Mapping multiple phases in curcumin binary solid dispersions by fluorescence contrasting

The microphases and miscibility in binary curcumin (Cur) solid dispersions (SDs) with amorphous polyvinylpyrrolidone K30 (PVP K30) and semi-crystalline poloxamer (P407) and poly(ethylene glycol) 6000 (PEG6000) as carriers were investigated by fluorescence contrasting utilizing confocal laser scanning microscopy. A super sensitive fluorophore P4 with typical aggregation-caused quenching properties was employed to stain the continuous polymer phases and contrasted with the autofluorescence of the model drug Cur. In addition, differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) were utilized to assist in explanation of the fluorescence results. In all three SD systems, there is always a homogenous polymer phase stained by P4 and it is difficult to adulterate Cur crystals by P4. Cur-enriched rather than polymer-enriched domains could be detected. In the Cur-PVP K30 system, Cur exists in an amorphous form at a Cur loading level of 50% and below, while Cur crystallines phase out and continuously grow with the increase of Cur loading from 60% to 90%. The phase behaviors in the Cur-P407 and Cur-PEG 6000 systems are similar but with minor differences. In both systems, Cur phases out as clusters of drug-enriched domains at a loading level of 20% and below, which however cannot be correlated with crystallization, as evidenced by both DSC and PXRD. There is a transition from an amorphous to a crystalline state from 20% to 30% Cur loading, above which Cur crystallines can be detected. It is interesting that a co-mix phase of both Cur- and PEG 6000-enriched domains can be identified at Cur loading levels of 10% and less. Taking together, it is concluded that contrasting Cur autofluorescence with the signals of P4 proves to be a functional strategy to reveal multiple phases in the binary SD systems investigated. Contrasting curcumin autofluorescence (blue) with the signals of P4 (red) utilized to stain the polymer matrix reveals multiple phases in the binary solid dispersion systems. [Display omitted]