We report a room-temperature photoinitiated polymerization-induced self-assembly (photo-PISA) of 2-hydroxypropyl methacrylate (HPMA) in the presence of silica nanoparticles using a poly(ethylene glycol) methyl ether (mPEG) macromolecular chain transfer agent (macro-CTA). Hybrid vesicles loaded with silica nanoparticles were obtained by this one-pot approach. The solids content of the polymer vesicles can be up to 25% w/w. A control experiment was conducted to prove that free silica nanoparticles can be removed via centrifugation-redispersion. Finally, CO₂-responsive hybrid vesicles were prepared by photo-PISA of HPMA and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Silica nanoparticles were subsequently released from the vesicles via CO₂ bubbling at room temperature.