Silica Oxide Particles Research Articles

Evaluation of Nevirapine Release Kinetics from Polycaprolactone Hybrids

The Nevirapine (NVP)/Polycaprolactone (PCL)/Nanoparticles hybrids systems have been developed as a potential platform for drug delivery, by solvent cast, as thin films. NVP, an antiretroviral drug, was included within PCL matrix containing three types of nanoparticles: an organoclay layered silicate Viscogel S7®(3% w/w), hydrophilic silica oxide particles Aerosil® A20 (0.25% w/w) and titanium dioxide particles (0.25% w/w). These systems were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), low-field nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy (UV), in-vitro dissolution testing and drug release mechanism kinetics. The PCL crystallization was affected by NVP incorporation, modifying its semi-crystalline structure to a less ordered structure. When nanoparticles and NVP were added, the T1H values increased, for PCL, PCL/S7, PCL/ SiO2 and PCL/TiO2 hybrids, suggesting that its addition produced a new material, with less molecular mobility, due to the new intermolecular interactions formation. It can consider a structure formation among the PCL chains, nanoparticles and NVP, with strong forces in the PCL/SiO2/NVP system. The amount of NVP included was around 1.5 ± 0.03 mg/cm2. In the in-vitro dissolution test, the PCL/SiO2/NVP system released the smallest amount of drug and this result could be attributed to the strong intermolecular interaction between the drug and the PCL/SiO2 system. Higuchi’s model was the mathematical model chosen to treat the release data, since this model presented the highest coefficient correlation (r) value. The drug release probably occur by diffusion through the matrix pores, thus, these materials are suitable for sustained release of NVP.

The effect of metal surface treatment on bond strength interface between metal/cement

Objective: This study evaluated the hypothesis that different treatments of surface upon three metal alloys for metal ceramic dental prostheses (Gold; Nickel-Chromium; Titanium) do not Influence the values of bond strength with resin cement. Material and Methods: Twenty blocks, 5x5x5 mm, of each alloy were divided into two subgroups (n = 10) according to surface treatments: 1 (Primer): sandblasting with aluminum oxide particles 110 µm (Al2O3) + Alloy Primer (Kuraray); 2 (Cojet): sandblasting with silica oxide particles with Cojet-Sand + Silane ESPE-Sil. The conditioned blocks of each group were cemented, with Panavia F, to resin blocks under constant load of 750 g/10 min. The sets were cut to obtain 4 samples with dimensions of 10x1x1 mm per block (n = 10) and the adhesive surface with approximately 1 mm2. The microtensile test was done in the universal testing machine at 1 mm/min crosshead speed. The values of bond strength and standard deviation (MPa) were: Au P: 7.33 ± 1.93d; Au C: 13.35 ± 2.18c; NiCr P: 23.56 ± 6.5b; NiCr C: 42.6 ± 5.84a; Ti P: 26.17 ± 1.94b; Ti C: 44.30 ± 2.3a. Data were analyzed by variance test (ANOVA) and Tukey’s test, p < 0.05. Results: The results indicated that the conditioning with treatment 2 increased the bond strength between the resin cement and alloys. The lowest bond strengths values were obtained with gold alloy, regardless the surface treatment. Conclusion: The results denied the hypothesis that the metallic alloys surface treatments do not alter the bond strengths values.

Shear bond strength of a new self-adhering flowable composite resin for lithium disilicate-reinforced CAD/CAM ceramic material.

PURPOSEThe purpose of this study was to evaluate and compare the effects of different surface pretreatment techniques on the surface roughness and shear bond strength of a new self-adhering flowable composite resin for use with lithium disilicate-reinforced CAD/CAM ceramic material.MATERIALS AND METHODSA total of one hundred thirty lithium disilicate CAD/CAM ceramic plates with dimensions of 6 mm × 4 mm and 3 mm thick were prepared. Specimens were then assigned into five groups (n=26) as follows: untreated control, coating with 30 µm silica oxide particles (Cojet™ Sand), 9.6% hydrofluoric acid etching, Er:YAG laser irradiation, and grinding with a high-speed fine diamond bur. A self-adhering flowable composite resin (Vertise Flow) was applied onto the pre-treated ceramic plates using the Ultradent shear bond Teflon mold system. Surface roughness was measured by atomic force microscopy. Shear bond strength test were performed using a universal testing machine at a crosshead speed of 1 mm/min. Surface roughness data were analyzed by one-way ANOVA and the Tukey HSD tests. Shear bond strength test values were analyzed by Kruskal-Wallis and Mann-Whitney U tests at α=.05.RESULTSHydrofluoric acid etching and grinding with high-speed fine diamond bur produced significantly higher surface roughness than the other pretreatment groups (P<.05). Hydrofluoric acid etching and silica coating yielded the highest shear bond strength values (P<.001).CONCLUSIONSelf-adhering flowable composite resin used as repair composite resin exhibited very low bond strength irrespective of the surface pretreatments used.

