Synergistic microfluidic and electrochemical strategy to activate and pattern surfaces selectively with ligands and cells

We show a straightforward, flexible synergistic approach that combines microfluidics, electrochemistry, and a general immobilization strategy to activate regions of a substrate selectively for the precise immobilization of ligands and cells in patterns for a variety of cell-based assays and cell migration and cell adhesion studies. We develop microfluidic microchips to control the delivery of electrolyte solution to select regions of an electroactive hydroquinone SAM. Once an electrical potential is applied to the substrate, only the hydroquinone exposed to electrolyte solution within the microfluidic channels oxidizes to the corresponding quinone. The quinone form can then react chemoselectively with oxyamine-tethered ligands to pattern the surface. Therefore, this microfluidic/electrochemistry strategy selectively activates the surface for ligand patterning that exactly matches the channel design of the microfluidic channel. We demonstrate the ease of this system by first quantitatively characterizing the electrochemical activation and immobilization of ligands on the surface. Second, we immobilize a fluorescent dye to show the fidelity of the methodology, and third, we show the immobilization of biospecific cell adhesive peptide ligands to pattern cells. This is the first report that combines microfluidics/electrochemistry and a general electroactive immobilization strategy to pattern ligands and cells. We believe that this strategy will be of broad utility for applications ranging from fundamental studies of cell behavior to patterning molecules on a variety of materials for molecular electronic devices.     

Geometric control of stem cell differentiation rate on surfaces

We develop a general methodology to create a patterned surface array that allows for the study of how the cell population, surface adhesion area, and pattern geometry combine to influence stem cell differentiation. We use a simple microfabrication technique to pattern human mesenchymal stem cells (hMSC's) on transparent surfaces and develop a new method to quantitate adipogenic differentiation. We found that the pattern geometry and therefore the cell population, rather than the cell adhesive area, influence the rate of adipogenic differentiation from hMSC's. Furthermore, the cells within the pattern behave more characteristically of a tissue than do individual cells because a certain critical threshold cell density is required to induce differentiation.     

Inclusion of aramid chains into the layered silicates through solution intercalation route

Aramid–organoclay nanocomposites were fabricated through solution intercalation technique. Montmorillonite was modified with p-amino benzoic acid in order to have compatibility with the matrix. The effect of clay dispersion and the interaction between clay and polyamide chains on the properties of nanocomposites were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile testing of thin films, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and water uptake measurements. Excessive clay dispersion was achieved even on the addition of high proportions of clay. The structural investigations confirmed the formation of delaminated nanostructures at low clay contents and disordered intercalated morphology at higher clay loadings. The tensile behavior and thermal stability significantly amplified while permeability reduced with increasing dispersibility of organoclay in the polyamide matrix.     

Identification of low molecular weight carbohydrates employing new binary mixtures for matrix-assisted laser desorption/ionisation mass spectrometry

Various energy-absorbing substances, aminopyrazine (AP), 4,4'-azodianiline (ADA), and 1-chloro-4-hydroxyisoquinoline (CHIQ), together with their binary mixtures with existing acidic MALDI matrices were subjected to matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) and evaluated for the analysis of low molecular weight carbohydrates. The newly introduced systems, especially AP and the combination of 2,5-dihydroxybenzoic acid and aminopyrazine (DHB-AP), have solved almost all the existing problems of the generally low sensitivity of carbohydrate analysis and of the strong background noise produced from single acidic matrices. In fact, especially at a mixing ratio of 3:1 (DHB/AP), outstanding results could be achieved, enabling the detection of analytes down to a concentration of 4 fmol/microL with mass accuracy of 37 ppm. The performance of the system was finally proven by analysing dextrins and biological samples each of which showed excellent signal intensity and signal-to-noise ratio.     

An isocratic reversed-phase high-performance liquid chromatographic method for the simultaneous determination of benzoyl peroxide and the related compounds benzoic acid, benzaldehyde, ethyl benzoate, methylparaben, and propylparaben in dermal preparations

A reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of benzoyl peroxide and the related compounds benzoic acid (BA), methylparaben, benzaldehyde, propylparaben, and ethyl benzoate. The compounds are separated on a column containing octadecyl silane chemically bonded to porous silica particles. The mobile phase is acetonitrile-buffer (45 + 55, v/v). Solutions are injected into the chromatographic system under isocratic conditions at a constant flow rate of 1.5 mL/min with UV detection at 235 nm. Analysis of stability samples showed rapid accumulation of BA by thermal degradation. A rationale has been established for the acceptable limit of BA in the formulation, which already contains BA (0.2%) as a preservative. The proposed method is efficient and determines the active compound and 5 related compounds in a run time of 20 min. The method was validated according to the guidelines of the International Conference on Harmonization and demonstrated good agreement with the validation requirements.     

Simultaneous determination of potassium clavulanate and cefixime in synthetic mixtures by high-performance liquid chromatography

A simple, precise, and sensitive high-performance liquid chromatographic method was developed and validated for the simultaneous determination of potassium clavulanate and cefixime in synthetic mixture form. The analytes were separated on a C18 column by using 0.03 M disodium hydrogen phosphate buffer (pH 6.5)-methanol (84 + 16, v/v) as the mobile phase with detection at 220 nm. The method exhibited high sensitivity and good linearity in the concentration ranges of 12.5-62.5 and 20-100 microg/mL for potassium clavulanate and cefixime, respectively. The total run time for the 2 components was <8 min, and the average recovery was >101.5% with a relative standard deviation of <1.0%. The proposed method was validated according to guidelines of the International Conference on Harmonization by evaluation of linearity, recovery, selectivity, robustness, limits of detection and quantitation, and within- and between-day precision. The results obtained for the synthetic mixture show that the method is highly precise and accurate for the simultaneous determination of potassium clavulanate and cefixime.     

Supported (nBuCp)2ZrCl2 Catalysts: Effects of Selected Lewis Acid Organotin Silica Surface Modifiers on Ethylene Polymerization

This study investigated the effects of several organotin silica surface modifiers on the ethylene polymerization performance of (ⁿBuCp)₂ZrCl₂‐based supported catalysts in which MAO and metallocene were sequentially loaded. Each organotin compound acted as a spacer, increasing the catalyst activity. However, the catalyst activity and of the resulting polyethylenes varied as follows: Activity and fractional Sn⁺ charge: ⁿBuSn(OH)₂Cl > MeSnCl₃ > ⁿBuSnCl₃ > Reference catalyst; and, : Reference catalyst > ⁿBuSnCl₃ > MeSnCl₃ > ⁿBuSn(OH)₂Cl. The above catalyst activity rating was explained considering the influence of the Lewis acidity, that is, the fractional Sn⁺ charge of the organotin modifiers on the generation, concentration, and electron density at the active [(ⁿBuCp)₂ZrMe]⁺ cation. All the catalysts showed fairly stable kinetic profiles and produced narrow molecular weight distribution resins; 2.8 ≤ PDI ≤ 3.

     

On the Internal and Boundary Stabilization of Timoshenko Beams

In this paper we consider Timoshenko systems with either internal or boundary feedbacks. We establish explicit and generalized decay results, without imposing restrictive growth assumption near the origin on the damping terms.      

Spirowallichiione: a rearranged multiflorane from Euphorbia wallichii Hook F. (Euphorbiaceae)

Euphorbia wallichii of the family Euphorbiaceae yielded a new rearranged pentacyclic triterpene of the multiflorane class which we have named spirowallichiione. The structure of this natural spirocompound was elucidated with the aid of modern spectroscopic techniques, including 2D-NMR.