Study of the microstructure of polymer based coatings for controlled drug delivery

Film coating of pellets is a common process to create drug delivery systems with controllable drug release kinetics. Film coatings are complex formulations composed of several compounds like film-forming polymers, plasticizers, pore forming agents and colorants that all contribute to the microstructure of the film and hence its permeability for drug molecules. Also the film formation process - solvent based or aqueous dispersion based – will contribute to the microstructure and hence drug diffusion kinetics. In a first part of this research project we will investigate how the microstructure of ethylcellulose and /HPMC-P based films is influenced by commonly used excipients. Special attention will be given to high molecular weight pore forming agents like cellulose derivatives (e.g. hydroxypropylcellulose). Isolated films will be prepared from organic solutions and pseudolatex systems by casting or spraying. To reach a breakthrough in understanding the microstructure and its dynamics, a combination of differential scanning calorimetry, scanning electron microscopy, vibrational spectroscopy and advanced surface analytical techniques will be developed and applied. In parallel, the permeability of the isolated films for model drugs will be quantified and correlated with the microstructure. In a second part we will investigate if and how the findings can be translated to industrially applied coating processes for pellets.