Controlled Release Microencapsulation

Transport Mechanisms of Controlled Release Wurster Coated Pellet

Mass transport mechanisms of drug release through a microencapsulation pellet formulation were investigated with focused ion beam scanning electron microscopy (FIB-SEM). Through careful control of imaging conditions, sub-surface cross sectional images were acquired on two coated pellet samples manufactured by a Wurster fluid bed coating process. Image analysis of microporosity, pore size distribution, and pore connectivity in 3D provided a matrix of parameters to quantitatively compare samples from different formulations and processing conditions.

FIB-SEM cross-section of a controlled release polymeric film showing microporosity network, with pore size distribution graph inset — FIB-SEM imaging and quantitative AI analysis can characterize microporosity networks in 3D, providing insights into mechanisms of controlled drug release. This cross-section was obtained on a microencapsulated pellet prepared by a Wurster coating process.

Image-based computational fluid dynamics simulations were employed to correlate membrane microporosity with flow permeability. Through high resolution FIB-SEM characterization, quantitative microporosity analysis, and mechanistic investigations of flow via image-based simulations, it was found that a 10% difference in the water content of the mixed aqueous-organic solvent used to dissolve polymers had a significant impact on the controlled release performance. This approach provides an analytical avenue to evaluate effects of permeation enhancers, solvents, and other process conditions on controlled release formulations and microencapsulations.