Controlled release from hydrogel-based solid matrices. A model accounting for water up-take, swelling and erosion.

Design and realization of drug delivery systems based on polymer matrices could be greatly improved by modeling the phenomena which take place after the systems administration. Availability of a reliable mathematical model, able to predict the release kinetic from drug delivery systems, could actually replace the resource-consuming trial-and-error procedures usually followed in the manufacture of these latter. In this work, the complex problem of drug release from polymer (HPMC) based matrices systems was faced. The phenomena, previously observed and experimentally quantified, of water up-take, system swelling and erosion, and drug release were here described by transient mass balances with diffusion. The resulting set of differential equations was solved by using finite element methods. Two different systems were investigated: cylindrical matrices in which the transport phenomena were allowed only by lateral surfaces ("radial" case), and cylindrical matrices with the overall surface exposed to the solvent ("overall" case). A code able to describe quantitatively all the observed phenomena has been obtained.