Suppression Of Crystal Growth Research Articles

Re-assembled Casein Micelles for Oral Delivery of Chemotherapeutic Combinations to Overcome Multidrug Resistance in Gastric Cancer

Multidrug resistance (MDR) mediated by ATP-dependent efflux transporters continues to be a dominant obstacle towards curative cancer therapy. We have previously demonstrated the ability of $\beta $-casein micelles ($\beta $-CM) to orally deliver a combination of individually encapsulated hydrophobic cargo of drugs and chemosensitizers designed to overcome MDR in gastric cancer. Herein we investigated the potential of re-assembled casein micelles (rCM) to serve as a target-activated delivery platform comprising a synergistic duo of a chemotherapeutic drug (paclitaxel) and a P-glycoprotein-specific transport inhibitor (tariquidar). The high binding affinity of paclitaxel and tariquidar to rCM was demonstrated by spectrofluorometry. Furthermore, solubilization of the drugs and suppression of crystal growth was shown by light microscopy and dynamic light scattering. A remarkable antitumor activity and complete MDR reversal were demonstrated in the in vitro cytotoxicity assay against MDR human gastric carcinoma cells overexpressing P-glycoprotein. The structure and cytotoxic activity of drug-loaded rCM were completely retained after freeze-drying and reconstitution as in $\beta $-CM. Hence, our findings highlight the great potential of casein-based nanovehicles as efficient platforms for oral delivery and local target-activated release of synergistic hydrophobic drug combinations to treat gastric cancer, and overcome of cancer chemoresistance, and for the possible treatment of non-malignant gastric disorders.

Surface Effects on the Crystallization of Ritonavir Glass

In our previous study, initiation time of crystallization was shown to be basically expressed as a function of only the reduced temperature, which was a ratio of storage and glass transition temperatures. This conclusion was obtained using quenched glasses with minimized surface area stored under a dried atmosphere. In this study, the surface effects on the crystallization were investigated using freeze-dried ritonavir (RTV) glass. Although quenched RTV glass exhibited exceptionally long initiation time, the initiation was accelerated by using the freeze-dried glasses. Storage of the samples under humid conditions further accelerated the crystallization. These surface effects eliminated the energetic barrier for nucleation, and the RTV glass exhibited universal initiation time. In contrast, subsequent crystal growth was slower for the freeze-dried glasses relative to the quenched one, presumably because of less condensed and porous structures that would suppress molecular cooperativity. Storage under a humid atmosphere also appeared to inhibit the crystal growth, presumably because of disruption of the molecular network by water. These findings support the existence of the universal initiation time for crystallization and indicated the importance of surface effects in crystallization behavior. Also, the suppression of crystal growth because of the void structure and incorporation of water molecules were indicated.

Structural and chemical properties of sputter-deposited Ti–Ge–N thin films

Ti–Ge–N single-layer and TiN/GeN-multilayer thin films were deposited by reactive magnetron sputtering on Si and WC–Co substrates at constant temperature T s = 240 °C, from confocal Ti and Ge targets in a mixed Ar/N 2 atmosphere. The nitrogen partial pressure, the TiN deposition time t Ti and the power on the Ti and Ge targets were kept constant. In order to obtain various GeN layer thicknesses in the films, the deposition time ratio t Ge/ t Ti was varied. TiN/GeN multilayer films with TiN thickness ∼ 5 nm and various GeN thicknesses between 0.5 and 5 nm were deposited. A nanocrystalline multilayer film is formed, where the suppression of crystal growth is controlled by the successive deposition of two phases. TEM investigations revealed important changes induced by GeN x thickness variation: the columnar single-layer morphology switches into a multilayer morphology. The critical GeN thickness for changing the type of morphology is controlled by the diffusion of Ge atoms at the TiN crystallite boundaries. The morphology modification from single-layer to multilayer type determines the film hardening. Electron probe microanalyses (EPMA), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), nanoindentation and X-ray diffraction (XRD) techniques were employed to characterize single- and multilayer films. The properties of alternate-deposited films are compared to those of co-deposited ones and interpreted.

The Crystal Structure of Ba-β-Alumina Materials for High-Temperature Catalytic Combustion

Structure refinement through Rietveld analysis has been performed on a series of Ba-Al-O samples with Al/Ba ratios in the range 9-14. This material is considered for its potential use in catalytic combustion. The results show that different β-Al2O3-type structures are obtained upon calcination at 1670 K depending on the Al/Ba ratio. A βII-Al2O3 phase forms for the lowest Al/Ba ratio and a βI-Al2O3 forms for the highest one. Small amounts of additional phases are present in the samples with the border compositions. For an in-between composition (Al/Ba = 12) a monophasic sample is obtained with crystal structure and calculated cell parameters intermediate between those of βI and βII. The sample with the intermediate composition exhibits the highest surface area. A strict relationship between surface area and aspect ratio of the crystallites has been observed. This indicates that the sintering resistance of these materials derives from the suppression of crystal growth along the crystallographic axis c. Experimental data also indicate that sintering resistance is closely related to Ba content.

Analytical Electron Microscope Analysis of the Formation of BaO · 6Al2O3

The formation process of barium hexaaluminate (BaO 6Al2O3) from BaCO3/γ‐Al2O3 powders or hydrolyzed alkoxides was studied by analytical electron microscopy. Barium hexaaluminate is produced by a two‐step solid‐state reaction from BaCO3 and Al2O3 via formation of BaO·Al2O3. Marked grain growth and inclusion of nonequilibrium phase were inevitable in this powder mixture process. However, in an alkoxide‐derived precursor, homogeneous mixing of components is attained and hence the formation of BaO·6Al2O3 proceeds readily. Powders obtained by this latter route consisted of fine planar particles with a uniform size and retained a large surface area (20.2 m2/g) even after heating at 1300°C. Electron diffraction results implied that suppression of crystal growth along the c axis is the reason for the large surface area of BaO·6Al2O3.