Microencapsulation of Lactobacillus paracasei by spray freeze drying

Improved human bioavailability of vemurafenib, a practically insoluble drug, using an amorphous polymer-stabilized solid dispersion prepared by a solvent-controlled coprecipitation process.

The objective of the present study was to determine the solid state solubility and miscibility of naproxen in poly(vinylpyrrolidone) (PVP) and the mutual interaction using the standard thermodynamic models and thermal analysis. Solid dispersions were prepared by spray drying several compositions of naproxen and PVP with different molecular weights, viz., PVP K 12, PVP K 25 and PVP K 90, and analyzed using modulated differential scanning calorimetry (mDSC). The kinetic miscibility limit in terms of a single mixed phase glass transition temperature was found to be relatively similar for the dispersions containing PVP with different chain lengths (≥50% w/w drug in PVP). But the systems with different PVP followed diverse patterns of composition dependent mixed phase glass transition temperature as well as the degree of plasticization by water. The crystalline solid solubility values of naproxen in PVP estimated by using its solubility data in n-methylpyrrolidone, a low molecular weight analogue of PVP, were ...

Theoretical and Experimental Investigation on the Solid Solubility and Miscibility of Naproxen in Poly(vinylpyrrolidone)

Experimental analysis and simulation of the gas transport in dense Hyflon® AD60X membranes: Influence of residual solvent

Al-Cu-Fe quasicrystal/ultra-high molecular weight polyethylene composites as biomaterials for acetabular cup prosthetics.

Because of negligible contributions of combinatorial entropy, miscibility of polymers is attributed predominantly to favorable (exothermic) enthalpic effects of mixing, i.e., to strong interactions between the blend components, which have to overcome the cohesive forces acting within the components. Miscibility of amorphous polymers usually is associated with the presence of a single glass temperature of the blend. Although stronger hetero-contact interactions are thermodynamically required for polymer miscibility, the majority of miscible binary polymer blends exhibit negative deviations of the glass temperature from values predicted by the free volume or flexible bond additivity rules, suggesting a looser packing within those blends. A reasonable explanation assumes that binary hetero-contact formation within the blend may be accompanied by local interchain orientation contributing consequently to conformational entropy changes. The smaller the induced interchain orientation by hetero-contact formation, the larger the mobility in the neighborhood of the contacts and the probability of related conformational entropy changes, causing an equivalent increase of the "free volume" within the blend, i.e., a corresponding decrease of the blend Tg, which finally can be situated below the values predicted by the additivity rules. Vice versa, the corresponding argument will hold for blends with higher interchain orientation induced by intensive exothermic hetero-contact forces.

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Hans Adam Schneider

Papers

Conformational Entropy Contributions to the Glass Temperature of Blends of Miscible Polymers.