The application of modeling techniques to film-coating processes

Background: The modeling of the processes for film coating of solid dosage forms can aid in the prediction and troubleshooting of coating operations. Aim: A review of the existing approaches to modeling the coating phenomena was undertaken with the aim of identifying key assumptions and limitations of each approach. Method: Models are categorized into macrolevel and microlevel approaches. Macrolevel models can predict mass coating uniformity for a batch of solids. On the other hand, microlevel models consider phenomena at the scale of the liquid droplets sprayed into the process. Macrolevel models consist either of phenomenological approaches, whereby the inherent variabilities in the coating process are described by probability distributions. Alternatively, first-principle models based on rigorous descriptions of solid and gas-phase motion can be used to describe the multiphase flow behavior in coating equipment. Result: The advantages of the rigorous macrolevel approach are that extrapolation of results for different operating conditions is more reliable than the phenomenological approach and much more information is available about the flow of both phases. However, these first-principle models are computationally intensive and cannot be used for real-time predictions. On the other hand, microlevel models describe chemical and physical phenomena occurring when droplets of coating solution impact the surfaces of the solid cores and are useful in determining the cause of morphological variations in coating properties. Conclusions: Both micro-and macro-level approaches can be used to predict and troubleshoot problems in coating processes. The use of such models in the control of coating operations is not widespread but offers significant potential to improve quality control.