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Gel Layer (gel + layer)
Selected AbstractsIntegrated Microanalytical System Coupling Permeation Liquid Membrane and Voltammetry for Trace Metal Speciation.ELECTROANALYSIS, Issue 10 2004Optimization, Technical Description Abstract A new minicell coupling the liquid-liquid extraction technique called permeation liquid membrane (PLM) with an integrated Ir-based Hg-plated microelectrode array for voltammetric detection has been developed for the speciation of heavy metals in natural waters. Lead and cadmium have been used as model compounds. The PLM consists of a carrier (0.1,M 22DD+0.1,M lauric acid) dissolved in 1,:,1 mixture of toluene/phenylhexane held in the small pores (30,nm) of a hydrophobic polypropylene membrane (Celgard 2500). One side of this membrane is in contact with a flowing source solution, containing the metal ions of interest. An acceptor or strip solution (pyrophosphate) is placed on the other side of the PLM with the microelectrode array placed at 480,,m of the PLM. The analyte is transported by the carrier from the source solution to the strip solution. The originality of the new minicell is that accumulation in the strip solution is voltammetrically followed by the integrated microelectrode array in real time, and at low concentration level, using square-wave anodic stripping voltammetry (SWASV). In order to protect the Hg microelectrodes from the adsorption of the hydrophobic carrier, the microelectrodes are embedded in a thin gel layer (280,,m) of 1.5% LGL agarose gel containing 10% of hydrophobic silica particles C18. The choice of optimum conditions is discussed in details in this article. Due to the very small effective strip volume of the new cell (less than 1,,L), high enrichment factor can be obtained (e.g., 330 for Pb) after 2,hours of accumulation. No deaeration of the solutions is required for SWASV measurements. Detection limits under these conditions are 2,pM and 75,pM for Pb and Cd, respectively, using a voltammetric deposition time of 5,min. In addition, no fouling effects were observed with natural water samples. [source] An investigation into the swelling properties, dimensional changes, and gel layer evolution in chitosan tablets undergoing hydrationADVANCES IN POLYMER TECHNOLOGY, Issue 1 2009Manuel Efentakis Abstract The purpose of this research is to determine several characteristics of chitosan lactate in tablet form such as dimensional changes, gel evolution, swelling (liquid uptake), and erosion using an image analysis method. The examination of these characteristics will be helpful in the design of oral drug delivery systems with this polymer. It has been demonstrated that image analysis is a valuable technique, allowing the study of quantitative measurements of dimensional and core changes and gel evolution. The dimensional expansion changes of the chitosan lactate tablets were greater in water, and the crushing strength and the stirring effect affected these attributes to a limited extent. The fastest and greatest liquid uptake was observed in water, whereas the greatest erosion was observed in HCl. The thickness of the gel layer increased considerably with time up to the eighth hour, indicating the formation and development of a thick and durable gel, particularly in water. This is an essential characteristic for potential sustained drug release delivery. Consequently, this polymer appears to be a versatile material and a promising vehicle for the preparation of various oral sustained release medications and relevant devices. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:32,39, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20147 [source] Swelling and polymer erosion for poly(ethylene oxide) tablets of different molecular weights polydispersitiesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2010Anna Körner Abstract The aim of the study was to determine and compare the degree of swelling and the swelling kinetics of poly(ethylene oxide) (PEO) hydrophilic matrix tablets without any additives for matrixes with different molecular weight polydispersities. A wide range of "mixed" polydisperse PEO tablets were obtained by mixing two PEO batches with average molecular weights of 105 and 2,×,106, respectively. These were compared with "single-batch" tablets with narrower mono-modal molecular weight distributions. A texture analyzer (TA) was used to determine, during the entire dissolution process, the thickness of the "gel" layer, the height of the dry tablet core and the total height of the tablet. The release of polymer from the tablet was also measured using a chromatographic method. Both the swelling histories and the polymer release rates varied strongly with molecular weight and agitation rate, whereas the rate of dissolution of the solid core varied much less with molecular weight. For single-batch and mixed tablets, tuned to give the same release rate, the swelling process was found to be very similar, regardless of the molecular polydispersity (between 1.2 and 8.8). These results support a previously proposed dissolution model with the key assumption of a constant critical viscosity, independent of time or polymer molecular weight, at the surface of the gel layer of a dissolving tablet. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1225,1238, 2010 [source] Controlled and complete release of a model poorly water-soluble drug, prednisolone, from hydroxypropyl methylcellulose matrix tablets using (SBE)7m -,-cyclodextrin as a solubilizing agentJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2001Venkatramana M. Rao Abstract Sustained-release formulations such as hydroxypropyl methylcellulose (HPMC)-based hydrophilic matrix tablets of poorly water-soluble drugs often result in incomplete release because of the poor solubility and dissolution rate of the drug in the hydrophilic matrix. Sulfobutylether-,-cyclodextrins ((SBE)7M -,-CDs) have been known to improve the solubility of such drugs by forming inclusion complexes. The present paper deals with the modification of drug release from an HPMC-based matrix tablet of a sparingly water-soluble drug, prednisolone (PDL), using (SBE)7M -,-CD as a solubilizing agent. Tablets were prepared by direct compression of a physically mixed PDL, (SBE)7M -,-CD, and polymer. On exposure to water, an in situ PDL:(SBE)7M -,-CD complex was formed in the gel layer, and enhanced drug release relative to a control formulation was observed (lactose used as the excipient instead of (SBE)7M -,-CD ). Other possible changes due to the incorporation of (SBE)7M -,-CD in the formulation were also probed. Incorporation of (SBE)7M -,-CD lead to a higher water uptake relative to the control (lactose) formulation. For a fixed total tablet weight, polymer type, and loading, the drug release rate appeared to depend on the molar ratio of (SBE)7M -,-CD to PDL and not the absolute amount of (SBE)7M -,-CD present in the matrix tablet. This work shows that incorporation of (SBE)7M -,-CD into the matrix tablets could be considered in designing a sustained-release tablet of poorly water-soluble drugs. