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The aims of this study were to investigate how the release of tadalafil is influenced by two grades of polyvinylpyrrolidone (Kollidon® 12 PF and Kollidon® VA 64) and various methods of preparing solid dispersions (solvent evaporation, spray drying and hot-melt extrusion). Tadalafil is poorly water-soluble and its high melting point makes it very sensitive to the solid dispersion preparation method. Therefore, the objectives were to make a comparative evaluation among different solid dispersions and to assess the effect of the physicochemical nature of solid dispersions on the drug release profile with respect to the erosion-diffusion mechanism. The solid dispersions were evaluated for dissolution profiles, XRD, SEM, FT-IR, DSC, and solubility or stability studies. It was found that tadalafil release was influenced by polymer molecular weight. Therefore, solid dispersions containing Kollidon® 12 PF showed a faster dissolution rate compared to Kollidon® VA 64. Tadalafil was released from solid dispersions containing Kollidon® 12 PF because of the combination of erosion and diffusion mechanisms. The diffusion mechanisms were predominant in the initial phase of the experiment and the slow erosion was dissolution-controlling at the second stage of the dissolution. On the contrary, the tadalafil release rate from solid dispersions containing Kollidon® VA 64 was controlled solely by the erosion mechanism.

In this work a combination of mechanical alloying and spark-plasma sintering was tested as a promising route for the preparation of a nanocrystalline NiTi shape-memory alloy. The mechanism of mechanical alloying was investigated. Results revealed that the Ti2Ni phase forms preferentially, being followed by the NiTi phase (austenite B2 structure) and a small amount of Ni3Ti. During spark-plasma sintering, only minor changes occurred in the phase composition, i.e., precipitation of the Ni4Ti3 phase and the partial transformation of NiTi to monoclinic martensite. The selected technology leads to a very high compression strength (approx. 2300 MPa), but also high brittleness. Keywords: mechanical alloying, spark plasma sintering, NiTi, shape memory alloy V delu je bila preizku{ena kombinacija mehanskega legiranja in sintranja z iskrilno plazmo, ki predstavlja obetajo~na~in za pripravo nanokristalne NiTi spominske zlitine. Preiskovan je bil mehanizem mehanskega legiranja. Rezultati so odkrili, da se najprej tvori faza Ti2Ni, ki ji sledi faza NiTi (avstenitna B2 struktura) in manj{i dele`Ni3Ti. Med sintranjem z iskrilno plazmo se pojavijo le manj{e razlike v sestavi faz, to je izlo~anje faze Ni4Ti3 in delna pretvorba NiTi v monoklinski martenzit. Izbrana tehnologija povzro~i veliko tla~no trdnost (okoli 2300 MPa) in tudi veliko krhkost materiala. Klju~ne besede: mehansko legiranje, sintranje z iskrilno plazmo, NiTi, zlitina z oblikovnim spominom

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