Synthesis of temperature-responsive poly(N-isopropyl acrylamide)/poly(methyl methacrylate)/silica hybrid capsules from inverse pickering emulsion polymerization and their application in controlled drug release.

Poly(N-isopropylacrylamide)/poly(methyl methacrylate)/silica hybrid capsules were prepared from inverse Pickering emulsion polymerization. A N-isopropylacrylamide aqueous solution was emulsified into an oil phase containing methyl methacrylate and divinyl benzene by sonication to obtain a W/O Pickering emulsion using modified silica nanoparticles as stabilizers. After the emulsion was polymerized, the hybrid capsules were obtained. The capsule wall contained two layers--a solid particle monolayer and a polymer layer--and the wall thickness could be controlled by adjusting the methyl methacrylate and divinyl benzene concentrations in the continuous oil phase before polymerization. The as-synthesized capsules exhibited temperature-responsive properties. The controlled release experiments showed that the release rate of a model drug from the hybrid capsules could be controlled by adjusting the wall thickness of the capsule or the temperature of the release medium.