Thermal and fractal analysis of diclofenac/Gelucire 50/13 microparticles obtained by ultrasound-assisted atomization.

The study describes the application of a spray-congealing technique, using a new ultrasound-assisted atomizer to prepare microparticles of diclofenac/Gelucire 50/13, with the aim to obtain a formulation of enhanced-release, at 10% w/w drug-to-excipient ratio, without any employ of solvent. Scanning electron microscopy showed that it was possible to obtain almost spherically shaped and non-aggregated microparticles; with good encapsulation efficiency (90% in most size fraction) and with a prevalent particle size in the range 150-350 mum. Image analysis results by SEM and the high fractal dimension value suggested that most particles have actually an ellipsoidal shape and a rather rough contour. Hot stage microscopy, differential scanning calorimetry, and X-ray powder diffractometry analysis were carried out to evaluate the nature of the solid state and the thermal behavior of the microparticles thus prepared. The in vitro tests displayed a significant increase of the diclofenac dissolution rate from ultrasound microparticles, compared with pure drug and with drug/Gelucire 50/13 physical mixtures.