Reconstructing the differentiation niche of embryonic stem cells using biomaterials

The biochemical cues and topographical architecture of the extracellular environment extensively influence ES cell fate. The microenvironment surrounding the developing embryo presents these instructive cues in a complex and interactive manner in order to guide cell fate decisions. Current stem cell research aims to reconstruct this multifaceted embryonic niche to recapitulate development in vitro. This review focuses on 2D and 3D differentiation niches created from natural and synthetic biomaterials to guide the differentiation of ES cells toward specific lineages. Biomaterials engineered to present specific physical constraints are also reviewed for their role in differentiation.     

Microwave‐Assisted Expedite Synthesis of 2‐Phenylimidazo[1,2‐a]pyridylquinoxalin‐2(1H)‐ones

An efficient methodology has been developed for the synthesis of quinoxalin‐2(1H)‐one derivatives of 2‐phenylimidazo[1,2‐a]pyridines by microwave‐irradiated Hinsberg heterocyclization between 2‐phenylimidazo[1,2‐a]pyridine‐3‐glyoxalates and o‐phenylenediamine using either montmorillonite K‐10 or Yb(OTf)₃ as catalysts. Montmorillonite K‐10 was proven to be an efficient catalyst for the heterocyclization reaction between sterically hindered glyoxalate and o‐phenylenediamine only under microwave conditions. The use of Yb(OTf)₃/tetrahydrofuran was also found to be an effective catalyst for the above chemical transformation among a series of Lewis acids screened under microwave conditions; however, comparatively lesser yields were obtained as compared with the use of montmorillonite K‐10.     

Unsteady Natural Convection Flow in a Square Cavity Filled with a Porous Medium Due to Impulsive Change in Wall Temperature

Unsteady natural convection flow in a two-dimensional square cavity filled with a porous material has been studied. The flow is initially steady where the left-hand vertical wall has temperature T _h and the right-hand vertical wall is maintained at temperature T _c (T _h > T _c) and the horizontal walls are insulated. At time t > 0, the left-hand vertical wall temperature is suddenly raised to which introduces unsteadiness in the flow field. The partial differential equations governing the unsteady natural convection flow have been solved numerically using a finite control volume method. The computation has been carried out until the final steady state is reached. It is found that the average Nusselt number attains a minimum during the transient period and that the time required to reach the final steady state is longer for low Rayleigh number and shorter for high Rayleigh number.     

Adsorption of51Cr(VI) on manganese dioxide from aqueous solution

Sorption of⁵¹Cr(VI) by MnO₂ has been studied as a function of pH and ionic concentration in the presence of certain added cations and anions. The findings are explained in the light of deprotonation/hydroxyl ion association reaction on oxide surface and its subsequent interaction with the tracer. Infrared spectroscopy has shown the chemical interaction of Cr(VI) on the surface of MnO₂. The influence of certain interfering ions has been shown on the sorption of⁵¹Cr(VI) on MnO₂ surface. An attempt has been made to concentrate traces of⁵¹Cr under optimum experimental conditions. The experimental observation shows that the activity sorbed under specified conditions can be recovered appreciably by leaching the pre-adsorbed carrier.     

Intermolecular organization of triphenylene-based discotic mesogens by interdigitation of alkyl chains

Two homologous series of 2,3,6,7,10,11-hexa-alkyloxy-substituted triphenylenes have been synthesized, such that alkyl chains of two different lengths alternate around the rigid triphenylene core in order to allow interdigitation of the chains between neighbouring columns in a hexagonal columnar mesophase. We report here the dependence of structural and thermal properties on the extent of interdigitation, as investigated by X-ray diffraction, polarized optical microscopy and differential scanning calorimetry.     

A facile one‐pot reactive solution blending approach for main‐chain donor–acceptor polymeric materials

A high‐temperature solution blending process has been used to synthesize a series of copolymers incorporating varying mole ratios of perylenebisimide (PBI) into the backbone of an engineering thermoplastic polyester [poly(1,4‐cyclohexylenedimethylene‐1,4‐cyclohexanedicarboxylate)] (PCCD). A random donor–acceptor copolymer incorporating oligo(p‐phenylene vinylene) (OPV) and PBI was also synthesized. The chemical incorporation of these chromophores into PCCD was confirmed by carrying out the melt condensation using 1,4‐cyclohexanedimethanol and 1,4‐dimethylcyclohexane dicarboxylate with hydroxyl‐functionalized PBI and OPV derivatives. Higher extent of incorporation of PBI (35 mol %) could be achieved using the blending approach retaining solubility, film‐forming ability, and higher molecular weights. The PBI polymers produced using the two different approaches exhibited structural variations. The polymers formed from the solution blending approach had a semicrystalline nature with blocks of PCCD separating the PBI units, whereas those produced using the melt condensation route were amorphous polymers. This structural variation was reflected in their photophysical properties also with the reactive solution‐blended polymers exhibiting higher fluorescence quantum yields. These results demonstrate the easy incorporation of suitably functionalized donor and acceptor moieties into a completely aliphatic polyester backbone to produce free‐standing films of hitherto nonprocessable polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Influence of pressure on the B2I phase transition of a banana-shaped liquid crystal

Employing a phenomenological mean field theory, we analyse the effect of high pressure on the B₂I phase transition properties of a bent-core liquid crystal. The basic idea of the work is to explain the phase transition behaviour of system by assuming that certain Landau coefficients associated with the order parameters coupling terms of the free-energy density expansion are pressure dependent. We observe excellent agreement between the theoretical and experimental results of mesogen PHDBB and that the B₂I transition remains first order even at the elevated pressures.     

Hydrothermal synthesis of highly crystalline nanotubes/nanoplates of pure and silver-doped anatase-titania using acid-catalyst-modified sol–gel precursors

Journal of Sol-Gel Science and Technology - Highly crystalline nanotubes/nanoplates of pure and Ag-doped anatase-titania (TiO2) having high aspect-ratio have been synthesized, without the...