Diffusional properties of zein membranes and matrices.

INTRODUCTION: Zein is a hydrophobic corn protein, rich in leucine, proline, and alanine, that has been investigated as an excipient in pharmaceutical formulations, maybe used as a biodegradable/biocompatible material for controlled release formulations. Zein's swelling behaviors under different conditions (e.g., pH, ionic strength, and permeant's charge) were investigated in a previous study and it showed that swelling indeed influenced zein's permeation.
METHODS: The diffusional behavior of model drugs through or from zein systems was investigated. Diffusional parameters such as effective diffusion coefficients, porosities, and tortuosities were calculated from release and membrane diffusion profiles for zein matrices and membranes. In addition, an alternative method of calculating porosity and tortuosity was proposed.
RESULTS: The diffusional properties of zein systems appear to be primarily through aqueous channels that form during hydration and swelling in aqueous media. Permeation and release results show that the amount of diffused or released drug depends on permeant solubility and matrix/membrane permeability parameters (i.e., porosity and tortuosity). DISCUSSION: Calculated diffusional parameters for zein matrices and membranes support the aqueous channel model.
CONCLUSIONS: Zein membranes and matrices hydrate and swell to form aqueous channels that are the dominant diffusional pathways.