Modeling drug release from bioerodible microspheres using a cellular automaton.

Mathematical modeling of drug release from biodegradable microspheres is designed to improve understanding of phenomena involved in this complex process. In spite of the considerable information obtained from conventional models, their use of equation curve fitting often limits the possibility to generalize their results. The objective of the presented study is to develop a model involving a three-dimensional cellular automaton to simulate both polymer erosion and drug diffusion independently. The model involves millions of independent cells in different states representing the components present in microspheres. The different states allow representation of polymer, drug, pores and solvent. For erosion, each cell is defined with a life expectancy and its chance of being eroded evolves according to the number of direct neighbours containing solvent. For diffusion, drug-containing cells are allowed to randomly diffuse their content in their neighbouring solvent-containing cells. Good correlations are obtained between simulations and two sets of experimental data obtained from release study at different pH. The model offers some insights about important drug release phases, like burst and subsequent release. Graphical representations obtained from the cellular automaton are also compared to SEM images. Cellular automaton proves to be an interesting tool for drug release modeling offering insights on the phenomena involved.