Multifactorial design of poly(d,l‐lactic‐co‐glycolic acid) capsules with various release properties for differently sized filling agents

The hydrolytic degradation and corresponding content release of capsules made of poly(d,l ‐lactic‐co‐glycolic acid) (PLGA) strongly depends on the composition and material properties of the initially applied copolymer. Consecutive or simultaneous release from capsule batches of combinable material compositions, therefore, offers high control over the bioavailability of an encapsulated drug. The keynote of this study was the creation of a superordinated database that addressed the correlation between the release kinetics of filling agents with different molecular weights from PLGA capsules of alternating composition. Fluorescein isothiocyanate (FITC)–dextran (with molecular weights of 4, 40, and 2000 kDa) was chosen as a model analyte, whereas the copolymers were taken from various 50:50 PLGA, 75:25 PLGA, and polylactide blends. With reference to recent publications, the capsule properties, such as the size, morphology, and encapsulation efficiency, were further modified during production. Hence, uniform microdisperse and polydisperse submicrometer nanocapsules were prepared by two different water‐in‐oil‐in‐water emulsification techniques, and additional effects on the size and morphology were achieved by capsule solidification in two different sodium salt buffers. The qualitative and quantitative examination of the physical capsule properties was performed by confocal laser scanning microscopy, scanning electron microscopy, and Coulter counting techniques to evaluate the capsule size distribution and the morphological appearance of the different batches. The corresponding agent release was quantified by fluorescence measurement of the FITC–dextran in the incubation media and by the direct measurement of the capsule brightness via fluorescence microscopy. In summary, the observed agent release showed a highly controllable flexibility depending on the PLGA blends, preparation methods, and molecular weight of the used filling substances. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4219–4228, 2013     

A NEW MODEL FOR THE ELECTRICAL DOUBLE LAYER INTERACTION BETWEEN TWO SURFACES IN AQUEOUS SOLUTIONS

A new theoretical model is developed to evaluate the total potential energy of interaction between two charged flat plates in aqueous solutions. Instead of using the Boltzmann distribution to predict the ionic concentrations of counterion and coion, which is not correct for small confined spaces, this modified model determines the ionic concentrations of counterion and coion based on the Poisson equation, the Nernst equation, and the mass conservation condition. Instead of the approximations used in the traditional model, the osmotic pressure is directly evaluated based on the ionic concentration distributions predicted by this new model. Finally, the total interaction energy is examined and compared with that predicted by the traditional model. It has been found that for high ionic concentration solutions, the traditional model tends to overestimate the total interaction energy due to the approximations employed in simplifying the osmotic pressure. However, for dilute solutions, the traditional model tends to underestimate the total interaction energy at small separation distance due to the misuse of the Boltzmann distribution in calculating the ionic concentration.     

CELL ADHESION TO POLYMER SUBSTRATES CHARACTERIZED BY THE MICROPIPETTE ASPIRATION TECHNIQUE

A micropipette suction method was adapted for the characterization of cell adhesion to polymer surfaces. The instrument was applied in experiments probing the adhesion of human erythrocytes to polymer films which had been precoated with monoclonal antibodies against two different transmembrane proteins of the cells. Cells were impinged on the polymer substrates and subsequently removed by stepwise micropipette aspiration. Variations of shape and contact area of the cells during micropipette aspiration-driven detachment were evaluated to determine the separation energy. A strong increase of the separation energy with decreased contact area was observed and explained by the smoothing of the cell membrane at elevated membrane tensions. The results indicate that the overall strength of attachment was determined by the amount and availability of the adsorbed antibodies, while the separation of the cells from the polymer substrates occurred, in general, due to dislocation of the transmembrane proteins from the membrane.     

Influence of frozen storage on herbicide degradation capacity in surface and subsurface sandy soils

The degradation of MCPA and metribuzin was investigated in laboratory batch experiments using fresh and frozen-stored soil samples from the unsaturated zone of a sandy soil. Mineralization potentials measured in fresh and frozen-stored soils were similar, and mineralization kinetics in surface and subsurface soils could be fitted using the same kinetic models. MCPA mineralization data from all three horizons were best described with the exponential growth form of the three-half-order model. During the mineralization of MCPA, growth in MCPA-degrading microbial populations was confirmed by increases in the abundance of tfdA genes following MCPA exposure. In contrast to MCPA, metribuzin mineralization followed zero-order kinetics, and very little metribuzin was mineralized (<1%) in all three of the investigated soil horizons. In addition, metribuzin dissipation and metabolite formation were also measured in surface and subsurface soils using LC-MS/MS. Differences in metribuzin dissipation were observed in the A-horizon at the beginning of the experiment and resulted in substantially different 50% disappearance time, DT50, values for frozen-stored (36 days) and fresh (<15 days) soil samples. However, the % of metribuzin remaining in fresh and frozen-stored surface soils was comparable from day 37 and thereafter.     

Investigating the use of an adjustment task to set preferred colour of ambient illumination

An experiment was carried out to examine the method of adjustment when determining user preferences for the colour appearance of ambient lighting. A booth was lit using luminaires containing an array of white and coloured light emitting diodes (LEDs), allowing continuous variation of correlated colour temperature (CCT) between 2736 and 4014 K. It was predicted that the preferred CCT would be influenced by the available stimulus range, the anchor (initial setting before adjustment), adaptation time before onset of adjustment action and type of control dial. Preference was estimated for three different CCT stimulus ranges within the available range. All three ranges led to significantly different results for preferred CCT: 3288, 3490 and 3671 K. The experimental results confirmed that stimulus range, anchor and adaptation time have significant effect on the preferred CCT determined using the adjustment task, and thus, the importance of considering and reporting this information in studies that employ the method of adjustment. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013     

Thixomolded AZ91D and MRI153M magnesium alloys and their enhanced corrosion resistance

AZ91D and MRI153M alloys were produced by thixomolding. Their corrosion resistance is significantly higher than that of similar materials produced by ingot or die-casting. A corrosion rate smaller than 0.2 mm/year in 5 wt% NaCl solution is measured for the thixomolded AZ91D alloy. The corrosion behaviour was evaluated using immersion tests, electrochemical impedance spectroscopy, hydrogen evolution, glow discharge optical emission spectroscopy, and atomic emission spectroelectrochemistry. A bimodal microstructure is observed for both alloys, with the presence of coarse primary α-Mg grains, fine secondary α-Mg grains, β-phase, and other phases with a minor volume fraction. The amount of coarse primary α-Mg is significantly higher for the AZ91D compared with the MRI153M. The network of β-phase around the fine secondary α-Mg grains is better established in the thixomolded AZ91D alloy. A combination of several factors such as the ratio of primary to secondary α-Mg grains, localised corrosion or barrier effect due to other phases, as well as regions of preferential dissolution of the α-Mg due to chemical segregation, are thought to be responsible for the high corrosion resistance exhibited by the thixomolded AZ91D and MRI153M.     

Hydrocarbon Oxidations with Hydrogen Peroxide Catalyzed by a Soluble Polymer‐Bound Manganese(IV) Complex with 1,4,7‐Triazacyclononane

Soluble manganese(IV) complexes with polymer‐bound 1,4,7‐triazacyclononanes as ligands (compound 2 ) catalyze the oxidation of alkanes by hydrogen peroxide in acetonitrile at room and lower temperatures. The corresponding alkyl hydroperoxides are the main products. The presence of a relatively small amount of acetic acid is obligatory for this reaction. The oxidation of alkanes and olefins exhibits some features (kinetic isotope effect, bond selectivities) that distinguish this system from an analogous one based on the dinuclear Mn(IV) complex 1 .