264,693 research outputs found
Development and in vitro characterization of chitosan based microspheres for nasal delivery of promethazineDrug Development and Industrial Pharmacy,
No full textConventional and composed promethazine-loaded microspheres
were prepared by spray drying of chitosan solution systems and double water-inoil-
in-water (W/O/W) emulsion systems, respectively. Double emulsions were
prepared in two different feed concentrations, with chitosan dissolved in both
water phases, and ethylcellulose dissolved in oil phase. Swelling and bioadhesive
properties of the microspheres depended on the chitosan content, type
and the feed concentration of spray-dried system. Results obtained suggested
that better ethylcellulose microcapsules with promethazine in the chitosan
matrix were formed when less concentrated emulsion systems were spray-dried.
Thus, in case of such a system, with ethylcellulose/chitosan weight ratio of
1:2, prolonged promethazine release was obtaine
Preparation and in vitro/in vivo characterisation of a melt pelletised paracetamol/stearic acid sustained release delivery system
No full textThe potential of a sustained release formulation for paracetamol produced by melt pelletisation was investigated.
After the production of the pellets, based on the combination of stearic acid as a melting binder and anhydrous lactose as a
filler, the 3000–2000 μm size fraction was selected in the light of the promising in vitro dissolution results for further characterisations,
including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area and
true density determination. Hence the release mechanism was analysed with the help of an appropriate mathematical model.
The mathematical model was built on the hypotheses that drug diffusion and solid drug dissolution in the release environment
are the key phenomena affecting drug release kinetics. Bioavailability of the developed formulation was evaluated in an in vivo
study in eight subject
Spray-dried carbamazepine-loaded chitosan and HPMC microspheres: preparation and characterisation.
No full textPreparation end in vitro/in vivo characterisation of melt pelletised paracetamol/stearic acid sustained release delivery system
No full textThe potential of a sustained release formulation for paracetamol produced by melt pelletisation was investigated. After the production of the pellets, based on the combination of stearic acid as a melting binder and anhydrous lactose as a filler, the 3000-2000 μm size fraction was selected in the light of the promising in vitro dissolution results for further characterisations, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area and true density determination. Hence the release mechanism was analysed with the help of an appropriate mathematical model. The mathematical model was built on the hypotheses that drug diffusion and solid drug dissolution in the release environment are the key phenomena affecting drug release kinetics. Bioavailability of the developed formulation was evaluated in an in vivo study in eight subjects
Preparation in high-shear mixer of sustained-release pellets by melt pelletisation
No full textThe preparation of sustained-release pellets by melt pelletisation was investigated in a 10-l high shear mixer and
ternary mixtures containing stearic acid as a melting binder, anhydrous lactose as a filler and theophylline as a model
drug. A translated Doehlert matrix was applied for the optimisation of process variables and quality control of pellets
characteristics. After determination of size distribution, the pellets were characterised with scanning electron
microscopy, X-ray photoelectron spectroscopy and porosimetric analysis. Finally, the in vitro release from every
single size fraction was evaluated and the release mechanism was analysed. Since the drug release rate decreased when
enhancing the pellet size fraction, the 2000-mm fraction, exhibiting a substantially zero-order release, was selected for
further in vivo biovailability studies. These data demonstrated that pellets based on the combination of stearic acid
and lactose can be used to formulate sustained release pellets for theophylline. © 2000 Elsevier Science B.V. All rights
reserved
Use of low-field NMR and rheology to evaluate the microstructure and stability of a poly(D,L-lactide-co-glycolide)-based W/O emulsion to be processed by spray drying
No full textDrug-loaded emulsions for spray drying should be optimised for their rheological behaviour and stability under operating conditions, as this is essential for achieving the desired physicochemical properties of the final dry product. Our aim was therefore to investigate the structure and stability of a water-in-oil (W/O) emulsion containing vancomycin hydrochloride as the active ingredient in the aqueous phase, poly(D,L-lactide-co-glycolide) as the structural polymer in the dichloromethane-based organic phase, and various stabilisers using low-field nuclear magnetic resonance (LF NMR) and rheological characterisation. Four emulsions were tested, namely-one without stabiliser, one with Poloxamer® 407, one with chitosan and SpanTM 80 and one with chitosan only. The theoretical interpretation of the rheological data allowed the determination of the velocity and the shear rate/stress profiles inside the feed path of the W/O emulsion, aspects that are critical for the industrial scale-up of the emulsion drying process. In addition, LF NMR demonstrated that shaking was sufficient to restore the original emulsion structure and that the droplet size of all emulsions was in the range of 1–10 μm, although the emulsion with chitosan had the narrowest droplet size distribution and the higher zero shear viscosity, which accounts for the increased long-term stability due to impeded droplets movement
