Characterization of Heterogeneity and Spatial Distribution of Phases in Complex Solid Dispersions by Thermal Analysis by Structural Characterization and X-ray Micro Computed Tomography.

PURPOSE: This study investigated the effect of drug-excipient miscibility on the heterogeneity and spatial distribution of phase separation in pharmaceutical solid dispersions at a micron-scale using two novel and complementary characterization techniques, thermal analysis by structural characterization (TASC) and X-ray micro-computed tomography (XµCT) in conjunction with conventional characterization methods. METHOD: Complex dispersions containing felodipine, TPGS, PEG and PEO were prepared using hot melt extrusion-injection moulding. The phase separation behavior of the samples was characterized using TASC and XµCT in conjunction with conventional thermal, microscopic and spectroscopic techniques. The in vitro drug release study was performed to demonstrate the impact of phase separation on dissolution of the dispersions. RESULTS: The conventional characterization results indicated the phase separating nature of the carrier materials in the patches and the presence of crystalline drug in the patches with the highest drug loading (30% w/w). TASC and XµCT where used to provide insight into the spatial configuration of the separate phases. TASC enabled assessment of the increased heterogeneity of the dispersions with increasing the drug loading. XµCT allowed the visualization of the accumulation of phase separated (crystalline) drug clusters at the interface of air pockets in the patches with highest drug loading which led to poor dissolution performance. Semi-quantitative assessment of the phase separated drug clusters in the patches were attempted using XµCT. CONCLUSION: TASC and XµCT can provide unique information regarding the phase separation behavior of solid dispersions which can be closely associated with important product quality indicators such as heterogeneity and microstructure.

The development of thermal nanoprobe methods as a means of characterizing and mapping plasticizer incorporation into ethylcellulose films.

PURPOSE: The phase composition and distribution of ethylcellulose (EC) films containing varying amounts of the plasticizer fractionated coconut oil (FCO) were studied using a novel combination of thermal and mapping approaches. METHODS: The thermal and thermomechanical properties of films containing up to 30% FCO were characterized using modulated temperature differential scanning calorimetry (MTDSC) and dynamic mechanical analysis (DMA). Film surfaces were mapped using atomic force microscopy (AFM; topographic and pulsed force modes) and the composition of specific regions identified using nanothermal probes. RESULTS: Clear evidence of distinct conjugate phases was obtained for the 20-30% FCO/EC film systems. We suggest a model whereby the composition of the distinct phases may be estimated via consideration of the glass transition temperatures observed using DSC and DMA. By combining pulsed force AFM and nano-thermal analysis we demonstrate that it is possible to map the two separated phases. In particular, the use of thermal probes allowed identification of the distinct regions via localized thermomechanical analysis, whereby nanoscale probe penetration is measured as a function of temperature. CONCLUSION: The study has indicated that by using thermal and imaging techniques in conjunction it is possible to both identify and map distinct regions in binary films.