Real-time image-based investigation of spheronization and drying phenomena using different pellet formulations

Extrusion-spheronization (ES) is a frequently used agglomeration process in the pharmaceutical industry to manufacture spherical solid units or pellets with a narrow size and shape distribution. In this study, photometric stereo imaging was applied in real-time during the final steps of the ES process, being spheronization and drying. In addition to the pellet size distribution of undispersed (wet) samples, the imaging technique captures visual information on pellet shape and surface brightness. Pellet samples were taken at 20 time points during spheronization and were imaged at-line (during spheronization) and off-line (after spheronization). Particle size distributions and visual image information were both used to characterise the spheronization behaviour of different formulations. Next, particle size distributions and surface brightness values calculated from the at-line obtained images during fluid bed drying of pellets were analysed. The particle size distribution and brightness value changes occurring during pellet drying were explained both by the reduction in residual moisture content and drug solid-state transition. Due to the rapidness of the technique with regard to sample preparation, sample measurement and the acquisition of results in combination with the possibility to measure undispersed (wet) samples, valuable information on spheronization and drying characteristics of different formulations was obtained in real-time.