted with either sintered reaction-bonded (SRBSN) or reaction-bonded (RBSN) 15-mm disks. Controls consisted of wells without Si(3)N(4) disks. Cells propagated at 37 degrees C, 5% CO(2) for 48 h on Si(3)N(4) disks and control polystyrene surfaces exhibited similar proliferative capacities (7000 and 4000 cpm/10(5) cells, respectively, p > 0.05). Cells incubated with 1, 10, or 100 microgram/ml of Si(3)N(4) particles (<1.00 to 5.00 micrometer) for 24 h did not exhibit a decrease in DNA synthetic activity: 12 +/- 1.3 x 10(4), 10.5 +/- 1.5 x 10(4), and 11.0 +/- 1.7 x 10(4) cpm, respectively, compared to 11.6 +/- 2.6 x 10(4) cpm/10(5) for the control cells, as indicated by (3)H-thymidine uptake. Cells propagated on RBSN displayed increased expression of cytokines IL-1beta and TNF-alpha compared to the control cells, as shown by reverse transcriptase-polymerase chain reaction (RT-PCR). In contrast, cells propagated on SRBSN surfaces expressed the same level of IL-1beta and TNF-alpha as that of control cells. Incubation of MG-63 cells with 1-10 microgram/mL of particles did not increase IL-1beta expression. However, at 100 microgram/mL, TNF-alpha expression was greater than that of the control cells. Silicon nitride, evaluated here as disks or as particulates (1-10 microgram/mL), is biocompatible and does not hinder the proliferation or induce proinflammatory cytokine expression of human osteoblast-like MG-63 cells in vitro.

Cell Culture Techniques↗
PubMed1993

Microvascular architecture of early gastric carcinoma. Microvascular-histopathologic correlates.

BACKGROUND: Gastric carcinoma is clinicopathologically divided into differentiated and undifferentiated types. The former is grossly protuberant and often causes hematogenous metastasis to the liver or lung, whereas the latter is mostly depressed or ulcerated from its early stage and rarely causes blood-borne metastasis. The purpose of this study is to clarify the microvascular architecture of early gastric carcinoma with reference to the histologic subtypes. METHODS: A silicone rubber compound (Microfil) injection method with a methyl salicylate clearing technique was used in 32 resected early gastric carcinomas. The microvascular architecture was observed both in the carcinoma and its surrounding noncancerous tissue in each specimen under a stereomicroscope and light microscope. RESULTS: Compared to the surrounding normal mucosa, the differentiated carcinomas (DC) mostly were hypervascular (24%) or normovascular (65%), whereas the undifferentiated carcinomas (UC) often were hypovascular (60%). Irregularity of tumor vessels (67%) and an arcade-like appearance (33%) was encountered frequently in UC, whereas hypervascularity of the surrounding noncancerous mucosa (29%) often was noticed in DC. Quantitative analysis, including vascular volume, mean vascular diameter, and cut section area, supported these differences between DC and UC. CONCLUSIONS: The results suggest that vascular structures of gastric carcinomas are characteristic with regard to their histologic subtypes; DC is normovascular or hypervascular, whereas UC is hypovascular.

Carcinoma↗
PubMed1980

Observations on the hypothalamo-hypophyseal portal vasculature in the developing human fetus.

Human fetuses, 11.5 to 16.8 weeks' gestational age, were perfused with silicone rubber compound to study the hypothalamo-hypophyseal portal system. Impregnated vessels were observed throughout the median eminence, infundibular stalk, pars tuberalis and both lobes of the pituitary gland in all specimens. The data suggest that an intact portal system for the transport of hypothalamic releasing factors to the pituitary gland is established as early as 11.5 weeks' gestation.

Female↗