Spherical
crystallization (SC) is a novel process intensification
strategy, which can substantially reduce the manufacturing cost for
solid oral dosage forms. However, although the manufacturability of
the product agglomerates could be controlled, control over the product
bioavailability has remained elusive. The major bottleneck over the
simultaneous control over product manufacturability and bioavailability
is the lack of in situ Process Analytical Technology (PAT) tools,
which allow for multiscale monitoring of particulate processes. In
this work, mechanistic population balance models (PBMs) have been
used to obtain a multiscale understanding of the droplet population,
as well as the crystal population within the droplets. The use of
mechanistic models enables multiscale process understanding, which
is very difficult with in situ PAT tools. The evolution of the crystal
population within the droplets is found to be widely different for
two different droplet sizes. The time scales of fundamental rate processes,
viz. crystal nucleation and growth, have also been elucidated for
different droplet sizes. The mathematical modeling framework developed
here enhances process understanding and can set the foundation for
implementation of a quality-by-design (QbD) framework for SC, which
is strongly encouraged by the U.S. Food and Drug Administration (FDA).