Formation of a sigmoidal release pattern of core particles coated with layers of soluble and permeable particles

A novel method was proposed for the sigmoidal release pattern of core material by dry-based coating of core particles with double layers of permeable particles over soluble particles dispersed in an impermeable wax. A mathematical model was constructed to describe the release curves. This model takes into account the variation of porous structure of the soluble-particle layer with release time due to the slow dissolution of soluble particles. As a result, the sigmoidal release curves were obtained experimentally and the model successfully described the release curves. The delay of release rate during the initial stage of release could be flexibly controlled to increase with a lower fraction of permeable particles in the outer layer, leading to slower dissolution of soluble particles due to the higher resistance to diffusion of soluble material in the permeable-particle layer.