Search

We unraveled the strain-induced topological insulating behavior in Ge2Sb2Te5 (GST) by means of ab initio calculations. The semiconductor-to-topological-insulator (TI) transition of Ge2Sb2Te5 were induced by the strains along the 〈100〉 and 〈110〉 direction as well as the shear strains. Ge2Sb2Te5 exhibits three types of TI-characterized conducting surface states: the single Dirac cone feature, the odd band-type and the Bi2Se3-type. The physical origin of the semiconductor-TI transition is the strain-induced inversion of the characterizations of conduction band minimum and valence band maximum with spin-orbit coupling. The present results suggest that GST-related materials are a new family of strain-induced TI. [ABSTRACT FROM AUTHOR]

Aceclofenac, a non-steroidal antiinflammatory drug, is used for posttraumatic pain and rheumatoid arthritis. Aceclofenac fast-dispersible tablets have been prepared by direct compression method. Effect of superdisintegrants (such as, croscarmellose sodium, sodium starch glycolate and crospovidone) on wetting time, disintegration time, drug content, in vitro release and stability parameters has been studied. Disintegration time and dissolution parameters (t50% and t80%) decreased with increase in the level of croscarmellose sodium. Where as, disintegration time and dissolution parameters increased with increase in the level of sodium starch glycolate in tablets. However, the disintegration time values did not reflect in the dissolution parameter values of crospovidone tablets and release was dependent on the aggregate size in the dissolution medium. Stability studies indicated that tablets containing superdisintegrants were sensitive to high humidity conditions. It is concluded that fast-dispersible aceclofenac tablets could be prepared by direct compression using superdisintegrants. [ABSTRACT FROM AUTHOR]

Propranolol-HCl, a water soluble drug, was bound to Indion 254®, a cation exchange resin, and the resulting resinate was microencapsulated with polystyrene using an oil-in-water emulsion-solvent evaporation method with a view to achieve prolonged drug release in simulated gastric and intestinal fluid. The effect of various formulation parameters on the characteristics of the microcapsules was studied. The diameter of the resinate-loaded polystyrene microcapsules increased with increase in the concentration of emulsion stabilizer and coat/core ratio and decreased with increase in the volume of organic disperse phase. The variation in the size of the microcapsules appeared to be related with the inter-facial viscosity which was influenced by the viscosity of both the aqueous dispersion medium and the organic disperse phase. The resinate encapsulation efficiency and hence the drug entrapment efficiency of the microcapsules increased with increase in the concentration of emulsion stabilizer and coat/core ratio and decreased with increase in the volume of organic disperse phase. These characteristics were found to depend on the extent of formation of fractured microcapsules and subsequent partitioning of the resinate into the aqueous dispersion medium. The degree of fracture on the microcapsules depended on the viscosity of the aqueous dispersion medium and the organic disperse phase. The uncoated resinate discharged the drug quite rapidly following the typical particle diffusion process. Although the desorption of the drug from the resinate was independent of pH of the dissolution media, increase in ionic strength increased the drug desorption. On the other hand, release of drug from the coated resinate was considerably prolonged and followed a diffusion controlled model. The prolongation of drug release was dependent on the uniformity of coating which was influenced by the formulation parameters. The drug release from the microcapsules was also found to be independent of pH of the dissolution media and increased with increase in ionic strength. The pH-independent release of the drug from both the uncoated and microencapsulated resinate was due to pH-independent solubility of the drug and high equilibrium concentration of the resinate in both the dissolution media. Polystyrene appeared to be a suitable polymer to provide prolonged release of propranolol independent of pH of the dissolution media. [ABSTRACT FROM AUTHOR]

The objective of this investigation is to develop a multi-unit sustained release dosage form of a water soluble drug from a completely aqueous environment avoiding the use of any organic solvent. The drug was complexed with resin and calcium alginate or polyethyleneimine-treated calcium alginate beads loaded with the resinate were prepared by a ionic/polyelectrolyte complexation method. The effect of different formulation variables on the characteristics of the beads was investigated. Although the drug release from spherical and smooth-surfaced calcium alginate beads in both acidic and alkaline dissolution media were slower than those obtained from plain resinate, none of the variables were found to prolong the drug release considerably due to rapid swelling and disintegration of calcium alginate beads in alkaline medium. On the other hand, drug release from polyethyleneimine-treated calcium alginate beads in acidic medium did not increase appreciably following a burst release. However, in alkaline medium, the drug release was found to increase gradually and extend over a different period of time depending on the intensity of polyethyleneimine treatment. Scanning electron micrographs revealed the formation of a dense membrane around the resinate-loaded calcium alginate matrix. The membrane appeared to be responsible for reduced swelling and protracted disintegration of the beads resulting in slow release of the drug. The results indicate that sustained release of a water soluble drug from polyethyleneimine-treated calcium alginate beads could be achieved by adjusting the formulation variables. [ABSTRACT FROM AUTHOR]