Six-flux absorption-scattering models for photocatalysis under wide-spectrum irradiation sources in annular and flat reactors using catalysts with different optical properties
No full textThe photocatalytic oxidation of 2-hydroxybenzoic acid (2-HBA) in an annular tubular reactor (R1) and a flat rectangular open channel reactor (R2), which were irradiated with light sources emitting in the UVB, UVA and visible range of the solar radiation spectrum, and using two photocatalysts, titanium dioxide (TiO2 P25) and Ag-modified TiO2 P25 (Ag@TiO2) was modeled. The local volumetric rate of photon absorption (LVRPA) in the reactors was evaluated by the six-flux absorption scattering model (SFM). The Langmuir-Hinshelwood kinetic model of the degradation of a model contaminant on irradiated aqueous suspensions of TiO2 P25 and Ag@TiO2 was combined with the SFM radiation model and light emission models to determine local reaction rates, and further integrated with the reactors hydrodynamics and material balances to model the degradation of 2-HBA in the photoreactors. The linear source spherical emission (LSSE) and extensive source superficial diffuse emission (ESSDE) models were compared in terms of incident and transmitted photon fluxes through the reactor. It was shown that both LSSE and ESSDE models could be successfully applied for the modeling of annular and flat reactors, considering the emission from tubular fluorescent light sources. Since current research calls for materials with wide absorption in the solar radiation spectrum, spanning from the UV to the visible, therefore, the SFM model was adapted to consider such wide distribution. The optical properties of the photocatalysts were averaged over narrow wavelength ranges of the solar spectrum, wherein the contributions by the UVA, UVB and visible light irradiation to the LVRPA and contaminant degradation rate were separated. The effects of catalyst concentration, liquid velocity profile and the photon flux from different light sources on the 2-HBA degradation rate were explored. The “intrinsic” reaction kinetic constants of 2-HBA photocatalytic oxidation independent of reactor type, catalyst concentration, irradiance levels and hydrodynamic conditions were determined by fitting the experimental data to the model results. It was shown that the model parameters were independent of the type of catalyst used, although the catalyst exhibited significantly different optical properties
Modeling the photocatalytic oxidation of carboxylic acids on aqueous TiO2 suspensions and on immobilized TiO2-chitosan thin films in different reactor geometries irradiated by UVA or UVC light sources
No full textPhotocatalytic reactor models incorporating radiation transport parameters and intrinsic kinetic parameters of photocatalytic decomposition of single-compound and mixtures of oxalic (OA) and formic acid (FA), in both slurry suspensions and immobilized photocatalytic thin films, were validated in two well-mixed annular photoreactors geometries irradiated with either UVA or UVC radiation. The six-flux absorption scattering model (SFM) predicted the radiation field in a titanium dioxide (TiO2 P25) catalyst suspension, the local volumetric rate of photon absorption (LVRPA) at each point of the reactor and, after volumetric integration, the lumped VRPA. The model combining the lumped VRPA, the kinetics models describing the adsorption and photocatalytic decomposition of OA and FA and the material balance of the reacting species was fitted to the experimental results of photocatalytic decomposition of OA and FO in a slurry TiO2 suspension, to determine the OA and FA intrinsic reaction kinetics parameters. Such intrinsic parameters were then used with the average surface rate of photon absorption (SRPA) to model and predict the photocatalytic oxidation of OA and FA on non-porous TiO2–chitosan films immobilized on glass plates immersed in the photoreactor. The models for both slurry suspensions and immobilized photocatalysts predicted the degradation and mineralization of OA and FA and of a mixture of them under diverse experimental conditions. This study demonstrates a systematic methodology for determining intrinsic reaction kinetics rate parameters of water contaminants that can also be used to represent the photocatalytic oxidation of such contaminants in irradiated slurries and in immobilized photocatalytic thin films and in any photoreactor geometry
Ivan Filipovic : Founding Father of Croatian Teachers' Societies
No full textTema ovog diplomskog rada je Ivan Filipovic, ucitelj, pedagog i književnik. Ivan
Filipovic bio je jedna od najistaknutijih osoba koja je utjecala na razvoj školstva u Hrvatskoj.
Živio je i radio u 19. stoljecu kada je Hrvatska bila u sastavu Austro - Ugarske Monarhije. U
vrijeme kada je položaj ucitelja bio veoma težak, zbog provoenja germanizacije u školama,
Filipovic je krenuo u organizaciju hrvatskih ucitelja i reorganizaciju puckog školstva. Cilj mu
je bio moralno podici ucitelje i potaknuti ih da krenu u borbu protiv nacionalnog ugnjetavanja
i crkvenog nadzora nad školama. Želio je da ucitelji poucavaju u samostalnim i slobodnim
školama. Njegovom zaslugom utemeljena su mnoga uciteljska društva poput Uciteljske
zadruge, najstarijeg uciteljskog društva, Saveza hrvatskih ucitelja i Hrvatsko pedagoško -
književnog zbora. Filipovic je organizirao i prve opce hrvatske uciteljske skupštine na kojima
se raspravljalo o problemima hrvatskih ucitelja. Sudjelovao je u dononošenju prvog hrvatskog
školskog zakona 1874. godine kojim Hrvatska prvi puta samostalno i autonomno ureuje
svoje školstvo.
Iak
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