Elucidation of spheroid formation with and without the extrusion step

Spheroid formation mechanisms were investigated using extrusion-spheronization (ES) and rotary processing (RP). Using ES (cross-hatch), ES (teardrop), and RP (teardrop), spheroids with similar mass median diameter (MMD) and span were produced using equivalent formulation and spheronization conditions. During spheronization, the teardrop-studded rotating frictional surface, with increased peripheral tip speed and duration, produced spheroids of equivalent MMD and span to those produced by the cross-hatch rotating frictional plate surface. The roundness of these spheroids was also similar. RP required less water to produce spheroids of MMD similar to that of spheroids produced by ES. However, these RP spheroids were less spherical. Image analysis of 625 spheroids per batch indicated that the size distribution of RP spheroids had significantly greater SD, positive skewness, and kurtosis. Morphological examination of time-sampled spheroids produced by ES indicated that spheroid formation occurred predominantly by attrition and layering, while RP spheroids were formed by nucleation, agglomeration, layering, and coalescence. RP produced spheroids with higher crushing strength than that of ES-produced spheroids. The amount of moisture lost during spheronization for spheroids produced by ES had minimal influence on their eventual size. Differences in process and formulation parameters, in addition to size distribution and observed morphological changes, enabled a greater understanding of spheroid formation and methods to optimize spheroid production.