Usage of Layer-by-Layer Method for Obtaining Polyelectrolyte Multilayer Films Containing Transition Metal Cations

&lt;p&gt;The alternating layer-by-layer deposition of oppositely charged polyelectrolytes at solid substrates is an attractive technique for preparation of nanostructured surface coatings of controlled thickness. This paper reports the results of covalently binding of cobalt (II) and copper (II) ions within polyelectrolyte multilayers (PEMs). We have used polycation as polyethyleneimine (BPEI) and polyanion as poly(acrylic acid) (PAA) and the electrostatic layer-by-layer assembly technique to make uniform thin film coating on solid template with controllable thickness. Thermodynamic characteristics as stability constant, free Gibbs energy, enthalpy and entropy of complex forming processes of these polyelectrolytes with Co(II) and Cu(II) cations in solution were calculated by modified method of Bjerrum. The correlation between log β values and some of the fundamental properties of the metal ions are discussed. It was found that the ratio of Me:L in water solvent is 1:4 in the investigating systems Cu&lt;sup&gt;2+&lt;/sup&gt;:BPEI and Co&lt;sup&gt;2+&lt;/sup&gt;:BPEI and in the systems Cо&lt;sup&gt;2+&lt;/sup&gt;:PAA and Cо&lt;sup&gt;2+&lt;/sup&gt;:PAA - 1:2. PEMs were deposited onto silicon wafers, glass slides, or coated on silica oxide particles. Dipping solutions of different pH were used in order to find the optimum conditions for absorbing maximum amount of metal cations. These PEMs films are found to offer high capacity and selectivity for copper over cobalt in both acidic and alkaline media. Preliminary investigation have shown that metal containing PEMs has catalytic activity for oxidation of toluene with molecular in mild condition. The alternating layer-by-layer deposition of oppositely charged polyelectrolytes at solid substrates is an attractive technique for preparation of nanostructured surface coatings of controlled thickness. This paper reports the results of covalently binding of cobalt (II) and copper (II) ions within polyelectrolyte multilayers (PEMs). We have used polycation as polyethyleneimine (BPEI) and polyanion as poly(acrylic acid) (PAA) and the electrostatic layer-by-layer assembly technique to make uniform thin film coating on solid template with controllable thickness. Thermodynamic characteristics as stability constant, free Gibbs energy, enthalpy and entropy of complex forming processes of these polyelectrolytes with Co(II) and Cu(II) cations in solution were calculated by modified method of Bjerrum. The correlation between log β values and some of the fundamental properties of the metal ions are discussed. It was found that the ratio of Me:L in water solvent is 1:4 in the investigating systems Cu&lt;sup&gt;2+&lt;/sup&gt;:BPEI and Co&lt;sup&gt;2+&lt;/sup&gt;:BPEI and in the systems Cо&lt;sup&gt;2+&lt;/sup&gt;:PAA and Cо&lt;sup&gt;2+&lt;/sup&gt; :PAA - 1:2. PEMs were deposited onto silicon wafers, glass slides, or coated on silica oxide particles. Dipping solutions of different pH were used in order to find the optimum conditions for absorbing maximum amount of metal cations. These PEMs films are found to offer high capacity and selectivity for copper over cobalt in both acidic and alkaline media. Preliminary investigation have shown that metal containing PEMs has catalytic activity for oxidation of toluene with molecular in mild condition.&lt;/p&gt;

Hybrids perfluorosulfonic acid ionomer and silicon oxide membrane for application in ion-exchange polymer-metal composite actuators

