Influence of the growth method upon the phase transition of RbCdCl

Structural properties of two RbCdCl3 samples grown either from the melt or from aqueous solution are studied via X-ray diffraction over a closed temperature cycle between 20 °C and 300 °C. During cooling step (300 $^\circ{\rm C}\to 20$ °C), the crystal grown from the melt undergoes a phase transition at 110 °C that drives it from the cubic structure into a tetragonal structure that still persists at 20 °C. It undergoes exactly the reverse phase transition at the same temperature during the heating ($20~^\circ{\rm C}\to 300~^\circ$C) step that immediately follows. The other crystal grows from aqueous solution at 20 °C in an orthorhombic structure (i.e. not tetragonal as that of the crystal grown from the melt and cooled down to this temperature). During the heating ($20~^\circ{\rm C}\to 300~^\circ$C) step, it undergoes a direct orthorhombic-cubic phase transition at 240 °C (without passing through the tetragonal phase) whereas, during subsequent cooling (300 $^\circ{\rm C}\to 20$ °C), it does not exhibit the corresponding reverse phase transition but rather exhibits exactly the same cubic-tetragonal phase transition at 110 °C as the crystal grown from the melt. However, for both crystals, this tetragonal phase observed at room temperature is unstable and slowly converts into an orthorhombic phase over the course of time. Complementary Differential Scanning Calorimetry (D.S.C.) and Thermo Gravimetric Analysis (T.G.A.) measurements have been carried out over the range ($20\to 300$) °C in order to interpret diffraction experiments

Drug release from PLGA microparticles can be slowed down by a surrounding hydrogel.

This study aimed to evaluate and better understand the potential impact that a layer of surrounding hydrogel (mimicking living tissue) can have on the drug release from PLGA microparticles. Ibuprofen-loaded microparticles were prepared with an emulsion solvent extraction/evaporation method. The drug loading was about 48%. The surface of the microparticles appeared initially smooth and non-porous. In contrast, the internal microstructure of the particles exhibited a continuous network of tiny pores. Ibuprofen release from single microparticles was measured into agarose gels and well-agitated phosphate buffer pH 7.4. Optical microscopy, scanning electron microscopy, differential scanning calorimetry, X-ray powder diffraction, and X-ray μCT imaging were used to characterize the microparticles before and after exposure to the release media. Importantly, ibuprofen release was much slower in the presence of a surrounding agarose gel, e.g., the complete release took two weeks vs. a few days in well agitated phosphate buffer. This can probably be attributed to the fact that the hydrogel sterically hinders substantial system swelling and, thus, slows down the related increase in drug mobility. In addition, in this particular case, the convective flow in agitated bulk fluid likely damages the thin PLGA layer at the microparticles' surface, giving the outer aqueous phase more rapid access to the inner continuous pore network: Upon contact with water, the drug dissolves and rapidly diffuses out through a continuous network of water-filled channels. Without direct surface access, most of the drug "has to wait" for the onset of substantial system swelling to be released

Metastability release of the form alpha of trehalose by isothermal solid state vitrification

International audienceKinetic investigations of the polymorphic form α of anhydrous trehalose have been performed below its apparent melting temperature (Tm) by differential scanning calorimetry (DSC) and X-ray diffraction. The results reveal a spontaneous isothermal vitrification process which indicates that the phase α is in a very unusual superheating situation. This behavior has been attributed to the fact that the effective melting temperature ( ) of the phase α is likely to be located far below the glass transition temperature (Tg) of this compound. The high viscosity of the liquid trehalose between and Tg is thus invoked to explain the long lifetime of the phase α in this temperature range

Hot melt extruded PLGA implants loaded with ibuprofen: How heat exposure alters the physical drug state

International audienceHot melt extrusion offers an interesting potential for the manufacturing of poly(lactic-co-glycolic acid) (PLGA)-based implants. However, the heat treatment might substantially alter the polymer, drug and degree of drug-polymer mixing. The aim of this study was to better understand the impact of varying the exposure time to 105 °C in the case of ibuprofen-loaded PLGA implants. In vitro drug release was measured in phosphate buffer pH 7.4. Optical and scanning electron microscopy, DSC, GPC, X-ray diffraction as well as gravimetric analysis were used to monitor dynamic changes of the implants’ morphology, dry & wet mass and average polymer molecular weight. Interestingly, increasing the exposure time from 3 to 15 min led to a decrease in the amount of crystalline drug present in the system, resulting in a slight decrease in the initial burst release. The average PLGA molecular weight also slightly decreased during the heat treatment. In contrast, the relatively rapid penetration of water into the implant and subsequent polymer degradation throughout the device did not seem to be affected to a noteworthy extent. Also the onset of substantial implant swelling after about 1 week and the subsequent beginning of the final rapid drug release phase (accounting for about 80% of the total drug dose) were not significantly altered. Thus, in this study, the changes in the physical state of the drug in the implant induced by prolonged heat exposure had only a limited impact on system performance. However, for different drugs and polymers, changes in their physical state as a function of the heat exposure time might have more importance consequences. Careful monitoring of these kinetic aspects is recommended to assure desired product quality