Controlled Encapsulation and Release of Substances Based on Temperature and Photoresponsive Nanocapsules

In this study, dual-responsive polymeric nanocapsules, in which the state (swelling or collapse) can be repeatedly controlled by external stimuli (i.e., temperature and light), have been designed and prepared through distillation-precipitation polymerization. Temperature sensitive monomers of N-isopropylacrylamide are cross-linked by photoresponsive bis(methacryloylamino) onto a silica nanospherical template to form a core-shell (SiO2-PNIPAM/Azo) structure. The silica core is then removed by hydrofluoric acid to produce PNIPAM/Azo nanocapsules (P/ANCs) of diameter ∼238 nm at ∼25 °C. The size of the nanocapsule is temperature responsive and, as such, its diameter could be reduced to ∼182 nm on increasing the temperature to 40 °C. In addition, the permeability of nanocapsules can be adjusted by UV irradiation. The cis-trans transformation of modified azobenzene allowed us to perform both the encapsulation and controlled release of molecules. Rhodamine B (RhB) was successfully encapsulated using the photomechanical method. In controlled release experiments, after the majority of RhB (∼45%) was released from the P/ANCs using temperature (∼40 °C) and UV light, a second stage of release could be triggered by lowering the temperature (∼18.4%) and applying UV-visible lighting cycles (∼29.4%), respectively. We found that the diffusion coefficient, D, was 45% larger under alternate irradiation than UV light alone. Our results demonstrate considerable potential for customizable delivery systems for a variety of drugs.