Controlled encapsulation and release of substances based on temperature and photoresponsive nanocapsules

Abstract

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.