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:807,816, 2001 [source] Electrically adjustable thermotropic windows based on polymer gelsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2003Tamįs Gyenes Abstract Several attempts have been made recently in order to develop "Smart" windows, which can moderate light and heat intensities. Based upon the phase transitions of polymer gels, a novel electrically adjustable window, which includes a gel layer, has been developed in our laboratory. Unlike other electrically controlled structures, the optical properties of the gel layer are abruptly modified by the Joule heat of audio frequency AC current. The so-called "gel-glass" becomes opaque when the temperature exceeds a critical value and changes back to its original transparent state when it is cooled down again. This method results in fast control and relatively low operational cost. Two types of gel-glasses,active and passive structures,have been developed and investigated. In this paper, we demonstrate the structural build-up and working of these novel electrically adjustable thermotropic windows. Experimental studies have been made at different frequencies and voltages. The optical properties, as well as the energy balance of the systems, have been reported. Copyright © 2003 John Wiley & Sons, Ltd. [source] Application of thin-layer chromatography/infrared matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometry to structural analysis of bacteria-binding glycosphingolipids selected by affinity detectionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2010Anne Müsken Glycosphingolipids (GSLs) play key roles in the manifestation of infectious diseases as attachment sites for pathogens. The thin-layer chromatography (TLC) overlay assay represents one of the most powerful approaches for the detection of GSL receptors of microorganisms. Here we report on the direct structural characterization of microbial GSL receptors by employment of the TLC overlay assay combined with infrared matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometry (IR-MALDI-o-TOF-MS). The procedure includes TLC separation of GSL mixtures, overlay of the chromatogram with GSL-specific bacteria, detection of bound microbes with primary antibodies against bacterial surface proteins and appropriate alkaline phosphatase labeled secondary antibodies, and in situ MS analysis of bacteria-specific GSL receptors. The combined method works on microgram scale of GSL mixtures and is advantageous in that it omits laborious and time-consuming GSL extraction from the silica gel layer. This technique was successfully applied to the compositional analysis of globo-series neutral GSLs recognized by P-fimbriated Escherichia coli bacteria, which were used as model microorganisms for infection of the human urinary tract. Thus, direct TLC/IR-MALDI-o-TOF-MS adds a novel facet to this fast and sensitive method offering a wide range of applications for the investigation of carbohydrate-specific pathogens involved in human infectious diseases. Copyright © 2010 John Wiley & Sons, Ltd. [source] Step-by-Step Build-Up of Biologically Active Cell-Containing Stratified Films Aimed at Tissue EngineeringADVANCED MATERIALS, Issue 6 2009Laurent Grossin Alginate gel layers containing viable cells with adjacent bioactive polyelectrolyte multilayers are fabricated, and their bioactivity is shown to originate mainly from the degradation of the cells. Alternate biofunctionalized multilayers and cell-containing layers are shown to be an essential step toward fabrication of stratified architectures, and tuning the cellular activity is possible by controlling the position of active molecules. [source] Novel repair method for technical enamels based on sol,gel and sol-dispersion coatings,MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2008S. Benfer The aim of the work presented here is the development of a novel repair method for technical enamels by using chemical nanotechnology. Good adhesion of coatings requires good wettability of the substrate by the repair solution. This was achieved by different pre-treatments of the steel substrates. Low sintering temperatures of the coatings can be ensured by the use of nanoparticle-based systems. Based on liquid metal alkoxides, a colloidal alumina sol and metal salts homogeneous sols with up to seven enamel compounds were prepared. The sols were brush coated onto plain and partly enamelled steel substrates and sintered in a furnace, by inductive heating or an IR emitter. Thin (single layer,,,1µm) crack-free layers were obtained on nearly all substrates independent of the sintering conditions investigated. The local sintering methods (IR emitter, inductive heating) allow to produce multiple coating systems in short times. Electrochemical impedance spectroscopy (EIS) provides evidence of the protective effect of these layers compared to the bare substrate, but as a result of their chemical composition the layers are not stable in the electrolytic environment for longer times. The thickness of such multiple coatings (20 layers, ,,8 µm) is still small compared to that of a technical enamel. Therefore, sol dispersion systems containing powder particles and sol components are applied on top of the sol,gel layers to increase the thickness of the sintered layers. [source] | |||||||||||||