Modeling of drug release from bulk-degrading polymers.

This paper aims to provide a comprehensive review of the various models or simulations for predicting drug release from bulk-degrading systems. A brief description of bulk degradation processes and factors affecting the degradation rate, and consequently the release kinetics, is presented first. Next, several important classical models, often used as the basis for subsequent model development, are discussed. Both mathematical models and Monte-Carlo based simulations have been developed for controlled release from bulk-degrading systems. The mathematical models can be further subdivided into two categories. First, the diffusion-based models whose transport mechanism is mainly governed by diffusion, but with degradation-dependent diffusion coefficients. These are generally simpler and easier to use and are sufficient to illustrate mono-phasic release. Second, comprehensive models that combine diffusion with other theories such as erosion, drug dissolution and/or pore percolations. These models usually involve more complex equations but provide good matches for multi-phasic release profiles.