Effects and efficacy of different sterilization and disinfection methods on electrospun drug delivery systems.

Microbiological quality of a pharmaceutical product is an essential requirement ensuring patient safety, thus effective sterilization/disinfection methods need to be found. The aim of this study was to evaluate the efficacy of different sterilization/disinfection methods on drug-loaded electrospun matrices and the impact of these treatments on the functionality related characteristics of these matrices. The sterilization efficacy of gamma-irradiation, ultraviolet-irradiation, in situ generated chlorine gas and low-pressure argon plasma treatment were evaluated on two different chloramphenicol-loaded electrospun matrices using pristine polycaprolactone (PCL) as a carrier polymer or PCL in combination with polyethylene oxide. Drug stability, solid state properties, morphology, mechanical properties, swelling, biodegradation and drug release kinetics were studied before and after the treatments. It was shown that all tested methods help to reduce bioburden and only plasma treated matrices were not sterile. At the same time drug degradation after the treatment can be considerable and depends not only on the susceptibility of the drug to degradation, but also on matrix properties (e.g. the nature of carrier polymers). Even though no morphological changes were observed, gamma sterilization increased the hardness and elasticity of PCL matrices as a result of increased crystallinity of the polymer. Plasma treatment was able to significantly enhance water absorption to otherwise hydrophobic PCL/CAM matrix and had tremendous impact on its drug release kinetics as the drug was instantly released from otherwise prolonged release formulation.

Metal Oxides as Catalysts and Adsorbents in Ozone Oxidation of NO x.

NO x represents an important group of pollutants that are formed in fuel combustion. As these pollutants cause significant environmental problems, removal of NO x from exhaust gases is necessary. The present study investigated the influence of metal oxide powders on the removal of NO x by oxidation with ozone. The aim of the study was to compare the catalytic effect of TiO2, Al2O3, and Fe2O3 and to investigate the dependence of the effective rate constant on temperature. NO (400 ppm) and a variable concentration of ozone in a mixture of N2 and O2 was directed through the catalyst chamber and heated to 60-140 °C. The addition of metal oxides resulted in a significant increase in the efficiency of the oxidation of NO to N2O5. Fe2O3 had the largest effect with a maximum of an approximately 3-fold increase in the effective rate constant at 100 °C. At the same time Fe2O3 had the lowest NO x adsorption capacity. In the case of all metal oxides, oxidation of NO to N2O5 caused an abrupt increase in adsorption of NO x.

Adsorption of Nitrogen Oxides on TiO2 Surface as a Function of NO2 and N2O5 Fraction in the Gas Phase.

The present study was devoted to the investigation of adsorption of nitrogen oxides on TiO2, with the focus on the effect of NO x concentration, composition, and flow rate. The inlet NO with a concentration of 200-800 ppm in pure N2 was mixed with ozone, produced from pure oxygen, and directed to a reactor with catalytic TiO2 powder. The oxidation of NO by ozone allowed to prepare mixtures with variable concentrations of NO and NO2 or NO2 and N2O5 which were adsorbed on the catalyst surface during the oxidation phase and were desorbed when only NO was flowing through the reactor. Diffuse reflectance infrared Fourier transform spectroscopy studies showed NO3- as the main adsorbed nitrogen oxide specimen on the surface. The amount of adsorbed nitrogen oxide species increased with the increasing fraction of NO2 in the gas phase and was inversely proportional with the gas-phase NO concentration. An important finding was the abrupt increase in the nitrogen oxide adsorption capacity of TiO2 when the inlet concentration of ozone became sufficiently large to oxidize NO x to N2O5. On the basis of the results, a model of the surface processes is proposed, involving the production of NO3 and N2O5 on the surface of TiO2.

Phase Formation Behavior in Ultrathin Iron Oxide.

Nanostructured iron oxides, and especially hematite, are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low-dimensional films is atomic layer deposition (ALD). Although a potent technique, ALD of ultrathin films is critically sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work, deposition at the border of the ALD window forming a hybrid ALD/pulsed CVD (pCVD) deposition is utilized to obtain a deposition less sensitive to the substrate. A thorough analysis of iron oxide phases formation on two different substrates, Si(100) and SiO2, was performed. Films between 3 and 50 nm were deposited and analyzed with diffraction techniques, high-resolution Raman spectroscopy, and optical spectroscopy. Below 10 nm nominal film thickness, island formation and phase dependent particle crystallization impose constraints for deposition of phase pure iron oxides on non-lattice-matching substrates. Films between 10 and 20 nm thickness on SiO2 could effectively be recrystallized into hematite whereas for the corresponding films on Si(100), no recrystallization occurred. For films thicker than 20 nm, phase pure hematite can be formed directly with ALD/pCVD with very low influence of the substrate on either Si or SiO2. For more lattice matched substrates such as SnO2:F, Raman spectroscopy indicated formation of the hematite phase already for films with 3 nm nominal thickness and clearly for 6 nm films. Analysis of the optical properties corroborated the analysis and showed a quantum confined blue-shift of the absorption edge for the thinnest films.

Dye-sensitized solar cells employing a SnO2-TiO2 core-shell structure made by atomic layer deposition.

This paper describes the synthesis and characterization of core-shell structures, based on SnO2 and TiO2, for use in dye-sensitized solar cells (DSC). Atomic layer deposition is employed to control and vary the thickness of the TiO2 shell. Increasing the TiO2 shell thickness to 2 nm improved the device performance of liquid electrolyte-based DSC from 0.7% to 3.5%. The increase in efficiency originates from a higher open-circuit potential and a higher short-circuit current, as well as from an improvement in the electron lifetime. SnO2-TiO2 core-shell DSC devices retain their photovoltage in darkness for longer than 500 seconds, demonstrating that the electrons are contained in the core material. Finally core-shell structures were used for solid-state DSC applications using the hole transporting material 2,2',7,7',-tetrakis(N, N-di-p-methoxyphenyl-amine)-9,9',-spirofluorene. Similar improvements in device performance were obtained for solid-state DSC devices.