Viscosity enhanced release (VER) effect in nanoporous drug delivery systems: phenomenon and mechanism

High viscosity is important for normal intracellular homeostasis. In this study, nanoporous drug delivery systems (DDSs), including mesoporous silica nanoparticles (MSNs) and layer by layer (LBL) microcapsules, with a viscosity enhanced release (VER) effect were designed and prepared, and their drug release behaviors in a sticky environment with a high viscosity were investigated using rhodamine B, methylene blue and doxorubicin (DOX) as model drugs. The results showed that the drug release rate from DDSs in a biomimetic high viscosity solution was 7 to 8 times higher than that in water. A semipermeable membrane model was used to explain the VER effect. The results indicate that the existence of macromolecules in the release medium caused a VER effect. The VER effect found in this study will provide a new concept to guide the design of DDSs in a high viscosity environment in vivo.