(719d) A Predictive Transport Model for Drying of Polymer Strip Films

Polymer strip films are flexible platforms for oral delivery of drugs. They have shown superior performance compared to traditional solid dosage forms [1]. These films are extensively used as a delivery form for water-soluble drugs but they can be promising candidates for the delivery of poorly water-soluble drugs, which attracted attention in recent years [1]. Drying is an important unit operation in the manufacturing process of polymer strip films. Drying process has significant effect on the morphology of the films and consequently on their quality and performance. Developing predictive models is crucial for optimal design and control of pharmaceutical processes. Fast drying and gentle process conditions are necessary to ensure quality films with the desired moisture content and thickness [2]. The drying model should capture external and intra-film transport processes as well as the shrinkage of the film, as water evaporates. A critical part in the drying model is the calculation of the diffusion coefficient in the polymer film. Different models have been proposed in the literature. A good review of the models has been published by Masaro and Zhu [3]. A significant contribution to modeling of the diffusion in polymer solutions was made by Vrentas and Duda [4,5]. They improved and extended the model based on free-volume theory originally developed by Fujita [6]. Although their model requires the estimation of several parameters, it is applicable to various polymer–solvent systems at different temperatures and polymer concentrations [3].

This work contributes to the development of a robust drying process for the production of polymer strip films containing poorly water-soluble drugs. A two-dimensional simulation and parametric study were done using Comsol Multiphysics and MATLAB for convective drying of the films considering the diffusivity model developed by Vrentas and Duda [4,5]. Polymer strip films containing hydroxypropyl methylcellulose (HPMC; Methocel E-15), glycerin, water and silica-coated drug particles (griseofulvin) were used in the drying experiments. The model results were validated and the required transport parameters were estimated based on the experimental data obtained from a batch drying set-up. Overall, this presentation will demonstrate how time-wise evolution of the moisture and film thickness, two critical quality attributes (CQAs) of strip films, can be predicted using a transport-based modeling framework along with model validation using a batch drying set-up.

1. Krull, S.M., Susarla, R., Afolabi, A., Li, M., Ying, Y., Iqbal, Z., Bilgili, E. and Davé, R.N., 2015. Polymer strip films as a robust, surfactant-free platform for delivery of BCS Class II drug nanoparticles. International journal of pharmaceutics, 489(1-2), pp.45-57.
2. Susarla, R., Sievens-Figueroa, L., Bhakay, A., Shen, Y., Jerez-Rozo, J.I., Engen, W., Khusid, B., Bilgili, E., Romanach, R.J., Morris, K.R. and Michniak-Kohn, B., 2013. Fast drying of biocompatible polymer films loaded with poorly water-soluble drug nano-particles via low temperature forced convection. International journal of pharmaceutics, 455(1-2), pp.93-103.
3. Masaro, L. and Zhu, X.X., 1999. Physical models of diffusion for polymer solutions, gels and solids. Progress in polymer science, 24(5), pp.731-775.
4. Vrentas, J.S. and Duda, J.L., 1977. Diffusion in polymer—solvent systems. I. Reexamination of the free‐volume theory. Journal of Polymer Science Part B: Polymer Physics, 15(3), pp.403-416.

5. Vrentas, J.S. and Duda, J.L., 1977. Diffusion in polymer–solvent systems. II. A predictive theory for the dependence of diffusion coefficients on temperature, concentration, and molecular weight. Journal of Polymer Science Part B: Polymer Physics, 15(3), pp.417-439.

6. Fujita, H., 1961. Diffusion in polymer-diluent systems. Fortschritte Der Hochpolymeren-Forschung, pp.1-47.