This paper reports a new technique to fabricate an ion-exchange polymer-metal composite (IPMC) actuator. This technique is based on a hybrid organic-inorganic composite membrane. In the fabrication course, silica oxide particles, prepared from hydrolysis of tetraethyl orthosilicate in situ with sol-gel reaction, co-crystallize with perfluorosulfonate acid (PFSA) ionomer. Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) analyses demonstrate that a highly water-saving hybrid membrane is formed. Measurements of mechanical properties reveal that elastic modulus and hardness of the hybrid membrane are about 2 times compared to a commercial PFSA membrane. Scanning electron microscopy (SEM) results show that the hybrid membrane has a high porosity. Inside the membrane pores, there exists a great quantity of micro scale channels in the range of 100–300 nm. After fabrication of IPMC actuator, an electric current sensor, a force sensor, and a high speed camera are assembled and used to evaluate IPMC performance. It is shown that, compared to an IPMC actuator made from a commercial membrane, the electromechanical performance of the new actuator increases 6–8 times; when it is actuated in air, its stable non-water working time is prolonged for 6–7 times.

Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic

The purpose of this study was to evaluate the microtensile bond strength of a repair composite resin to a leucite-reinforced feldspathic ceramic (Omega 900, VITA) submitted to two surface conditionings methods: 1) etching with hydrofluoric acid + silane application or 2) tribochemical silica coating. The null hypothesis is that both surface treatments can generate similar bond strengths. Ten ceramic blocks (6x6x6 mm) were fabricated and randomly assigned to 2 groups (n=5), according to the conditioning method: G1- 10% hydrofluoric acid application for 2 min plus rinsing and drying, followed by silane application for 30 s; G2- airborne particle abrasion with 30 microm silica oxide particles (CoJet-Sand) for 20 s using a chairside air-abrasion device (CoJet System), followed by silane application for 5 min. Single Bond adhesive system was applied to the surfaces and light cured (40 s). Z-250 composite resin was placed incrementally on the treated ceramic surface to build a 6x6x6 mm block. Bar specimens with an adhesive area of approximately 1 +/- 0.1 mm(2) were obtained from the composite-ceramic blocks (6 per block and 30 per group) for microtensile testing. No statistically significant difference was observed between G1 (10.19 +/- 3.1 MPa) and G2 (10.17 +/- 3.1 MPa) (p=0.982) (Student's t test; á = 0.05). The null hypothesis was, therefore, accepted. In conclusion, both surface conditioning methods provided similar microtensile bond strengths between the repair composite resin and the ceramic. Further studies using long-term aging procedures should be conducted.

Preparation of Spherical Hydrous Silica Oxide Particles under Acidic Condition via Sol-Gel Processing

Preparation of spherical hydrous silica oxide particles via sol-gel processing was rarely reported. In this study, spherical silica particles were obtained in TEOS/AcOEt/AcOH 50% aq. system. The combination of AcOEt and AcOH 50% aq. widened the spherical particle-forming region. Their size ranged from some ten micrometers to some hundreds micrometers. Hydrophilic molecules or powders like Rhodamine 6G and phosphorescent powders were encapsulated in the spherical particles.

Catalytic Dehydrogenation of Cyclohexane Using Coated Silica Oxide Ceramic Membranes

Experiments were conducted to characterize US Filter ceramic membranes used in the catalytic dehydrogenation of cyclohexane to benzene. The reaction yield was studied as a function of membrane pore size for 50, 100, 200, and 2000 A membranes. The effect on reaction yield, membrane permeability, and membrane selectivity of altering pore size by addition of successive thin film layers (silica oxide particles in an iron(III) supported solution) to the membrane surfaces was the primary focus of the study. The membranes were also characterized with a nonreactive He/N2 separation to determine the effect of successive thin film layers on the extent of Knudsen diffusion as the transport mechanism. This characterization demonstrated that Knudsen behavior could be obtained in a large pore diameter membrane by adding thin film layers to the surface. Reaction experiments showed a 300% increase in yield from that which was obtained in an impermeable reactor under similar conditions. Most significantly, the coated membranes operating in the Knudsen regime rendered a higher reaction yield than the uncoated 50 A membrane, whose transport mechanism was also Knudsen dominated. This phenomena can be explained by favorable surface effects between the thin film material and the reaction species. Thus, it was concluded, that a thin film (added to the surface membrane), which operates in the Knudsen regime and creates favorable surface effects to enhance membrane selectivity, can shift reaction equilibrium to a higher product yield than a membrane which only exhibits Knudsen diffusion.